abstract: Nickel-Copper metallization for silicon solar cells offers a cost effective alternative to traditional screen printed silver paste technology. The main objective of this work is to study the formation of nickel silicide contacts with and without native silicon dioxide SiO2. The effect of native SiO2 on the silicide formation has been studied using Raman spectroscopy, Rutherford backscattering spectrometry and sheet resistance measurements which shows that SiO 2 acts as a diffusion barrier for silicidation at low temperatures of 350°C. At 400°C the presence of SiO2 results in the increased formation of nickel mono-silicide phase with reduced thickness when compared to samples without any native oxide. Pre and post-anneal measurements of Suns Voc, photoluminescence and Illuminated lock in thermography show effect of annealing on electrical characteristics of the device. The presence of native oxide is found to prevent degradation of the solar cells when compared to cells without any native oxide. A process flow for fabricating silicon solar cells using light induced plating of nickel and copper with and without native oxide (SiO2) has been developed and cell results for devices fabricated on 156mm wafers have been discussed. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2016

abstract: The work contained in this dissertation is focused on the structural and optical properties of III-V semiconductor structures for solar cell applications. By using transmission electron microscopy, many of their structural properties have been investigated, including morphology, defects, and strain relaxation. The optical properties of the semiconductor structures have been studied by photoluminescence and cathodoluminescence. Part of this work is focused on InAs quantum dots (QDs) embedded in AlGaAs matrices. This QD system is important for the realization of intermediate-band solar cells, which has three light absorption paths for high efficiency photovoltaics. The suppression of plastic strain relaxation in the QDs shows a significant improvement of the optoelectronic properties. A partial capping followed by a thermal annealing step is used to achieve spool-shaped QDs with a uniform height following the thickness of the capping layer. This step keeps the height of the QDs below a critical value that is required for plastic relaxation. The spool-shaped QDs exhibit two photoluminescence peaks that are attributed to ground and excited state transitions. The luminescence peak width is associated with the QD diameter distribution. An InAs cover layer formed during annealing is found responsible for the loss of the confinement of the excited states in smaller QDs. The second part of this work is focused on the investigation of the InxGa1-xN thin films having different bandgaps for double-junction solar cells. InxGa1-xN films with x ≤ 0.15 were grown by metal organic chemical vapor deposition. The defects in films with different indium contents have been studied. Their effect on the optical properties of the film have been investigated by cathodoluminescence. InxGa1-xN films with indium contents higher than 20% were grown by molecular beam epitaxy. The strain relaxation in the films has been measured from electron diffraction patterns taken in cross-sectional TEM specimens. Moiré fringes in some of the films reveal interfacial strain relaxation that is explained by a critical thickness model. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2016

Organic photovoltaics have shown much promise as an alternative photovoltaic technology for application in low-cost, large-scale and flexible solar cells. The application of metal oxides in organic solar cells (OSCs) and the impact of the properties of metal oxide/organic hetero-interfaces on cell performance have attracted a lot of attention. The metal oxide/organic interfaces have a crucial impact on interfacial charge transfer, charge collection and the overall device performance. This thesis is aimed at clarifying the principal interfacial phenomena occurring at the metal oxide/organic hetero-interfaces as well as effective engineering of those interfacial properties in OSCs. Photo-generated electrons and holes undergo different recombination processes, e.g., bimolecular recombination and trap-assisted recombination, before being collected by the electrodes in OSCs. Light intensity-dependent current densityvoltage (JV) characteristics of OSCs were analyzed to study the effect of recombination on charge collection