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Carlos F. O. Graeff,
Mirko Congiu, Silvia L. Fernandes
CEPID/CDMF
2013/07296-2
Materials for the Optimization of
Solar Ene...
The earth’s population consumes ~ 21 trillion kWhrs of electricity, with ~ 2/3
generated using fossil fuels
2018
World Ene...
20182018
World Energy Production Outlook
4
China
United States
Japan
Germany
Italy
India
Spain
France
Australia
South Chorea
Belgium
Other
Greece
United Kingdom
Wo...
Overall: 312 MW
Main Industries Energy cost evaluation A sector-specific view..
Maximum installed Power classified by appl...
oneelectronenergy
space
Generalized picture
• Metastable high and low
energy states
• Absorber transfers charges into
high...
7
Measuring a solar cell
Voc
Jsc
dark
light
reverse
forward
Fill Factor =
area of the curve
8
• Silicon
• Dye sensitized
• Organic
• Perovskites
Types of solar cells
Conductive FTO
Porous TiO2
Dye
REDOX
Cathode on FTO
e- h+
• Low production costs
• Low processing temperatures
• Does not ...
VB
CB LUMO
HOMO
REDOX
TiO2 Dye
e-
h+
F
T
O
F
T
O
Counter
electrode
LOAD
EF
Dyes:
N3 D5
Electrolytes:
Counter Electrodes:
I...
• Efficiency: More efficient dyes, transparent dyes (NIR)
• Cost: Replacement of expensive component such as Pt and Ru-bas...
ANODE CATHODE ELECTROLYTE
TiO2 : Synthesis (hydrothermal
and sol-gel) paste preparation
and film deposition
CoS counter el...
• Fundamental part of the DSSC
• Reestablishes the redox equilibrium
• Catalytic material deposited on FTO
• Transparency
...
Narrow-gap p-type semiconductor, cheap,
abundant and highly catalytic for the redox
process involving I-/I3
-
Cobalt Sulfi...
1. The precursor is dissolved into an appropriate solvent
2. The obtained Ink is spread on the substrate to obtain a film
...
Targets:
1. Synthesize a cheap chemical precursor
2. Soluble in water
3. Lower the thermal treatment temperature
4. Study ...
1
• 1mL TGA in 10mL H2O
2
• NH4OH 7M dropped
• pH 7,5 - 8,0
3
• 1:1 CoCl2
• Separation by adding ethanol(c.a. 20mL)
M. Con...
TGA is a bidentate ligand:
Two moieties (SH and COOH)
The characteristic peak of
S-H stretching is missing in
the complex
...
Loss of H2O
Degradation (loss of 39%
of initial mass)
Constant weight
• Molecular weight of CoSCH2CO2 is 149.02 g/mol
• Af...
The deposition process...
M. Congiu et al., Solar Energy 122: 87-96-December 2015
CoLE FCE
Co(II)Co(III) shuttles
ACN:MPN
70:30
ferrocene/ferrocenium
PC
• Iodine/iodide is corrosive and, in some condition...
Electrolyte CE Rs (Ωcm2 ) Rct (Ωcm2) Cdl(μFcm-2) n Ws-R Ws-T Ws-P
HSE CoS 13.34 ± 1.50 1.53 ± 0.25 12.0 ± 0.1 0.81 ± 0.10 ...
Photoanode Dye Electrolyte Conter electrode Area (cm2) Jsc(mAcm2) Voc (mV) FF(%) η(%)
SP D5 HSE Pt 0.25 15.7 ± 0.8 705 ± 1...
• Easy to process
• Water-based
• High efficient CoS electrodes
• Compatible with iodine-free electrolytes
Main Results
Light
CB
VB
HOMO
LUMO
LOAD
I-/I3
-
REDOX
NiO
h+
3 I-  I3
- + 2e-
Very low efficiency from 0.2 to 0.03%
Congiu, M. ; Bonom...
• There are dyes specific for p-type DSSCs: Erythrosine B
and P1
• Photocathode NiO Rapid Discharge Sintering RDS (UCD,
Du...
p-DSC configuration VOC / mV JSC /mA cm-2 FF / % η / %
NiO/ERYB/Pt-FTO 80 -1.059 34.8 0.030
NiO/ERYB/CoS 74 -1.051 32.5 0....
