This document discusses current solar cell technologies and how nanomaterials can improve their efficiency. It summarizes that fossil fuels currently dominate energy production but renewable technologies are advancing. Nanoscience has potential to enhance band gap utilization, spectral absorption, and reduce toxicity in photovoltaics. Nanowires and nanoarrays can scatter light and absorb more radiation to reduce losses. The document also reviews mechanisms like down conversion, intermediate bands, hot carriers, and dye-sensitized cells that may utilize nanomaterials to surpass efficiency limits of conventional solar cells.
p-i-n Solar Cell Modeling with Graphene as ElectrodeWahiduzzaman Khan
Graphene is a 2-D atomic layer of carbon atoms with unique electronic properties like outstanding carrier mobility, high carrier saturation velocity, excellent thermal conductivity, high mechanical strength, transparency, thinness, and flexibility which make graphene an excellent choice of material for advanced applications in future solar cell design. We modeled a solar cell using graphene as the front electrode to study its performance and compare the performance with that of other possible contenders- indium tin oxide (ITO), widely used material at present and carbon nanotube (CNT), another promising material in this regard. Numerical solutions of the electrostatic and transport equations were obtained using the finite-element method. It was found that solar cell with graphene electrode can outperform the others. We also studied its performance as a function of various parameters. The developed model and obtained results are important for the design of solar cell with graphene as electrode.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
3 d single gaas co axial nanowire solar cell for nanopillar-array photovoltai...ijcsa
Nanopillar array photovoltaics give unique advantages over today’s planar thin films in the areas of
optical properties and carrier collection, arising from their 3D geometry. The choice of the material
system, however, is essential in order to gain the advantage of the large surface/interface area associated
with nanopillars. Therefore, a well known Si and GaAs material are used in the design and studied in this
nanowire application. This work calculates and analyses the performance of the coaxial GaAs nanowire
and compared with that of Si nanowire using a semi-classical method. The current-voltage characteristics
are investigated for both under dark and AM1.5G illumination. It is found that GaAs nanowire gives almost
double efficiency with its counterpart Si nanowire. Their TCAD simulations can be validated reasonably
with that of published experimental result.
Quantum Dot-sensitized Solar Cells: A ReviewjournalBEEI
Quantum dot-sensitized solar cell (QDSSC) has an analogous structure and working principle to the dye sensitizer solar cell (DSSC). It has drawn great attention due to its unique features, like multiple exciton generation (MEG), simple fabrication and low cost. The power conversion efficiency (PCE) of QDSSC is lower than that of DSSC. To increase the PCE of QDSSC, it is required to develop new types of working electrodes, sensitizers, counter electrodes and electrolytes. This review highlights recent developments in QDSSCs and their key components, including the photoanode, sensitizer, electrolyte and counter electrode.
Communication has become a key aspect of our daily life, becoming increasingly portable and mobile. This would need the use of micro strip antennas. The rapid growth has led to the need of antennas with smaller size, increased bandwidth and high gain. In this paper, a new version of micro strip patch antenna is designed by adopting double layered substrate concept and adding a layer of metamaterial structure to a square micro strip antenna. The antenna properties gain, return loss and bandwidth are studied to achieve better performance. The designed patch antenna has an improved bandwidth of 60% at a resonant frequency of 2.47 GHz. This antenna is designed and simulated by using HFSS software.
p-i-n Solar Cell Modeling with Graphene as ElectrodeWahiduzzaman Khan
Graphene is a 2-D atomic layer of carbon atoms with unique electronic properties like outstanding carrier mobility, high carrier saturation velocity, excellent thermal conductivity, high mechanical strength, transparency, thinness, and flexibility which make graphene an excellent choice of material for advanced applications in future solar cell design. We modeled a solar cell using graphene as the front electrode to study its performance and compare the performance with that of other possible contenders- indium tin oxide (ITO), widely used material at present and carbon nanotube (CNT), another promising material in this regard. Numerical solutions of the electrostatic and transport equations were obtained using the finite-element method. It was found that solar cell with graphene electrode can outperform the others. We also studied its performance as a function of various parameters. The developed model and obtained results are important for the design of solar cell with graphene as electrode.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
3 d single gaas co axial nanowire solar cell for nanopillar-array photovoltai...ijcsa
Nanopillar array photovoltaics give unique advantages over today’s planar thin films in the areas of
optical properties and carrier collection, arising from their 3D geometry. The choice of the material
system, however, is essential in order to gain the advantage of the large surface/interface area associated
with nanopillars. Therefore, a well known Si and GaAs material are used in the design and studied in this
nanowire application. This work calculates and analyses the performance of the coaxial GaAs nanowire
and compared with that of Si nanowire using a semi-classical method. The current-voltage characteristics
are investigated for both under dark and AM1.5G illumination. It is found that GaAs nanowire gives almost
double efficiency with its counterpart Si nanowire. Their TCAD simulations can be validated reasonably
with that of published experimental result.