efficiency. Effect of metal oxide/organic hetero-interfaces on charge transfers at organic/electrode interface was analyzed using transient photocurrent (TPC) measurements. Light intensity-dependent JV characteristics and TPC characteristics were applied to explore the charge recombination dynamics in OSCs with a metal oxide interlayer. This project concentrated on an in-depth investigation of the physics and the interface phenomena such as interfacial exciton dissociation, charge recombination processes, charge collection and interface engineering for high performing OSCs. The fundamentals about light intensity-dependent J-V characteristics for OSCs were summarized. The relationship between the charge recombination dynamics and light intensity-dependent J-V characteristics in OSCs were developed. Light intensity-dependent JSC, VOC and FF in OSCs made with different bulk-heterojunction (BHJ) systems of PTB7:PC70BM, PTB7-Th:PC70BM and PNB4:PC70BM were investigated. It is found that bimolecular recombination is the most prominent factor limiting the performance of OSCs. For freshly made OSCs fabricated based on the commercial polymers, e.g. PTB7 & PTB7-Th, and the new polymer PNB4 synthesized in-house, the trap-assisted charge recombination process in the BHJ active layer plays a relatively small role. This suggests that reducing the bimolecular recombination in OSCs through selecting proper materials and device structures is crucial for enhancing the power conversion efficiency (PCE) of OCSs. In this work, device structures which enable reducing bimolecular recombination in OSCs were investigated. The effect of ZnO interlayer at the interface between BHJ and Al cathode on the performance of PTB7:PC71BM based OSCs was studied by a combination of theoretical simulation and experimental characterization techniques, e.g., using light intensity-dependent JV characteristic and TPC measurements etc. It shows that ZnO interlayer has a profound effect on the performance of the PTB7:PC70BM-based OSCs, although it does not have a significant influence on the maximum absorptance in the active layer. The origin of the improvement in the cell performance is associated with the efficient charge collection due to the favorable exciton dissociation at the electrode/active layer interface. It is shown that the presence of the ZnO interlayer allows using a thinner active layer without moderating the absorption in the optically optimized control OSCs without the ZnO interlayer. OSCs with a ~10 nm thick ZnO interlayer are found to be favorable for the efficient charge collection, and thereby improving the cell performance. The TPC measurements also reveal that the dissociation of excitons at the metal/organic interface of regular OSCs hinders the electron collection. The unfavorable interfacial exciton dissociation can be removed by interposing a ZnO interlayer at the Al/organic interface, thus bimolecular recombination at the electrode/active layer interface can be reduced for improving the charge collection efficiency. PCE of the OSCs using ZnO interlayer was 6.5%, which is about 20% higher than a control cell (5.4%), having an identical device configuration without a ZnO interlayer. Solution-processed anode interlayer, a mixture of solution-processed MoOX and PEDOT:PSS, was adopted for application in inverted PTB7:PC71BM-based OSCs. The ratio of MoOX to PEDOT:PSS in the mixed solution was optimized for achieving the best cell performance. A PCE of 7.4% was obtained for OSCs with an optimal MoOX-PEDOT:PSS based interlayer, interposed between the BHJ active layer and Ag anode, which means 10% enhancement over the PCE of control cell made with an evaporated MoOX interlayer. Light intensity-dependent JV characteristics implied that the bimolecular recombination in OSCs with a MoOX-PEDOT:PSS interlayer was reduced. TPC measurements showed that the favorable exciton dissociation occurs at the organic/MoOX interface for the inverted OSCs. The favorable interfacial exciton dissociation generates an electrical field within a very small space near the interface, contributing significant additional photocurrent when the effective bias across the active layer in the OSCs is low, and thereby assisting in an efficient charge collection at the organic/electrode interface. In addition to the improvement in the cell performance, the solution-processed MoOX-PEDOT:PSS interlayer does not require a post-annealing treatment, which is beneficial for application in solution-processed tandem and flexible OSCs.