• Interfacial Sulfurization
of Cu(II)acetylacetonate
with thiourea
• Water/DCM (interface)
Iodine/Iodide redox couple is c...
• The CuS nanocrystals suspension (ink) is drop-casted on
clean FTO
• After a fast (10 minutes) thermal treatment (200 oC)...
• Corrosion tests
.CONGIU, M. ; NUNES-NETO, O. ; DE MARCO, M.L. ; DINI, D. ; Graeff, C.F.O. . Cu2−xS
films as counter-elec...
Electrochemical trials in dummy cells EIS determination of charge transfer resistance (Rct)
• In annealed electrodes Rct s...
CV stress characterization
THE
ELECTROCATALYTIC
ACTIVITY IS
MANTAINED OVER
HUNDREDS OF
REPEATED CV
SCANS
We obtained a rel...
A tandem solar cell is a PV device with a photoanode and a photocathode (instead of a CE)
• The use of a photoactive catho...
In order to soften the photocurrent mismatch, a low efficiency anode could be applied such as
Fe2O3
Advantages of hematite...
Spherical nanoparticles have been fabricated by thermal decomposition of Fe(III) tris-acetylacetonate
PASTE PREPARATION
PR...
25 30 35 40 45 50 55 60 65
0.5
1.0
1.5
2.0
2.5
3.0
B
D
A
Intensity(arb.u.)
(deg.)
C
XRD Al %
0 %
1 %
5 %
10 %
* AlFe2O3
...
Table of PV parameters of Al doped hematite photoanodes with
different Al concentrations
** the transmittance at 500 nm wa...
1. n-type DSSCs based on porous Fe2O3
shown better PV performance using D5
instead of N3
2. The charge recombination param...
Perovskite solar cells (PSCs)
PSCs- Cheap and easily processable material
Combines distinct merits of several PV technolog...
Perovskite material
A + cations
methylammonium (MA +); formamidinium (FA+);
cesium (Cs+), rubidium (Rb+); ethylammonium
(E...
Efficiency of perovskite cells
HTM
Nature Communications 5, Article number: 3834 doi:10.1038/ncomms4834
Work Principle of perovskite solar cells
48
Degradation
•Intrinsic defect of perovskite material
(volatile organic cations, ions diffusion)
• Interfaces,
• Stable ...
Nb2O5 vs TiO2
Nb2O5 is similar to TiO2, with
• better chemical stability
• higher electronegativity than TiO2
• band gap a...
FAPESP bulletin
Our contribution
Main results
• Study of Nb2O5 as hole transport layer
• Origin of hysteresis in perovskite solar cells
•Use of different n...
NO HYSTERESIS : BETTER ELECTRON EXTRACTION DUE THE BAND GAP
ENGINEERING !
Nb2O5 –
better stability
and no J-V
hysteresis
C...
-7.3
-4.0
S.L. Fernandes, A.C. Véron, N.F.A. Neto, F.A. Nüesch, et al., Nb2O5 hole blocking layer for hysteresis-free pero...
Efficient interfacial charge extraction is crucial for mitigating the impact of oxygen-induced degradation.
Combination of...
Comparing different thickness of Nb2O5
Nb2O5 50 nm
no J-V hysteresis
better charge extraction
Recent results
Exploring the properties of niobium oxide films for perovskite solar cells
X-Ray Diffraction UV-Vis
110 nm ...
57
Current-voltage and conductivity of the niobium oxides films.
Exploring the properties of niobium oxide films for perov...
58
Exploring the properties of niobium oxide films for perovskite solar cells
High performance of 3.5NbO
based solar cells
59
Exploring the properties of niobium oxide films for perovskite solar cells
High conductivity 3.5NbO films,
high Jsc cel...
60
Exploring the properties of niobium oxide films for perovskite solar cells
In addition to high conductivity of
Nb-O fil...
Nb2O5 is an excellent material to be use as hole blocking layer in
perovskite solar improving the stability of the devices...
Prof. Franco Decker (University of Rome “La Sapienza”, Italy)
Claudia Barollo (University of Turim- Italy)
Danilo Dini (Un...