Quantum Dot-sensitized Solar Cells: A ReviewjournalBEEI
Quantum dot-sensitized solar cell (QDSSC) has an analogous structure and working principle to the dye sensitizer solar cell (DSSC). It has drawn great attention due to its unique features, like multiple exciton generation (MEG), simple fabrication and low cost. The power conversion efficiency (PCE) of QDSSC is lower than that of DSSC. To increase the PCE of QDSSC, it is required to develop new types of working electrodes, sensitizers, counter electrodes and electrolytes. This review highlights recent developments in QDSSCs and their key components, including the photoanode, sensitizer, electrolyte and counter electrode.
Communication has become a key aspect of our daily life, becoming increasingly portable and mobile. This would need the use of micro strip antennas. The rapid growth has led to the need of antennas with smaller size, increased bandwidth and high gain. In this paper, a new version of micro strip patch antenna is designed by adopting double layered substrate concept and adding a layer of metamaterial structure to a square micro strip antenna. The antenna properties gain, return loss and bandwidth are studied to achieve better performance. The designed patch antenna has an improved bandwidth of 60% at a resonant frequency of 2.47 GHz. This antenna is designed and simulated by using HFSS software.
Comparison of Different types of Solar Cells – a Reviewiosrjce
IOSR Journal of Electrical and Electronics Engineering(IOSR-JEEE) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of electrical and electronics engineering and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in electrical and electronics engineering. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
Acceptor–donor–acceptor small molecules based on derivatives of 3,4-ethylened...Boniface Y. Antwi
Simple EDOT based photo-active molecules have been synthesised by fewer synthetic steps. The molecules separately acted as donor units in organic solar cells fabrications. Best device efficiency was 1.36%.
Effects of Variation of Quantum Well Numbers on Gain Characteristics of Type-...journalBEEI
This paper reports the effects of variation of number of quantum wells in material gain characteristics and lasing wavelength of step index separately confined type-I InGaAsP/InP lasing nano-heterostructure for different carrier concentrations at room temperature in TE (Transverse Electric) mode of polarization. Peak material gain is found to be highest when the number of quantum well is one in the structure. However, for the case of 3QWs, 5QWs and 7QWs, it is almost same at a particular carrier density. Lasing wavelength at peak material gain considerably increases as the number of quantum well layers vary from single quantum well layer to three quantum well layers in the active region and after that it will remain almost same by any further increase in number of quantum wells for a particular carrier density. Furthermore, negative gain condition in the material gain spectra exists in the case of multiple quantum wells only at carrier concentration of 2×1018/cm3. The results suggest that the proposed nano-heterostructure is highly suitable as a light source in fiber optic links for long distance communication.
International Journal of Computational Engineering Research(IJCER)ijceronline
International Journal of Computational Engineering Research(IJCER) is an intentional online Journal in English monthly publishing journal. This Journal publish original research work that contributes significantly to further the scientific knowledge in engineering and Technology.
Mutual Coupling Reduction in Antenna Using EBG on Double SubstrateTELKOMNIKA JOURNAL
Malaysia
*Corresponding author, e-mail: raimidewan@gmail.com
Abstract
In this paper, a mutual coupling study is conducted between two-element array
antenna on dual substrate. A single patch antenna is firstly designed on dual substrate layer to
testify appropriate performance at 2.45 GHz. Subsequently, an array of two element patches on
dual substrate are constructed with one of them is incorporated with three EBG unit cell on the
bottom substrate. The radiating patch is on the top substrate, while the EBG unit cell is on the
bottom substrate. With EBGs in separate layers from the antenna array, the antenna elements
are closely separated by a distance of 22 mm with a significant reduced mutual coupling of -
26.61 dB. This corresponds to a distance reduction of 34.68%. The proposed structure
implemented only three EBG unit cells. Apart from that, the study of overlapped case of EBG
with the antenna is also presented.
Everything you need to know about climate change, in cartoons!Little Climate
Presentation on climate change - the science, impacts and solutions, using cartoons! Data from "Little Climate" book, sourced from the United Nations IPCC 5th Assessment Report and other scientific published papers. Presentation for the #lepakinsg eco-events group here in Singapore!
