The sun provides us with a surplus of energy convertible to electricity using solar cells. This thesis focuses on solar cells based on chalcopyrite (CIGSe) as well as kesterite (CZTS(e)) absorber layers. These materials yield record efficiencies of 20.4 % and 11.1 %, respectively. Especially for CZTS(e), the absorber layers often do not consist of one single desired phase but can exhibit areas with deviating material properties, referred to as secondary phases. Furthermore, several material layers are required for a working solar cell, each exhibiting interfaces. Even though secondary phases and interfaces represent a very small fraction of the solar cell they can have a profound influence on the over-all electrical solar cell characteristics. As such, it is crucial to understand how secondary phases and interfaces influence the local electrical characteristics. Characterising secondary phases and interfaces is challenging due to their small sample volume and relatively small differences in composition amongst others. This is where electronmicroscopy, especially transmission electron microscopy, offers valuable insight to material properties on the microscopic scale. The main challenge is, however, to link these material properties to the corresponding electrical characteristics of a solar cell. This thesis uses electron beam induced current imaging and introduces a new method for JV characterisation of solar cells on the micron scale. Combining microscopic structural and electrical characterisation techniques allowed identifying and characterising local defects found in the absorber layer of CIGS solar cells after thermal treatment. Furthermore, CZTSe solar cells in this thesis exhibited a low photo-current density which is traced to the formation of a current blocking ZnSe secondary phase at the front contact interface. The electron microscopy work has contributed to an understanding of the chemical stability of CZTS and has shown the need for an optimised back contact interface in order to avoid chemical decomposition reactions and formation of detrimental secondary phases. With this additional knowledge, a comprehensive picture of the material properties from the macroscopic down to the microscopic level can be attained throughout all required material layers.

Direct conversion of solar energy, which is the most powerful and unlimited one among the renewable energy sources / into the electrical energy by the photovoltaic devices, is a promising way of meeting the energy needs of future. Thin film semiconductor materials show great promise for the production of efficient, low-cost solar cell devices. Recently advanced research on thin film photovoltaics in all aspects, has attracted intense attention. Thin film semiconductors for the photovoltaic applications are deposited in large areas by different methods. In this study, deposition and characterization of CuIn1-x GaxSe2 ( CIGS ) semiconductor thin films by thermal evaporation and e-beam evaporation methods were investigated. Material properties and deposition parameters of the thin films are aimed to be optimized for solar cell applications. Structural properties of the deposited CIGS thin films were examined through X-ray diffraction and Energy Dispersive X-ray Analysis. The temperature dependent electrical conductivity, Hall effect and photoconductivity of these samples have been measured between 100 and 400 K. For the optical characterization of CIGS thin films, the transmission measurements have been carried out in the wavelength region of 325-900 nm. The changes in the structural, electrical and optical properties of samples through post-depositional annealing effect were also analyzed.

Ces travaux de thèse ont pour but de développer des cellules photovoltaïques à base de Cu(In,Ga)Se2 (CIGS) sur des substrats métalliques. L'objectif principal consiste à résoudre les différentes problématiques liées à l'utilisation de ces substrats (Ti et acier inoxydable) en s'appuyant sur une adaptation de l'électrode arrière. L'étude est focalisée sur l'élaboration de contacts arrière en Mo par pulvérisation cathodique. Dans un premier temps, des contacts arrières en monocouches et en bicouches sont comparés, démontrant les intérêts des structures en bicouches. Ces dernières sont obtenues en utilisant successivement deux pressions différentes pendant le dépôt du contact arrière. Nous montrons que la pression utilisée pendant le dépôt de la couche inférieure influe sur la morphologie de la couche supérieure. Il en résulte des modifications de l'orientation cristalline du CIGS et des performances photovoltaïques. Dans une seconde étude, la couche inférieure est déposée à partir d'une cible de molybdène contenant du sodium (Mo:Na) afin d'apporter du Na dans le CIGS. Les différences entre le Mo et le Mo:Na sont d'abord étudiées. Nous montrons ensuite que la diffusion du sodium vers le CIGS dépend de la pression de dépôt de la couche de Mo:Na. Dans le cas de substrats en Ti, des rendements équivalents aux substrats en verre sodo-calcique sont obtenus en utilisant le molybdène dopé au sodium. Nous montrons aussi qu'en présence de sodium, l'effet de la pression de dépôt de la couche inférieure sur les performances est minimisé.

