While vertically oriented metal oxide nanowires have been intensely researched for use as electron transport layers (ETLs) in halide perovskite solar cells (HPSCs), horizontal nanowires (oriented roughly parallel to the substrate) have received much less attention despite their higher photonic strength due to overlapping electric and magnetic dipolar Mie resonance modes. Herein, we demonstrate the fabrication of an assembly of horizontally aligned TiO2 nanorods (HATNRs) on FTO substrates via a facile hydrothermal route. The HATNRs are employed as the ETL to achieve 15.03% power conversion efficiency (PCE) in HPSCs which is higher than the PCE of compact TiO2 based devices (10.12%) by a factor of nearly 1.5. A mixed halide, mixed cation organometal perovskite FA0.83MA0.17Pb(Br0.17I0.83)3 with optimized composition is used as the active layer. The excellent refractive index matching between the perovskite and TiO2, coupled with strong Mie scattering in the nanorod geometry results in broadband near-zero backscattering and high forward scattering, upon coating of HATNRs with perovskite. The maximum suppression of backscattering is found at ∼600 nm. The HATNRs ETL also improves the extraction of electrons from the perovskite layer and results in superior blocking of carrier recombination at the perovskite layer/FTO interface.
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34−xFexO6−δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ (BCNFCo), exhibited an optical absorption edge at ∼800 nm, p-type conduction and a distinct photoresponse up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent-assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm−2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ∼88%.
Polymeric carbon nitride-based photocatalysts for photoreforming of biomass d...Pawan Kumar
Photoreforming of biomass to value-added chemicals and fuels is a chemical approach to extract photosynthetically-trapped energy in complex biomolecules which otherwise disintegrate naturally in the environment. Designing precise photocatalytic materials that can selectively break the sturdy, nature-designed biomass with multiplex chemical composition/bonding and inaccessible sites is central to deploying this technology. Polymeric carbon nitride (CN) comprised of a 2D network of condensed heptazine/triazine (C6N7/C3N3) core has shown great promise for photoreforming of biomass derivatives due to intriguing physicochemical and optical properties. This review comprehensively summarizes the state-of-the-art applications of CN-based photocatalysts for the conversion of lignocellulosic biomass derivatives. Various chemical and structural modifications in CN structure such as doping, surface functionalization, hybridization entailing to higher selectivity and conversion have been discussed aiming at providing valuable guidance for future CN-based materials design.
Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Co...Pawan Kumar
We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C3N5 is a low-band-gap (Eg = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C3N5 heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm2 V–1 s–1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm2 V–1 s–1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J–V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core–shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.
Polymeric carbon nitride-based photocatalysts for photoreforming of biomass d...Pawan Kumar
Photoreforming of biomass to value-added chemicals and fuels is a chemical approach to extract photosynthetically-trapped energy in complex biomolecules which otherwise disintegrate naturally in the environment. Designing precise photocatalytic materials that can selectively break the sturdy, nature-designed biomass with multiplex chemical composition/bonding and inaccessible sites is central to deploying this technology. Polymeric carbon nitride (CN) comprised of a 2D network of condensed heptazine/triazine (C6N7/C3N3) core has shown great promise for photoreforming of biomass derivatives due to intriguing physicochemical and optical properties. This review comprehensively summarizes the state-of-the-art applications of CN-based photocatalysts for the conversion of lignocellulosic biomass derivatives. Various chemical and structural modifications in CN structure such as doping, surface functionalization, hybridization entailing to higher selectivity and conversion have been discussed aiming at providing valuable guidance for future CN-based materials design.
Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems...Pawan Kumar
Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.
TiO2-HfN Radial Nano-Heterojunction: A Hot Carrier Photoanode for Sunlight-Dr...Pawan Kumar
The lack of active, stable, earth-abundant, and visible-light absorbing materials to replace
plasmonic noble metals is a critical obstacle for researchers in developing highly efficient and costeffective photocatalytic systems. Herein, a core–shell nanotube catalyst was fabricated consisting of
atomic layer deposited HfN shell and anodic TiO2 support layer with full-visible regime photoactivity
for photoelectrochemical water splitting. The HfN active layer has two unique characteristics: (1) a
large bandgap between optical and acoustic phonon modes (2) and no electronic bandgap, which
allows a large population of long life-time hot carriers, which are used to enhance the photoelectrochemical performance. The photocurrent density (≈2.5 mA·cm−2 at 1 V vs. Ag/AgCl) obtained in
this study under AM 1.5G 1 Sun illumination is unprecedented, as it is superior to most existing
plasmonic noble metal-decorated catalysts and surprisingly indicates a photocurrent response that
extends to 730 nm. The result demonstrates the far-reaching application potential of replacing active
HER/HOR noble metals such as Au, Ag, Pt, Pd, etc. with low-cost plasmonic ceramics.
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34−xFexO6−δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ (BCNFCo), exhibited an optical absorption edge at ∼800 nm, p-type conduction and a distinct photoresponse up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent-assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm−2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ∼88%.
Polymeric carbon nitride-based photocatalysts for photoreforming of biomass d...Pawan Kumar
Photoreforming of biomass to value-added chemicals and fuels is a chemical approach to extract photosynthetically-trapped energy in complex biomolecules which otherwise disintegrate naturally in the environment. Designing precise photocatalytic materials that can selectively break the sturdy, nature-designed biomass with multiplex chemical composition/bonding and inaccessible sites is central to deploying this technology. Polymeric carbon nitride (CN) comprised of a 2D network of condensed heptazine/triazine (C6N7/C3N3) core has shown great promise for photoreforming of biomass derivatives due to intriguing physicochemical and optical properties. This review comprehensively summarizes the state-of-the-art applications of CN-based photocatalysts for the conversion of lignocellulosic biomass derivatives. Various chemical and structural modifications in CN structure such as doping, surface functionalization, hybridization entailing to higher selectivity and conversion have been discussed aiming at providing valuable guidance for future CN-based materials design.
Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Co...Pawan Kumar
We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C3N5 is a low-band-gap (Eg = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C3N5 heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm2 V–1 s–1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm2 V–1 s–1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J–V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core–shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.
Polymeric carbon nitride-based photocatalysts for photoreforming of biomass d...Pawan Kumar
Photoreforming of biomass to value-added chemicals and fuels is a chemical approach to extract photosynthetically-trapped energy in complex biomolecules which otherwise disintegrate naturally in the environment. Designing precise photocatalytic materials that can selectively break the sturdy, nature-designed biomass with multiplex chemical composition/bonding and inaccessible sites is central to deploying this technology. Polymeric carbon nitride (CN) comprised of a 2D network of condensed heptazine/triazine (C6N7/C3N3) core has shown great promise for photoreforming of biomass derivatives due to intriguing physicochemical and optical properties. This review comprehensively summarizes the state-of-the-art applications of CN-based photocatalysts for the conversion of lignocellulosic biomass derivatives. Various chemical and structural modifications in CN structure such as doping, surface functionalization, hybridization entailing to higher selectivity and conversion have been discussed aiming at providing valuable guidance for future CN-based materials design.
Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems...Pawan Kumar
Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.
TiO2-HfN Radial Nano-Heterojunction: A Hot Carrier Photoanode for Sunlight-Dr...Pawan Kumar
The lack of active, stable, earth-abundant, and visible-light absorbing materials to replace
plasmonic noble metals is a critical obstacle for researchers in developing highly efficient and costeffective photocatalytic systems. Herein, a core–shell nanotube catalyst was fabricated consisting of
atomic layer deposited HfN shell and anodic TiO2 support layer with full-visible regime photoactivity
for photoelectrochemical water splitting. The HfN active layer has two unique characteristics: (1) a
large bandgap between optical and acoustic phonon modes (2) and no electronic bandgap, which
allows a large population of long life-time hot carriers, which are used to enhance the photoelectrochemical performance. The photocurrent density (≈2.5 mA·cm−2 at 1 V vs. Ag/AgCl) obtained in
this study under AM 1.5G 1 Sun illumination is unprecedented, as it is superior to most existing
plasmonic noble metal-decorated catalysts and surprisingly indicates a photocurrent response that
extends to 730 nm. The result demonstrates the far-reaching application potential of replacing active
HER/HOR noble metals such as Au, Ag, Pt, Pd, etc. with low-cost plasmonic ceramics.
Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Co...Pawan Kumar
We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C3N5 is a low-band-gap (Eg = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C3N5 heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm2 V–1 s–1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm2 V–1 s–1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J–V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core–shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.
A ruthenium trinuclear polyazine complex was synthesized and subsequently immobilized through
complexation to a graphene oxide support containing phenanthroline ligands (GO-phen). The developed
photocatalyst was used for the photocatalytic reduction of CO2 to methanol, using a 20 watt white cold
LED flood light, in a dimethyl formamide–water mixture containing triethylamine as a reductive
quencher. After 48 h illumination, the yield of methanol was found to be 3977.57 5.60 mmol gcat
1.
The developed photocatalyst exhibited a higher photocatalytic activity than graphene oxide, which
provided a yield of 2201.40 8.76 mmol gcat
1. After the reaction, the catalyst was easily recovered and
reused for four subsequent runs without a significant loss of catalytic activity and no leaching of the
metal/ligand was detected during the reaction.
Arrays of TiO2 nanorods embedded with fluorine doped carbon nitride quantum d...Pawan Kumar
Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photocatalytic activity of nanostructured TiO2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO2 for photoelectrochemical water splitting. Arrays of rutile phase TiO2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO2 under visible light irradiation and …
Arrays of TiO2 nanorods embedded with fluorine doped carbon nitride quantum d...Pawan Kumar
Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photocatalytic activity of nanostructured TiO2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO2 for photoelectrochemical water splitting. Arrays of rutile phase TiO2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO2 under visible light irradiation and transfer of holes to the aqueous electrolyte. CNFQD-sensitized TiO2 nanorods exhibited a strong photoelectrochemical response up to 500 nm. Reuse experiments confirmed robustness and long term stability of the sample without exhausting the catalytic performance. The present work demonstrates a new pathway to sensitize TiO2 to visible photons by the in situ formation of embedded heterojunctions with fluorine doped carbon nitride quantum dots
Synthesis of flower-like magnetite nanoassembly: Application in the efficient...Pawan Kumar
A facile approach for the synthesis of magnetite microspheres with flower-like morphology is reported that proceeds via the reduction of iron (III) oxide under hydrogen atmosphere. The ensuing magnetic catalyst is well characterized by XRD, FE-SEM, TEM, N2 adsorption-desorption isotherm and Mössbauer spectroscopy and explored for a simple yetbut efficient transfer hydrogenation reduction of a variety of nitroarenes to respective anilines in good to excellent yields (up to 98%) employing hydrazine hydrate. . The catalyst could be easily separated at the end of reaction using an external magnet and can be recycled up to 10 times without any loss in catalytic activity.
Heterostructured nanocomposite tin phthalocyanine@mesoporous ceria (SnPc@CeO2...Pawan Kumar
Heterostructured tin phthalocyanine supported to mesoporous ceria was synthesized and used a
photocatalyst for CO2 reduction under visible light. The photoreduction CO2 activities of the
heterostructures were investigated in the presence of triethylamine as sacrificial agent. The developed
photocatalyst exhibited high catalytic activity for photoreduction of CO2 and after 24 hours of visible
light irradiation 2342 mmol g1 cat of methanol (fMeOH ¼ 0.0223 or 2.23%) and 840 mmol g1 cat of CO
(fCO ¼ 0.0026 or 0.26%) were obtained as the major reaction products. The methanol formation rate
(RMeOH) and CO formation rate (RCO) was found to be 97.5 mmol h1 g1 cat and 35.0 mmol h1 g1 cat
respectively. While under the identical experimental conditions mesoporous ceria (meso-CeO2) gave
only 316 mmol g1 cat of methanol (fMeOH ¼ 0.003 or 0.30%) and 126 mmol g1 cat CO (fCO ¼ 0.0004
or 0.04%) with product formation rate RMeOH ¼ 13.2 mmol h1 g1 cat and RCO ¼ 5.3 mmol h1 g1 cat.