Our team
64
65
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Materials for the Optimization of Solar Energy Harvesting.

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Plenary lecture given by Carlos F. O. Graeff (Unesp) at the XVII B-MRS Meeting, in Natal (Brazil), on September 19, 2018.

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Materials for the Optimization of Solar Energy Harvesting.

  1. 1. Carlos F. O. Graeff, Mirko Congiu, Silvia L. Fernandes CEPID/CDMF 2013/07296-2 Materials for the Optimization of Solar Energy Harvesting
  2. 2. The earth’s population consumes ~ 21 trillion kWhrs of electricity, with ~ 2/3 generated using fossil fuels 2018 World Energy Consumption
  3. 3. 20182018 World Energy Production Outlook
  4. 4. 4 China United States Japan Germany Italy India Spain France Australia South Chorea Belgium Other Greece United Kingdom World World (TWh) %/total* *% calculated considering the global electrical energy production Global Solar generation for each country Country South Africa Canada WORLD ENERGY SOURCES HYDRO 1 TIMES TYDAL 2 TIMES GEOTHERMAL 5 TIMES BIOMASS 20 TIMES SOLAR ENERGY 2850 TIMES WIND 200 TIMES All renewable energy sources provide 3078x the global energy demand Outlook on Global Solar Energy
  5. 5. Overall: 312 MW Main Industries Energy cost evaluation A sector-specific view.. Maximum installed Power classified by application sector (MW) – 09/10/2017 Trade market Industry Habitational Rural Others % Power % Units KW per Unit Country 2020 2050 Australia, part of Central Asia, Chile, India (Gujarat and Rajasthan), Mexico, Middle East, North Africa, Peru, South Africa, United States (southwest) 5% 40% United States (remaining area) 3% 20% Europe (import) and Turkey 3% 15% Africa (remaining area), Argentina, Brazil and India (remaining area) 1% 15% Indonesia (import) 0,5% 7% China, Russia (import) 0,5% 4% A global view of installed power Economic Overview of Brazilian Solar Energy 160.041 MW Total Instaled power
  6. 6. oneelectronenergy space Generalized picture • Metastable high and low energy states • Absorber transfers charges into high and low energy state • Driving force brings charges to contacts • Selective contacts Green, M.A., Photovoltaic principles. Physica E, 14 (2002) 11-17 High energy state Low energy state Absorber e- p+ contact contact The Photovoltaic (PV) Effect
  7. 7. 7 Measuring a solar cell Voc Jsc dark light reverse forward Fill Factor = area of the curve
  8. 8. 8
  9. 9. • Silicon • Dye sensitized • Organic • Perovskites Types of solar cells
  10. 10. Conductive FTO Porous TiO2 Dye REDOX Cathode on FTO e- h+ • Low production costs • Low processing temperatures • Does not contain toxic materials (As, Ga..) • Efficiency up to 13% • Transparent (windows) Dye Sensitized Solar Cell (DSSC)
  11. 11. VB CB LUMO HOMO REDOX TiO2 Dye e- h+ F T O F T O Counter electrode LOAD EF Dyes: N3 D5 Electrolytes: Counter Electrodes: Iodine/iodide Co(II)/(III) polypyridines Ferrocene Carbon clustersPt Cobalt Sulfide Charge Separation in DSSC
  12. 12. • Efficiency: More efficient dyes, transparent dyes (NIR) • Cost: Replacement of expensive component such as Pt and Ru-based dyes with natural ones • Stability: Replacement of liquid electrolytes with gels or solid and reduce the content of iodine (corrosive) Challenges in DSSCs improvement
  13. 13. ANODE CATHODE ELECTROLYTE TiO2 : Synthesis (hydrothermal and sol-gel) paste preparation and film deposition CoS counter electrodes: preparation via print- compatible techniques Co(II)/(III) based electrolytes for high stability DSSCs and compatibility with CoS/CuS Fe2O3: for tandem solar cell applications CuS counter electrodes: preparation and characterization with iodine- free electrolytes Our contribution on DSSCs