Pour que l'énergie photovoltaïque devienne compétitive, les coûts de production doivent être baissés et l'efficacité des cellules augmentée. Les cellules solaires à base de nanocristaux semi-conducteurs constituent une approche prometteuse pour remplir ces objectifs combinant une mise en œuvre par voie liquide avec la possibilité d'ajuster précisément la largeur de bande interdite et les niveaux électroniques. Aujourd'hui, les rendements de conversion des cellules constituées de nanocristaux de sulfure de plomb approchent les 7%. Seulement, à cause des normes européennes destinées à l'affranchissement du plomb du fait de ses risques pour la santé et l'environnement, de nouveaux matériaux doivent être trouvés. Cette thèse concerne la synthèse de nouveaux types de nanocristaux semi-conducteurs et leur application dans des cellules solaires. La synthèse des nanocristaux de CuInSe2 et de SnS de taille et de forme contrôlées a été effectuée, notamment par des voies de synthèses reproductibles dont le passage à grande échelle est facilement possible. Une analyse approfondie de la structure des nanocristaux de SnS par spectroscopie Mössbauer a montré que ces nanocristaux avaient une forte tendance à s'oxyder, ce qui limite leur utilisation dans des dispositifs électroniques après exposition à l'air. La constitution de couches minces continues ayant de bonnes propriétés électriques a été effectuée par le dépôt contrôlé de nanocristaux ainsi que l'échange de leurs ligands de surface. En particulier, un nouveau type de ligand inorganique a été utilisé qui a montré une augmentation de la conductivité des films multiplié par quatre ordres de grandeurs par rapport aux ligands initiaux. Enfin, la préparation de cellules solaires basées sur ces couches minces de nanocristaux a montré des résultats encourageants et notamment un clair effet photovoltaïque lorsque le dépôt est effectué sous atmosphère inerte. / In order to be cost-effective, photovoltaic energy conversion needs to improve the solar cell efficiencies while decreasing the production costs. Nanocrystal based solar cells could fulfil these requirements through solution-processing, band gap and energy level engineering. PbS nanocrystal thin films already proved their potential for use as solar cell active materials with power conversion efficiencies approaching 7%. However, since lead based compounds are not compatible with European regulations and present high risks for health and environment, semiconductor nanocrystals of alternative materials have to be developed. This thesis focuses on novel types of semiconductor nanocrystals and their application in photovoltaics. The first part of the study deals with the synthesis of size- and shape-controlled CuInSe2 and SnS nanocrystals. An in-depth investigation of the structure of SnS nanocrystals using Mössbauer spectroscopy revealed their high oxidation sensitivity, which limits their usability in optoelectronic devices after air exposure. The second part deals with the thin film preparation and the surface ligand exchange of the obtained nanocrystals. Using a fully inorganic nanocrystal-surface ligand system, the deposited films exhibited a current density improved by four orders of magnitude as compared to the initial ligands. Finally, solar cell devices based on nanocrystal thin films were fabricated, which showed encouraging results with a clear photovoltaic effect when processed under inert atmosphere.

Cu(In,Ga)Se2 (CIGS) is a semiconductor material and the basis of the promising thin-film photovoltaic technology with the same name. The CIGS film has a typical thickness of 1-2 mm, and solar cells based on CIGS technology has recently reached efficiencies of 23.3%. Ultra-thin CIGS solar cells use sub-micrometer thick films that require significantly less material and can be manufactured in a shorter amount oftime than films with typical thicknesses. With decreasing thickness, both electrical and optical losses get more significant and lower the overall performance. Electrical losses can be decreased by increasing the overall film quality and by utilising a graded bandgap throughout the CIGS layer. The band gap can be changed by varying the[Ga]/([Ga]+[In]) (GGI) ratio. Higher overall film quality and a higher band-gap towards the back of the absorber are expected to increase the performance. In this work, sputtered CIGS solar cells were made with different CIGS layer thicknesses, that ranged between 550-950 nm. Increased heat during deposition was examined and shown to increase the film quality and performance for all thicknesses. Two different ways of doping CIGS with Na was examined and it was found that higher Na content lead to an increasing predominance of the (112) plane. The bandgap was graded by varying the GGI composition throughout the CIGS layer and depth profiles were made with Glow-Discharge Optical Emission Spectroscopy (GDOES). It was found that a sputtered CuGaSe2 (CGS)layer below the CIGS-layer lead to a steep increase of the GGI near the back contact. When CGS made up 10% of the total CIGS layer thickness, a significant increase in performance was observed for all thicknesses. CIGS-absorbers with a less graded region with low GGI, making up 30% or 60% of the total CIGS layer thickness were made. A decrease in GGI in that region, was shown to increase the current but lower the voltage. No substantial increase in total performance compared to a fully graded CIGS layer was seen regardless of layer thickness. For further work the optical losses needs to be addressed and work on increasing the optical path in the CIGS layer needs to be done.