Furthermore, the recovered catalyst showed consistent catalytic activity for at least five runs without any
significant loss in product yields
Research proposal on organic-inorganic halide perovskite light harvesting mat...Rajan K. Singh
Organic-Inorganic perovskite materials has many applications in the field of opto-electronics such as photo-voltaic cells, LEDs, sensors, memory devices etc. due to its excellent optical and electrical properties. Presence of Pb in such type of perovskite is the biggest challenge for researchers.
Hot hole transfer from Ag nanoparticles to multiferroic YMn2O5 nanowires enab...Pawan Kumar
Plasmonic hot carriers with a nonthermal distribution of kinetic energies have opened up new avenues in photovoltaics, photodetection and photocatalysis. While several articles have reported ultrafast hot electron injection from coinage metals into n-type semiconductors across Schottky barriers and efficient subsequent utilization of injected hot electrons, reports of hot hole harvesting are comparatively rare due to the difficulty in forming Schottky junctions between p-type semiconductors and high work function metals. In this communication, we report the fabrication, characterization and theoretical calculations of a novel integrated multiferroic-plasmonic system comprising YMn2O5 nanowires decorated on their surface with Ag nanoparticles (NPs). A Schottky barrier for holes exists at the YMn2O5-Ag hetero-interface and hot holes were injected from Ag across this barrier. The synthesized hybrid along with bare Ag NPs were tested for Raman surface photocatalytic reduction of 4-NBT (4-nitrobenzenethiol) to DMAB (p, p′-dimercaptoazobenzene) where the composite demonstrated superior activity compared to the bare metal. Ultraviolet photoelectron spectroscopy (UPS) revealed a significantly reduced work function of the composite compared to the pristine Ag, indicative of more energetic hot electrons on the surface of the composite required for efficient photoreduction. Density functional theory (DFT)-based calculations revealed localization of molecular orbitals supportive of a possible hole transfer from YMn2O5 to Ag and a reorganization of electronic states beneficial for plasmon-induced charge carrier enhancement. DFT results also indicated a purely electronic contribution to the ferroelectric polarization of YMn2O5 over and above the ionic contribution, which originated from the magnetic polarization of O 2p states.
Photo-assisted oxidation of thiols to disulfides using cobalt ‘‘Nanorust’’ un...Pawan Kumar
Heterogeneous ‘‘Nanorust’’ containing cobalt oxide has been developed for the visible light assisted
oxidation of thiols to disulfides using molecular oxygen as an oxidant under alkaline free conditions and
therefore more environmentally friendly. Pyrolysis of heterogenized tetrasulfonated cobalt(II) phthalocyanine
(CoPcS) supported on mesoporous ceria (CeO2) transforms it into a novel heterogeneous ‘‘Nanorust’’
containing CoOx-C,N@CeO2 which exhibited higher catalytic activity than the homogeneous CoPcS as well
as the ceria immobilized CoPcS catalyst. Importantly, these catalysts could easily be recovered and recycled
for several runs, which makes the process greener and cost-effective.
Photo-induced reduction of CO2 using a magnetically separable Ru-CoPc@TiO2@Si...Pawan Kumar
An efficient photo-induced reduction of CO2 using magnetically separable Ru-CoPc@TiO2@SiO2@Fe3O4
as a heterogeneous catalyst in which CoPc and Ru(bpy)2phene complexes were attached to a solid
support via covalent attachment under visible light is described. The as-synthesized catalyst was characterized
by a series of techniques including FTIR, UV-Vis, XRD, SEM, TEM, etc. and subsequently tested for
the photocatalytic reduction of carbon dioxide using triethylamine as a sacrificial donor and water as a
reaction medium. The developed photocatalyst exhibited a significantly higher catalytic activity to give a
methanol yield of 2570.78 μmol per g cat after 48 h.
V mn-mcm-41 catalyst for the vapor phase oxidation of o-xylenesunitha81
The role of V and Mn incorporated mesoporous molecular sieves was
investigated for the vapor phase oxidation of o-xylene. Mesoporous monometallic
V-MCM-41 (Si/V = 25, 50, 75 and 100), Mn-MCM-41 (Si/Mn = 50) and bimetallic
V-Mn-MCM-41 (Si/(V ? Mn) = 100) molecular sieves were synthesized by
a direct hydrothermal (DHT) process and characterized by various techniques such
as X-ray diffraction, DRUV-Vis spectroscopy, EPR, and transmission electron
microscopy (TEM). From the DRUV-Vis and EPR spectral study, it was found that
most of the V species are present as vanadyl ions (VO2?) in the as-synthesized
catalysts and as highly dispersed V5? ions in tetrahedral coordination in the calcined
catalysts. The activity of the catalysts was measured and compared with each other
for the gas phase oxidation of o-xylene in the presence of atmospheric air as an
oxidant at 573 K. Among the various catalysts, V-MCM-41 with Si/V = 50
exhibited high activity towards production of phthalic anhydride under the experimental
condition. The correlation between the phthalic anhydride selectivity and
the physico-chemical characteristics of the catalyst was found. It is concluded that
V5? species present in the MCM-41 silica matrix are the active sites responsible for
the selective formation of phthalic anhydride during the vapor phase oxidation of
o-xylene.
Vapor growth of binary and ternary phosphorus-based semiconductors into TiO 2...Pawan Kumar
We report successful synthesis of low band gap inorganic polyphosphide and TiO2 heterostructures with the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP7, SnIP, and (CuI)3P12) were successfully reacted and deposited into electrochemically fabricated TiO2 nanotubes. Employing vapor phase reaction deposition, the cavities of 100 μm long TiO2 nanotubes were infiltrated; approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP7. Intensive characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the substances on and inside the nanotubes. The polyphosphide@TiO2 hybrids exhibited superior water splitting performance compared to pristine materials and were found to be more active at higher wavelengths. SnIP …
Vapor Deposition of Semiconducting Phosphorus Allotropes into TiO2 Nanotube A...Pawan Kumar
Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward
exploiting alternative energy resources such as solar energy. Here, we
report the successful low-cost and easily accessible synthesis of hybrid
semiconductor@TiO2 nanotube photocatalysts. In order to realize its
maximum potential in harvesting photons in the visible-light range, TiO2
nanotubes have been loaded with earth-abundant, low-band-gap fibrous
red and black phosphorus (P). Scanning electron microscopy− and
scanning transmission electron microscopy−energy-dispersive X-ray
spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV−vis measurements have been performed,
substantiating the deposition of fibrous red and black P on top and
inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular morphology of titania and a vapor-transport technique are utilized to form heterojunctions of P and
TiO2. Compared to pristine anatase 3.2 eV TiO2 nanotubes, the creation of heterojunctions in the hybrid material resulted in
1.5−2.1 eV photoelectrocatalysts. An enhanced photoelectrochemical water-splitting performance under visible light compared
with the individual components resulted for the P@TiO2 hybrids. This feature is due to synergistically improved charge
separation in the heterojunction and more effective visible-light absorption. The electronic band structure and charge-carrier
dynamics are investigated in detail using ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy to elucidate
the charge-separation mechanism. A Fermi-level alignment in P@TiO2 heterojunctions leads to a more reductive flat-band
potential and a deeper valence band compared to pristine P and thus facilitates a better water-splitting performance. Our results
demonstrate effective conversion efficiencies for the nanostructured hybrids, which may enable future applications in
optoelectronic applications such as photodetectors, photovoltaics, photoelectrochemical catalysts, and sensors.
Vapor Deposition of Semiconducting Phosphorus Allotropes into TiO2 Nanotube A...Pawan Kumar
Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward exploiting alternative energy resources such as solar energy. Here, we report the successful low-cost and easily accessible synthesis of hybrid semiconductor@TiO2 nanotube photocatalysts. In order to realize its maximum potential in harvesting photons in the visible-light range, TiO2 nanotubes have been loaded with earth-abundant, low-band-gap fibrous red and black phosphorus (P). Scanning electron microscopy– and scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV–vis measurements have been performed, substantiating the deposition of fibrous red and black P on top and inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular …
Vapor growth of binary and ternary phosphorusbased semiconductors into TiO2 n...Pawan Kumar
We report successful synthesis of low band gap inorganic polyphosphide and TiO2 heterostructures with
the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP7, SnIP, and (CuI)3P12)
were successfully reacted and deposited into electrochemically fabricated TiO2 nanotubes. Employing
vapor phase reaction deposition, the cavities of 100 mm long TiO2 nanotubes were infiltrated;
approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP7. Intensive
characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman
spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the
substances on and inside the nanotubes. The polyphosphide@TiO2 hybrids exhibited superior water
splitting performance compared to pristine materials and were found to be more active at higher
wavelengths. SnIP@TiO2 emerged to be the most active among the polyphosphide@TiO2 materials. The
improved photocatalytic performance might be due to Fermi level re-alignment and a lower charge
transfer resistance which facilitated better charge separation from inorganic phosphides to TiO2.
Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Co...Pawan Kumar
We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C3N5 is a low-band-gap (Eg = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C3N5 heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm2 V–1 s–1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm2 V–1 s–1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J–V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core–shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.
A ruthenium trinuclear polyazine complex was synthesized and subsequently immobilized through
complexation to a graphene oxide support containing phenanthroline ligands (GO-phen). The developed
photocatalyst was used for the photocatalytic reduction of CO2 to methanol, using a 20 watt white cold
LED flood light, in a dimethyl formamide–water mixture containing triethylamine as a reductive
quencher. After 48 h illumination, the yield of methanol was found to be 3977.57 5.60 mmol gcat
1.
The developed photocatalyst exhibited a higher photocatalytic activity than graphene oxide, which
provided a yield of 2201.40 8.76 mmol gcat
1. After the reaction, the catalyst was easily recovered and
reused for four subsequent runs without a significant loss of catalytic activity and no leaching of the
metal/ligand was detected during the reaction.
Arrays of TiO2 nanorods embedded with fluorine doped carbon nitride quantum d...Pawan Kumar
Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photocatalytic activity of nanostructured TiO2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO2 for photoelectrochemical water splitting. Arrays of rutile phase TiO2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO2 under visible light irradiation and …
Arrays of TiO2 nanorods embedded with fluorine doped carbon nitride quantum d...Pawan Kumar
Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photocatalytic activity of nanostructured TiO2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO2 for photoelectrochemical water splitting. Arrays of rutile phase TiO2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO2 under visible light irradiation and transfer of holes to the aqueous electrolyte. CNFQD-sensitized TiO2 nanorods exhibited a strong photoelectrochemical response up to 500 nm. Reuse experiments confirmed robustness and long term stability of the sample without exhausting the catalytic performance. The present work demonstrates a new pathway to sensitize TiO2 to visible photons by the in situ formation of embedded heterojunctions with fluorine doped carbon nitride quantum dots
Synthesis of flower-like magnetite nanoassembly: Application in the efficient...Pawan Kumar
A facile approach for the synthesis of magnetite microspheres with flower-like morphology is reported that proceeds via the reduction of iron (III) oxide under hydrogen atmosphere. The ensuing magnetic catalyst is well characterized by XRD, FE-SEM, TEM, N2 adsorption-desorption isotherm and Mössbauer spectroscopy and explored for a simple yetbut efficient transfer hydrogenation reduction of a variety of nitroarenes to respective anilines in good to excellent yields (up to 98%) employing hydrazine hydrate. . The catalyst could be easily separated at the end of reaction using an external magnet and can be recycled up to 10 times without any loss in catalytic activity.