Materials and device concepts for renewable solar hydrogen production, and size dependent properties of ZnO quantum dots are the two main themes of this thesis. ZnO particles with diameters less than 10 nm, which are small enough for electronic quantum confinement, were synthesized by hydrolysis in alkaline zinc acetate solutions. Properties investigated include: the band gap - particle size relation, phonon quantum confinement, visible and UV-fluorescence as well as photocatalytic performance. In order to determine the absolute energetic position of the band edges and the position of trap levels involved in the visible fluorescence, methods based on combining linear sweep voltammetry and optical measurements were developed. The large band gap of ZnO prevents absorption of visible light, and in order to construct devices capable of utilizing a larger part of the solar spectrum, other materials were also investigated, like hematite , Fe2O3, and CIGS, CuIn1-xGaxSe2. The optical properties of hematite were investigated as a function of film thickness on films deposited by ALD. For films thinner than 20 nm, a blue shift was observed for both the absorption maximum, the indirect band gap as well as for the direct transitions. The probability for the indirect transition decreased substantially for thinner films due to a suppressed photon/phonon coupling. These effects decrease the visible absorption for films thin enough for effective charge transport in photocatalytic applications. CIGS was demonstrated to be a highly interesting material for solar hydrogen production. CIGS based photocathodes demonstrated high photocurrents for the hydrogen evolution half reaction. The electrode stability was problematic, but was solved by introducing a modular approach based on spatial separation of the basic functionalities in the device. To construct devices capable of driving the full reaction, the possibility to use cells interconnected in series as an alternative to tandem devices were investigated. A stable, monolithic device based on three CIGS cells interconnected in series, reaching beyond 10 % STH-efficiency, was finally demonstrated. With experimental support from the CIGS-devices, the entire process of solar hydrogen production was reviewed with respect to the underlying physical processes, with special focus on the similarities and differences between various device concepts.

Solar cells constitute the most direct way of converting solar energy to electricity, and thin-film solar-cell technologies have lately been growing in importance, allowing the fabrication of less expensive modules that nonetheless have good power-conversion efficiencies. This thesis focuses on solar cells based on Cu(In,Ga)Se2, which is the thin-film technology that has shown the highest conversion efficiency to date, reaching 20.3 % on the laboratory scale. Solar modules still have some way to go to become entirely competitive with existing energy technologies, and there are two possible paths to this goal: Firstly, reducing their manufacturing costs, for instance by minimizing the material usage per module and/or by increasing the throughput of a given factory; and secondly, increasing the power output per module in other words, the module efficiency. The subject matters of this thesis are related to those two approaches. The first issue investigated is the possibility for reducing the thickness of the Cu(In,Ga)Se2 layer and compensating for lost absorption by using a ZrN back reflector. ZrN layers are fabricated by reactive sputtering and I present a method for tuning the sputtering parameters so as to obtain a back reflector with good optical, electrical and mechanical properties. The reflector layer cannot be used directly in CIGS devices, but relatively good devices can be achieved with a precursor providing a homogeneous supply of Na, the addition of a very thin sacrificial Mo layer that allows the formation of a film of MoSe2 passivating the back contact, and optionally a Ga gradient that further keeps electrons away from the back contact. The second field of study concerns the three-stage CIGS coevaporation process, which is widely used in research labs around the world and has yielded small-area cells with highest efficiencies, but has not yet made it to large scale production. My focus lies on the development and the effect of gradients in the [Ga]/[In+Ga] ratio. On the one hand, I investigate 'intrinsic' gradients (ones that form autonomously during the evaporation), and present a formation model based on the differing diffusivity of Ga and In atoms in CIGS and on the development along the quasi-binary tie line between (In,Ga)2Se3 and Cu2Se. On the other hand, I determine how the process should be designed in order to preserve 'extrinsic' gradients due to interdiffusion. Lastly, I examine the electrical effects of Ga-enhancement at the back and at the front of the absorber and of In-enhancement at the front. Over a wide range, In-rich top layers prove to have no or a weakly beneficial effect, while Ga-rich top regions pose a high risk to have a devastating effect on device performance.

Thin film chalcogenide solar cells are promising photovoltaic technologies. Cu(In,Ga)Se2 (CIGS)-based devices are already produced at industrial scale and record laboratory efficiency surpasses 22 %. Cu2ZnSn(S,Se)4 (CZTS) is an alternative material that is based on earth-abundant elements. CZTS device efficiency above 12 % has been obtained, indicating a high potential for improvement. In this thesis, in-line vacuum, sputtering-based processes for the fabrication of complete thin film chalcogenide solar cells on stainless steel substrates are studied. CIGS absorbers are deposited in a one-step high-temperature process using compound targets. CZTS precursors are first deposited by room temperature sputtering and absorbers are then formed by high temperature crystallization in a controlled atmosphere. In both cases, strategies for absorber layer improvement are identified and implemented. The impact of CZTS annealing temperature is studied and it is observed that the absorber grain size increases with annealing temperature up to 550 °C. While performance also improves from 420 to 510 °C, a drop in all solar cell parameters is observed for higher temperature. This loss is caused by blisters forming in the absorber during annealing. Blister formation is found to originate from gas entrapment during precursor sputtering. Increase in substrate temperature or sputtering pressure leads to drastic reduction of gas entrapment and hence alleviate blister formation resulting in improved solar cell parameters, including efficiency. An investigation of bandgap grading in industrial CIGS devices is conducted through one-dimensional simulations and experimental verification. It is found that a single gradient in the conduction band edge extending throughout the absorber combined with a steeper back-grading leads to improved solar cell performance, mainly due to charge carrier collection enhancement. The uniformity of both CIGS and CZTS 6-inch solar cells is assessed. For CZTS, the device uniformity is mainly limited by the in-line annealing process. Uneven heat and gas distribution resulting from natural convection phenomenon leads to significant lateral variation in material properties and device performance. CIGS solar cell uniformity is studied through laterally-resolved material and device characterization combined with SPICE network modeling. The absorber material is found to be laterally homogeneous. Moderate variations observed at the device level are discussed in the context of large area sample characterization. Power conversion efficiency values above 15 % for 225 cm2 CIGS cells and up to 5.1 % for 1 cm2 CZTS solar cells are obtained.

