Tesi sul tema "Photovoltaic cells"
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1
Joseph, Savina Rita. "Current generation in photovoltaic cells". Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:ed430576-6066-43bd-86fa-ead9c44c20c5.
Testo completoAbstract (sommario):
In this thesis we present an analysis of the operation of a particular type of hybrid photovoltaic device called a solid-state dye-sensitised solar cell. A mathematical model is used to describe the cell's operation, from the moment the photon reaches the surface of the device, until it is collected at the end electrodes. The invention of the solid-state dye-sensitised solar cells is recent and is part of the greater search for stable, low cost and efficient alternative means of energy generation. As the physical and chemical analysis has progressed in recent years, there is a need to establish a mathematical model to describe their behaviour. This thesis includes such mathematical analysis, based on our current knowledge of semiconductors and opto-electrochemical properties of solid-state material. The effect of these properties and of the geometry of the cell are examined in detail using analytical, but also numerical techniques that allow to circumvent the complexities involved. In this thesis, we show how conducting electrons can be generated by absorbing photons within an internal dye layer and are then transported via diffusion in the device until they reach the electrodes connecting it to an external electric circuit. While there are several limiting factors in the analysis, including the geometry of the device, the mathematical model appears to agree qualitatively well with available data on the current generation of solid-state dye-sensitised solar cells.
2
Kang, Moon Hee. "Development of high-efficiency silicon solar cells and modeling the impact of system parameters on levelized cost of electricity". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47647.
Testo completoAbstract (sommario):
The objective of this thesis is to develop low-cost high-efficiency crystalline silicon solar cells which are at the right intersection of cost and performance to make photovoltaics (PV) affordable. The goal was addressed by improving the optical and electrical performance of silicon solar cells through process optimization, device modeling, clever cell design, fundamental understanding, and minimization of loss mechanisms. To define the right intersection of cost and performance, analytical models to assess the premium or value associated with efficiency, temperature coefficient, balance of system cost, and solar insolation were developed and detailed cost analysis was performed to quantify the impact of key system and financial parameters in the levelized cost of electricity from PV.
3
Wijayantha, Kahagala Gamage Upul. "Characterisation of dye sensitised photovoltaic cells". Thesis, University of Bath, 2001. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341703.
Testo completo
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Shaw, Nicola Jane. "Studies of dye sensitised photovoltaic cells". Thesis, University of Bath, 1999. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301538.
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5
Zhao, Lin. "Polymer-based photovoltaic devices /". View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202003%20ZHAO.
Testo completoAbstract (sommario):
Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003.Includes bibliographical references (leaves 79-82). Also available in electronic version. Access restricted to campus users.
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Pendyala, Raghu Kishore. "Automated Simulation of Organic Photovoltaic Solar Cells". Thesis, Linköping University, The Department of Physics, Chemistry and Biology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-15338.
Testo completoAbstract (sommario):
This project is an extension of a pre-existing simulation program (‘Simulation_2dioden’). This simulation program was first developed in Konarka Technologies. The main purpose of the project ‘Simulation_2dioden’ is to calibrate the values of different parameters like, Shunt resistance, Series resistance, Ideality factor, Diode current, epsilon, tau, contact probability, AbsCT, intensity, etc; This is one of the curve fitting procedure’s. This calibration is done by using different equations. Diode equation is one of the main equation’s used in calculating different currents and voltages, from the values generated by diode equation all the other parameters are calculated.
The reason for designing this simulation_2dioden is to calculate the values of different parameters of a device and the researcher would know which parameter effects more in the device efficiency, accordingly they change the composition of the materials used in the device to acquire a better efficiency. The platform used to design this project is ‘Microsoft Excel’, and the tool used to design the program is ‘Visual basics’. The program could be otherwise called as a ‘Virtual Solar cell’. The whole Virtual Solar cell is programmed in a single excel sheet.
An Automated working solution is suggested which could save a lot of time for the researchers, which is the main aim of this project. To calibrate the parameter values, one has to load the J-V characteristics and simulate the program by just clicking one button. And the parameters extracted by using this automated simulation are Parallel resistance, Series resistance, Diode ideality, Saturation current, Contact properties, and Charge carrier mobility.
Finally, a basic working solution has been initiated by automating the simulation program for calibrating the parameter values.
7
Potscavage, William J. Jr. "Physics and engineering of organic solar cells". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/39634.
Testo completoAbstract (sommario):
Organic solar cells have the potential to be portable power sources that are light-weight, flexible, and inexpensive. However, the highest power conversion efficiency for organic solar cells to date is ~8%, and most high-efficiency solar cells have an area of less than 1 cm². This thesis advances the field of organic solar cells by studying the physics and engineering of the devices to understand the reverse saturation current, which is related to efficiency, and the effects of area scaling.
The most commonly accepted models to describe the physics of organic photovoltaic devices are reviewed and applied to planar heterojunction solar cells based on pentacene / C60 as a model system. The equivalent circuit model developed for inorganic solar cells is shown to work well to describe the behavior of organic devices and parameterize their current-voltage characteristics with five parameters. Changes in the parameters with different material combinations or device structures are analyzed to better understand the operation of the presented organic solar cells. A one-dimensional diffusion model for the behavior of excitons and treatment of the organic layers as planes is demonstrated to adequately model the external quantum efficiency and photocurrent in pentacene / C60 solar cells.
The origin of the open-circuit voltage is studied using cells with different electrodes and different donor materials. While changing the electrodes does not affect open-circuit voltage, it is greatly modified by changes in the donor. Tests with additional semiconductors show the change in open-circuit voltage is not consistent from donor to donor as the acceptor is varied, suggesting a more complex relation than just the difference in energy levels. Study of the temperature dependence of the equivalent circuit parameters shows that the reverse saturation current, which has a significant role in determining the open-circuit voltage, has a thermally activated behavior. From this behavior, the reverse saturation current is related back to charge transfer at the donor / acceptor heterojunction to suggest that both the effective energy barrier presented by the energy levels and the electronic coupling are important in determining the reverse saturation current and open-circuit voltage. This marks a shift from just considering a built-in voltage or the energy levels to also considering the electronic coupling of the donor and acceptor materials. Temperature-dependent performance characteristics are also used to show key differences between organic and inorganic devices.
Finally, the effect of area scaling is explored with pentacene / C60 solar cells having areas of 0.11, 7, and 36.4 cm². Analysis with the equivalent circuit model shows that performance decreases as area increases because of an increasing series resistance presented by the transparent electrode. A metal grid, to provide low resistance pathways for current, fabricated on top of the transparent electrode is proposed to reduce the effective resistance. The grid is unique in that it is placed between the electrode and the semiconductor layer and must be passivated to prevent shorts through the thin semiconductor to the back metal electrode. Analysis of the grid predicts greatly reduced series resistance, and experimental results show reduced resistance and improved performance for the 7 cm² and 36.4 cm² devices when including the grid.
8
Schultz, Ross Dane. "On the design of concentrator photovoltaic modules". Thesis, Nelson Mandela Metropolitan University, 2012. http://hdl.handle.net/10948/d1015766.