Submitted by Morgana Silva (morgana_linhares@yahoo.com.br) on 2016-07-27T16:43:01Z No. of bitstreams: 1 arquivototal.pdf: 1307807 bytes, checksum: 77d4794b09c164cec707cb914d2e0bfe (MD5) / Made available in DSpace on 2016-07-27T16:43:01Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1307807 bytes, checksum: 77d4794b09c164cec707cb914d2e0bfe (MD5) Previous issue date: 2016-02-26 / Due to increasing demand in the global energy sector, research are being grounded in the pursuit of new nonpolluting energy resources. With concepts of use already well-established, solar energy has been highlighted in its capture and transformation into electricity. One way of using solar energy with great impact on energy network is the transformation through the solar cells, which are devices for direct conversion of solar energy into electricity through the photovoltaic effect. This raises a number of challenges to their development as it relates to new materials that allow greater efficiency in this transformation. Photovoltaic cells need to be efficient, stable, and its manufacturing cost must be competitive. Considering these factors, this paper presents the assembly of solar cells sensitized by titanium dioxide pigment (TiO2) most commonly found in the literature. Based on this, the solar cell has been developed using the Pechini method. The methodology is consolidated and objective, an optimization of all steps involved in the assembly process of the cells to improve the efficiency of energy conversion. To check the performance of the cell, its efficiency is calculated. This estimate requires a fill factor (FF) extracted from the I-V curve. For this purpose, Newton Rapson and Levenberg-Marquardt algorithms are used to plot the curve and find the cell parameters. The experimental results show that the cell built with an area of 6,25 square centimeters and the efficiency value η = 3.21% is effective in the transformation of solar energy into electricity. / Devido à demanda crescente no setor de energia mundial, trabalhos de pesquisas estão sendo fundamentados na procura de novos recursos energéticos não poluentes. Com conceitos de utilização já bem consolidados a energia solar tem tido destaque na sua captação e transformação em energia elétrica. Uma das formas de utilização da energia solar com grande impacto na rede energética é a transformação através das células solares, que são dispositivos de conversão direta de energia solar em energia elétrica por meio do efeito fotovoltaico. Neste contexto, surgem vários desafios para o seu desenvolvimento no que se refere a novos materiais que possibilitem maior eficiência nessa transformação. As células fotovoltaicas precisam ser eficientes, estáveis e seu custo de fabricação deve ser competitivo. Considerando esses fatores, este trabalho de pesquisa apresenta a montagem de células solares sensibilizadas por corante de dióxido de titânio (TiO2) mais comumente encontradas na literatura. Baseado nisso, foi desenvolvida a célula solar utilizando o método Pechini. A metodologia é consolidada e objetiva, uma otimização de todas as etapas envolvidas no processo de montagem das células para melhorar a eficiência da conversão energética. Para verificar o desempenho da célula, calcula-se a sua eficiência. Esta estimativa necessita de um fator de preenchimento (FF) extraído da curva I-V. Para este propósito, os algoritmos de Newton Rapson e Levenberg Marquardt são aplicados para plotar a curva e achar os parâmetros da célula. Os resultados experimentais comprovam que a célula construída com uma área de 6,25 cm2 e o valor de eficiência η = 3,21 %, é eficaz na transformação da energia solar em eletricidade.