  14. 14. • Fundamental part of the DSSC • Reestablishes the redox equilibrium • Catalytic material deposited on FTO • Transparency • Low charge-transfer resistance (Rct) • Stable • Cheap Conductive FTO REDOX Catalyst FTO Characteristics: Desired features: Sketch: • Gold • Platinum • NiS and CoS • other chalcogenides • graphite Available catalysts: $ The counter electrode (Cathode of n-DSSCs)
  15. 15. Narrow-gap p-type semiconductor, cheap, abundant and highly catalytic for the redox process involving I-/I3 - Cobalt Sulfide: LOW-ENERGY: S.I.L.A.R., electrodeposition, chemical bath, hydrothermal HIGH-ENERGY: sputtering, CVD, sulfurization Classic fabrication methods: Based on a single chemical precursor ink, spread on the substrate and thermally activated. We proposed two inks: • The first based on organic solvent (thinner), suitable for small devices.. • The second based on a water soluble precursor. Suitable for large-area applications Our strategy: Our water-based method for the deposition of CoS thin films
  16. 16. 1. The precursor is dissolved into an appropriate solvent 2. The obtained Ink is spread on the substrate to obtain a film 3. Thermal treatment converts the precursor film into a CoS film deposition Precursor film CoS thin film Temp. Chemical Precursor Method
  17. 17. Targets: 1. Synthesize a cheap chemical precursor 2. Soluble in water 3. Lower the thermal treatment temperature 4. Study the compatibility of CoS with other redox pairs Thioglycolic acid Ammonium thioglycolate pKa1= 3.83 Perm. salt pKa2= 9. 30 Lower toxicity Toxic NH3 NH3, Co2+ M. Congiu et al., Solar Energy 122: 87-96-December 2015 Methodology- a water-based ink
  18. 18. 1 • 1mL TGA in 10mL H2O 2 • NH4OH 7M dropped • pH 7,5 - 8,0 3 • 1:1 CoCl2 • Separation by adding ethanol(c.a. 20mL) M. Congiu et al., Solar Energy 122: 87-96-December 2015 Preparation and characterization of CoSCH2CO2
  19. 19. TGA is a bidentate ligand: Two moieties (SH and COOH) The characteristic peak of S-H stretching is missing in the complex How TGA is binding the metal ion?
  20. 20. Loss of H2O Degradation (loss of 39% of initial mass) Constant weight • Molecular weight of CoSCH2CO2 is 149.02 g/mol • After a loss of 39%  90.88 g/mol • CoS molecular weight is 90.99 g/mol So it is very probable that the chemical composition of the residue is Co:S 1:1 M. Congiu et al., Solar Energy 122: 87-96-December 2015 Other gaseous species Thermal Degradation Study
  21. 21. The deposition process... M. Congiu et al., Solar Energy 122: 87-96-December 2015
  22. 22. CoLE FCE Co(II)Co(III) shuttles ACN:MPN 70:30 ferrocene/ferrocenium PC • Iodine/iodide is corrosive and, in some conditions, produces bleaching of the dye • It produces radicals under UV radiation (addition to double bonds) • Is aggressive also against TiO2 and the sealing materials of the device M. Congiu et al., Solar Energy 122: 87-96-December 2015 Efficiency world record Suitable for natural dyes Alternative Electrolytes
  23. 23. Electrolyte CE Rs (Ωcm2 ) Rct (Ωcm2) Cdl(μFcm-2) n Ws-R Ws-T Ws-P HSE CoS 13.34 ± 1.50 1.53 ± 0.25 12.0 ± 0.1 0.81 ± 0.10 2.31 ± 0.50 1.32 ± 0.15 0.38 ± 0.10 HSE Pt 12.33 ± 1.34 2.32 ± 0.15 40.9 ± 3.5 0.96 ± 0.12 2.54 ± 0.43 1.16 ± 0.21 0.51 ± 0.09 CoLE CoS 12.25 ± 1.07 2.40 ± 0.20 18.0 ± 2.2 0.80± 0.15 13.00± 1.35 2.81 ± 0.20 0.44 ±0.10 FCE CoS 12.70 ± 1.20 2.23 ± 0.25 4.1 ± 0.6 0.79 ± 0.19 10.46 ± 2.17 0.83 ± 0.12 0.38 ±0.15 IT WORKS WITH IODINE-FREE ELECTROLYTES !! M. Congiu et al., Solar Energy 122: 87-96-December 2015 Electrochemical analysis of our CoS electrodes with different electrolytes