Testo completoAbstract (sommario):
High concentration photovoltaics (HCPV) promise a more efficient, higher power output than traditional photovoltaic modules. This is achieved by concentrating sunlight onto a small 1 cm2 triple junction (CTJ) InGaP/InGaAs/Ge cell by using precision optics. In order to achieve high performance, careful and informed design decisions must be made in the development of a HCPV module . This project investigated the design of a HCPV module and is divided into sections that concentrate on the optical design, thermal dissipation and electrical characterization of a concentration triple junction cell. The first HCPV module (Module I) design was based on the Sandia III Baseline Fresnel module which comprised of a Fresnel lens and truncated reflective secondary as the optical elements. The parameters of the CTJ cell in Module I increased with increased concentration. This included the short circuit current, open circuit voltage, power and efficiency. The best performance achieved was at 336 times operational concentration which produced 10.3 W per cell, a cell efficiency of 38.4 percent, and module efficiency of 24.2 percent Investigation of the optical subsystem revealed that the optics played a large role in the operation of the CTJ cell. Characterization of the optical elements showed a transmission loss of 15 percent of concentrated sunlight for the irradiance of which 66 percent of the loss occurred in wavelength region where the InGaP subcell is active. Characterization of the optical subsystem indicated regions of non-uniform irradiance and spectral intensity across the CTJ cell surface. The optical subsystem caused the InGaP subcell of the series monolithic connected CTJ cell to be current limiting. This was confirmed by the CTJ cell having the same short circuit current as the InGaP subcell. The performance of the CTJ cell decreased with an increase in operational temperature. A form of thermal dissipation was needed as 168 times more heat needs to be dissipated when compared to a flat plate photovoltaic module. The thermal dissipation was achieved by passive means with a heat sink which reduced the operational temperature of the CTJ cell from 50 oC to 21 oC above ambient. Cell damage was noted in Module I due to bubbles in the encapsulation epoxy bursting from a high, non-uniform intensity distribution. The development of the second module (Module II) employed a pre-monitoring criteria that characterized the CTJ cells and eliminated faulty cells from the system. These criteria included visual inspection of the cell, electroluminescence and one sun current-voltage (I-V) characteristic curves. Module II was designed as separate units which comprised of a Fresnel lens, refractive secondary, CTJ cell and heatsink. The optimal configuration between the two modules were compared. The CTJ cells in module II showed no form of degradation in the I-V characteristics and in the detected defects. The units under thermal and optical stress showed a progressive degradation. A feature in the I-V curve at V > Vmax was noted for the thermally stressed unit. This feature in the I-V curve may be attributed to the breakdown of the Ge subcell in the CTJ cell. Based on the results obtained from the two experimental HCPV modules, recommendations for an optimal HCPV module were made.
9
Levy, Michael Yehuda. "Design, experiment, and analysis of a photovoltaic absorbing medium with intermediate levels". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24703.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008.Committee Chair: Honsberg, Christiana; Committee Co-Chair: Citrin, David; Committee Member: Doolittle, Alan; Committee Member: First, Phillip; Committee Member: Ralph, Stephen; Committee Member: Rohatgi, Ajeet
10
Vaynzof, Yana. "Inverted hybrid solar cells". Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609823.
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Parlevliet, David Adam. "Silicon nanowires for photovoltaic applications /". Murdoch University Digital Theses Program, 2008. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20090930.140302.
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Al-Husenawi, Dhiyaa Kareem Muslem. "Studies of low cost biological photovoltaic cells". Thesis, Bangor University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.664461.
Testo completoAbstract (sommario):
This thesis has focused on three different aspects. The first was improving of biophotovoltaic cells based on dye-sensitized sensitized solar cells (DSC) based mainly on using extract of spinach as natural and cheap dye instead of laboratory-synthesized dyes. The extraction was performed using four methods with solvents of acetone, petroleum ether, methanol and dioxane. The yield of extract was 0.16-0.31 mg from 200 g of spinach leaves. Then the extract was used to manufacture DSC devices. The factors that can affect the efficiency of the cells have been studied including the dyeing solvent, the temperature and time of sintering, the thickness of the Ti02 film, the treatment of photoelectrode films with acids and/or TiC4 solution, the type of Ti02 paste used, the electrolyte and the design of cell. The highest efficiency and short current (Jsc) reached were 0.71% and 1.77 mA.cm-2 , respectively by passive dyeing which increased using ultra-fast sensitization to 1.13% and 2.67 mA.cm-2, respectively. To our knowledge, this is a higher efficiency for a spinach extract than that published in the literature. Afterwards, the Mg2+ ion in chlorophyll was replaced by metal ions (either Zn2+ or Cu2l to prepare Zn-chlorophyll or Cu-chlorophyll, respectively which were then used in DSC devices that achieved efficiency of 0.93% and 0.30%, respectively. The extract of spinach was separated by two techniques, column chromatography or preparative TLC. The separated pigments which included chlorophyll-a, chlorophyll-b, carotene and xanthophylls were characterized by colour, TLC, DV -Vis spectroscopy and HPLC, and then were introduced to manufacture bio-photovoltaic cells that recorded 0.14,0.09,0.15 and 0.18%, respectively. Chlorophyll and N719 dye were used as co-sensitizing dyes to manufacture DSC cell. The efficiencies were 1.34% (3.38 mA.cm-2) and 4.31% (10.95 mA.cm-2) using 90/10 and 10/90 v/v of chlorophyl1lN719, respectively compared to 0.92% (2.29 mA.cm-2) and 4.04% (9.98 mA.cm-2) using chlorophyll and N719 dye respectively when DSC photoelectrodes were dyed individually. The second aspect was the development of a new procedure to manufacture Ti02 photoelectrodes at low temperature (300·C) by adding metal peroxides to P25 paste. The films were characterized by TGA, XRD, BET, UV-Vis spectroscopy and dye adsorption studies. A typical cell that used N719 dye and ZnOiP25 sintered at 300°C showed efficiency of 3.94% that increased to 4.57% after the sinteri.~g at 300°C followed by UV treatment compared to cell used P25 sintered at 450°C that showed efficiency of 3.23% or 3.63% after the sintering at 450°C followed by UV treatment. Zn021P25 films made using the same conditions (sintering at 300°C followed by DV treatment) were used to manufacture bio-photovoltaic cell with chlorophyll dye and achieving efficiency of 0.64%. The last aspect for this study focused on development of flexible solar cells. Photoelectrodes were prepared using ITO-plastic substrates instead of FTO glass substrates were prepared by UV treatment and with or without sintering at 120°C. The best efficiencies for these devices were 3.24% and 0.18% when using N719 or chlorophyll as sensitizers, respectively.
13
Blair, Emily. "Characterisation of poly (2,7-carbazole) photovoltaic cells". Thesis, Université Laval, 2011. http://www.theses.ulaval.ca/2011/28384/28384.pdf.
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Mohammad, Jassim M. H. "Characterization of hydrogenated amorphous silicon photovoltaic cells". Thesis, Heriot-Watt University, 1987. http://hdl.handle.net/10399/1012.
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15
Ghamande, Maithili. "Optical Modeling of Organic Photovoltaic Solar Cells". University of Akron / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1320329919.
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Celik, Ilke. "Eco-design of Emerging Photovoltaic (PV) Cells". University of Toledo / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1533123980079904.
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Tan, Swee Ching. "Photosynthetic proteins photovoltaic devices". Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609050.
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Alam, Mohammad Saad. "Real-time maximum power tracking and robust load matching of a stand-alone photovoltaic system a dissertation presented to the faculty of the Graduate School, Tennessee Technological University /". Click to access online, 2009. http://proquest.umi.com/pqdweb?index=0&did=1756844361&SrchMode=1&sid=2&Fmt=6&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1280170042&clientId=28564.
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Crozier, Jacqueline Louise. "Characterisation of performance limiting defects in photovoltaic devices using electroluminescence and related techniques". Thesis, Nelson Mandela Metropolitan University, 2015. http://hdl.handle.net/10948/11004.