Heterostructured nanocomposite tin phthalocyanine@mesoporous ceria (SnPc@CeO2...Pawan Kumar
Heterostructured tin phthalocyanine supported to mesoporous ceria was synthesized and used a
photocatalyst for CO2 reduction under visible light. The photoreduction CO2 activities of the
heterostructures were investigated in the presence of triethylamine as sacrificial agent. The developed
photocatalyst exhibited high catalytic activity for photoreduction of CO2 and after 24 hours of visible
light irradiation 2342 mmol g1 cat of methanol (fMeOH ¼ 0.0223 or 2.23%) and 840 mmol g1 cat of CO
(fCO ¼ 0.0026 or 0.26%) were obtained as the major reaction products. The methanol formation rate
(RMeOH) and CO formation rate (RCO) was found to be 97.5 mmol h1 g1 cat and 35.0 mmol h1 g1 cat
respectively. While under the identical experimental conditions mesoporous ceria (meso-CeO2) gave
only 316 mmol g1 cat of methanol (fMeOH ¼ 0.003 or 0.30%) and 126 mmol g1 cat CO (fCO ¼ 0.0004
or 0.04%) with product formation rate RMeOH ¼ 13.2 mmol h1 g1 cat and RCO ¼ 5.3 mmol h1 g1 cat.
Furthermore, the recovered catalyst showed consistent catalytic activity for at least five runs without any
significant loss in product yields
Research proposal on organic-inorganic halide perovskite light harvesting mat...Rajan K. Singh
Organic-Inorganic perovskite materials has many applications in the field of opto-electronics such as photo-voltaic cells, LEDs, sensors, memory devices etc. due to its excellent optical and electrical properties. Presence of Pb in such type of perovskite is the biggest challenge for researchers.
Hot hole transfer from Ag nanoparticles to multiferroic YMn2O5 nanowires enab...Pawan Kumar
Plasmonic hot carriers with a nonthermal distribution of kinetic energies have opened up new avenues in photovoltaics, photodetection and photocatalysis. While several articles have reported ultrafast hot electron injection from coinage metals into n-type semiconductors across Schottky barriers and efficient subsequent utilization of injected hot electrons, reports of hot hole harvesting are comparatively rare due to the difficulty in forming Schottky junctions between p-type semiconductors and high work function metals. In this communication, we report the fabrication, characterization and theoretical calculations of a novel integrated multiferroic-plasmonic system comprising YMn2O5 nanowires decorated on their surface with Ag nanoparticles (NPs). A Schottky barrier for holes exists at the YMn2O5-Ag hetero-interface and hot holes were injected from Ag across this barrier. The synthesized hybrid along with bare Ag NPs were tested for Raman surface photocatalytic reduction of 4-NBT (4-nitrobenzenethiol) to DMAB (p, p′-dimercaptoazobenzene) where the composite demonstrated superior activity compared to the bare metal. Ultraviolet photoelectron spectroscopy (UPS) revealed a significantly reduced work function of the composite compared to the pristine Ag, indicative of more energetic hot electrons on the surface of the composite required for efficient photoreduction. Density functional theory (DFT)-based calculations revealed localization of molecular orbitals supportive of a possible hole transfer from YMn2O5 to Ag and a reorganization of electronic states beneficial for plasmon-induced charge carrier enhancement. DFT results also indicated a purely electronic contribution to the ferroelectric polarization of YMn2O5 over and above the ionic contribution, which originated from the magnetic polarization of O 2p states.
Photo-assisted oxidation of thiols to disulfides using cobalt ‘‘Nanorust’’ un...Pawan Kumar
Heterogeneous ‘‘Nanorust’’ containing cobalt oxide has been developed for the visible light assisted
oxidation of thiols to disulfides using molecular oxygen as an oxidant under alkaline free conditions and
therefore more environmentally friendly. Pyrolysis of heterogenized tetrasulfonated cobalt(II) phthalocyanine
(CoPcS) supported on mesoporous ceria (CeO2) transforms it into a novel heterogeneous ‘‘Nanorust’’
containing CoOx-C,N@CeO2 which exhibited higher catalytic activity than the homogeneous CoPcS as well
as the ceria immobilized CoPcS catalyst. Importantly, these catalysts could easily be recovered and recycled
for several runs, which makes the process greener and cost-effective.
Photo-induced reduction of CO2 using a magnetically separable Ru-CoPc@TiO2@Si...Pawan Kumar
An efficient photo-induced reduction of CO2 using magnetically separable Ru-CoPc@TiO2@SiO2@Fe3O4
as a heterogeneous catalyst in which CoPc and Ru(bpy)2phene complexes were attached to a solid
support via covalent attachment under visible light is described. The as-synthesized catalyst was characterized
by a series of techniques including FTIR, UV-Vis, XRD, SEM, TEM, etc. and subsequently tested for
the photocatalytic reduction of carbon dioxide using triethylamine as a sacrificial donor and water as a
reaction medium. The developed photocatalyst exhibited a significantly higher catalytic activity to give a
methanol yield of 2570.78 μmol per g cat after 48 h.
V mn-mcm-41 catalyst for the vapor phase oxidation of o-xylenesunitha81
The role of V and Mn incorporated mesoporous molecular sieves was
investigated for the vapor phase oxidation of o-xylene. Mesoporous monometallic
V-MCM-41 (Si/V = 25, 50, 75 and 100), Mn-MCM-41 (Si/Mn = 50) and bimetallic
V-Mn-MCM-41 (Si/(V ? Mn) = 100) molecular sieves were synthesized by
a direct hydrothermal (DHT) process and characterized by various techniques such
as X-ray diffraction, DRUV-Vis spectroscopy, EPR, and transmission electron
microscopy (TEM). From the DRUV-Vis and EPR spectral study, it was found that
most of the V species are present as vanadyl ions (VO2?) in the as-synthesized
catalysts and as highly dispersed V5? ions in tetrahedral coordination in the calcined
catalysts. The activity of the catalysts was measured and compared with each other
for the gas phase oxidation of o-xylene in the presence of atmospheric air as an
oxidant at 573 K. Among the various catalysts, V-MCM-41 with Si/V = 50
exhibited high activity towards production of phthalic anhydride under the experimental
condition. The correlation between the phthalic anhydride selectivity and
the physico-chemical characteristics of the catalyst was found. It is concluded that
V5? species present in the MCM-41 silica matrix are the active sites responsible for
the selective formation of phthalic anhydride during the vapor phase oxidation of
o-xylene.
Vapor growth of binary and ternary phosphorus-based semiconductors into TiO 2...Pawan Kumar
We report successful synthesis of low band gap inorganic polyphosphide and TiO2 heterostructures with the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP7, SnIP, and (CuI)3P12) were successfully reacted and deposited into electrochemically fabricated TiO2 nanotubes. Employing vapor phase reaction deposition, the cavities of 100 μm long TiO2 nanotubes were infiltrated; approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP7. Intensive characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the substances on and inside the nanotubes. The polyphosphide@TiO2 hybrids exhibited superior water splitting performance compared to pristine materials and were found to be more active at higher wavelengths. SnIP …
Vapor Deposition of Semiconducting Phosphorus Allotropes into TiO2 Nanotube A...Pawan Kumar
Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward
exploiting alternative energy resources such as solar energy. Here, we
report the successful low-cost and easily accessible synthesis of hybrid
semiconductor@TiO2 nanotube photocatalysts. In order to realize its
maximum potential in harvesting photons in the visible-light range, TiO2
nanotubes have been loaded with earth-abundant, low-band-gap fibrous
red and black phosphorus (P). Scanning electron microscopy− and
scanning transmission electron microscopy−energy-dispersive X-ray
spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV−vis measurements have been performed,
substantiating the deposition of fibrous red and black P on top and
inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular morphology of titania and a vapor-transport technique are utilized to form heterojunctions of P and
TiO2. Compared to pristine anatase 3.2 eV TiO2 nanotubes, the creation of heterojunctions in the hybrid material resulted in
1.5−2.1 eV photoelectrocatalysts. An enhanced photoelectrochemical water-splitting performance under visible light compared
with the individual components resulted for the P@TiO2 hybrids. This feature is due to synergistically improved charge
separation in the heterojunction and more effective visible-light absorption. The electronic band structure and charge-carrier
dynamics are investigated in detail using ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy to elucidate
the charge-separation mechanism. A Fermi-level alignment in P@TiO2 heterojunctions leads to a more reductive flat-band
potential and a deeper valence band compared to pristine P and thus facilitates a better water-splitting performance. Our results
demonstrate effective conversion efficiencies for the nanostructured hybrids, which may enable future applications in
optoelectronic applications such as photodetectors, photovoltaics, photoelectrochemical catalysts, and sensors.
Vapor Deposition of Semiconducting Phosphorus Allotropes into TiO2 Nanotube A...Pawan Kumar
Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward exploiting alternative energy resources such as solar energy. Here, we report the successful low-cost and easily accessible synthesis of hybrid semiconductor@TiO2 nanotube photocatalysts. In order to realize its maximum potential in harvesting photons in the visible-light range, TiO2 nanotubes have been loaded with earth-abundant, low-band-gap fibrous red and black phosphorus (P). Scanning electron microscopy– and scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV–vis measurements have been performed, substantiating the deposition of fibrous red and black P on top and inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular …
Vapor growth of binary and ternary phosphorusbased semiconductors into TiO2 n...Pawan Kumar
We report successful synthesis of low band gap inorganic polyphosphide and TiO2 heterostructures with
the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP7, SnIP, and (CuI)3P12)
were successfully reacted and deposited into electrochemically fabricated TiO2 nanotubes. Employing
vapor phase reaction deposition, the cavities of 100 mm long TiO2 nanotubes were infiltrated;
approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP7. Intensive
characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman
spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the
substances on and inside the nanotubes. The polyphosphide@TiO2 hybrids exhibited superior water
splitting performance compared to pristine materials and were found to be more active at higher
wavelengths. SnIP@TiO2 emerged to be the most active among the polyphosphide@TiO2 materials. The
improved photocatalytic performance might be due to Fermi level re-alignment and a lower charge
transfer resistance which facilitated better charge separation from inorganic phosphides to TiO2.
Effect of morphology on the photoelectrochemical performance of nanostructure...Pawan Kumar
Cu2O is a promising earth-abundant semiconductor photocathode for sunlight-driven water splitting. Characterization results are presented to show how the photocurrent density (Jph), onset potential (Eonset), band edges, carrier density (NA), and interfacial charge transfer resistance (Rct) are affected by the morphology and method used to deposit Cu2O on a copper foil. Mesoscopic and planar morphologies exhibit large differences in the values of NA and Rct. However, these differences are not observed to translate to other photocatalytic properties of Cu2O. Mesoscopic and planar morphologies exhibit similar bandgap (e.g.) and flat band potential (Efb) values of 1.93 ± 0.04 eV and 0.48 ± 0.06 eV respectively. Eonset of 0.48 ± 0.04 eV obtained for these systems is close to the Efb indicating negligible water reduction overpotential. Electrochemically deposited planar Cu2O provides the highest photocurrent density of 5.0 mA cm−2 at 0 V vs reversible hydrogen electrode (RHE) of all the morphologies studied. The photocurrent densities observed in this study are among the highest reported values for bare Cu2O photocathodes.
The present work demonstrates for the first time the facile fabrication of TiO2
nanotube arrays (TNTAs) by a fluoride-free
solid-state anodization process using LiClO4
containing solid polymeric electrolyte. The resulting nanotubes were tested
for photoelectrochemical water splitting. The elimination of liquid electrolytes in electrochemical anodization constitutes
a paradigm shift for the formation of nanoporous and nanotubular metal oxides. Our results open a new area of research
that uses the distinctive properties of solid polymer electrolytes to achieve targeted doping and nano-morphologies. Characterization
of the grown TNTAs indicated solid state anodized TNTAs to consist purely of the anatase phase of titania.
The solid-state anodization process provides several advantages over conventional liquid electrolytes such as easy handling
and processing, better charge transport, environmentally benign chemicals and methodology. Photoelectrochemical water
splitting experiments were performed which confirmed the viability of TNTAs grown by the new solid-state process for
photocatalytic applications.
A perovskite solar cell is a type of solar cell which includes a perovskite structured compound, most commonly a hybrid organic-inorganic lead or tin halide-based material, as the light-harvesting active layer.