All cartoon images used with permission from Little Climate. www.littleclimate.com
Comparison of Different types of Solar Cells – a Reviewiosrjce
IOSR Journal of Electrical and Electronics Engineering(IOSR-JEEE) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of electrical and electronics engineering and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in electrical and electronics engineering. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
Acceptor–donor–acceptor small molecules based on derivatives of 3,4-ethylened...Boniface Y. Antwi
Simple EDOT based photo-active molecules have been synthesised by fewer synthetic steps. The molecules separately acted as donor units in organic solar cells fabrications. Best device efficiency was 1.36%.
Effects of Variation of Quantum Well Numbers on Gain Characteristics of Type-...journalBEEI
This paper reports the effects of variation of number of quantum wells in material gain characteristics and lasing wavelength of step index separately confined type-I InGaAsP/InP lasing nano-heterostructure for different carrier concentrations at room temperature in TE (Transverse Electric) mode of polarization. Peak material gain is found to be highest when the number of quantum well is one in the structure. However, for the case of 3QWs, 5QWs and 7QWs, it is almost same at a particular carrier density. Lasing wavelength at peak material gain considerably increases as the number of quantum well layers vary from single quantum well layer to three quantum well layers in the active region and after that it will remain almost same by any further increase in number of quantum wells for a particular carrier density. Furthermore, negative gain condition in the material gain spectra exists in the case of multiple quantum wells only at carrier concentration of 2×1018/cm3. The results suggest that the proposed nano-heterostructure is highly suitable as a light source in fiber optic links for long distance communication.
International Journal of Computational Engineering Research(IJCER)ijceronline
International Journal of Computational Engineering Research(IJCER) is an intentional online Journal in English monthly publishing journal. This Journal publish original research work that contributes significantly to further the scientific knowledge in engineering and Technology.
Mutual Coupling Reduction in Antenna Using EBG on Double SubstrateTELKOMNIKA JOURNAL
Malaysia
*Corresponding author, e-mail: raimidewan@gmail.com
Abstract
In this paper, a mutual coupling study is conducted between two-element array
antenna on dual substrate. A single patch antenna is firstly designed on dual substrate layer to
testify appropriate performance at 2.45 GHz. Subsequently, an array of two element patches on
dual substrate are constructed with one of them is incorporated with three EBG unit cell on the
bottom substrate. The radiating patch is on the top substrate, while the EBG unit cell is on the
bottom substrate. With EBGs in separate layers from the antenna array, the antenna elements
are closely separated by a distance of 22 mm with a significant reduced mutual coupling of -
26.61 dB. This corresponds to a distance reduction of 34.68%. The proposed structure
implemented only three EBG unit cells. Apart from that, the study of overlapped case of EBG
with the antenna is also presented.
Everything you need to know about climate change, in cartoons!Little Climate
Presentation on climate change - the science, impacts and solutions, using cartoons! Data from "Little Climate" book, sourced from the United Nations IPCC 5th Assessment Report and other scientific published papers. Presentation for the #lepakinsg eco-events group here in Singapore!
All cartoon images used with permission from Little Climate. www.littleclimate.com
Dealing with Eco-Anxiety! by Little ClimateLittle Climate
How drawing cartoons and starting little everyday eco actions helped me cope with climate trauma and depresssion, to take back control of climate change.
Super Stove! The Lao Cookbook: People and their StovesLittle Climate
Wonderful cookbook showcasing the Super Stove, part of the Improved Cookstove Program in Laos, managed by the local non-profit ARMI (Association for Rural Mobilisation and Improvement), SNV and Oxfam.
More information:
http://www.snv.org/public/cms/sites/default/files/explore/download/snv_cookbook_2015_web.pdf
http://www.switch-asia.eu/projects/cook-stoves-programme-laos/
Without a doubt, 2015 was an extraordinary year for Australian cattle markets. So what’s in store for 2016? Will the market continue the good fortune, or are we in for a few bumps in the road? In this webinar, MLA’s Ben Thomas joins Mecardo's Rob Herrmann to outline MLA's latest five-year cattle industry projections and what they mean for cattle prices. - See more
Carbon per Capita 5 Facts You Need To Know (infographic)Little Climate
Climate change is such a broad and complex issue – many of us struggle to connect the dots to what we do on a daily basis. But, there’s a simple number that gets us to a good start – our carbon dioxide emissions per person (or carbon per capita). Learn about carbon per capita, the difference between Production and Consumption carbon approaches, explore the case study of how Sweden has rapidly decarbonized, and consider the moral issues of the widening climate inequality and future carbon convergence.
Learning colors for Children - All colors in oneKids Academy Co
Let's start learning colors with perfectly painted printable worksheets produced by the best designers at Kids Academy. Visit our site site to get more printable worksheets for your kid www.kidsacademy.mobi
October 2016 Cattle outlook and 101 Cattle Forwards Andrew Whitelaw
In this webinar, Meat & Livestock Australia’s (MLA’s) Manager, Market Information, Ben Thomas will outline the key points of MLA’s latest five-year cattle industry projections, released in mid-October.