Submitted by SILVIA LETICIA FERNANDES null (sy.fernandes@hotmail.com) on 2016-05-31T17:30:17Z No. of bitstreams: 1 Tese_Silvia Leticia Fernandes.pdf: 5734164 bytes, checksum: 5485bc4d14d63bd72484d78e0e3a1907 (MD5) / Rejected by Ana Paula Grisoto (grisotoana@reitoria.unesp.br), reason: Solicitamos que realize uma nova submissão seguindo a orientação abaixo: O arquivo submetido está sem a ficha catalográfica. A versão submetida por você é considerada a versão final da dissertação/tese, portanto não poderá ocorrer qualquer alteração em seu conteúdo após a aprovação. Corrija esta informação e realize uma nova submissão contendo o arquivo correto. Agradecemos a compreensão. on 2016-05-31T20:24:02Z (GMT) / Submitted by SILVIA LETICIA FERNANDES null (sy.fernandes@hotmail.com) on 2016-05-31T22:31:21Z No. of bitstreams: 1 Tese_Silvia Leticia Fernandes.pdf: 5362328 bytes, checksum: 3ad1eb46dfedf8840bc516a67f927a4f (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-06-01T14:17:17Z (GMT) No. of bitstreams: 1 fernandes_sl_dr_bauru.pdf: 5362328 bytes, checksum: 3ad1eb46dfedf8840bc516a67f927a4f (MD5) / Made available in DSpace on 2016-06-01T14:17:17Z (GMT). No. of bitstreams: 1 fernandes_sl_dr_bauru.pdf: 5362328 bytes, checksum: 3ad1eb46dfedf8840bc516a67f927a4f (MD5) Previous issue date: 2016-04-27 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O desenvolvimento das células solares de perovskita foi acompanhado por uma revolução no campo dos dispositivos fotovoltaicos. Células solares de perovskita atingiram eficiências de conversão de energia maiores que 21% em apenas 5 anos após sua descoberta, colocando-as em competição com as células solares comerciais de silício. Apesar de promissores, os dispositivos de perovskita enfrentam desafios que impedem sua comercialização, sendo o maior deles o problema de estabilidade. Nesse âmbito, a presente tese teve como principal foco o desenvolvimento de células solares de perovskita baseadas em filmes nanoestruturados de Nb2O5 e TiO2, visando melhor compreensão do funcionamento desses dispositivos afim de se obter a solução dos problemas hoje enfrentados. Os resultados obtidos mostram eficiências maiores que 13% para o sistema: filme compacto de Nb2O5/ filme mesoporoso de TiO2/ CH3NH3PbI3; e eficiências tão elevadas quanto 15% para sistema usando filme compacto e mesoporoso de TiO2/ CH3NH3PbI3. As melhores células solares montadas com filmes compactos de Nb2O5 apresentaram correntes de curto circuito de 19 mA/cm2, tensão de circuito aberto de 960 mV, fator de preenchimento de 75% e eficiências de 13%. Para as células formadas com filmes de compactos de TiO2 foram obtidas correntes de curto circuito de 20 mA/cm2, tensão de circuito aberto de 1V, fator de preenchimento de 70% e eficiências de 15%. A estabilidade dos dispositivos e a presença de histerese nas curvas de tensão-corrente foram estudadas variando parâmetros como a composição da camada compacta (TiO2 versus Nb2O5), a espessura dessa camada; assim como o método de síntese utilizado para preparar os filmes de perovskitas (método de deposição sequencial versus método de engenharia dos solventes). De maneira geral, os resultados mostraram que células solares preparadas com filmes de Nb2O5 de 50 nm em conjunto com perovskitas preparada pelo método de deposição sequencial resultaram em dispositivos sem histerese e com maior estabilidade do que os preparados com filmes de TiO2 ou mais espessos que 50nm. / The development of perovskite solar cells was accompanied by a revolution in the photovoltaics field. Perovskite solar cells have reached higher energy