Testo completoAbstract (sommario):
Solar cells allow the energy from the sun to be converted into electrical energy; this makes solar energy an environmentally friendly, sustainable alternative to fossil fuel energy sources. Solar cells are connected together in a photovoltaic (PV) module to provide the higher current, voltage and power outputs necessary for electrical applications. However, the performance of PV modules can limited by the degradation and defects. PV modules can be characterised using various opto-electronic techniques, each providing information about the performance of the module. The current-voltage (I-V) characteristic curve of a module being the most commonly used characterisation technique. The I-V curve is typically measured in outdoor, fully illuminated, conditions. This allows performance parameters such as short circuit current (ISC), open circuit voltage (VOC) and maximum power (PMAX) to be determined. However, it can be difficult to determine the root cause of the performance drop from the I-V curve alone. Electroluminescence (EL) is a module characterisation technique that allows defects and failures in PV modules to be successfully identified. This study investigates the characterisation of solar cells and photovoltaic modules using EL. EL occurs when a solar cell or module is forward biased and the injected electron-hole pairs recombine radiatively. The intensity of the emitted EL is related the applied voltage and the material properties. EL imaging is a useful characterisation technique in identifying module defects and failures. Defects such as micro-cracks, broken contact fingers and fractures are detected in EL images as well as material features such as grain boundaries. The common defects in crystalline silicon are catalogued and the possible causes are discussed. An experimental setup was developed in order to systematically take a high resolution EL image of every cell in the module and record the applied voltage and current. This produces a very detailed, clear, image of each cell with a pixel size in the micrometre range. This process is time consuming to acquire an EL image of an entire module so alternatively a different setup can be used and an EL image of a whole module can be captured in a single frame with an increased pixel size in the millimetre range. For EL imaging a silicon charge-coupled device (CCD) camera was used because it has very good spatial resolution however this sensor is only sensitive to wavelength in the range of 300-1200 nm. There is an overlap in wavelengths from about 900 to 1100 nm allowing the EL emitted from silicon solar cells to be detected. In conjunction with the high-resolution EL system an image processing program was developed to crop, adjust and align the images so only the relevant cell was included. This program also automatically detects certain defects that have a regular shape. Micro-cracks, broken fingers and striation rings are automatically identified. The program has an adjustable sensitivity to identify small or large defects. Defective cells are distinguished from undamaged cells by comparing the binary images to the ideal, undamaged cell. The current-voltage curves and the performance parameters of modules were compared with the EL images in order to discuss and identify power limiting defects. Features that remove significant portions of the cell from electrical contact such as micro-cracks are shown to have a larger effect of the performance of the module. Other features such as broken contact fingers, contact forming failures and striation rings do not significantly lower the performance of the module. Thus an understanding of how different features affect the module performance is important in order to correctly interpret the EL results. The intensity of the luminescence emitted is related to the applied voltage and the quantum efficiency of the cell material. The spectrum of the emitted luminescence was modelled and related to the recombination properties of the cell such as surface recombination velocity and minority carrier diffusion length/lifetime. In this study the emitted spectrum was modelled and the effects of recombination properties of the cell on the emitted spectrum were examined. The spectrum of the detected EL was modelled, dependent on the sensitivity of the camera, the transmission of the filters and the emitted photon flux. The integration of short-pass filters into the experimental setup in order to isolate short-wavelength luminescence was discussed. There is a proportional relationship between the intensity of the emitted EL and the local junction voltage. Resistive losses like series and shunt resistances lower the applied voltage and thus affect the EL image. The voltage dependence was assessed by comparing EL images taken at different applied biases. Analysis of the variation in EL intensity with voltage was successful in determining the origin of certain features in an EL image. Certain defects, those that are related to series resistance or shunting are highly voltage dependent. When a feature has little or no dependence on voltage then the defect could be in the laminate layers and not in the cell material. The results of this study allow for in-depth analysis of the defects found in PV modules using the high resolution EL imaging system and the image processing routine. The development of an image processing routine allows the interpretation of the EL image to be done automatically, resulting in a faster and more efficient process. By understanding the defects visible in the EL image, the test is more meaningful and allows the results to be used to predict module performance and potential failures.
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Benecke, Mario Andrew. "On the optical and electrical design of low concentrator photovoltaic modules". Thesis, Nelson Mandela Metropolitan University, 2012. http://hdl.handle.net/10948/d1013102.
Testo completoAbstract (sommario):
The increasing interest in non-fossil fuel based electricity generation has caused a prominent boost for the renewable energy sector, especially the field of Photovoltaics (PV) with one of the main reasons being the decrease in cost of PV electricity generation. However, over the last few years a saturation in the efficiency of solar cells have been reached leading into a renewed search for other means to further reduce the cost of electricity generation from photovoltaic sources. One of the technologies that has attracted a lot of attention is low concentration photovoltaics (LCPV). LCPV investigates an alternative strategy to replace costly semiconductor material with relatively cheap optical materials by developing a Low Concentration Photovoltaic (LCPV) module. A LCPV module is divided into three subsystems, namely, the optical, electrical and thermal subsystem. This study focussed on the design, construction and characterisation of an optical subsystem accompanied by a thorough investigation into the design of an electrical subsystem. A facetted parabolic concentrator using a vertical receiver was modelled and a first prototype was constructed having a geometric concentration factor of 6.00 X. Upon electrical characterisation of this first vertical receiver LCPV prototype a concentration of only 4.53 X (receiver 1) and 4.71 X (receiver 2) was obtained. The first vertical receiver LCPV prototype did not reach the expected concentration factor due to optical losses and misalignment of optical elements. The illumination profile obtained from the reflector element was investigated and an undesirable non-uniform illumination profile was discovered. A second vertical receiver LCPV prototype was constructed in an attempt to improve on the first prototype, this second vertical receiver prototype had a geometrical concentration factor of 5.80 X. The results indicated a much improved illumination profile, yet still containing a number of non-uniformities. The second vertical receiver LCPV module yielded an operational concentration factor of 5.34 X. From the preliminary results obtained it was discovered that under concentrated illumination there was a limitation on the maximum power that could be obtained from the receiver. Upon further investigation it was discovered that this limitation was due to the higher current levels under concentrated illumination accompanied by a high series resistance of the receiver. This lead to the construction of new PV receivers, where this limitation could be minimised. 3 cell, 4 cell, 6 cell and 8 cell string configurations were constructed and used for the electrical characterisation of the prototypes. Due to non-uniformity of the illumination profile obtained from the second LCPV prototype a third vertical receiver LCPV prototype was constructed. This vertical receiver design illustrated more uniformity in the obtained illumination distribution and had a geometrical concentration factor of 4.61 X, although under operation only 4.26 X could be obtained. It is important to note that the geometric concentration factor does not account for reflective losses of the reflective material. One of the main reasons for the difficulty in obtaining a uniform illumination profile with the vertical receiver design is that the facetted reflector element is far away from the PV receiver. This enhances the effect of the slightest misalignment of any of the optical elements. This large distance also increases the effect of lensing from each facet. These factors lead to the consideration of a second design, which would counteract these factors. A horizontal receiver LCPV module design implementing a facetted parabolic reflector was considered to counteract these effects. From a mathematical model a horizontal receiver LCPV prototype was constructed having a geometrical concentration factor 5.3 X. The optical characterisation of the illumination profile showed a much improved illumination profile, which was much more uniform than the previous illumination profiles obtained from the other LCPV prototypes. The uniformity of the illumination profile could be seen in results obtained from the electrical characterisation where the concentrator reached operational concentration factor of 5.01 X. The reliability of the third vertical receiver LCPV prototype and the horizontal receiver LCPV prototype as well as the receivers were investigated by placing each receiver under stressed operational conditions for 60 sun hours. I-V characteristics were obtained after every five sun hours to investigate any signs of degradation. After 60 sun hours none of the receiver displayed any signs of degradation or reduction in electrical performance.
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Yandt, Mark. "Characterization and Performance Analysis of High Efficiency Solar Cells and Concentrating Photovoltaic Systems". Thesis, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/20535.
Testo completoAbstract (sommario):
As part of the SUNRISE project (Semiconductors Using Nanostructures for Record Increases in Solar-cell Efficiency), high efficiency, III-V semiconductor, quantum-dot-enhanced, triple-junction solar cells designed and manufactured by Cyrium Technologies Inc. were integrated into OPEL Solar, MK-I, Fresnel-lens-based, 550x concentrating modules carried on a dual axis tracker.
Over its first year of operation 1.8 MWh of AC electrical energy was exported to the grid. Measurements of the direct and indirect components of the insolation, as well as the spectral irradiance of light incident on the demonstrator in Ottawa, Canada are presented. The system efficiency is measured and compared to that predicted by a system model to identify loss mechanisms so that they can be minimized in future deployments.
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Macabebe, Erees Queen Barrido. "Investigation of device and performance parameters of photovoltaic devices". Thesis, Nelson Mandela Metropolitan University, 2009. http://hdl.handle.net/10948/1003.