Mecardo’s Matt Dalgleish will then look at what these projections mean for prices, and a short explanation of cattle forwards.
In this research, the effects of magnetic field intensity on electrical characteristics of a monocrystalline silicon solar cell were investigated. The experimental test-rig under Standard Test Condition was set up and tested to observe the respective effects. The electrical characteristics in terms of current-voltage-power curves, critical solar cell parameters and fill factor were then examined and analyzed. The outcome of this study demonstrates that the external magnetic field has a positive impact on electrical parameters, the experimental results showed that applying magnetic intensity of 60-260mT significantly affected the electrical characteristics of the cell; i.e., maximized cell current, voltage and power by 12.20, 7.12 and 23.60%, respectively. In addition, this positive impact consequencely happened on the i-v and p-v electrical characteristics curves of the solar cell; reflected by 3.69% increasing in the fill factor.
The advent of micro grid has enticed a lot of interest in the research of distribution generation thereby bringing into existence an intelligent electrical generation networks. It ensures security, reliability, stability, and sustainable of energy. Micro grid may include both renewable and non-renewable energy sources. It has been proven to possess the promising potential of providing clean, efficient, and reliable power. The energy sources include solar photovoltaic, wind, fuel cell, micro turbine, bio- mass micro hydro. Various architecture of a micro grid are available and are developed the factors dependable upon availability of renewable resources, geographical location, load demand. For effective and efficient operation unlike main grid, it needs to employ special and control this is so because of combination of conventional and renewable energy sources.
Multi-Junction Solar Cells: Snapshots from the First Decade of the Twenty-Fir...CrimsonPublishersRDMS
Multi-Junction Solar Cells: Snapshots from the First Decade of the Twenty-First Century by Guy Francis Mongelli* in Crimson Publishers: Peer Reviewed Material Science Journals
Seminar report on Flexible Photovoltaic TechnologyKumudGarg3
This report is relate to topic of Flexible Solar Cell. In this report you get content is introduction, introduction to flexible solar cell, types of solar cell, types of flexible solar cell, application n etc.
Comparative Study of Parallel Vertical Junction Solar Cell Photovoltagesijtsrd
This work aims, through a theoretical study, to make a comparison of three different parallel vertical junction solar cells photovoltages Si silicon, InAs indium arsenide and GaAs gallium arsenide . For this we have showed the evolution of these voltages with regard to temperature and the collection of the charge carrier velocity. The photovoltaic cell having the voltage most important is probably more performant.These cells have the same dimensions, are doped with the same doping level and are used under the same conditions of illumination and temperature. The comparative study is made only on their electric photovoltage. This important size for the characterization of cell performance is deduced from the continuity equation resolution. The photovoltages are studied according to the temperature and according to charge carrier's collection velocity. Dieme Nf. | Sane M. | Honadia P. Ab. Aziz | Barro F. Id. "Comparative Study of Parallel Vertical Junction Solar Cell Photovoltages" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-6 , October 2019, URL: https://www.ijtsrd.com/papers/ijtsrd29193.pdf Paper URL: https://www.ijtsrd.com/engineering/chassis-engineering/29193/comparative-study-of-parallel-vertical-junction-solar-cell-photovoltages/dieme-nf
The electrical and environmental parameters of polymer solar cells (PSC) provide important information on their performance. In the present article we study the influence of temperature on the voltage-current (I-V) characteristic at different temperatures from 10 °C to 90 °C, and important parameters like bandgap energy Eg, and the energy conversion efficiency η. The one-diode electrical model, normally used for semiconductor cells, has been tested and validated for the polemeral junction. The PSC used in our study are formed by the poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM). Our technique is based on the combination of two steps; the first use the Least Mean Squares (LMS) method while the second use the Newton-Raphson algorithm. The found results are compared to other recently published works, they show that the developed approach is very accurate. This precision is proved by the minimal values of statistical errors (RMSE) and the good agreement between both the experimental data and the I-V simulated curves. The obtained results show a clear and a monotonic dependence of the cell efficiency on the studied parameters.
A Systematic Review of Renewable Energy Trend.pdfssuser793b4e
This paper systematically and successfully reviewed the renewable energy trend from 2010 to 2023. This review
detailed the difference renewable energy and conclusion was drawn that solar photovoltaic (PV) energy has the
leading trend in power generation growth and innovation. This research work explained in detail the most recent
solar photovoltaic optimization techniques and it was observed from the review that hybridization of intelligent and
non-intelligent maximum power point tracking technique has the best tracking power conversion efficiency. The
advantages and disadvantage of solar PV together with the solar optimization and innovational growth trends were
examined. This research showed that clean and renewable energy sources will continue to grow and the solar energy
industry is expected to experience significant growth and rapid innovation in the next 10 years. From the observed
rapid growth and innovation trend in solar energy, the world will have a very cheap, abundant and clean energy
before 2050.