Photo-induced reduction of CO2 using a magnetically separable Ru-CoPc@TiO2@Si...Pawan Kumar
An efficient photo-induced reduction of CO2 using magnetically separable Ru-CoPc@TiO2@SiO2@Fe3O4
as a heterogeneous catalyst in which CoPc and Ru(bpy)2phene complexes were attached to a solid
support via covalent attachment under visible light is described. The as-synthesized catalyst was characterized
by a series of techniques including FTIR, UV-Vis, XRD, SEM, TEM, etc. and subsequently tested for
the photocatalytic reduction of carbon dioxide using triethylamine as a sacrificial donor and water as a
reaction medium. The developed photocatalyst exhibited a significantly higher catalytic activity to give a
methanol yield of 2570.78 μmol per g cat after 48 h.
We'd like to understand how you use our websites in order to improve them. Re...Pawan Kumar
The present work demonstrates for the first time the facile fabrication of TiO2 nanotube arrays (TNTAs) by a fluoride-free solid-state anodization process using LiClO4 containing solid polymeric electrolyte. The resulting nanotubes were tested for photoelectrochemical water splitting. The elimination of liquid electrolytes in electrochemical anodization constitutes a paradigm shift for the formation of nanoporous and nanotubular metal oxides. Our results open a new area of research that uses the distinctive properties of solid polymer electrolytes to achieve targeted doping and nano-morphologies. Characterization of the grown TNTAs indicated solid state anodized TNTAs to consist purely of the anatase phase of titania. The solid-state anodization process provides several advantages over conventional liquid electrolytes such as easy handling and processing, better charge transport, environmentally benign …
Using triple-layer remote phosphor structures LaVO4:Eu3+ and ZnS:Cu,Sn to imp...TELKOMNIKA JOURNAL
This research paper investigates the novel triple remote phosphor layer for improving the remote phosphor’s angular chroma uniformity (ACU) of down-light lamps by using remote micro-patterned phosphor layers (RMPP). In addition, introducing the triple-layer (TL) RMPP is introduced to offer the potential approach to this objective. This analysis also measures the optical efficiency of the layers and the angle distribution of angular correlated color temperature (ACCT). Drawing a comparison between the traditional
dual-layer (DL) RMPP and the proposed TL is furthermore critical to this study. According to the findings, the triple-layer phosphor configuration can achieve greater hue consistency while having a correlating colour temperature (CCT) variance merely measured at 441 K. Results in the single RMPP layer are 1390 K of the remote phosphor (RP) sheet setting and
556 K for the ACCT deviation. The recreation employing finite-difference
time-domain (FDTD) as well as the approach of ray-tracing ensures an increase in angular color uniformity (ACU). The structure of DL and TL RMPPs results in a 6.68 % and 4.69 % gain in luminous efficiency, respectively, with the standard RMPP layer at a currently driving of 350 mA. The micro-patterned layer’s scattering characteristic and mixing effect may account for the increased ACU and luminous efficiency.
Isolated Iridium Sites on Potassium-Doped Carbon-nitride wrapped Tellurium Na...Pawan Kumar
Many industrial processes such transesterification of fatty acid for biodiesel production, soap manufacturing and biosynthesis of ethanol generate glycerol as a major by-product that can be used to produce commodity chemicals. Photocatalytic transformation of glycerol is an enticing approach that can exclude the need of harsh oxidants and extraneous thermal energy. However, the product yield and selectivity remain poor due to low absorption and unsymmetrical site distribution on the catalyst surface. Herein, tellurium (Te) nanorods/nanosheets (TeNRs/NSs) wrapped potassium-doped carbon nitride (KCN) van der Waal (vdW) heterojunction (TeKCN) is designed to enhance charge separation and visible-NIR absorption. The iridium (Ir) single atom sites decoration on the TeKCN core-shell structure (TeKCNIr) promotes selective oxidation of glycerol to glyceraldehyde with a conversion of 45.6% and selectivity of 61.6% under AM1.5G irradiation. The catalytic selectivity can reach up to 88% under 450 nm monochromatic light. X-ray absorption spectroscopy (XAS) demonstrates the presence of undercoordinated IrN2O2 sites which improved catalytic selectivity for glycol oxidation. Band energies and computational calculations reveal faile charge transfer in the TeKCNIr heterostructure. EPR and scavenger tests discern that superoxide (O2•−) and hydroxyl (•OH) radicals are prime components driving glycerol oxidation.
Isolated Iridium Sites on Potassium-Doped Carbon-nitride wrapped Tellurium Na...Pawan Kumar
Many industrial processes such transesterification of fatty acid for biodiesel production, soap manufacturing and biosynthesis of ethanol generate glycerol as a major by-product that can be used to produce commodity chemicals. Photocatalytic transformation of glycerol is an enticing approach that can exclude the need of harsh oxidants and extraneous thermal energy. However, the product yield and selectivity remain poor due to low absorption and unsymmetrical site distribution on the catalyst surface. Herein, tellurium (Te) nanorods/nanosheets (TeNRs/NSs) wrapped potassium-doped carbon nitride (KCN) van der Waal (vdW) heterojunction (TeKCN) is designed to enhance charge separation and visible-NIR absorption. The iridium (Ir) single atom sites decoration on the TeKCN core-shell structure (TeKCNIr) promotes selective oxidation of glycerol to glyceraldehyde with a conversion of 45.6% and selectivity of 61.6% under AM1.5G irradiation. The catalytic selectivity can reach up to 88% under 450 nm monochromatic light. X-ray absorption spectroscopy (XAS) demonstrates the presence of undercoordinated IrN2O2 sites which improved catalytic selectivity for glycol oxidation. Band energies and computational calculations reveal faile charge transfer in the TeKCNIr heterostructure. EPR and scavenger tests discern that superoxide (O2•−) and hydroxyl (•OH) radicals are prime components driving glycerol oxidation.
Isolated Iridium Sites on Potassium-Doped Carbon-nitride wrapped Tellurium Na...Pawan Kumar
Many industrial processes such transesterification of fatty acid for biodiesel production, soap manufacturing and biosynthesis of ethanol generate glycerol as a major by-product that can be used to produce commodity chemicals. Photocatalytic transformation of glycerol is an enticing approach that can exclude the need of harsh oxidants and extraneous thermal energy. However, the product yield and selectivity remain poor due to low absorption and unsymmetrical site distribution on the catalyst surface. Herein, tellurium (Te) nanorods/nanosheets (TeNRs/NSs) wrapped potassium-doped carbon nitride (KCN) van der Waal (vdW) heterojunction (TeKCN) is designed to enhance charge separation and visible-NIR absorption. The iridium (Ir) single atom sites decoration on the TeKCN core-shell structure (TeKCNIr) promotes selective oxidation of glycerol to glyceraldehyde with a conversion of 45.6% and selectivity of 61.6% under AM1.5G irradiation. The catalytic selectivity can reach up to 88% under 450 nm monochromatic light. X-ray absorption spectroscopy (XAS) demonstrates the presence of undercoordinated IrN2O2 sites which improved catalytic selectivity for glycol oxidation. Band energies and computational calculations reveal faile charge transfer in the TeKCNIr heterostructure. EPR and scavenger tests discern that superoxide (O2•−) and hydroxyl (•OH) radicals are prime components driving glycerol oxidation.
Solar-Driven Cellulose Photorefining into Arabinose over Oxygen-Doped Carbon ...Pawan Kumar
Biomass photorefining is a promising strategy to address the energy crisis and transition toward carbon carbon-neutral society. Here, we demonstrate the feasibility of direct cellulose photorefining into arabinose by a rationally designed oxygen-doped polymeric carbon nitride, which generates favorable oxidative species (e.g., O2–, •OH) for selective oxidative reactions at neutral conditions. In addition, we also illustrate the mechanism of the photocatalytic cellulose to arabinose conversion by density functional theory calculations. The oxygen insertion derived from oxidative radicals at the C1 position of glucose within cellulose leads to oxidative cleavage of β-1,4 glycosidic linkages, resulting in the subsequent gluconic acid formation. The following decarboxylation process of gluconic acid via C1–C2 α-scissions, triggered by surface oxygen-doped active sites, generates arabinose and formic acid, respectively. This work not only offers a mechanistic understanding of cellulose photorefining to arabinose but also sets up an example for illuminating the path toward direct cellulose photorefining into value-added bioproducts under mild conditions.
Solar-Driven Cellulose Photorefining into Arabinose over Oxygen-Doped Carbon ...Pawan Kumar
Biomass photorefining is a promising strategy to address the energy crisis and transition toward carbon carbon-neutral society. Here, we demonstrate the feasibility of direct cellulose photorefining into arabinose by a rationally designed oxygen-doped polymeric carbon nitride, which generates favorable oxidative species (e.g., O2–, •OH) for selective oxidative reactions at neutral conditions. In addition, we also illustrate the mechanism of the photocatalytic cellulose to arabinose conversion by density functional theory calculations. The oxygen insertion derived from oxidative radicals at the C1 position of glucose within cellulose leads to oxidative cleavage of β-1,4 glycosidic linkages, resulting in the subsequent gluconic acid formation. The following decarboxylation process of gluconic acid via C1–C2 α-scissions, triggered by surface oxygen-doped active sites, generates arabinose and formic acid, respectively. This work not only offers a mechanistic understanding of cellulose photorefining to arabinose but also sets up an example for illuminating the path toward direct cellulose photorefining into value-added bioproducts under mild conditions.
Solar-Driven Cellulose Photorefining into Arabinose over Oxygen-Doped Carbon ...Pawan Kumar
Biomass photorefining is a promising strategy to address the energy crisis and transition toward carbon carbon-neutral society. Here, we demonstrate the feasibility of direct cellulose photorefining into arabinose by a rationally designed oxygen-doped polymeric carbon nitride, which generates favorable oxidative species (e.g., O2–, •OH) for selective oxidative reactions at neutral conditions. In addition, we also illustrate the mechanism of the photocatalytic cellulose to arabinose conversion by density functional theory calculations. The oxygen insertion derived from oxidative radicals at the C1 position of glucose within cellulose leads to oxidative cleavage of β-1,4 glycosidic linkages, resulting in the subsequent gluconic acid formation. The following decarboxylation process of gluconic acid via C1–C2 α-scissions, triggered by surface oxygen-doped active sites, generates arabinose and formic acid, respectively. This work not only offers a mechanistic understanding of cellulose photorefining to arabinose but also sets up an example for illuminating the path toward direct cellulose photorefining into value-added bioproducts under mild conditions.
Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single...Pawan Kumar
Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer–Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIII═O) sites and selective C─H bond cleavage to generate •CH3 radicals on Ni centers, which can combine with •OH radicals to generate CH3OH.
Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single...Pawan Kumar
Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer–Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIII═O) sites and selective C─H bond cleavage to generate •CH3 radicals on Ni centers, which can combine with •OH radicals to generate CH3OH.
Selective Cellobiose Photoreforming for Simultaneous Gluconic Acid and Syngas...Pawan Kumar
Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O2− during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (~56 μmol g-1 h-1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition.
Selective Cellobiose Photoreforming for Simultaneous Gluconic Acid and Syngas...Pawan Kumar
Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O2− during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (~56 μmol g-1 h-1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition.
Selective Cellobiose Photoreforming for Simultaneous Gluconic Acid and Syngas...Pawan Kumar
Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O2− during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (~56 μmol g-1 h-1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition.
Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single...Pawan Kumar
Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer–Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIII═O) sites and selective C─H bond cleavage to generate •CH3 radicals on Ni centers, which can combine with •OH radicals to generate CH3OH.
Recent advancements in tuning the electronic structures of transitional metal...Pawan Kumar
The smooth transition from finite non-renewables to renewable energy conversion technologies will require efficient electrocatalysts which can harness intermittent energies to store in the form of chemical bonds. The oxygen evolution reaction (OER) impedes the widespread usage of water electrolyzers to convert H2O into H2 and persists as a bottleneck, including other energy conversion devices with sluggish four H+/e− kinetics. In this context, designing highly active and stable catalysts capable of driving a lower overpotential in the OER to produce continuous hydrogen (H2) is a primary demanded. This chapter discussed the mechanism of the OER in conventional adsorbate oxygen and lattice oxygen participation in transition metal oxides (TMOs). Further, the influences of surface engineering, doping, and defects in the TMOs and understanding the electronic structure to screen electrodes towards the structure–activity relationship are highlighted. Specifically, the adsorption strength of O 2p is understood in detail as its binding ability over the surface of TMOs can be correlated directly to the OER activity. The iterative development of TMOs in terms of understanding electronic structural attributes is essential for the commercial deployment of energy conversion technologies. The comprehensive outlook of this chapter investigates thoroughly how TMOs can be used as significant materials for the OER in the near future.