conversion efficiencies of 21% in just 5 years after its discovery, putting them in competition with commercial silicon solar cells. Although promising, the perovskite devices face some challenges which delay their commercialization, and one of most important is the stability. In this context, the present thesis intended the development of perovskite solar cells based on nanostructured films of Nb2O5 and TiO2, in order to better understand the functioning of these devices. Efficiencies up to 13% were obtained for the system composed of: compact Nb2O5 / mesoporous TiO2/ CH3NH3PbI3 and efficiencies as high as 15% for compact system using compact TiO2/ mesoporous TiO2/ CH3NH3PbI3. The best solar cells prepared using compact Nb2O5 films showed a short circuit current of 19 mA/cm 2 , open circuit voltage of 900 mV, fill factor of 75% and 13% of efficiency. Devices prepared using compact TiO2 films reached short circuit current of 20 mA/cm2 , open circuit voltage of 1V, fill factor of 70% and 15% of efficiency. The stability of the devices and the presence of current-voltage hysteresis were studied by changing parameters such as the composition and the thickness of the compact layer (TiO2 vs. Nb2O5), as well as the synthesis method used to prepare the perovskite films (sequential deposition method vs solvent-engineering method). Overall, the results showed that solar cells prepared with 50 nm Nb2O5 film in combination with perovskite prepared by sequential deposition method have resulted in devices without hysteresis and greater stability than those prepared with TiO2 films or thicker than 50nm. / FAPESP: 2012-07745-9

Thesis (DTech (Engineering))--Cape Peninsula University of Technology, 2017. / The world has been experiencing energy-related problems following pressuring energy demands which go along with the global economy growth. These problems can be phrased in three paradoxical statements: Firstly, in spite of a massive and costless solar energy, global unprecedented energy crisis has prevailed, resulting in skyrocketing costs. Secondly, though the sun releases a clean energy, yet conventional plants are mainly being run on unclean energy sources despite their part in the climate changes and global warming. Thirdly, while a negligible percentage of the solar energy is used for power generation purposes, it is not optimally exploited since more than its half is wasted in the form of heat which contributes to lowering efficiency of solar cells and causes their premature degradation and anticipated ageing. The research is geared at addressing the issue related to unsatisfactory efficiencies and anticipated ageing of solar modules. The methodology adopted to achieve the research aim consisted of a literature survey which in turn inspired the devising of a high-efficiency novel thermal electric solar power panel. Through an in-depth overview, the literature survey outlined the rationale of the research interest, factors affecting the performance of PVs as well as existing strategies towards addressing spotted shortcomings. While photovoltaic (PV) panels could be identified as the most reliable platform for sunlight-to-electricity conversion, they exhibit a shortcoming in terms of following the sun so as to maximize exposure to sunlight which negatively affects PVs’ efficiencies in one hand. On the other hand, the inability of solar cells to reflect the unusable heat energy present in the sunlight poses as a lifespan threat. Strategies and techniques in place to track the sun and keep PVs in nominal operational temperatures were therefore reviewed.