Ultra-optical characterization of thin film solar cells materials using core...IJECEIAES
This paper investigates on new design of heterojunction quantum dot (HJQD) photovoltaics solar cells CdS/PbS that is based on quantum dot metallics PbS core/shell absorber layer and quantum dot window layer. It has been enhanced the performance of traditional HJQD thin film solar cells model based on quantum dot absorber layer and bulk window layer. The new design has been used sub-micro absorber layer thickness to achieve high efficiency with material reduction, low cost, and time. Metallicssemiconductor core/shell absorber layer has been succeeded for improving the optical characteristics such energy band gap and the absorption of absorber layer materials, also enhancing the performance of HJQD ITO/CdS/QDPbS/Au, sub micro thin film solar cells. Finally, it has been formulating the quantum dot (QD) metallic cores concentration effect on the absorption, energy band gap and electron-hole generation rate in absorber layers, external quantum efficiency, energy conversion efficiency, fill factor of the innovative design of HJQD cells.
A Study of Shading Effect on Photovoltaic Modules with Proposed P&O Checking ...Yayah Zakaria
Sun irradiation levels and associated temperature changes are the main factors that influence the conversion of solar energy into electricity. Most energy is produced during a hot sunny day as the sun irradiation is at the maximum level and uniform throughout the solar photovoltaic (PV). However, most solar PV were frequently get shadowed, completely or partially, by the neighbouring buildings, trees and passing clouds. Consequently, the solar PV has lower voltage and current output, hence,
multiple maximum power points (MPP) are existed on the PV curve, which could cause confusion to the conventional Maximum Power Point Tracker (MPPT) to track the true MPP for the PV system. Thus, it is important to examine the impacts of partial shading on the solar PV in order to extract the maximum possible power. This paper presents a MATLAB-based modelling for simulation and experimental setup to study the I-V and P-V characteristics of a solar module under a non-uniform irradiation due to partial shading condition (PSC). Furthermore, this study is also proposed an effective method (a variable step size of P&O with checking algorithm) that is low cost and higher tracking efficiency. Thus, this study is essential in improving and evaluating any new MPPT algorithm under the PSC.
A Study of Shading Effect on Photovoltaic Modules with Proposed P&O Checking ...IJECEIAES
Sun irradiation levels and associated temperature changes are the main factors that influence the conversion of solar energy into electricity. Most energy is produced during a hot sunny day as the sun irradiation is at the maximum level and uniform throughout the solar photovoltaic (PV). However, most solar PV were frequently get shadowed, completely or partially, by the neighbouring buildings, trees and passing clouds. Consequently, the solar PV has lower voltage and current output, hence, multiple maximum power points (MPP) are existed on the PV curve, which could cause confusion to the conventional Maximum Power Point Tracker (MPPT) to track the true MPP for the PV system. Thus, it is important to examine the impacts of partial shading on the solar PV in order to extract the maximum possible power. This paper presents a MATLAB-based modelling for simulation and experimental setup to study the I-V and P-V characteristics of a solar module under a non-uniform irradiation due to partial shading condition (PSC). Furthermore, this study is also proposed an effective method (a variable step size of P&O with checking algorithm) that is low cost and higher tracking efficiency. Thus, this study is essential in improving and evaluating any new MPPT algorithm under the PSC.
1. Current Solar Cell Technologies and the Application of Nanomaterials
in Photovoltaics
Jennifer Cook
February 11, 2016
Abstract
Worldwide energy usage has increased by approximately 49% over the last 30 years, and the current, total,
global power requirement stands above 1.7 TW.1
At present, the main source of energy conversion, are fossil
fuels, with a larger amount of energy sourced from coal, rather than oil or gas. Technological advances in
nanoscience has opened many doors in the field of renewable energy conversion, particularly for photovoltaic
(PV) devices. Constant progress is being made to improve band gap utilisation, spectral utilisation and
to reduce toxicity. Nanowires and 1D nanoarrays can help to reduce parasitic losses via enhanced light
scattering and increase the amount of incident radiation absorbed into the device. Intermediate band
structures may offer a wider utilisation of the spectrum, with quantum dots offering further efficiency
enhancements. With the ability to tune many properties of nano architectures, as well as control their
size and morphology, it is not only third generation photovoltaics that will benefit from nano-technological
advancements. Current successful applications include the combination of nanoparticles with dyes for use
in dye-sensitised cells, as well as the development of hybrid cells. Nanomaterials hold exciting prospects for
the optimisation of solar power and the future of global energy production, provided the limitations they
pose, can be sufficiently supressed, for them to serve as a more efficient and economically viable option over
current technologies.