Testo completoAbstract (sommario):
In order to investigate the influence of parasitic resistances, saturation current and diode ideality factor on the performance of photovoltaic devices, parameter extraction routines employing the standard iteration (SI) method and the particle swarm optimization (PSO) method were developed to extract the series resistance, shunt resistance, saturation current and ideality factor from the I-V characteristics of solar cells and PV modules. The well-known one- and two-diode models were used to describe the behavior of the I-V curve and the parameters of the models were determined by approximation and iteration techniques. The SI and the PSO extraction programmes were used to assess the suitability of the one- and the two-diode solar cell models in describing the I-V characteristics of mono- and multicrystalline silicon solar cells, CISS- and CIGSS-based solar cells. This exercise revealed that the two-diode model provides more information regarding the different processes involved in solar cell operation. Between the two methods developed, the PSO method is faster, yielded fitted curves with lower standard deviation of residuals and, therefore, was the preferred extraction method. The PSO method was then used to extract the device parameters of CISS-based solar cells with the CISS layer selenized under different selenization process conditions and CIGSS-based solar cells with varying i-ZnO layer thickness. For the CISS-based solar cells, the detrimental effect of parasitic resistances on device performance increased when the temperature and duration of the selenization process was increased. For the CIGSS-based devices, photogeneration improved with increasing i-ZnO layer thickness. At high forward bias, bulk recombination and/or tunneling-assisted recombination were the dominant processes affecting the I-V characteristics of the devices. v Lastly, device and performance parameters of mono-, multicrystalline silicon and CIS modules derived from I-V characteristics obtained under dark and illuminated conditions were analyzed considering the effects of temperature on the performance of the devices. Results showed that the effects of parasitic resistances are greater under illumination and, under outdoor conditions, the values further declined due to increasing temperature. The saturation current and ideality factor also increased under outdoor conditions which suggest increased recombination and, coupled with the adverse effects of parasitic resistances, these factors result in lower FF and lower maximum power point. Analysis performed on crystalline silicon and thin film devices utilized in this study revealed that parameter extraction from I-V characteristics of photovoltaic devices and, in particular, the implementation of PSO in solar cell device parameter extraction developed in this work is a useful characterization technique.
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Black, David. "Fabrication of hybrid inorganic and organic photovoltaic cells". Thesis, De Montfort University, 2011. http://hdl.handle.net/2086/5299.
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Zhang, Weifeng. "Novel thiophene-based molecular materials with enhanced functional properties for photovoltaic applications". HKBU Institutional Repository, 2011. http://repository.hkbu.edu.hk/etd_ra/1215.
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Ho, Carr Hoi Yi. "Toward better performing organic solar cells: impact of charge carrier transport and electronic interactions in bulk heterojunction blends /Ho Hoi Yi, Carr". HKBU Institutional Repository, 2017. https://repository.hkbu.edu.hk/etd_oa/359.
Testo completoAbstract (sommario):
Organic photovoltaic (OPV) is an exciting energy harvesting technique. Although its power conversion efficiency (PCE) now exceeds 10% in a research laboratory, the processing window of an OPV cell is still narrow. A fundamental understanding of the OPV materials is desired. This thesis presents the charge carrier transport properties and electronic interactions in the bulk heterojunction (BHJ) active layer of OPV cells. They were found to be well correlated with OPV device performances. Space-charge-limited current (SCLC) measurements and admittance spectroscopy (AS) were employed to study the charge transports, while photothermal deflection spectroscopy (PDS) was used to probe the trap densities inside the materials. Beneficial effects of a common solvent additive, 1,8-diiodooctance (DIO), on PTB7:PC71BM OPV cells have been investigated. With DIO present in the casting solution, the resulting BHJ films have much enhanced electron mobilities, whereas the impact on the hole mobility is negligible. The origin of increased electron mobility is the reduced average electron hopping distance for those films prepared with DIO solvent additive. A balance of hole-electron mobility by tuning the DIO concentration was demonstrated to be the way to optimize the OPV device performance. In light of carrier transport measurement results, a "polymer-rich" strategy with preserved device performance was demonstrated. After understanding the importance of balanced hole-electron mobility, the impact of donor-acceptor weight ratio on the performance of PTB7 : PC71BM based OPV cells was explored. Early stage electronic donor-acceptor interactions were revealed using ultra-low dosages of fullerenes. Before electron transport pathways percolate, the unconnected fullerene domains act as traps and hinder electron transport. From PDS, the trap density observed inside BHJ films was found to be anti-correlated with the fill factor of OPV devices. The origin of low FFs is mainly due to electron traps and localized states from fullerenes. Based on the observations, it is proposed that PC71BM tends to intercalate with PTB7 backbone instead of forming self-aggregates before the electron pathway percolation. Apart from investigating the fundamentals in OPV devices, a solution to improve its processing window was proposed in this thesis. Thermally stable polymer : fullerene OPV cells were fabricated by employing fluorenone-based solid additives. A charge transfer interaction between the additives and donor moiety of polymer formed a locked network which freezes the BHJ morphology under thermal stress. The most promising result retains 90% of the origin efficiency, upon thermal aging at 100 °C for more than 20 hours in PTB7:PC71BM solar cells. Besides fullerene-based OPV, all-polymer photovoltaic solar cells (all-PSCs) were also investigated. Two new difluorobenzene-naphthalene diimide based polymer electron acceptors, one random (P1) and one regioregular (P2) structure, were compared. P2 exhibited a much better molecular packing, a higher electron mobility and more balanced hole-electron mobilities in its composite film with polymer donor, PTB7-Th. An optimized PTB7-Th:P2 device can achieve a respectably high PCE over 5% for all-PSC devices. These all-PSCs should open a new avenue for next generation OPVs.
26
Kroposki, Benjamin David. "A methodology to study photovoltaics and storage system interactions". Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-03242009-040410/.
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Vorster, Frederick Jacobus. "On the characterization of photovoltaic devices for concentrator purposes". Thesis, Nelson Mandela Metropolitan University, 2007. http://hdl.handle.net/10948/639.
Testo completoAbstract (sommario):
This study originated from an evaluation of the performance of a commercially available high concentration point focus concentrator PV system. The effect of module design flaws was studied by using current-voltage (I-V) curves obtained from each module in the array. The position of reverse bias steps revealed the severity of mismatch in a string of series-connected cells. By understanding the effects of the various types of mismatch, power losses and damage to the solar cells resulting from hot spot formation can be minimized and several recommendations for improving the basic performance of similar systems were made. Concern over the extent and type of defect failure of the concentrator photovoltaic (CPV) cells prompted an investigation into the use of a light beam induced current (LBIC) technique to investigate the spatial distribution of defects. An overview of current and developing LBIC techniques revealed that the original standard LBIC techniques have found widespread application, and that far-reaching and important developments of the technique have taken place over the years. These developments are driven by natural progression as well as the availability of newly developed advanced measurement equipment. Several techniques such as Lock-in hermography and the use of infrared cameras have developed as complementary techniques to advanced LBIC techniques. As an accurate contactless evaluation tool that is able to image spatially distributed defects in cell material, the basis of this method seemed promising for the evaluation of concentrator cells.
28
Qiu, C. X. (Xing Xing). "Investigation of electrodeposited CuInSe2 films for photovoltaic cells". Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39267.