Este trabalho foi desenvolvido em duas etapas: i) síntese, caracterização e aplicação de pontos quânticos de CdS, CdSe e CdTe em células solares. ii) modificação da superfície dos pontos quânticos de CdSe através de troca de ligante, seguida de caracterização e aplicação em células solares. Os pontos quânticos foram sintetizados utilizando acetatos de cádmio, selênio, telúrio e enxofre como precursores e ácido oleico como agente de estabilização. Na segunda etapa o ácido oleico foi substituído por ligantes com maior afinidade eletrônica pelos sítios de Cd2+: ácido 3-mercaptopropiônico, 4-ácido-mercaptobenzóico e ácido 11-mercaptoundecanóico. As amostras foram caracterizadas por UV-Vis, fluorescência, microscopia eletrônica de transmissão, difratometria de raios-X e voltametria cíclica. Adicionalmente, testes de solubilidade, análises de TGA e de RMN foram realizadas para confirmar a troca de ligante. Através dos resultados, verificou-se que todos os pontos quânticos sintetizados são adequados para sensibilização de TiO2 em dispositivos fotovoltaicos. No entanto, os pontos quânticos de CdSe e CdTe apresentaram fatores que evidenciam maior confinamento quântico, sendo que a maior estabilidade do éxciton foi obtida para o CdSe. Através das análises de RMN foi possível verificar que não existe apenas uma confirguração espacial preferencial para a adsorção do ligante sobre a superfície deste ponto quântico enquanto que curvas de corrente versus potencial e de eficiência de conversão de fóton incidente mostraram que a eficiência do dispositivo é fracamente dependente do ligante. Contudo, a troca de ligantes favorece a solubilidade em solventes com diferentes polaridades, inclusive água, o que amplia as possibilidades de aplicação dos pontos quânticos sintetizados neste trabalho. / This work was developed in two stages: i) synthesis, characterization and application of CdS, CdSe and CdTe quantum dots to assemble solar cells, ii) surface modification, characterization and application of CdSe quantum dots to assemble solar cells. The quantum dots were synthesized by using cadmium acetate, Se, S or Te as precursors and oleic acid as stabilizing agent. In the second stage the oleic acid capping layer was replaced by other ligands with higher electron affinity to Cd2+: 3-mercaptopropionic acid, 4-mercaptobenzoic acid and 11-mercaptoundecanoic acid. The samples were characterized by UV-Vis, fluorescence, transmission electron microscopy, x-ray diffractometry and cyclic voltammetry. Additionally, solubility tests, TGA analysis and NMR were performed to evaluate the CdSe surface modification. The results showed that all quantum dots synthesized are adequate to sensitize TiO2 in photovoltaic devices. However, CdSe and CdTe quantum dots presented better quantum confinement and the exciton generated in CdSe presented the higher stability. NMR analysis provided information about the non-preferential orientation for adsorption of the ligands on the CdSe surface, meanwhile measurements of current vs. potential and incident photon current efficiency showed a weak dependence of photovoltaic device efficiency with the nature of the ligand. On the other side, the surface modification favors the solubility in solvents with different polarizabilities, including water, widening the range for applications of the quantum dots synthesized in this work.

abstract: The objective of this thesis is to achieve a detailed understanding of the loss mechanisms in SHJ solar cells. The working principles of these cells and what affects the cell operation, e.g. the IV characteristics at the maximum power point (MPP) and the correspondingly ll factor (FF) are investigated. Dierent loss sources are analyzed separately, and the weight of each in the total loss at the MPP are evaluated. The total series resistance is measured and then compared with the value obtained through summation over each of its components. In other words, series resistance losses due to recombination, vertical and lateral carrier transport, metalization, etc, are individually evaluated, and then by adding all these components together, the total loss is calculated. The concept of ll factor and its direct dependence on the loss mechanisms at the MPP of the device is explained, and its sensitivity to nearly every processing step of the cell fabrication is investigated. This analysis provides a focus lens to identify the main source of losses in SHJ solar cells and pave the path for further improvements in cell efficiency. In this thesis, we provide a detailed understanding of the FF concept; we explain how it can be directly measured; how it can be calculated and what expressions can better approximate its value and under what operating conditions. The relation between FF and cell operating condition at the MPP is investigated. We separately analyzed the main FF sources of losses including recombination, sheet resistance, contact resistance and metalization. We study FF loss due to recombination and its separate components which include the Augur, radiative and SRH recombination is investigated. We study FF loss due to contact resistance and its separate components which include the contact resistance of dierent interfaces, e.g. between the intrinsic and doped a-Si layers, TCO and a-Si layers. We also study FF loss due to lateral transport and its components that including the TCO sheet resistance, the nger and the busbars resistances. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2018