1 Introduction
Energy conversion for electricity using renewables in
the UK, has undergone an increase of 550% from the
year 2000 to 2014 as seen in figure 1.2
The graph dis-
plays the main renewable energy sources and the cor-
responding amount of energy produced in each year
in the UK. Increasing interest into photovoltaics as a
viable solution to the energy crisis has led to the pub-
lication of numerous research papers in this field.
Solar cells can be categorised by three generations (Fig-
ure 2).3
Dotted lines are shown with a positive, linear
correlation; in general, the larger the gradient of the
line, the better the solar cell technology, in terms of its
efficiency to cost ratio.
First generation solar cells were based on single crys-
tal or multi-crystalline wafer technologies, and mainly
on single-junctions, therefore possessing a theoretical
conversion efficiency limit, known as the ‘Shockley-
Queisser limit’,4
which stands at approximately 32%
for single junction cells.
Second generation thin-film PV technologies combine
the efforts to improve conversion efficiencies, whilst
maintaining the economic viability of solar cells (Fig-
ure 2). By incorporating nanomaterials into current
PV technologies, efficiency improvements can be made,
even exceeding the Shockley-Queisser limit.
2 P-n Junctions and the Photo-
voltaic cell
Traditional solar cells are based on p-n junction semi-
conductors. As with all p-n junctions, the drift current
is controlled by the density of minority charge carriers.
When light is applied, it acts as a bias voltage to the
junction and the density of the minority charge carri-
ers in each region increases which increases the drift.
When the p/n regions are connected with a conductive
material, a current is produced in the closed circuit.
The electrons flow from the n-region through the cir-
cuit and recombine with a hole in the p-region. If the
circuit is opened, an ‘open circuit voltage’ is produced.
This is known as a photovoltaic cell.5
2.1 Performance of a solar cell
The band structure for a typical semiconductor is shown
in figure 6.3
The band gap energy is directly propor-
tional to the open circuit voltage, and can be increased
by increasing the lifetime τ of the minority charge car-
riers where τ is determined by the recombination rate.
Recombination happens via three main mechanisms:
Shockley Read Hall (SRH),6
Auger7
and Radiative.8
The radiative method is dominant within direct band
gap materials such as GaAs, as additional momentum
does not need to be supplied for recombination. Re-
combination also affects the diffusion length Lp, and as
a rule, the thickness of the solar cell must not exceed
Lp.9
1
2. Figure 1
The graph displays the main renewable energy sources
and the corresponding amount of energy produced in each
year. The largest increase in percentage FiT capacity
from 2013-2014 was from solar photovoltaics (PV), with
an increase of 565MW.
Figure 2
(a) Energy diagram to show the spectral utilisation of
multiple junctions.(b) Spectral splitting mechanism in the
solar cell.
Figure 54
represents excitation within a single junction
cell, where much of the incident light is useless in the
production of charge carriers. The external quantum
efficiency (EQE), measures the ratio of charge carriers
produced from incident light.10
One way of increasing
the EQE, would be to use a multi-junction cell (Figure
2),4
which utilises a wider range of spectral light. In
addition, changing the absorption coefficient α of the
solar cell material can change its absorbency efficiency,
which in turn has an impact on how thick the cell can
be.
2.2 Parasitic Losses
Optical loss mechanisms such as shading and reflection
of light from the cell surface reduce absorption. In ad-
dition, non-active PV layers in anti-reflection coatings
will absorb the light without contributing to charge
carrier generation (parasitic absorption). Another pos-
sible way to reduce reflective losses is to texture the
film (Figure 3).11
Radiation may also be transmitted
through the length of the cell without absorption if the
film is too thin.12
Figure 3
Textured surface of a solar cell, used to increase
absorption via light scattering.
Figure 4
Graphical representation of solar cell efficiency (%) vs cell
cost (US$/ m2
). The oval shaped regions demonstrate how
the three generations of solar cell technology, compare.
3 Thin-film PV technologies
The most promising thin film PV technologies have
shown to be copper indium gallium deselenide (CIGS)
and cadmium telluride (CdTe).13
However, much re-
search is being undertaken to eliminate the amount of
cadmium used in photovoltaics due to its bio-toxicity.14
3.1 CIGS
Copper indium gallium selenide (CIGS) solar cells, have
conversion efficiencies around 20% and are being pro-
duced at the fastest rate among thin film solar cells.
They have high absorption coefficients as they possess
Figure 5
Single junction cell band gap. Not all incident light has
sufficient energy to breach the band gap (qVoc).