Hole transport materials (HTMs) have a significant impact on the effectiveness of organic electronic devices; therefore, we present a molecular architecture of pyrazino[2,3-g]quinoxaline (PQ10)-based room-temperature organic liquid crystalline semiconductor (OLCS) as an alternative HTM. The PQ10 compound exhibits three different rectangular columnar (Colr) phases offering an impressive hole mobility of 8.8 × 10−3 cm2V−1s−1 which is found to be dexterous than most of existing polymeric hole transport materials. The charge transport mechanism is governed by the hole polarons hopping through H-aggregates of the PQ10 molecules and the hole mobility remains nearly constant throughout the mesophase range, but it decreases with increasing applied electric field. The current-voltage characteristics of the PQ10 have also been investigated in all three Colr phases and explained via the Poole-Frenkel conduction mechanism. The dielectric spectroscopy has been eventually carried out to understand the nature of dielectric permittivity and conductivity as a function of temperature and a correlation is established between the molecular architecture of the Colr phases and aforementioned physical properties. Solar cell simulation has been additionally performed to demonstrate that the PQ10 material can be a better choice as HTM for organic electronics and photovoltaic applications.
Multifunctional carbon nitride nanoarchitectures for catalysisPawan Kumar
Catalysis is at the heart of modern-day chemical and pharmaceutical industries, and there is an urgent demand to develop metal-free, high surface area, and efficient catalysts in a scalable, reproducible and economic manner. Amongst the ever-expanding two-dimensional materials family, carbon nitride (CN) has emerged as the most researched material for catalytic applications due to its unique molecular structure with tunable visible range band gap, surface defects, basic sites, and nitrogen functionalities. These properties also endow it with anchoring capability with a large number of catalytically active sites and provide opportunities for doping, hybridization, sensitization, etc. To make considerable progress in the use of CN as a highly effective catalyst for various applications, it is critical to have an in-depth understanding of its synthesis, structure and surface sites. The present review provides an overview of the recent advances in synthetic approaches of CN, its physicochemical properties, and band gap engineering, with a focus on its exclusive usage in a variety of catalytic reactions, including hydrogen evolution reactions, overall water splitting, water oxidation, CO2 reduction, nitrogen reduction reactions, pollutant degradation, and organocatalysis. While the structural design and band gap engineering of catalysts are elaborated, the surface chemistry is dealt with in detail to demonstrate efficient catalytic performances. Burning challenges in catalytic design and future outlook are elucidated.
Production of Renewable Fuels by the Photocatalytic Reduction of CO2 using Ma...Pawan Kumar
The photo-reductive performance of natural ilmenite was boosted and the production of renewable fuels from the reduction of CO2 was enhanced by doping the natural mineral with magnesium. The doping was achieved by high energy ball milling in the presence of MgO and Mg(NO3)2. The photo-reduction of CO2 in aqueous solution led to the evolution of H2, CH4, C2H4, and C2H6, and the insertion of Mg in the structure of ilmenite enabled increases of up to 1245% in the fuel production yield, reaching total production of 210.9 µmol h-1 gcat-1. Displacements of the conduction band to more negative potentials were evidenced for the samples doped with magnesium. Indirect effects such as increases in the valence band maximum, and the introduction of intermediate energy levels were also evidenced through the measurement of the crystallite size and the determination of the band structure of the materials. Mott-Schottky analyses of the samples showed the n-type nature of the semiconductor materials and enabled the estimation of the density of charge carriers, which strongly influenced the photocatalytic performance. The strong potential of the application of natural ilmenite in gas phase artificial photosynthesis was proved by the evaluation of CO2 reduction in gas conditions, which allowed the enhancement in the selectivity and significantly increased the production of CH4 as compared to aqueous solution, reaching an important yield of CH4 of 16.1 µmol h-1 gcat-1.
Nanoengineered Au-Carbon Nitride Interfaces Enhance PhotoCatalytic Pure Water...Pawan Kumar
Photocatalytic pure water splitting using solar energy is one of the promising routes to produce sustainable green hydrogen (H2). Tuning the interfacial active site density at catalytic heterojunctions and better light management are imperative to steer the structure-activity correlations to enhance the photo-efficiency of nanocomposite photocatalysts. Herein, we report the decoration of nitrogen defects-rich carbon nitride CN(T) with metallic Au nanostructures of different morphologies and sizes to investigate their influence on the photocatalytic hydrogen evolution reactions (HER). The CN(T)-7-NP nano-heterostructure comprises Au nanoparticles (NPs) of ~7 nm and thiourea-derived defective CN exhibits an excellent H2 production rate of 76.8 µmol g–1 h–1 from pure water under simulated AM 1.5 solar irradiation. In contrast to large-size Au nanorods, the high activity of CN(T)-7-NP was attributed to their strong localized surface plasmon resonance (LSPR) mediated visible absorption and interfacial charge separation. The surface ligands used to control Au nanostructures morphology were found to play a major role in the stabilization of NPs and improve interfacial charge transport between Au NPs and CN(T). First-principles calculations revealed that defects in CN and Au-CN interfacial sites in these nanocomposites facilitate the separation of e-/h+ pairs after light excitation and provide lower energy barrier pathways for H2 production by photocatalytic water splitting.
Nanoengineered Au-Carbon Nitride Interfaces Enhance Photo-Catalytic Pure Wate...Pawan Kumar
Photocatalytic pure water splitting using solar energy is one of the promising routes to produce sustainable green hydrogen (H2). Tuning the interfacial active site density at catalytic heterojunctions and better light management are imperative to steer the structure-activity correlations to enhance the photo-efficiency of nanocomposite photocatalysts. Herein, we report the decoration of nitrogen defects-rich carbon nitride CN(T) with metallic Au nanostructures of different morphologies and sizes to investigate their influence on the photocatalytic hydrogen evolution reactions (HER). The CN(T)-7-NP nano-heterostructure comprises Au nanoparticles (NPs) of ~7 nm and thiourea-derived defective CN exhibits an excellent H2 production rate of 76.8 µmol g–1 h–1 from pure water under simulated AM 1.5 solar irradiation. In contrast to large-size Au nanorods, the high activity of CN(T)-7-NP was attributed to their strong localized surface plasmon resonance (LSPR) mediated visible absorption and interfacial charge separation. The surface ligands used to control Au nanostructures morphology were found to play a major role in the stabilization of NPs and improve interfacial charge transport between Au NPs and CN(T). First-principles calculations revealed that defects in CN and Au-CN interfacial sites in these nanocomposites facilitate the separation of e-/h+ pairs after light excitation and provide lower energy barrier pathways for H2 production by photocatalytic water splitting.
Cooperative Copper Single Atom Catalyst in Two-dimensional Carbon Nitride for...Pawan Kumar
Renewable electricity powered carbon dioxide (CO2) reduction (eCO2R) to high-value fuels like methane (CH4) holds the potential to close the carbon cycle at meaningful scales. However, this kinetically staggered 8-electron multistep reduction still suffers from inadequate catalytic efficiency and current density. Atomic Cu-structures can boost eCO2R-to-CH4 selectivity due to enhanced intermediate binding energies (BEs) resulting from favorably shifted d-band centers. Herein, we exploit two-dimensional carbon nitride (CN) matrices, viz. Na-polyheptazine (PHI) and Li-polytriazine imides (PTI), to host Cu-N2 type single atom sites with high density (∼1.5 at%), via a facile metal ion exchange process. Optimized Cu loading in nanocrystalline Cu-PTI maximizes eCO2R-to-CH4 performance with Faradaic efficiency (FECH4) of ≈68% and a high partial current density of 348 mA cm−2 at a low potential of -0.84 V versus RHE, surpassing the state-of-the-art catalysts. Multi-Cu substituted N-appended nanopores in the CN frameworks yield thermodynamically stable quasi-dual/triple sites with large interatomic distances dictated by the pore dimensions. First-principles calculations elucidate the relative Cu-CN cooperative effects between the two matrices and how the Cu-Cu distance and local environment dictate the adsorbate BEs, density of states, and CO2-to-CH4 energy profile landscape. The 9N pores in Cu-PTI yield cooperative Cu-Cu sites that synergistically enhance the kinetics of the rate-limiting steps in the eCO2R-to-CH4 pathway.
Bioinspired multimetal electrocatalyst for selective methane oxidationPawan Kumar
Selective partial electrooxidation of methane (CH4) to liquid oxygenates has been a long-sought goal. However, the high activation energy of C–H bonds and competing oxygen evolution reaction limit product selectivity and reaction rates. Inspired by iron (IV)-oxo containing metalloenzymes’ functionality to activate the C–H bond, here we report on the design of a copper-iron-nickel catalyst for selective oxidation of CH4 to formate via a peroxide-assisted pathway. Each catalyst serves a specific role which is confirmed via electrochemical, in situ, and theoretical studies. A combination of electrochemical and in situ spectroelectrochemical studies revealed that H2O2 oxidation on nickel led to the formation of active oxygen species which trigger the formation of iron (IV) at low voltages. Density functional theory analysis helped reveal the role of iron (IV)-oxo species in reducing the activation energy barrier for CH4 deprotonation and the critical role of copper to suppress overoxidation. Our multimetal catalyst exhibits a formate faradaic efficiency of 42% at an applied potential of 0.9 V versus a reversible hydrogen electrode.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
2. 1. Introduction
Sunlight is by far the most abundant renewable energy resource,
and it will be necessary to harvest increasing amounts of sunlight to
meet steadily growing global energy demand, estimated to reach 50 TW
by 2050. The field of non-silicon non-chalcogenide photovoltaics has
seen astonishing improvements in performance through the use of ha-
lide perovskite semiconductors in the active layer. While photo-
conversion efficiencies (PCEs) of over 23% have been demonstrated,
there remains further room for improvement in the open circuit vol-
tages (Voc) and short circuit current densities (Jsc) achievable [1–3]. To
improve the efficiency of perovskite solar cells, several possibilities are
being investigated such as developing and doping electron/hole trans-
porting materials, and incorporating quantum dots in perovskite ab-
sorbing layers [4–11]. However, not much effort has been devoted to-
wards the management of photons in the solar cells for efficiency
improvements. Atwater et al. reported that inefficiencies in the
management of photons are the largest source of losses in Jsc and Voc
due to poor harvesting of photons near the semiconductor band-edge,
non-radiative carrier recombination losses limiting the match of the
solar cell to a black body radiator at the same temperature, poorly
optimized angular distribution of emission due to radiative re-
combination of carriers, and changes in the entropy of photons [12].
The use of active layer light management through the use of nano-
photonic architectures offers the largest potential to overcome these
losses.
Strong forward scattering in the layer immediately preceding the
halide perovskite absorber concomitant with suppressed backscattering
is extremely useful in boosting solar cell efficiencies by allowing the use
of thinner absorber layers. Multiple scattering slows down light pro-
pagation and increases the probability of photons being absorbed in the
active layer. Thinner absorber layers that harvest the same amount of
sunlight result in improved performance parameters (Voc, Jsc, FF) due to
shorter carrier extraction paths and reduced recombination. Thinner
Fig. 1. Graphical representation of perovskite solar cells made with (a) Compact TiO2 and (b) Nanostructured HATNRs obtained by hydrothermal method;
Topographic FESEM image of (c) compact and (d) HATNRs. Cross-sectional view of a perovskite solar cell made with (e) Compact TiO2 layer and (f) HATNR arrays.
U.K. Thakur, et al. Journal of Power Sources 417 (2019) 176–187
177
3. absorber layers are associated with lower non-radiative recombination
losses, which in turn increases Voc [13].