Testo completoAbstract (sommario):
Uniform polycrysalline p-type CuInSe$ sb2$ films, thicknesses ranging from 1 to 4 $ mu$m, were deposited by a stable electrodeposition process developed in our laboratory. A (112) preferred orientation was found for the films. Vacuum annealing experiment results showed an improvement in the crystalline quality of the films after the annealing. The metal ratio of the films was not altered significantly by the annealing process. Al/CuInSe$ sb2$ Schottky junctions fabricated on p-type CuInSe$ sb2$ films showed that the current transport mechanism in the intermediate voltage region was governed by a recombination component. A dispersion effect of the capacitance-voltage curves with frequency, observed on the Schottky junctions suggested the presence of either enhanced interface states or deep levels in the depletion region. Solar cells of CdS/CuInSe$ sb2$ were fabricated by vacuum evaporating low resistivity n-type CdS layers on the electrodeposited p-type CuInSe$ sb2$ films. The highest AM1 active area conversion efficiency, for the 0.9 cm$ sp2$ cells, was 5.2% after an air heat treatment at 200$ sp circ$C. The efficiency value was increased to 5.6% in small area devices fabricated using a similar procedure. The air heat treatment was found to reduce the apparent carrier concentration in the CuInSe$ sb2$ films. Current-voltage (I-V) characteristics of the cells showed a definite relationship between the short circuit current and the indium to copper ratio in the CuInSe$ sb2$ films. Temperature dependent I-V curves revealed a dominant recombination current component for the heterojunction cells. The value of barrier height for a cell was estimated to be 0.64 eV. It was found that the differential capacitance values depended on measurement frequencies, resulting in frequency-dependent voltage intercepts. The C$ sp{-2}$-V curves were also observed to shift to more negative voltages under illumination. Interface states were believed to be responsible for all these effec
29
Qiu, Chunong. "Development of photovoltaic cells on electrodeposited CuInSe2 films". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39982.
Testo completoAbstract (sommario):
Using polycrystalline thin films of CuInSe$ sb2$ (thickness 1.5 $ mu$m) prepared by an electrodeposition method, photovoltaic cells of the form ZnO/CdS/CuInSe$ sb2$ have been fabricated and studied. Before the cell fabrication, properties of the electrodeposited CuInSe$ sb2$ were first studied. Conditions for the preparation of high resistivity CdS thin films (thickness 360 A) by a chemical bath deposition method were then established. This was achieved by varying the deposition temperature and amount of NH$ sb4$OH in the solution. It was observed that the quality of CdS films deposited at a temperature of 60$ sp circ$C and an NH$ sb4$OH concentration of 0.48 M was the best. Thermal stability of low resistivity, In- or Ar-doped, rf-sputtered ZnO thin films (thickness 1$ mu$m) was also studied. This was done by heat treating the ZnO films in air, O$ sb2$ and N$ sb2$ at temperature in a range from 200 to 350$ sp circ$C. It was observed that the amount of increase of resistivity at a given temperature decreased as the doping concentration was increased from 0.5 to 5.3 wt.%. For the films containing 2 wt.% In or Al, the resistivity increased as the treating temperature was increased from 200 to 350$ sp circ$C. For the samples treated at 200$ sp circ$C, the increase in resistivity was about 1 order of magnitude.The high resistivity CdS and low resistivity ZnO thin films were then deposited on electrodeposited CuInSe$ sb2$ to fabricate cells of the form ZnO/CdS(high $ rho$)/CuInSe$ sb2$. For comparison, cells of CdS(low $ rho$)/CdS(high $ rho$)/CuInSe$ sb2$ were also fabricated by evaporation of low resistivity CdS. The CuInSe$ sb2$ films used were treated either in vacuum or Ar. For those treated in vacuum, very poor properties were observed. The properties improved after a post fabrication heat treatment in air, however, the efficiency of these cells was below 2%. The low conversion efficiency was due to the low open circuit voltage. From capacitance-voltage measurements, this was found to be due to a high acceptor concentration on the surface of the vacuum treated CuInSe$ sb2$ films (10$ sp{17}$ cm$ sp{-3}$). For the cells fabricated on the CuInSe$ sb2$ films treated in Ar, photovoltaic effects were present before the air heat treatment. An efficiency of 6.8% was obtained for one of the best cells, sample J8-4 (with low resistivity CdS window). For cells with ZnO window, a conversion efficiency of 6.3% was obtained (cell O51). For these cells, the acceptor concentration in CuInSe$ sb2$ was 10$ sp{16}$ cm$ sp{-3}$, which was one order of magnitude lower than that of CuInSe$ sb2$ films treated in vacuum.
The diffusion length of minority carriers (electrons) in the electrodeposited, p-type CuInSe$ sb2$ was first measured using the photocurrent and capacitance methods. For the vacuum treated CuInSe$ sb2$ films, the electron diffusion length was small (less than 0.1 $ mu$m). For those treated in Ar, values of the electron diffusion length were about 0.5 $ mu$m. These values are close to those reported for evaporated CuInSe$ sb2$ thin films.
Some of the fabricated cells were also studied using an electron beam induced current (EBIC) method. From the EBIC experiments, the effective diffusion lengths of electrons with values greater than 1 $ mu$m were obtained. Considering the surface recombination effect, the electron diffusion length of the electrodeposited CuInSe$ sb2$ was finally found to be 2.4 $ mu$m. This large electron diffusion length was consistent with the high short circuit current density observed in I-V measurements of the electrodeposited CuInSe$ sb2$ cells.
30
Schrader, Manuel [Verfasser]. "Charge transport in organic photovoltaic cells / Manuel Schrader". Mainz : Universitätsbibliothek Mainz, 2013. http://d-nb.info/1046203487/34.
Testo completo
31
Marsh, Robert Alexander. "Charge recombination and separation in excitonic photovoltaic cells". Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611592.
Testo completo
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Hardy, Dorothy Anne. "Integrating crystalline-silicon photovoltaic cells into decorative glazing". Thesis, Heriot-Watt University, 2015. http://hdl.handle.net/10399/2854.
Testo completoAbstract (sommario):
Photovoltaic cells are often perceived as an ugly addition to glazing. Improvements could make photovoltaics more attractive for use in architecture, increasing the opportunities to generate electricity on the surfaces of buildings. This research demonstrates methods of integrating crystalline-silicon photovoltaic cells into decorative glazing. The aim was to explore the use of a combination of opaque, reflective and coloured materials with crystalline-silicon photovoltaic cells in glazing designs, to enhance appearance whilst maintaining good photovoltaic generation. Colour was incorporated through the use of Lumogen F dyes (BASF) added to the photovoltaic encapsulants Sylgard 184 (Dow Corning) and EVA (ethylene vinyl acetate: Solutia Vistasolar Fastcure 486.00). The absorption and emission properties of these new material combinations were measured. The dyes degraded quickly under both accelerated and outdoor testing. Glazing designs were created that incorporated Lumogen dyes, plus opaque and reflective materials. The opaque and reflective materials were used to disguise the square photovoltaic cells. This demonstrated that crystalline-silicon photovoltaic cells could be assimilated into a wide variety of architectural glazing. Reflective materials and fluorescent dyes were shown to improve maximum electrical current from widely-spaced crystalline-silicon photovoltaic cells. Further work is recommended to establish durable material combinations for use with photovoltaics in decorative glazing.
33
Brooks, William. "Spatially resolved characterisation of CdTe photovoltaic solar cells". Thesis, Bangor University, 2012. https://research.bangor.ac.uk/portal/en/theses/spatially-resolved-characterisation-of-cdte-photovoltaic-solar-cells(2395fac6-edd7-4e9e-8c81-f35aaa79b51b).html.
Testo completoAbstract (sommario):
Spatially resolved measurements of CdTe thin film photovoltaic solar cells were performed using both laser beam induced current (LBIC) and scanning probe microscopy (SPM) techniques. The triple wavelength LBIC system was used to assess the thickness uniformity of Cd1-xZnxS window layers incorporated into CdTe solar cells. A blue laser was used to reveal window ~r • layer absorption and transmission characteristics. This was observed to influence . photoresponse at longer wavelengths where lateral variations in minority carrier lifetime were leading to variable carrier collection. This was found to be caused by localised regions of ~ 50 run thin Cd1-xZnxS forming a defective depletion region. The moderate to high clustering of pin-holes in both thick and thin regions of Cd1-xZnxS and CdTe layers was found to contribute to shunt resistance losses independently of the Cd1-xZnxS thickness distribution. Quantum dot (QD) luminescent down shifting layers incorporated into Cd1_xZnxS/CdTe devices were studied using the LBIC technique where, using a 405 run excitation wavelength, QD isotropic emission was observed to increase the overall lateral carrier collection area of : the cell. Scanning Kelvin probe microscopy (SKPM) was used to study the Fermi level shift in Arsenic doped CdTe devices where the contact potential-difference (CPD) between probe tip and sample surface revealed that increasing As concentrations in CdTe led to a decrease in CPD. This highlighted a downward shift in the CdTe Fermi level and an increase in CdTe work function. Absolute CdTe work function values between 3.88 and 4.09 eV were calculated using a highly oriented pyrolytic graphite reference sample. A localised shift in CPD at grains boundaries with increased As doping was observed. This was proposed to reduce carrier recombination by channelling minority carriers away from the grain boundary. Conductive atomic force microscopy revealed differences in bulk grain and grain boundary conductivity. The localised CdTe Er and the barrier formed at the tip/surface interface was observed to determine the measured current.