2
3. Figure 6
Band structure detailing various loss mechanisms: (1)
Thermal loss, (2) Junction/contact voltage losses,
(4)Recombination loss.
Figure 7
Cross section of a CIGS solar cell, showing the materials
used in each layer and their approximate thicknesses.
a direct band gap structure. Figure 7 shows the cross
section of a typical CIGS cell.15
CIGS may be considered unsustainable, because in-
dium is not an abundant element, presenting a po-
tential limit on their up-scaling. CZTS may offer a
replacement to CIGS in solving this issue, as they are
non-toxic and currently more abundant in availabil-
ity.16
Deb, et al.17
and Kolodinski, et al.18
, have described
an increase in cell efficiency through the creation of
multiple electron-hole pairs upon a single incident pho-
ton.
This is supported by similar work (Figure 8) published
by Semonin, et al.,19
confirming that EQEs above 100%
can be achieved via MEG(Figure 9).20
The intention is
to reduce energy loss via heat, by utilising carriers ex-
cited to higher levels in the conduction band, in order
to generate more electron-hole pairs.
4 Mechanisms
4.1 Down Conversion
The general concept behind down conversion involves
splitting the energy received from energetic photons
into multiple lower energy photons, prior to absorp-
tion into the PV active material.
Nanoparticles prove to be extremely useful when utilis-
Figure 8
Graph of EQE (%) vs Photon Energy (eV), showing the
energies at which the EQE surpassed 100%.
Figure 9
Schematic diagram detailing multiple exciton generation.
An incident photon induces the creation of two e-/h+
pairs (b and c). Non-radiative relaxation follows via
phonon emission (d). The resulting biexciton decays into
single exciton. in this diagram, Franceschetti, et al. have
denoted dissipative processes as dashed arrows and
energy-conserved processes as the solid arrows.
ing this mechanism. In figure 10, van Wijngaarden, et
al.21
have proposed a mechanism for the Pr+3
- Yb+3
couple. The quantised energy of an electron excited
into the conduction band in such nanoparticle systems,
will not be transferred as heat to the lattice. Instead,
the energy is transferred to a neighbouring quantum
dot, which can then excite an electron into the con-
duction band of this neighbouring nanocrystal. Two
different excitons have essentially been produced from
the irradiation of a single, high energy photon.
Now, lower energy photons, produced from the radia-
tive recombination of the QDs, may be absorbed by
the PV material, provided other recombination meth-
ods can be supressed.
Yang, et al.22
, proved that down conversion using quan-
tum dots, can be enhanced even further, by embedding
the QDs into fabricated photonic crystals, which im-
proves the conversion efficiency in contrast to the lone
QDs.
3
4. Figure 10
(a) energy level scheme depicting the simultaneous
transfer of the Y b+
3 ions. (b) Down conversion - the 1G
4
state is used as a bridging level.
Figure 11
Triple-band intermediate cell.
4.2 Intermediate Band Cell
Figure 113
is a schematic representation of a solar cell
with one intermediate band, which helps to utilise a
wider range of incident spectral light. Luque, et al.,23
attempted to increase cell efficiency upon addition of a
third impurity band, and proved that the efficiency ex-
ceeded the Shockley-Quiesser limit both for ideal and
double-tandem cells.
However, the addition of an intermediate level may in-
crease the rate of recombination. This effect is inves-
tigated by Ichimura, et al.24
, where it was duly con-
cluded, that implanting silicon wafers with hydrogen
did not produce significant efficiency improvements.
This suggests that the choice of material when consid-
ering intermediate level addition is also an important
factor.
4.3 Hot Carrier Solar Cell
Energy losses in the form of phonons may be avoided
through the use of a ’hot carrier cell’, appropriately
named for its ability to help eliminate heat losses. Fig-
ure 123
shows how the energy that would traditionally
be lost in a conventional cell, may be stored by a ‘hot
carrier’. In addition, figure 13 shows how the use of
quantum dots in hot carrier cells may also prove ben-
eficial.3
Figure 12
(a) Carriers have reached thermal equilibrium within
the lattice. (b) Hot carrier distribution - carriers can
be held in higher energy states (storing excess
energy).
Figure 13
Simple schematic of the use of quantum dots in hot carrier
solar cells.
5 Dye-sensitised Solar Cells
Dye-sensitised solar cells (DSSC), are based on a photo-
electrochemical system as opposed to a p-n junction.25
They are promising for solar energy conversion, due to
their low production costs and energy-efficient manu-
facturing process, usually favoured when aesthetics are
important.
DSSC’s possess a similar theoretical conversion effi-
ciency of the Si solar cell,26
and are currently the most
efficient27
of the excitonic cells.