  24. 24. Photoanode Dye Electrolyte Conter electrode Area (cm2) Jsc(mAcm2) Voc (mV) FF(%) η(%) SP D5 HSE Pt 0.25 15.7 ± 0.8 705 ± 15 61.4 ± 1.1 6.9 ± 0.5 SP D5 HSE CoS 0.25 16.4 ± 0.9 685 ± 25 61.3 ± 0.8 6.8 ± 0.5 DB D5 HSE Pt 1.00 7.2 ± 1.4 655 ± 18 62.1 ± 1.1 3.1 ± 0.9 DB D5 HSE CoS 1.00 7.2 ± 1.6 665 ± 21 63.4 ± 0.7 3.1 ± 0.9 DB N719 HSE Pt 1.00 9.0 ± 0.8 702 ± 7 56.4 ± 1.2 3.6 ± 0.5 DB N719 HSE CoS 1.00 9.1 ± 0.8 700 ± 11 51.3 ± 1.1 3.5 ± 0.5 M. Congiu et al., Solar Energy 122: 87-96-December 2015 DSSC and Stability
  25. 25. • Easy to process • Water-based • High efficient CoS electrodes • Compatible with iodine-free electrolytes Main Results
  26. 26. Light CB VB HOMO LUMO LOAD I-/I3 - REDOX NiO h+ 3 I-  I3 - + 2e- Very low efficiency from 0.2 to 0.03% Congiu, M. ; Bonomo, M. ; de marco, M. L.; Dowling, D. P. ; Di Carlo, A. ; Dini, D. ; Graeff’, C. F. O. . Cobalt sulfide as counter electrode in p-type dye- sensitized solar cells. Chemistryselect, v. 1, p. 2808-2815, 2016 The first application of CoS in p-type DSC
  27. 27. • There are dyes specific for p-type DSSCs: Erythrosine B and P1 • Photocathode NiO Rapid Discharge Sintering RDS (UCD, Dublin) Waveguide MW generator Vacuum Quartz window Sample’s holder Awais et al., 2011 Application in p-type DSSCs
  28. 28. p-DSC configuration VOC / mV JSC /mA cm-2 FF / % η / % NiO/ERYB/Pt-FTO 80 -1.059 34.8 0.030 NiO/ERYB/CoS 74 -1.051 32.5 0.026 NiO/P1/Pt-FTO 94 -2.650 32.6 0.119 NiO/P1/CoS 94 -2.500 31.6 0.074 Characterization under AM 1.5
  29. 29. • Interfacial Sulfurization of Cu(II)acetylacetonate with thiourea • Water/DCM (interface) Iodine/Iodide redox couple is corrosive, lead to the formation of free-radicals under Uv-radiation (halogen) • Cu2-xS are a class of cheap and highly conductive p-type semiconductors Bottom-up built of hexagonal stacked CuS nanoplates HIGH POROSITY • Water/methanol • Isopropyl alcohol • Powder product Washing and purification of CuS • A suspension of hexagonal stacked nanoplates of CuS is prepared in ethanol (1 mg/mL) Dispersion in Ethanol and preparation of the ink In another investigation... We discover an excellent efficient Cu2-xS with ferrocene electrolyte
  30. 30. • The CuS nanocrystals suspension (ink) is drop-casted on clean FTO • After a fast (10 minutes) thermal treatment (200 oC) in air, CuS is converted into Cu2-xS (partial desulfurization) • A mechanically adherent rough surface coating is then obtained FM imaging XRD Annealed (digenite (Cu1.8S, 47–1748) and djurleite (Cu1,97S, 20–0365). JCPDS) As deposited (covellite CuS, 79–2321, JCPDS) FTO substrate Preparation of Cu2-xS electrodes
  31. 31. • Corrosion tests .CONGIU, M. ; NUNES-NETO, O. ; DE MARCO, M.L. ; DINI, D. ; Graeff, C.F.O. . Cu2−xS films as counter-electrodes for dye solar cells with ferrocene-based liquid electrolytes. Thin Solid Films , v. 612, p. 22-28, 2016. On the other hand.. Cu2-xS is fully compatible with FCE showing high electrocatalytic performances This electrode is not suitable for Iodine-based electrolytes…
  32. 32. Electrochemical trials in dummy cells EIS determination of charge transfer resistance (Rct) • In annealed electrodes Rct stabilizes after 100 hours (plateau) Characterization with FCE electrolyte Diffusion of the electrolyte