34
Gerber, Jacques Dewald. "On the thermal and electrical properties of low concentrator photovoltaic systems". Thesis, Nelson Mandela Metropolitan University, 2012. http://hdl.handle.net/10948/d1021219.
Testo completoAbstract (sommario):
Low concentrator photovoltaic systems are capable of increasing the power produced by conventional silicon photovoltaic cells, thus effectively lowering the cost per kWh. However, power losses associated with resistance and temperature have limited the large scale implementation of this technology. In this study, the optical-,electrical- and thermal sub-systems of a low concentrator photovoltaic system are theoretically and experimentally evaluated with the aim of minimizing the power losses associated with series resistance and temperature. A 7-facet reflector system, with an effective concentration ratio of 4.7, is used to focus irradiance along a string of series connected poly-crystalline photovoltaic cells. I-V characteristics of 4-, 6- and 8-cell photovoltaic receivers are measured under 1-sun and 4.83-sun conditions. Under concentration, the 8-cell photovoltaic receiver produced 23 percent more power than the 4-cell photovoltaic receiver, which suggests that the effect of series resistance can be minimized if smaller, lower current photovoltaic cells are used. A thermal model, which may be used to predict operating temperatures of a low concentrator photovoltaic system, is experimentally evaluated within a thermally insulated enclosure. The temperatures predicted by the thermal model are generally within 5 percent of the experimental temperatures. The high operating temperatures associated with the low concentrator photovoltaic system are significantly reduced by the addition of aluminium heat sink. In addition, the results of a thermal stress test indicated that these high operating temperatures do not degrade the photovoltaic cells used in this study. The results of this study suggest that the power output of low concentrator photovoltaic systems can be maximized by decreasing the size of the photovoltaic cells and including an appropriate heat sink to aid convective cooling.
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Thantsha, Nicolas Matome. "On the characterisation of copper indium diselenide based photovoltaic devices". Thesis, Nelson Mandela Metropolitan University, 2006. http://hdl.handle.net/10948/443.
Testo completoAbstract (sommario):
Photovoltaic (PV) modules based on thin film systems of CuInSe2 (CIS) and its alloys on low cost substrates are promising candidates to meet the long term efficiency, reliability and manufacturing cost goals. The attention to the CIS solar cell technology is because of the high absorption coefficient of the solar cell absorber layer. Solar cells and PV modules are conventionally assessed by measuring the currentvoltage characteristic of the device. This thesis presents an assessment procedure developed capable of assessing the device parameters with reference to I-V measurements. This thesis then characterizes the performance of the CIS based solar cells and modules in conjunction with other PV modules of different technologies such as crystalline Silicon modules by analyzing the light and dark I-V measurements of the devices. The light and dark I-V characteristics of PV devices were investigated and device parameters were extracted from the I-V data. The extraction and interpretation of these device parameters has a variety of important applications. It has been proven that the device parameters can be used for quality control during production and to provide insights into the operation of the PV devices, thereby improving the efficiency of the devices. The assessment comprises light I-V measurements at standard test conditions (STC), irradiance dependence measurements, parasitic series and shunt resistances measurements and the dark I-V measurements of the PV devices. The PV modules assessed comprise different technologies, namely, thin film based modules (CIS and a-Si) and multicrystalline Si and Edged-defined Film-fed Growth Si (EFG-Si). The dark I-V measurements results showed that the EFG-Si module has acceptable shunt (900 W) and series (0.4 W) resistances, thereby leading to the higher power output depicted from the light I-V measurements. The low quality cells of a-Si module were so low that the fill factor was the smallest (43%). In addition, the dark I-V measurements results revealed that CIS modules are less dependent to temperature at high voltages.
36
Crozier, Jacqueline Louise. "Characterization of cell mismatch in photovoltaic modules using electroluminescence and associated electro-optic techniques". Thesis, Nelson Mandela Metropolitan University, 2012. http://hdl.handle.net/10948/d1015059.
Testo completoAbstract (sommario):
Solar cells allow the energy from the sun to be converted into electrical energy; this makes solar energy much more environmentally friendly than fossil fuel energy sources. These solar cells are connected together in a photovoltaic (PV) module to provide the higher current, voltage and power outputs necessary for electrical applications. However, the performance of the PV module is limited by the performance of the individual cells. Cell mismatch occurs when some cells are damaged or shaded and produce lower current output than the other cells in the series connected string. The cell mismatch lowers the module performance and can result in further damage as the weak cells are reverse biased and dissipate heat. Bypass diodes can be connected into the module to increase the module current output and prevent further damage. Since cell mismatch results in a significant decrease in the performance of deployed modules it is important to fully understand and characterise its effect on PV modules. PV modules can be characterised using various techniques, each providing important information about the performance of the module. Most commonly the current-voltage (I-V) characteristic curve of a module is measured in outdoor, fully illuminated conditions. This allows performance parameters such as short circuit current (Isc), open circuit voltage (Voc) and maximum power (Pmax) to be determined. In addition to this the shape of the curve allows device parameters like series and shunt resistances to be determined using parameter extraction algorithms like Particle Swarm Optimisation (PSO). The extracted parameters can be entered into the diode equation to model the I-V curve of the module. The I-V characteristic of the module can also be used to identify poor current producing cells in the module by using the worst-case cell determination method. In this technique a cell is shaded and the greater the drop in current in the whole module the better the current production of the shaded cell. The photoresponse of cells in a module can be determined by the Large-area Light Beam Induced Current (LA-LBIC) technique which involves scanning a module with a laser beam and recording the current generated. Electroluminescence (EL) is emitted by a forward biased PV module and is used to identify defects in cell material. Defects such as cracks and broken fingers can be detected as well as material features such as grain boundaries. These techniques are used to in conjunction to characterise the modules used in this study. The modules investigated in this study each exhibit cell mismatch resulting from different causes. Each module is characterised using a combination of characterisation techniques which allows the effect of cell mismatch be investigated. EL imaging enabled cracks and defects, invisible to the naked eye, to be detected allowing the reduced performance observed in I-V curves to be explained. It was seen that the cracked cells have a significant effect on the current produced by a string, while the effect of delaminated areas is less severe. Hot spots are observed on weak cells indicating they are in reverse bias conditions and will degrade further with time. PSO parameter extraction from I-V curves revealed that the effect of module degradation of device parameters like series and shunt resistances. A module with cracked cells and degradation of the antireflective coating has low shunt resistance indicating current losses due to shunting. Similar shunting is observed in a module with delamination and moisture ingress. The extracted parameters are used to simulate the I-V curves of modules with reasonable fit. The fit could be improved around the “knee” of the I-V curve by improving the methods of parameter extraction. This study has shown the effects of cell mismatch on the performance and I-V curves of the PV modules. The different causes of cell mismatch are discussed and modules with different cell configuration and damage are characterised. The characterisation techniques used on each module provide information about the photoresponse, current generation, material properties and cell defects. A comprehensive understanding of these techniques allows the cell mismatch in the modules to be fully characterized.