Keeping this in mind, we examined near-horizontal nano-raft geo-
metries to improve the utilization of photons. There are a number of
theoretical works (and some experimental ones as well) showing that
horizontal disc-shaped structures made of high refractive index mate-
rials can preferentially suppress backscattering by approaching the first
Kerker condition [14–16]. While Kerker found that magnetic spheres
suppressed backscattering, overlapping or interfering electric dipole
and magnetic dipole modes in ellipsoidal or disc shaped high index
materials such as GaAs and Si have been used to generate either a si-
milar broadband suppression of the backscattering or a relative en-
hancement of the forward scattering [17–20]. Rutile phase TiO2 has a
lower refractive index (2.7) than GaAs (3.5) and Si (3.7) but is never-
theless high enough to show appreciable nanophotonic effects in the
proper geometry.
One dimensional (1-D) nanostructures such as nanotubes and na-
norods possess unique light trapping and charge transport properties
[21–25]. Nanorods exhibit high electron mobility, long diffusion
length, and better pore filling properties in comparison to compact and
mesoporous TiO2 films [26]. Most reports on the use of nanorods, have
applied vertically oriented TiO2 nanorod arrays as the electron trans-
port layer in perovskite solar cells [27–30]. In comparison, there are
almost no reports on horizontal or near-horizontal nanorods as the ETL
in perovskite solar cells despite their superior photonic strength. Hy-
drothermal growth is the primary route for the synthesis of various TiO2
nanostructures, wherein a TiO2 precursor is hydrolyzed in the presence
of water, heat and stabilizers. The hydrothermal method provides us
the flexibility to engineer the architecture of the grown nanorods by
changing the physical parameters such as growth time, temperature,
precursor concentration, solvent, and the substrate positioning inside of
the autoclave [27,31].
2. Results and discussion
2.1. Growth of near-horizontally aligned TiO2 nanorod ETLs
Compact TiO2 film on FTO glass substrate was obtained by spin
coating precursor solution and annealing at 500 °C while the HATNRs
were grown on TiO2 seed layers deposited on FTO glass via a facile
hydrothermal reaction using titanium (IV) n-butoxide as TiO2 precursor
in the presence of hydrochloric acid (HCl), acetic acid (HAc) and water.
Both films showed negligible parasitic absorption loss over the entire
visible range (Fig. S1). Fig. 1a and b are schematic illustrations of n-i-p
type perovskite solar cells made with compact TiO2 and HATNR re-
spectively. Fig. 1c and d are the top-view field emission scanning
electron microscope (FESEM) images of the compact TiO2 and HATNR
respectively. In our previous report, we demonstrated the effect of the
precursor concentration on the morphology of the resulting vertically
oriented TiO2 nanorods and its impact on the performance of perovskite
solar cells based on them [25,27]. In this non-organic recipe, we used
titanium n-butoxide (TBO) as precursor and DI water as the primary
solvent in which the nanorod growth reactions takes place. HCl and
HAc both affect the morphology of the structure during growth. More
specifically, the acids provide H+
ions which suppress the fast hydro-
lysis of TBO precursor, thereby leaving more precursor available for the
growth of the nanorods. The growth of the crystal is mainly determined
by the relative growth of the various crystal faces which bound a unit
cell of the TiO2 lattice. In rutile TiO2, each Ti atom is bound to 6 oxygen
atoms in an octahedral unit cell, and the growth of each face depends
on the available coordination polyhedron. The crystal grows in the
direction which minimizes surface energy, and thus is the most ther-
modynamically stable. The FTO substrate has a tetragonal rutile crystal
structure, and the lattice mismatch between the tetragonal FTO
(a = b = 0.4687 nm) and rutile TiO2 (a = b = 0.4594) is only about
1.98% which promotes the nucleation and growth of the rutile phase
TiO2 nanostructures on the substrate [32–37]. Furthermore, the acids
contribute Cl−
and CH3COO−
ions which help in tuning the mor-
phology of the crystalline nanostructures by retarding the growth rate
of the (110) plane. The size of the solvated ion affects the spacing be-
tween the individual nanorods grown. The morphology of the nanos-
tructures is dependent on the recipe used during fabrication as well as
on the substrate orientation. It is known that the effect of the angle at
which the substrate is placed (with respect to the base of the Teflon
reaction vessel) greatly affects the direction in which the nanorod ar-
rays grow. This is true since the substrate orientation affects the pre-
cursor deposition which in turn affects the nucleation sites for further
growth. We used these principles to tune the morphology of the TiO2
nanostructures via the hydrothermal growth process such that near-
horizontal bunches of nanorods (“nano-rafts”) formed instead of the
typically observed vertical nanowire arrays.
The FESEM images (Fig. 1c and e) of compact TiO2 deposited on
FTO depicts an irregular film thickness with numerous discontinuous
features or pin holes (see also Figs. S2a and S2d). The deposition of
perovskite over this irregular and discontinuous TiO2 layer results in a
high probability of direct contact between bare FTO substrate and
perovskite layer. The formation of this poor hole blocking layer pro-
motes faster electron-hole recombination between the FTO and the
perovskite layer which in turn reduces the charge transport efficacy of
the ETL. The non-uniform compact TiO2 layer, along with the presence
of pinholes significantly reduces the performance of the device. These
pinholes can be reduced by increasing the thickness of the compact
TiO2 film which would improve the hole blocking property of the film.
However, the resulting thick and smooth compact TiO2 surface in-
creases the series resistance and reduces the interfacial area between
the perovskite and ETL. This results in deterioration in the fill factor
and the current density of the device. The FESEM images of titania
nanorods grown on TiO2 compact layer deposited FTO glass exhibit
randomly distributed near-horizontally aligned nanorods bunched to-
gether as nanorafts (Fig. 1d). It can be seen in Fig. 1f, Figs. S2b and S2c
that hydrothermally grown, TiO2 nanorod films deposited over the FTO
substrates provides better film uniformity, and well defined near-hor-
izontally oriented nanorods. It is evident that the hydrothermal treat-
ment promotes filling of the pinholes present in the compact TiO2 layer
and hence provides superior hole blocking. On the other hand, it also
provides a highly irregular surface which significantly improves the
mesoscopic effect, thus helping to improve the current density, and
hence the PCE of the device.
Ultrafine morphological attributes of HATNRs were determined
using high resolution transmission electron microscopy (HRTEM). TEM
images of HATNRs at low magnification shows cylindrical nanorods
clumped together as bundle and average diameter of single nanorod
was found to be ca. 17–19 nm (Fig. 2a and b). The high-resolution TEM
images at higher magnification clearly show lattice fringes with
0.33 nm interplanar spacing corresponding to the (110) plane of rutile
phase TiO2. Further, EDX pattern clearly shows sharp peaks of Ti and O,
and confirms the presence of TiO2 (Fig. 2e). The peaks corresponding to
C and Cu arise from carbon coated TEM grids. EDX elemental mapping
in STEM mode shows an even distribution of Ti and O in nanorods and
averaged images show homogeneous composition, which further con-
firms stoichiometric and highly crystalline TiO2 nanorods (Fig. 2f).
The surface and sub-surface (up to ∼ 10 nm) chemical composition
of compact TiO2 and HATNR was investigated using X-ray photoelec-
tron microscopy (XPS) (Fig. 3a and b). XPS survey scan for elemental
analysis of compact TiO2 and HATNRs exhibited all the peaks relevant
to Ti2p and O1s along with other low and high core level peaks (Ti3s,
Ti3p, TiLLM, OKLL and O3s etc) (Fig. S3). Core-level high resolution
XPS (HR-XPS) spectra of both compact TiO2 and HATNRs show two
symmetric peaks at binding energies of 458.57 and 464.22 eV assigned
to Ti2p3/2 and Ti2p1/2 peak components of Ti4+
state in TiO2 crystal
lattice (Fig. 3a) [38,39]. The positions of Ti2p3/2 and Ti2p1/2 peaks
with a peak splitting of 5.76 eV verify O2−
coordinated Ti4+
in compact
U.K. Thakur, et al. Journal of Power Sources 417 (2019) 176–187
178
4. TiO2 and HATNR [40,41]. Ti2p peaks observed for anatase phase
compact TiO2 and rutile phase HATNRs were identical, as they are
constiuated of the same compound. HR-XPS spectra of compact TiO2 in
O1s region can be deconvoluted into two peak components located at
BE ≈ 529.78 and 531.34 eV. The peak component at BE value of
529.78 eV was attributed to crystal lattice oxygen bonded to Ti (Ti-O-
Ti), while peak component centered at binding energy 531.34 eV ori-
ginated from surface adsorbed -OH groups and non-lattice adventitious
oxygens (Fig. 3b) [42]. The two O1s peak components for HATNRs
were located at BE ≈ 529.74 and 531.11 eV corresponding to lattice
bonded oxygens and surface adsorbed non-lattice adventitious oxygen.
A very small shift (0.04 eV) in O1s components of HATNRs at 529.74 eV
might be due to the different chemical environment of oxygen in rutile
TiO2 (tetragonal geometry with slightly orthorhombic distortion of
TiO6 octahedron) and anatase state (tetragonal) in compact TiO2
[43,44].
To investigate the electronic band structure of the synthesized ETLs,
work function and valence band spectra were measured using ultra-
violet photoelectron spectroscopy (UPS) (Fig. 3c and d). The value of
the work function (WF) was estimated from work function spectra using
the expression WF (ϕ) = 21.21−Ecut-off, where 21.21 eV is the energy
of the incident He laser light, and Ecut-off is the cut-off energy of sec-
ondary electrons. The point of intersection by extrapolation of linear
region of graph in horizontal and vertical regions gives the value of cut-
off energy of secondary electrons Ecut-off). The Ecut-off values for compact
TiO2 and HATNR arrays were found to be 17.17 and 16.96 eV, and the
corresponding work function values (ϕ) were calculated to be 4.04 and
4.25 eV, respectively (Fig. 3c and inset). Furthermore, the intersecting
point of linear region in UPS valance band spectra gave the position of
valence band maxima (VBmax). The VBmax values for the compact TiO2
and HATNRs were calculated to be 2.95 and 3.08 eV below the Fermi
level (Fig. 3d).
X-ray diffraction patterns of compact TiO2 thin film and HATNR
arrays were collected to investigate any change in crystallinity and
phase structure (Fig. 4a). The XRD pattern of compact TiO2 layer over
FTO does not reveal any peak corresponding to the very thin compact
TiO2 layer due to the suppression of TiO2 peaks by strong FTO dif-
fraction peaks. However, the XRD pattern of the blocking TiO2 layer
over the bare glass substrate clearly reveals anatase peaks which match
with JCPDS file no. 21–1272 and confirms the compact layer was
composed of anatase TiO2 (Inset of Fig. 4a). For HATNR, two distinct
rutile peaks at 2θ values of 62.82° and 36.09° were observed which was
in excellent agreement with JCPDS file no. 21–1276 for tetragonal ru-
tile phase TiO2. HATNR array on compact TiO2 can be considered as
mixed phase TiO2 because of the presence of underlying anatase com-
pact TiO2 and rutile nanorods. It is well documented in the literature
that the conduction band of anatase phase TiO2 is 0.2 eV higher than
rutile phase TiO2 in the absence of any heterojunction [45,46]. This
also evident from UPS data where the difference between Fermi levels
of anatase form in compact TiO2 and rutile phase HATNRs was calcu-
lated to be 0.21 eV. Based on the UPS results we constructed the energy
band diagram of solar cells made with compact TiO2 and HATNR arrays
and shown in Fig. 4b and c. Although not depicted in the figure, het-
erojunction formation between anatase and rutile phase leads to a type
II (staggered) energy band alignment. Fermi level alignment in mixed
phase anatase-rutile heterojunctions proceeds via charge redistribution
and band bending which creates an n-n heterojunction possessing a
higher conduction band position of rutile TiO2 than anatase state.