Developments have been made regarding the efficiency
and economic viability of DSSCs in recent years. ‘Liq-
uid electrolyte-based dye sensitised solar cells’ have
made advancements through the introduction of TiO2
nanoparticle films used to capture more incident pho-
tons, promoting dye absorption.27
Efficiencies for this
type of DSSC have been improved, by using varying
nanoparticle morphologies as opposed to spherical par-
ticulates, in order to reduce energy losses.28 29
Smooth 1D nano arrays have been seen to possess su-
perior properties over nano-particulates,30
however, do
not have sufficient roughness for dye attachment.31
In-
vestigations have been undertaken, to raise the rough-
ness factor of the nanoarrays. Varghese, et al.32
de-
posited titanium films onto fluorine-doped glass sub-
4
5. Figure 14
Results from investigation by Standridge, et al., showing
the IPCE (%) vs irradiation wavelength (nm).
strates and noted that the fill factor for DSSCs was
approximatelt 25% lower than the nanoparticle counter
parts. The group suggested that this occurred due to
an increase in width at the TNO-FTO interface and
that by increasing the nanotube roughness factor, this
problem could be resolved and greater efficiencies could
be achieved. Liao, et al.33
confirmed this hypothe-
sis, by proving that an increase in surface roughness
of TiO2 nano architectures, will create surfaces more
adapt for sunlight harvesting and dye absorption.
Standridge, et al.34
showed that the combination of sil-
ver nanoparticles and dye, promoted the production of
more electrons than in TiO2 or the dye alone. Figure
14 displays part of the group’s results, which clearly
show that at almost all wavelengths, the incident pho-
ton conversion efficiency (IPCE) is higher with the NP-
Dye combination.
Controlling the plasmonic frequency of nanoparticles
for efficiency optimisation, has proven to be a difficult
task. However, groups have discovered that variation
in nano architecture morphology, does shift the plas-
mon frequency and boost the IPCE in DSSCs.35 36
There is no doubt on the success in the enhancement
of DSSCs through the use of nanostructured materi-
als, however currently, their economic viability is not
promising, due to the complex methods involved in
their syntheses.3 37
6 Polymer-hybrid Cells
Polymer-hybrid cells offer easier manufacture, in com-
bination with high absorption coefficients, typical of
polymers (105
cm−1
).38
They offer large scale solar en-
ergy conversion with thin cells at lower costs.
The disadvantage, however, being that PV devices con-
taining polymers tend to possess poor charge trans-
port,39
suggesting that if maximum efficiencies are re-
Figure 15
Scanning electron microscopy (SEM) images of different
nanowire arrays; (a) Si, (b) ZnO, (c) InGaN.
quired, nanowire arrays may be ideal.40
7 Semiconductor Nanowires and
Nano architectures
Nanowires can be identified as long flexible rods with a
diameter in the range 1 – 100 nm as seen in figure 15.41
In contrast to the bulk, the nanoscale materials have
promising prospects for higher efficiency photovoltaic
devices.
Conventional silicon wafers often have to be thick to
absorb enough light, adding to the recombination rate.
Nanowires may offer a solution to this problem by re-
ducing the diffusion length of the minority charge car-
riers. Kato, et al.42
investigated surface passivation
techniques on nanowires and discovered that atomic
layer deposition (ALD) did increase the lifetime of the
charge carriers. Nanowire diameters also affect resis-
tance43
suggesting a change in the occupied volume by
conduction carriers.
Studies based on Si-nanowire PV applications, reveal
that longer nanowires enhance the absorption and ge-
ometry based on nanowire arrays provide more efficient
light scattering, in comparison to thin films.44
Fang, et
al. discovered that although ’slantingly-aligned’ nanowire
arrays are superior to the original vertical alignment,
they are still limited by a high rates of surface recom-
bination.45
Numerous groups have undertaken research on the P3HT
- ZnO nanowire arrays. Greene et.al46
significantly
increased efficiencies through the addition of polycrys-
talline TiO2 with confirmation of this result from Plank
5
6. et.al47
through the incorporation of an MgO shell.
8 Conclusion
Many aspects of solar technologies currently on the
market have been discussed, as well as the importance
of developing innovative new materials, to keep up with
the ever increasing demand for energy and the ongoing
quest to reduce environmental impacts.
It is evident that there are countless applications for
the incorporation of nanomaterials into PV devices,
ranging from technologies modelled purely around nano-
materials to small additions such as quantum dots or
nanoparticle-dye mixtures. If researchers can sufficiently
suppress the current limitations, that some advanced
concepts pose, nanomaterials really could be the key
to efficient, sustainable energy. There is no doubt that
the future is bright for solar energy.
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