37
Jiang, Chu-Wei School of Photovoltaic Engineering UNSW. "Theoretical and experimental study of energy selective contacts for hot carrier solar cells and extensions to tandem cells". Awarded by:University of New South Wales. School of Photovoltaic Engineering, 2005. http://handle.unsw.edu.au/1959.4/23065.
Testo completoAbstract (sommario):
Photovoltaics is currently the fastest growing energy source in the world. Increasing the conversion efficiency towards the thermodynamic limits is the trend in research development. ???Third generation??? photovoltaics involves the investigation of ideas that may achieve this goal. Among the third generation concepts, the tandem cell structure has experimentally proven to have conversion efficiencies higher than a standard p-n junction solar cell. The alternative hot carrier solar cell design is one of the most elegant approaches. Energy selective contacts are crucial elements for the operation of hot carrier solar cells. Besides the carrier cooling problem within the absorber, carrier extraction has to be done through a narrow range of energy to minimise the interaction between the hot carriers in the absorber and the cooler carriers in the contacts. Resonant tunnelling through localised states, such as associated with atomic defects or with quantum dots in a dielectric matrix, may provide the required energy selectivity. A new model in studying the properties of resonant tunnelling through defects in an insulator is proposed and investigated. The resulting calculations are simple and useful in obtaining physical insight into the underlying tunneling processes. It is found that defects having a normal distribution along the tunnelling direction do not reduce the transmission coefficient dramatically, which increases the engineering prospects for fabrication. Silicon quantum dots embedded in an oxide provide the required deep energy confinement for room temperature resonant tunnelling operation. A single layer of silicon quantum dots in the centre of an oxide matrix are prepared by RF magnetron sputtering. The method has the advantage of controlling the dot size and the dot spatial position along the tunnelling direction. The presence of these crystalline silicon dots in the oxide is confirmed by high resolution transmission electron microscopy (HRTEM). A negative-differential resistance characteristic has been measured at room temperature on such structures fabricated on an N-type degenerated silicon wafer, a feature that can be explained by the desired resonant tunnelling process. A silicon quantum dot superlattice can be made by stacking multiple layers of silicon quantum dots. A model is proposed for calculating the band structure of such a silicon quantum dot superlattice, with the anisotropic silicon effective mass being taken into account. It suggests a high density of silicon quantum dots in a carbide matrix may provide the bandgap and required mobility for the top cell in the stacks for the recently proposed all-silicon tandem solar cell. The resonant tunnelling modeling and silicon quantum dot experiments developed have demonstrated new results relevant to energy selective contacts for hot carrier solar cells. Building on this work, the modeling study on silicon quantum dots may provide the theoretical basis for bandgap engineering of all-silicon tandem cells.
38
Dönertaş, Yavaş Medine Elif Güneş Mehmet. "The effects of native and light induced defects in the optical and electronic properties of hydrogenated amorphous silicon Germanium (a-SiGe:H) alloy thin films/". [s.l.]: [s.n.], 2005. http://library.iyte.edu.tr/tezlerengelli/master/fizik/T000336.pdf.
Testo completo
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Michalopoulos, Panayiotis. "A novel approach for the development and optimization of state-of-the-art photovoltaic devices using Silvaco". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Mar%5FMichalopoulos.pdf.
Testo completoAbstract (sommario):
Thesis (M.S. in Electrical Engineering and M.S. in Computer Science)--Naval Postgraduate School, March 2002.Thesis advisor(s): Sherif Michael, Bret Michael, Todd Weatherford. Includes bibliographical references (p. 167-169). Also available online.
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Vijh, Aarohi. "Triple Junction Amorphous Silicon based Flexible Photovoltaic Submodules on Polyimide Substrates". Connect to full text in OhioLINK ETD Center, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1122656006.
Testo completo
41
Moore, Jennifer Rose. "New materials for solution-processible solar cells". Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609301.
Testo completo
42
Tvingstedt, Kristofer. "Light Trapping and Alternative Electrodes for Organic Photovoltaic Devices". Doctoral thesis, Linköpings universitet, Biomolekylär och Organisk Elektronik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-17229.
Testo completoAbstract (sommario):
Organic materials, such as conjugated polymers, have emerged as a promising alternative for the production of inexpensive and flexible photovoltaic cells. As conjugated polymers are soluble, liquid based printing techniques enable production on large scale to a price much lower than that for inorganic based solar cells. Present day state of the art conjugated polymer photovoltaic cells are comprised by blends of a semiconducting polymer and a soluble derivative of fullerene molecules. Such bulk heterojunction solar cells now show power conversion efficiencies of up to 4-6%. The quantum efficiency of thin film organic solar cells is however still limited by several processes, of which the most prominent limitations are the comparatively low mobility and the high level of charge recombination. Hence organic cells do not yet perform as well as their more expensive inorganic counterparts. In order to overcome this present drawback of conjugated polymer photovoltaics, efforts are continuously devoted to developing materials or devices with increased absorption or with better charge carrier transporting properties. The latter can be facilitated by increasing the mobility of the pure material or by introducing beneficial morphology to prevent carrier recombination. Minimizing the active layer film thickness is an alternative route to collect more of the generated free charge carriers. However, a minimum film thickness is always required for sufficient photon absorption. A further limitation for low cost large scale production has been the dependence on expensive transparent electrodes such as indium tin oxide. The development of cheaper electrodes compatible with fast processing is therefore of high importance. The primary aim of this work has been to increase the absorption in solar cells made from thin films of organic materials. Device construction, deploying new geometries, and evaluation of different methods to provide for light trapping and photon recycling have been strived for. Different routes to construct and incorporate light trapping structures that enable higher photon absorption in a thinner film are presented. By recycling the reflected photons and enhancing the optical path length within a thinner cell, the absorption rate, as well as the collection of more charge carriers, is provided for. Attempts have been performed by utilizing a range of different structures with feature sizes ranging from nanometers up to centimeters. Surface plasmons, Lambertian scatterers, micro lenses, tandem cells as well as larger folded cell structures have been evaluated. Naturally, some of these methods have turned out to be more successful than others. From this work it can nevertheless be concluded that proper light trapping, in thin films of organic materials for photovoltaic energy conversion, is a technique capable of improving the cell performance. In addition to the study of light trapping, two new alternative electrodes for polymer photovoltaic devices are suggested and evaluated.
43
Bollinger, Joshua David. "Applications of solar energy to power stand-alone area and street lighting". Diss., Rolla, Mo. : University of Missouri-Rolla, 2007. http://scholarsmine.umr.edu/thesis/pdf/Joshua_Bollinger_Thesis_09007dcc8031b71d.pdf.
Testo completoAbstract (sommario):
Thesis (M.S.)--University of Missouri--Rolla, 2007.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 17, 2007) Includes bibliographical references (p. 88-91).
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Thantsha, Nicolas Matome. "Spatially resolved opto-electric measurements of photovoltaic materials and devices". Thesis, Nelson Mandela Metropolitan University, 2010. http://hdl.handle.net/10948/1123.