  33. 33. CV stress characterization THE ELECTROCATALYTIC ACTIVITY IS MANTAINED OVER HUNDREDS OF REPEATED CV SCANS We obtained a reliable material for application in FCE-based DSSCs
  34. 34. A tandem solar cell is a PV device with a photoanode and a photocathode (instead of a CE) • The use of a photoactive cathode increases the Voc of the device (series) • This effect should lead to a device with higher efficiency. HOWEVER The mismatch in the photocurrents results in a lower performance of the tandem device.. For this reason, nowadays does not exist a tandem solar cell more efficient than the most efficient n-DSSC (TiO2) (~13%) While the most efficient p-DSSC remains around 5% This is due to the high mismatch in anodic and cathodic photocurrents Pristine and Al-doped Hematite as an interesting photoanode of tandem DSSCs
  35. 35. In order to soften the photocurrent mismatch, a low efficiency anode could be applied such as Fe2O3 Advantages of hematite: 1. Is a cheap and abundant material 2. Low toxicity 3. Ease of preparation 4. Normally exhibits n-type semiconducting behavior Main applications: 1. Water-splitting solar devices (Al-doped) 2. Magnetic nanoparticles (pollutants scavenger-water) 3. Just few application in DSSCs due to the lower performance Aims of our investigation: • Provide a reliable method to fabricate porous pastes • Improve the efficiency of Fe2O3 anodes using different dyes • Study the effect of Al-doping on the cells parameters Use of a lower efficiency anode
  36. 36. Spherical nanoparticles have been fabricated by thermal decomposition of Fe(III) tris-acetylacetonate PASTE PREPARATION PROCEDURE Hematite powder mix Terpineol acetylacetone Ethylcellulose Ethanol Water milling Viscous spreadable paste 3 Notice! Al(C5H8O2)3 can be easily mixed with the precursor prior to the thermal degradation Fabrication of the paste
  37. 37. 25 30 35 40 45 50 55 60 65 0.5 1.0 1.5 2.0 2.5 3.0 B D A Intensity(arb.u.) (deg.) C XRD Al % 0 % 1 % 5 % 10 % * AlFe2O3 hercynite α-Fe2O3 1% Al 10 % Al Smaller particles (coarsening) CONFOCAL MICROSCOPY AFM TOPOGRAPHY Pristine and Al doped hematite porous layers
  38. 38. Table of PV parameters of Al doped hematite photoanodes with different Al concentrations ** the transmittance at 500 nm was considered as a transparency index Two different dyes, the first (N3) is a Ru-complex well known in DSSCs While the second is an organic dye (D5). I vs V under 1 sun N3 D5 D5 dyes has shown a higher efficiency with Fe2O3 .CONGIU, MIRKO ; DE MARCO, MARIA L. ; BONOMO, MATTEO ; NUNES-NETO, OSWALDO ; DINI, DANILO ; Graeff, Carlos F.O. . Pristine and Al-doped hematite printed films as photoanodes of p-type dye-sensitized solar cells. Journal of Nanoparticle Research (Online) , v. 19, p. 1-10, 2016. PV parameters close to those obtained with NiO in p- type DSSCs (better photocurrent matching) Sensitization with D5 and N3 dyes and DSSCs results
  39. 39. 1. n-type DSSCs based on porous Fe2O3 shown better PV performance using D5 instead of N3 2. The charge recombination parameter, calculated from EIS, are similar to those of a typical p-type DSSC based on NiO sensitized with erythrosine All considered Hematite should be considered as photoanode For a tandem DSSCs which could really shown an Efficiency higher than the respective p an n cells working alone Conclusions
  40. 40. Perovskite solar cells (PSCs) PSCs- Cheap and easily processable material Combines distinct merits of several PV technologies
  41. 41. Perovskite material A + cations methylammonium (MA +); formamidinium (FA+); cesium (Cs+), rubidium (Rb+); ethylammonium (EA+); guanidinium (GA+) X− anions (I−; Br−, Cl−) B2+ cations (Pb+2; Sn+2; Ge+2) Most used material : CH3NH3PbI3