Scalon et al. demonstrated that in such a heterojunction, the conduction
band of rutile phase TiO2 is 0.4 eV higher than anatase form TiO2,
which facilitates facile transfer of electrons from the rutile to anatase
TiO2 [47]. Furthermore, anatase TiO2 possesses low-energy shallow
traps 0.8 eV below the conduction band of rutile so electrons can flow
from rutile to anatase [47–49]; this further helps in electron transfer
and results in a significant improvement in the photovoltaic perfor-
mance of HATNRs based solar cells. It is also well known that the
Fig. 2. (a, b) HR-TEM images HATNRs images at 50 nm scale bar showing bundles of nanorods and inset showing individual nanorods and their respective diameter
(c, d) high magnification images at 5 nm scale bar showing lattice fringes (e) EDX pattern showing presence of Ti and O and (f) Bright field image and EDX elemental
mapping for Ti, O and their summed-up image.
U.K. Thakur, et al. Journal of Power Sources 417 (2019) 176–187
179
5. carrier transport efficiency of mixed phase TiO2 is better compared to
the pure anatase TiO2 [50–54]. Furthermore, because of the presence of
pinholes in the compact TiO2, perovskite can contact directly with the
FTO electrode,free electrons that have already been transferred to FTO
can get reinjected into the valence band of perovskite as there is a low
interfacial energy barrier. This results in front surface recombination;
however, in HATNR samples the exposed FTO surface is passivated by
rutile nanorods which results in elimination of direct contact between
FTO and the perovskite layer.
2.2. ETL dependent Carrier dynamics in halide perovskite solar cells
To probe the carrier dynamics of these two different TiO2 electron
transporting layers, we compared the steady state photoluminescence
(PL) spectra of perovskite on FTO glass with perovskite/compact TiO2/
FTO glass and perovskite/HATNR arrays/FTO as shown in Fig. 5 (a).
The PL spectra of all samples exhibit an emission peak at 775 nm. The
integrated PL intensity of perovskite on FTO glass was found to be
highest, followed by perovskite/compact TiO2/FTO glass, and
perovskite/HATNR arrays/FTO samples respectively. Therefore, the
HATNR array produced the greatest quenching of the perovskite lu-
minescence. This observed PL quenching behavior was attributed to
charge carrier extraction from the perovskite layer to the TiO2 layers
(ETLs). The higher PL quenching for nanostructured HATNR sample in
comparison to the compact TiO2 sample clearly indicates that the rate
of electron transfer from the perovskite to the HATNR array assembly
was faster than for compact TiO2.
Time-resolved photoluminescence (TRPL) decay data were collected
from the samples with compact TiO2 and HTNR layers coated with
perovskite, as well as from a perovskite sample without TiO2 layers
(Fig. 5b). The PL decay appears at least bi-exponential and the data
were therefore fitted to the model:
I(t) = A1e−t/τ1
+ A2 e−t/τ2
(1)
where A1 and A2 are scaling parameters, and τ1 and τ2 are the lifetimes
of the shorter and longer decay components respectively. Both com-
ponents are present almost equally in the perovskite layer, even in the
absence of the ETLs, and the corresponding lifetimes τ1 and τ2 were
Fig. 3. HR XPS spectra of compact TiO2 and HATNR array in (a) Ti2p region and (b) O1s region; (c) UPS work function spectra of compact TiO2 and HATNR array.
Inset shows the secondary electron cut-off energy (Ecut-off) while the value of work function (WF) was determined using the equation, WF (ϕ) = 21.21 – Ecut-off, where
21.21 eV is the energy of the incident He laser used for UPS (d) UPS valence band spectra showing position of valence band maxima (VBmax) below Fermi level.
U.K. Thakur, et al. Journal of Power Sources 417 (2019) 176–187
180
6. 19.7 ns and 282.3 ns respectively, while the system response time is
∼0.1 ns. For the ETL free samples, the decay is attributed mainly to
trap-assisted recombination. The fast component is attributed to the
bimolecular recombination of charge carriers trapped at the perovskite
grain boundaries while the longer-lived component is most likely the
radiative recombination of free electron-hole pairs. For the samples
with ETL, the faster component is mainly related to the electron ex-
traction from the perovskite layer to the electron transporting layer and
the longer-lived component is attributed to the excited-state decay time
or recombination dynamics of perovskite absorber [55–63]. For the
sample with the compact TiO2 layer, the prefactor was slightly larger
for the fast decay process while the corresponding lifetimes τ1 and τ2
were both significantly shorter (2.4 ns and 36.3 ns, respectively). For
the HATNR based sample, the fast decay was dominant (the prefactor
was almost 4 times larger) and the values of τ1 and τ2 were 2.9 ns and
23.4 ns, respectively. From these biexponential components, an average
life time (τave) can be obtained from a weighted mean by using eqn. (2)
[64,65].
τave = (A1τ1
2
+ A2τ2
2
)/ (A1τ1 + A2τ2) (2)
The average lifetimes of ETL-free, compact TiO2 and HATNR sam-
ples were found to be 265.7 ns, 34.3 ns and 17.3 ns respectively. Thus,
the HATNRs appear to create an especially fast non-radiative decay
pathway, indicating that they effectively capture excited charge carriers
in the perovskite layer. The shorter average lifetime of HATNRs relative
to compact TiO2 is consistent with a more effective electron transfer
from the perovskite layer to the HATNRs, in agreement with the ob-
served quenching of the steady-state PL.
Fig. S10 shows the topographical image of the perovskite layer
deposited on top of the compact (Fig. S10a), and HATNR layers (Fig.
S10b). Generally, the grain size of the polycrystalline perovskite layer
depends on the deposition technique and the precursor used. However,
Fig. 4. (a) X-ray diffractograms of compact TiO2 (red) and HATNR array (black) on FTO substrate. Inset shows XRD pattern of compact TiO2 on bare glass substrate.
Energy band diagram of perovskite solar cells made with (c) Compact TiO2 and (c) HATNR arrays. (For interpretation of the references to colour in this figure legend,
the reader is referred to the Web version of this article.)
Fig. 5. (a) Steady state photoluminescence (PL) spectra of glass/perovskite (blue), perovskite deposited over compact TiO2 (red) and perovskite/HATNR array
(black); (b) The PL lifetime decay curve of perovskite with no ETL (blue; double exponential fit, magenta line), compact TiO2 (red; double exponential fit, yellow line)
and perovskite/HATNR array (black, double exponential fit, cyan). (For interpretation of the references to colour in this figure legend, the reader is referred to the
Web version of this article.)
U.K. Thakur, et al. Journal of Power Sources 417 (2019) 176–187
181
7. we found that in spite of having an identical deposition technique and
precursors, the average grain size of the perovskite deposited over the
HATNR samples was larger than the average perovskite grain size de-
posited over the compact TiO2 layer. The large grain size of perovskite
over HATNRs can be explained by better entrapment of perovskite
precursor solution in the voids between the HATNRs. As recombination
(trap) centers in the polycrystalline perovskite layer are generated by
grain boundaries, having a larger grain size helps to reduce undesirable
non-radiative recombination and improve device performance
[63,66–69].
Kelvin Probe Force Microscopy (KPFM) is being intensively used to
elucidate the nature of charge transport and recombination dynamics of
charge transporting layers; we utilized it here to probe the transport
properties of compact TiO2 and HATNR [70–80]. Fig. S4 is the
schematic illustration of KPFM measurement. Fig. 6a and b reveal the
topography of halide perovskite layer deposited over compact TiO2 film
and HATNR arrays respectively. Fig. 6c and d represent the surface
potential distribution on perovskite layer deposited over the compact
TiO2 and HATNR arrays in dark respectively. A key observation is that
the surface potential is distributed evenly over the surface for per-
ovskite coated on both the compact TiO2 sample and the HATNR
sample and is not influenced by the topographical variations seen in the
AFM images. The KPFM measurement in dark (Fig. 6c and d) shows a
contact potential difference (CPD) of −668 mV and −368 mV for
compact TiO2 and HATNR samples respectively. Thus, in the dark, the
CPD (with respect to the FTO substrate) was strongly negative in both
kinds of samples, which is attributed to downward bending of the
electronic bands of perovskite at the perovskite-TiO2 interface; this
Fig. 6. Topography of perovskite layer deposited over compact TiO2 (a) and HATNR (b). Surface potential map of perovskite deposited over compact TiO2 (c) and
HATNR (d) in dark. Surface potential map of perovskite deposited over compact TiO2 (e) and HATNR (f) under illumination with 450 nm laser. Surface potential
distribution on perovskite layer deposited over (g) compact TiO2 and (h) HATNR in dark and under illumination with 450 nm laser.
U.K. Thakur, et al. Journal of Power Sources 417 (2019) 176–187
182
8. result agrees well with previous reports [76,77]. The surface potential
of FTO/compact TiO2/perovskite sample was more negative compared
to FTO/HATNR/perovskite sample, indicating greater band-bending
and redistribution of charge at the interface of the perovskite and
compact TiO2. The higher surface potential (less negative) in the dark in
FTO/HATNR arrays/perovskite sample is indicative of a lower equili-
brium electron density (ND) in the HATNR arrays, in harmony with
previously published reports on the low carrier concentrations obtained
in hydrothermally synthesized TiO2 nanorods [81,82]. In a subsequent
scan at the same position, the CPD recorded with continuous illumi-
nation using 450 nm laser was found to be shifted ca. +50 mV and
+170 mV for compact TiO2 and HATNRs (Fig. 6e and f) respectively
due to effective charge separation, i.e. electrons moving to FTO through
TiO2 after extraction from perovskite with hole remaining in the per-
ovskite (Figs. 6d and 5e). The much higher surface potential of HATNR/
perovskite samples provides direct evidence of superior charge se-
paration and lower carrier recombination, which in turn, is indicative
of lower surface defects and hence fewer electron traps compared to
compact TiO2/perovskite sample.
The observed shift was found to be reversible after switching off the
laser, which confirms that holes are accumulated on the surface of the
perovskite while electrons transit through the ETL to the ground elec-
trode (FTO substrate). Taken together, the surface potential data im-
plies better charge separation and transport ability of HATNR ETL
compared to compact TiO2 ETL.
2.3. ETL dependent performance of halide perovskite solar cells
To probe the advantages of the near-horizontally aligned TiO2 na-
norods over the compact TiO2, we fabricated perovskite solar cells with
the procedure described in the methodology section 1.3(Section in ESI).
Fig. 7a depicts the J-V curves of perovskite solar cells fabricated with
the compact TiO2 and HATNR ETLs. The champion device employing
the HATNRs exhibits a power conversion efficiency (PCE) of 15.03%,
with a short circuit current density, open circuit voltage, and fill factor
of 22.85 mA cm−2
, 0.99 V and 0.67 respectively. The champion device
employing the compact TiO2 layer exhibits a power conversion effi-
ciency of 10.12% with a short circuit current density, open circuit
voltage, and fill factor of 16.58 mA cm−2
, 0.99 V and 0.62 respectively.