Testo completoAbstract (sommario):
The objective of this study is to characterize and analyse defects in solar cell devices. Materials used to fabricate solar cells are not defects free and therefore, there is a need to investigate defects in cells. To investigate this, a topographical technique was developed and employed which uses a non-destructive methodology to analyse solar cells. A system was built which uses a technique based on a laser beam induced current (LBIC). LBIC technique involves focusing light on to a surface of a solar cell device in order to create a photo-generated current that can be measured in the external circuit for analyses. The advantage of this technique is that it allows parameter extraction. Parameters that can be extracted include short-circuit current, carrier lifetime and also the external and internal quantum efficiency of a solar cell. In this thesis, LBIC measurements in the form of picture maps are used to indicate the distribution of the localized beam induced current within solar cells. Areas with low minority carrier lifetime in solar cells are made visible by LBIC mapping. Surface reflection intensity measurements of cells can also be mapped using the LBIC system developed in this study. The system is also capable of mapping photo-generated current of a cell below and above room temperature. This thesis also presents an assessment procedure capable of assessing the device and performance parameters with reference to I-V measurements. The dark and illuminated I-V characteristics of solar cells were investigated. The illuminated I-V characteristics of solar cells were obtained using a defocused laser beam. Dark I-V measurements were performed by applying voltage across the cell in the dark and measuring a current through it. The device parameters which describe the behaviour of I-V characteristic were extracted from the I-V data using Particle Swarm Optimization (PSO) method based on a one-and two-diode solar cell models. Solar cells of different technologies were analysed, namely, single-crystalline (c-Si) and multicrystalline (mc-Si) silicon, Edge-defined Film-fed Growth Si (EFG-Si) and Cu(In,Ga)(Se,S)2 (CIGSS) thin film based cells. The LBIC results illustrated the effect of surface reflection features and material defects in the solar cell investigated. IQE at a wavelength of 660 nm were measured on these cells and the results in general emphasised the importance of correcting optical losses, i.e. reflection loss, when characterizing different types of defects. The agreement between the IQE measurements and I-V characteristics of a cell showed that the differences in crystal grains influence the performance of a mc-Si cell. The temperature-dependence of I-V characteristics of a CIGSS solar cell was investigated. The results showed that, for this material, the photo response is reduced at elevated temperatures. In addition to LBIC using a laser beam, solar spectral radiation was employed to obtained device performance parameters. The results emphasised the effect of grain boundaries as a recombination centres for photo-generated hole-pairs. Lastly, mesa diode characterizations of solar cells were investigated. Mesa diodes are achieved by etching down a solar cell so that the plateau regions are formed. Mesa diodes expose the p-n junction, and therefore mesa diode analysis provides a better way of determining and revealing the fundamental current conduction mechanism at the junction. Mesa diodes avoid possible edge effects. This study showed that mesa diodes can be used to characterize spatial non-uniformities in solar cells. The results obtained in this study indicate that LBIC is a useful tool for defect characterization in solar cells. Also LBIC complements other characterization techniques such as I-V characterization.
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McCracken, R. O. "The copper-bismuth-sulphur material system and thin film deposition of Cu3BiS3 by sputtering and evaporation for the application of photovoltaic cells". Thesis, University of Leeds, 2016. http://dspace.lib.cranfield.ac.uk/handle/1826/9927.
Testo completoAbstract (sommario):
The semiconducting sulphosalt Wittichenite has been identified as a possible absorber material for thin film photovoltaic devices. It has the chemical formula Cu3BiS3 and its component elements are those of low toxicity and high abundance making it a very attractive prospect for photovoltaic devices.
The copper bismuth sulphur material system is not very well understood and information on it limited to a few small regions. To aid understanding of this system a pseudo-binary phase diagram along the CuS-Bi join of the Cu-Bi-S ternary phase diagram was constructed by making bulk samples of various compositions along the join and analysing them using X-ray diffraction and differential scanning calorimetry. This join was chosen because is crosses the point at which Cu3BiS3 would be expected to occur due to its stoichiometry. The CuS-Bi phase diagram shows Cu3BiS3 forms across a wide compositional range but is mixed with either bismuth metal or copper sulphides depending on composition.
Films of Cu3BiS3 were made using sputtered copper and bismuth films annealed in a sulphur atmosphere and thermal co- evaporation of copper sulphide and bismuth.
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Ropp, Michael Eugene. "Design issues for grid-connected photovoltaic systems". Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/13456.
Testo completo
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Mbambisa, Gcineka. "Polymeric-bimetallic oxide nanoalloy for the construction of photovoltaic cells". University of the Western Cape, 2014. http://hdl.handle.net/11394/4364.
Testo completoAbstract (sommario):
Philosophiae Doctor - PhDResearch in renewable energy has become a focal point as a solution to the energy crisis. One of renewable forms of energy is solar energy, with the main challenge in the development of the solar cells being the high cost. This has led to the exploration of the use of organic molecules to construct solar cells since it will lead to lowered costs of construction. The focus of this research is on the synthesis and characterisation of the polyaniline derivatives materials and zinc gallate for application in the construction of hybrid solar cells with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an acceptor. The polyaniline (PANi) and doped polyaniline derivatives, polyaniline phenathrene sulfonic acid (PANi-PSA), poly[ortho-methyl aniline] phenanthrene sulfonc acid (POMA-PSA) poly[ortho-methyl aniline] anthracene sulfonc acid (POMA-ASA) were produced via chemical synthetic procedures. The zinc gallate (ZnGa2O4) was also produced using a chemical method. The vibrational and electronic spectra of the polymers and zinc gallate were interrogated independently and dependently. Electronic transitions due to charge defects (polarons and bipolarons) were observed for the polymers that are doped. The PANi was the one with the lowest band gap of 2.4 eV with the POMA-ASA having the widest bandgap of 3.0 eV. The XRD and TEM analysis of the polymers revealed characteristics that show that the PANi has the highest level of crystallinity and the POMA-ASA displayed the least level of crystallinity. The electronic data, XRD, TEM data led to the conclusion that the conductivity of the polymers is decreasing in the following sequence, PANi > PANi-PSA > POMA-PSA > POMA-ASA. The photoluminescence of the polymers alone and with the nanoparticles was investigated in solution and on an ITO coated glass substrate. Photoluminescence was observed for the polymers due to relaxation of the exciton and also from the formation of excimers. The relaxation due to the exciton was observed at higher energy levels, while the one that is as a result of the excimer formation was seen at lower energy levels. Enhancement of the peak due to the excimer was observed when the compound is mixed with the nanoparticles in solution. When the analysis was done on the ITO coated glass substrate, it was found that zinc gallate does not lead to quenching of the emission of the polymers; hence it can not be used as an acceptor in this particular system. The electrochemical behaviour of the polyaniline derivatives was investigated using cyclic voltammetry and electrochemical impedance spectroscopy. Interaction of the polymers with the PCBM (acceptor) was investigated using UV-visible absorption spectroscopy and photoluminescence spectroscopy. It was able to quench the photoluminescence of the polymers. Hence it was used as an acceptor in the construction of the photovoltaic cells. The polymers alone and with the nanoparticles were used in the formation of bulk heterojunction photovoltaic cells with PCBM as an acceptor. The photovoltaic behaviour was investigated and PANi was the one that displayed the highest efficiency.
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Chen, Jen-kon. "Fabrication of a SeCdO photovoltaic cell using a mixed gas sputtering technique". Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63150.
Testo completo
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Attygalle, Dinesh. "Electrochemical Deposition of Transparent Conducting Oxides for Photovoltaic Applications". Connect to full text in OhioLINK ETD Center, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1229464154.
Testo completo
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Kim, Yongjin. "Experimental investigation of the interfacial fracture toughness in organic photovoltaics". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47605.
Testo completoAbstract (sommario):
The development of organic photovoltaics (OPVs) has attracted a lot of attention due to their potential to create a low cost flexible solar cell platform. In general, an OPV is comprised of a number of layers of thin films that include the electrodes, active layers and barrier films. Thus, with all of the interfaces within OPV devices, the potential for failure exists in numerous locations if adhesion at the interface between layers is inherently low or if a loss of adhesion due to device aging is encountered. To date, few studies have focused on the basic properties of adhesion in organic photovoltaics and its implications on device reliability. In this dissertation, we investigated the adhesion between interfaces for a model multilayer barrier film (SiNx/PMMA) used to encapsulate OPVs. The barrier films were manufactured using plasma enhanced chemical vapor deposition (PECVD) and the interfacial fracture toughness (Gc, J/m2) between the SiNx and PMMA were quantified. The fundamentals of the adhesion at these interfaces and methods to increase the adhesion were investigated. In addition, we investigated the adhesive/cohesive behavior of inverted OPVs with different electrode materials and interface treatments. Inverted OPVs were fabricated incorporating different interface modification techniques to understand their impact on adhesion determined through the interfacial fracture toughness (Gc, J/m2). Overall, the goal of this study is to quantify the adhesion at typical interfaces used in inverted OPVs and barrier films, to understand methods that influence the adhesion, and to determine methods to improve the adhesion for the long term mechanical reliability of OPV devices.