  42. 42. Efficiency of perovskite cells
  43. 43. HTM Nature Communications 5, Article number: 3834 doi:10.1038/ncomms4834 Work Principle of perovskite solar cells
  44. 44. 48 Degradation •Intrinsic defect of perovskite material (volatile organic cations, ions diffusion) • Interfaces, • Stable conductive hole material, • Encapsulation Hysteresis • Charge traps- charge accumulation • Mobile ions (I-, Cl-, methylamonium+) • Ferroeletric dipoles Challenges in perovskite solar cells degraded
  45. 45. Nb2O5 vs TiO2 Nb2O5 is similar to TiO2, with • better chemical stability • higher electronegativity than TiO2 • band gap allows higher Voc Brazil - the largest mineral reserves of niobium
  46. 46. FAPESP bulletin Our contribution
  47. 47. Main results • Study of Nb2O5 as hole transport layer • Origin of hysteresis in perovskite solar cells •Use of different niobium oxide films and its influence on the performance of the solar cells
  48. 48. NO HYSTERESIS : BETTER ELECTRON EXTRACTION DUE THE BAND GAP ENGINEERING ! Nb2O5 – better stability and no J-V hysteresis Comparing TiO2 x Nb2O5
  49. 49. -7.3 -4.0 S.L. Fernandes, A.C. Véron, N.F.A. Neto, F.A. Nüesch, et al., Nb2O5 hole blocking layer for hysteresis-free perovskite solar cells., Materials Letter, 181 (2016) 103–107. doi: band gap engineering glass FTO TiO2 - + - + - + - + - + - + glass FTO Nb2O5 - + - + - + - + - + - +-- + No hysteresis: Better electron extraction
  50. 50. Efficient interfacial charge extraction is crucial for mitigating the impact of oxygen-induced degradation. Combination of non extracted electrons and molecular oxygen decomposed the perovskite materials High stability: Better electron extraction RSC Adv., 2016, 6, 38079–38091 | 38079
  51. 51. Comparing different thickness of Nb2O5 Nb2O5 50 nm no J-V hysteresis better charge extraction
  52. 52. Recent results Exploring the properties of niobium oxide films for perovskite solar cells X-Ray Diffraction UV-Vis 110 nm thick films
  53. 53. 57 Current-voltage and conductivity of the niobium oxides films. Exploring the properties of niobium oxide films for perovskite solar cells Films deposited at 3.5sccm - higher conductivity
  54. 54. 58 Exploring the properties of niobium oxide films for perovskite solar cells High performance of 3.5NbO based solar cells
  55. 55. 59 Exploring the properties of niobium oxide films for perovskite solar cells High conductivity 3.5NbO films, high Jsc cell, improved efficiency
  56. 56. 60 Exploring the properties of niobium oxide films for perovskite solar cells In addition to high conductivity of Nb-O films, we found a better charge transfer between 3.5Nb-O and perovskite films Photoluminescence
  57. 57. Nb2O5 is an excellent material to be use as hole blocking layer in perovskite solar improving the stability of the devices, and resulting in hysteresis free devices The conductivity of niobium oxide films were improved by changing the oxygen content improving the efficiency of the cells. In addition, we found a better charge transfer between 3.5Nb-O and perovskite films Conclusions
  58. 58. Prof. Franco Decker (University of Rome “La Sapienza”, Italy) Claudia Barollo (University of Turim- Italy) Danilo Dini (University of Rome “La Sapienza”, Italy) Alessandro Lanuti (CHOSE, Italy) Aldo di Carlo (CHOSE, Italy) Anna C.Véron (EMPA, Switzerland) Frank A. Nüesch (EMPA, Switzerland) Thank you
  59. 59. Our team
  60. 60. 64
  61. 61. 65

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