We further compared the performance of HATNR with vertically
oriented TiO2 nanorod arrays (VOTNRs). VOTNRs were fabricated
using the same recipe used to fabricate HATNRs, except the FTO sub-
strate was placed at an angle about 60° with respect to the bottom of
autoclave. Cross-sectional and top view of resulting vertically oriented
nanorods are shown in Figs. S5a and S5b respectively. Device made
about 100 nm of vertically oriented TiO2 nanorods gave a short circuit
current density, open circuit voltage, and fill factor of 21.82 mA cm−2
,
0.96 V and 0.69 respectively which resulted in a PCE of 14.52% (Fig.
S5c) which is comparable to our previous report [27]. The ETL com-
posed of an assembly of HATNRs dramatically outperformed the com-
pact TiO2 and vertically oriented TiO2 nanorod ETL and displayed
48.5% higher device efficiency compared to compact TiO2 ETL. The
performance of halide perovskite solar cells made with compact TiO2
and HATNRs measured at AM 1.5G is summarized in Fig. S6 and Table
S1. The improvement in the PCE was due to improvements in the short
circuit current density and the fill factor which are related to the
electron transfer and transport properties of ETL. To obtain additional
insights into the electron transport and recombination dynamics in the
photovoltaic devices with compact TiO2 and HATNRs ETLs, small signal
perturbation measurements, namely intensity modulated photovoltage
Fig. 7. Current density–voltage (J–V) curves measured under AM 1.5G condition (a), IMVS Nyquist plots measured with 633 nm LED (b), IMPS Nyquist plots
measured with 633 nm LED (c) and external quantum yield of best-performing perovskite solar cells based on compact TiO2 (red) and HATNR (black) electron
transporting layers (d). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
U.K. Thakur, et al. Journal of Power Sources 417 (2019) 176–187
183
9. spectroscopy (IMVS), and intensity modulated photocurrent spectro-
scopy (IMPS), were performed. Recently, these small perturbation
techniques have been frequently used to study the charge carrier dy-
namics in perovskite solar cells [83–92]. Fig. 7b shows the IMVS re-
sponse of a perovskite solar cell in the range of 0.1 Hz–100 kHz. From
the measurements, two semicircles - one in the high frequency region
and another in the low frequency region were obtained with time
constants τhf and τlf respectively. The obtained plot clearly shows two
well resolved semicircles similar to the planar perovskite solar cells
reported by Pockett et al. [93]. The recombination lifetimes of per-
ovskite solar cells fabricated with HATNR and compact TiO2 film were
calculated by considering the frequency of the minimum point (fmin) of
the high frequency semicircle, using eqn. (3).
τr = 1/2πfmin (3)
τet = 1/2πfmin (4)
The recombination time τr was calculated to be 3.14 μs for HATNR
and 3.20 μs for compact TiO2 solar cells. Similarly, the recombination
lifetimes of HATNR and compact TiO2 based solar cells in dark were
calculated using solid state impedance spectroscopy shown (Fig. S7). As
time constants corresponding to carrier recombination for both types of
electron transport layer are almost identical, no significant difference in
the open circuit voltage is expected. To understand the charge transport
properties of HATNR and compact TiO2 films as ETLs, IMPS was used,
and the resulting Nyquist plots are shown in Fig. 7c. The IMPS Nyquist
plot of the perovskite solar cell has two distinct semicircles. One
semicircle is in the first quadrant and the other is in the lower quadrant
as reported in the literature for perovskite solar cells [93,94]. Electron
transport times (τet) within each ETL at short-circuit condition were
calculated using eqn. (4), at the frequency corresponding to the minima
of the imaginary photocurrent. τet was calculated to be 36.70 μs for
HATNR and 73.80 μs for compact TiO2 based solar cells. The lower
transport time of HATNR indicates better charge transport efficiency of
HATNRs, which leads to improvement in the charge collection effi-
ciency of the HATNR and hence the short-circuit current density.
D = d2
/2.35. τet (5)
LD = (D.τr)1/2
(6)
Charge transport rates within the ETL were calculated by estimating
the electron diffusion coefficient, D, using eqn. (5), where the thick-
nesses (d) of the ETLs in the solar cells were considered. Values of D
were found to be 46.70 × 10−6
cm2
s−1
for HATNR arrays and
28.25 × 10−6
cm2
s−1
for compact TiO2 based solar cells, implying
faster electron transport in HATNRs than in compact TiO2. The corre-
sponding carrier mobilities were estimated using the Einstein relation
to be 1.80 × 10−3
cm2
V−1
s−1
for the HATNR and
1.09 × 10−3
cm2
V−1
s−1
for the compact TiO2 ETL. Due to their high
surface area, the nanorods are expected to have a large population of
carrier traps that limit their mobility [82]. However, the diffusion
coefficient (and electron mobility) of the HATNRs are more in line with
surface passivated rutile TiO2 nanorods [26,81,95], suggesting that the
perovskite coating might be at least partially passivating the surface of
the HATNRs. Considering the values of D and τr, the effective electron
diffusion length LD was determined using eqn. (6) and were calculated
to be 12.16 μm for the HATNR based solar cell and 10.61 μm for the
compact TiO2 based solar cell. The 15% higher electron diffusion length
is expected to result in higher photocurrent densities and fill factors in
HATNR array-based perovskite solar cells. The incident photon-to-
electron conversion efficiency (IPCE) shown in Fig. 7d agreed well with
the Jsc values obtained in the J-V curve. The IPCE values for the HATNR
based perovskite solar cells were significantly larger than those for the
compact TiO2 based perovskite solar cells for the spectral range from
430 nm to 770 nm. The IPCE is given by product of the light harvesting
efficiency (LHE), the charge separation efficiency (CSE) and the charge
collection efficiency (CCE) as eqn. (7),
IPCE (%) = ηLHE × ηCSE × ηCCE (7)
The improved carrier extraction by the HATNR ETL demonstrated
through stronger PL quenching and CPD shift in KPFM implies a higher
charge separation efficiency while the higher electron diffusion lengths
in the HATNR ETL inferred from IMPS data implies a higher charge
collection efficiency resulting in higher IPCE and hence higher short-
circuit current density of perovskite solar cells made with HATNR
compared to the compact TiO2.
2.4. Nanophotonic enhancement of halide perovskite solar cells due to
HATNR ETL
To understand the light harvesting properties (ηLHE in eqn. (7)) of
the compact, and HATNRs nanostructures, we performed UV–Vis
measurements. The UV–Vis spectra of perovskite layer deposited TiO2
structures are depicted in Fig. S9. The significantly lower diffuse re-
flectance of the perovskite coated HATNR ETL (black curve in Fig. S9a)
compared to the perovskite coated compact TiO2 ETL (red curve in Fig.
S9a) for the same perovskite thickness demonstrates the suppression of
backscattering in the HATNR ETL-based solar cells. Likewise, the in-
tegrated absorptance of perovskite films on the HATNR ETL was found
to be dramatically higher in comparison to the compact TiO2 film in
Fig. S9b over the entire visible range. The methodology of measurement
of the integrated absorptance is explained in Section S1.4 and Fig. S8 in
ESI. The strong forward light scattering by the HATNR slows down the
propagation of light and also randomizes the direction of propagation,
and both these effects enhance the absorption of photons within the
perovskite active layer. When the morphology consists of one-dimen-
sional nanostructures aligned horizontally on the substrate, they act as
light scattering centers and facilitate the diffusion of photons, and
hence increase the light absorption. Similar results have been reported
by the Gao et al. when they used a TiO2 nanotube network as the
electron transport layer for perovskite solar cells [96].
Electromagnetic simulations using Lumerical FDTD Solutions were
performed to validate our hypothesis that the HATNR nanostructure
serves as a scatterer which facilitates light diffusion and enhanced light
absorption. The compact layer was set up as 60 nm thick anatase TiO2,
while the individual nanorods were 20 nm in width and 100 nm in
length. The HATNR ETL was composed of nanorafts composed of
square-shaped rutile TiO2 nanorods tilted at 30° lying on FTO glass. All
the simulation parameters were based on FESEM images. To better
understand light scattering effects and their relationship with the film
morphology, far field scattering simulations were performed for both
compact TiO2 and HATNR ETLs with and without perovskite. Two
different perovskite layer thicknesses were used 200 nm and 800 nm.
The polar plots directly reveal the direction and intensity of scattering
light. In the simulation, the light source is placed below the sample and
the sample is illuminated upwards along the z-direction. The substrate
lies in the x-y plane. Forward-scattering is presented as the top semi-
circle from 0° to 180° while backscattering from 180° to 360° in both
polar plots. Fig. 8a demonstrates that the compact TiO2 ETL samples
exhibit extremely strong backscattering, which is a major source of
photon losses. For the compact TiO2 ETL, although the forward-scat-
tering decreases after increasing the thickness of the perovskite layer,
the backscattering is little changed as seen in Fig. 8a. Meanwhile, it is
obvious from Fig. 8b that backscattering is well suppressed for the
HATNR ETL, and the dramatic decrease of forward scattering intensity
is attributed to enhanced absorption of diffused light by the perovskite
layer on the top of the HATNR ETL. Fig. 8c is a simulated Poynting
vector distribution in the x-y plane showing hotspots near the ex-
tremities of the major axis of the nanorods where maximum light ab-
sorption takes place. Fig. 8d consists of the simulated absorption spectra
of two ETLs after coating with perovskite, and the enhanced light
U.K. Thakur, et al. Journal of Power Sources 417 (2019) 176–187
184
10. harvesting by the HATNR ETL based samples seen in the experimental
data (Fig. 7d) is confirmed. These results fully validated our theory that
high photonic strength of the near-horizontally aligned nanorods cou-
pled with near-perfect refractive index matching with the perovskite
layer, ensures maximum utilization of incident light within the per-
ovskite layer. These results are applicable to other types of solar cells as
well (such as those based on Si and GaAs). Nanorafts consisting of non-
absorbing or weakly absorbing horizontal nanorods aligned in the
substrate plane will suppress backscattering and enhance forward
scattering, provided that the refractive index of the nanorods is well-
matched with the real part of the complex refractive index of the
medium in which the nanorafts are embedded (typically the active
layer absorber). More information about the simulations is provided in
the supporting information, such as architecture parameters, light
source and monitors.
3. Conclusion
In summary, we demonstrated a facile approach to prepare near-
horizontally aligned TiO2 nanorod (HATNR) arrays via a hydrothermal
route. Scanning electron microscopy showed the formation of larger
grained perovskite films on the HATNR electron transport layer (ETL).
Time-resolved photoluminescence measurements indicated that the
HATNR extracted electrons more efficiently from the perovskite layer
compared to the commonly used compact TiO2 electron transport layer
while intensity modulated photocurrent spectroscopy suggested faster
transport in the HATNR ETL. The HATNR ETL also resulted in a na-
nophotonic enhancement of the absorption in the perovskite active
layer. Both experimentally measured and simulated optical spectra
demonstrated a strong suppression of the backscattering in perovskite-
coated nanorod layers relative to perovskite-coated compact TiO2
layers, and a forward scattering-mediated enhancement of the light
harvesting. As a consequence of the nanophotonic enhancement in the
utilization of photons in the active layer as well as improved electron
extraction and electron transport in perovskite solar cells employing
HATNR ETLs, a dramatic enhancement of the overall solar cell per-
formance was observed. Perovskite solar cells constructed using the
HATNR ETL exhibited an average photoconversion efficiency (PCE) of
13.9 ± 0.8% and a champion device PCE of 15.0%, which is nearly
50% higher than perovskite solar cells constructed using the compact
TiO2 ETL, which exhibited an average photoconversion efficiency (PCE)
of 9.4 ± 0.8% and a champion device PCE of 10.1%.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
The authors would like to thank the Natural Sciences and
Fig. 8. Simulation data showing (a) scattering polar plot of compact TiO2 ETL coated with perovskite thin films of 200 nm thickness (black curve) and 800 nm
thickness (red curve) (b) scattering polar plot HATNR ETL coated with perovskite thin films of 200 nm thickness (black curve) and 800 nm thickness (red curve) (c)
Electric field intensity in substrate plane for HATNR ETL immersed in perovskite matrix and (d) Absorption of compact TiO2 (red) and TiO2 nanorods (black) with
800 nm thick perovskite layer deposited on top is. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this
article.)
U.K. Thakur, et al. Journal of Power Sources 417 (2019) 176–187
185
11. Engineering Research Council of Canada, the National Research Council
Canada, Future Energy Systems (FES) and CMC Microsystems for fi-
nancial assistance. UKT would like to thank Alberta Innovates for
graduate student scholarship funding. The University of Alberta
Nanofab and National Research Council - National Institute for
Nanotechnology are acknowledged for providing access to character-
ization and fabrication facilities. Photovoltaic device fabrication and
testing facilities used equipment made available to Karthik Shankar
through a Canada foundation for Innovation (CFI) grant, which was
matched by the Alberta Small Equipment Grants Program (SEGP). Dr.
Kai Kui, NRC-NINT is kindly acknowledged for HR-TEM analysis.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.jpowsour.2018.11.089.
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