To cope with energy requirements the utilization of renewable energies, particularly the Sun supplies the biggest and abundant energy source in Earth. Photo-voltaic and solar cell are the well advance and burning technology and a field of hot research. Majority of research centers and universities are working in this field. 1G, 2G, 3G and next generation of photo-voltaic cells have been developed and still to improve its efficiency and to decrease it 0.2 $/W cost. Our work mainly based on the theoretical and physical analysis of thin-film Photovoltaic devices. We will explore different software used for the analysis of PV cells, and will analyse different simulation related to solar cells like open circuit voltage VOC, Short circuit current JSC, Fill Factor FF (%) and external Quantum efficiency (%) for thin film solar cell including CIGS, CIS, CGS, CdTe, SnS/CdS/ZnO etc. To have different analysis for different combination and different replacement for materials used in the solar cell fabrication. To cope with the PV cost and environmental hazards we have to find alternate solutions. / Ullah, H. (2015). Simulation studies of photovoltaic thin film devices [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/48800 / TESIS

Devices with ZnCdS/ZnS heterojunction partner layer have shown better blue photon response due to higher band gap of these compounds as compared to devices with CdS heterojunction partner layer. CdS heterojunction partner layer has shown high photovoltaic conversion efficiencies with CIGS absorber layer while efficiencies are lower with CuIn1-xGaxS2 (CIGS2). A negative conduction band offset has been observed for CdS/CIGS2 as compared to near flat conduction band alignment in case of CdS/CIGS devices, which results in higher interface dominated recombination. Moreover, it has been predicted that optimum band offsets for higher efficiency solar cells may be achieved for cells with alternative heterojunction partner such as ZnS. With varying ratio of Zn/ (Zn+Cd) in ZnxCd1-xS a range of bandgap energies can be obtained and thus an optimum band offset can be engineered. For reducing interface dominated recombination better lattice match between absorber and heterojunction partners is desirable. Although CdS has better lattice match with CuIn1-xGaxS2 absorber layer, same is not true for CuIn1-xGaxS2 absorber layers. Utilizing ZnxCd1-xS as heterojunction partner provides a range of lattice constant (between aZnS= ~5.4 Ǻ and aCdS= ~5.7 Ǻ) depending on Zn/(Zn+Cd). Therefore better lattice match can be obtained between heterojunction partner and absorber layer. Better lattice match will lead to lower interface dominated recombination, hence higher open circuit voltages. In the present study chemical bath deposition parameters are near optimized for high efficiency CIGS2 Solar cells. Effect of various chemical bath deposition parameters on device performance was studied and attempts were made to optimize the deposition parameters in order to improve the device performance.In/(In+Ga) ratio in absorber layer is varied to obtain good lattice match and optimum band alignment. Solar cells with conversion efficiencies comparable to conventional CdS/CIGS2 has been obtained with ZnxCd1-xS /CIGS2. High short current as well as higher open circuit voltages were obtained with ZnxCd1-xS as alternative heterojunction partner for CIGS2 solar cells as compared to SLG/Mo/CIGS2/ CdS / i-ZnO/ZnO:Al.

No description available.

[ES] Este proyecto de investigación se centra en el campo de las energías renovables y más concretamente de la energía solar fotovoltaica. La tesis se ha focalizado en el desarrollo de películas delgadas de Cobre-Indio-GalioSelenio o Sulfuro (CuIn1-xGax(Se,S)2) con técnicas de bajo coste. La mayoría de las celdas basadas en CIGS utilizan el CdS como capa de búfer. En nuestro experimento, usaremos otra capa de tampón como SnS2 o ZnO1-xSx como alternativa a CdS para mejorar nuestra célula. El estudio se centrará en el contacto tampón/absorbedor para reducir la recombinación. En este trabajo, reportamos la investigación experimental del desarrollo y desarrollo de la caracterización de la calcopirita de cobre, indio, galio y selenio (CIGS) por la técnica de electrodeposición y pulverización. Además, nos hemos centrado en el contacto entre la capa generadora que es el absorbedor y el circuito externo. Las propiedades eléctricas de este contacto dependen principalmente del proceso de deposición de la capa absorbente en el contacto trasero utilizado. Por lo tanto, será necesario controlar el crecimiento de la capa interfacial de MoSe2 entre el absorbedor y el contacto posterior en el caso del molibdeno para obtener un rendimiento óptimo. Por supuesto, la eficiencia de la célula depende de un gran número de parámetros experimentales y varía según los métodos de fabricación, especialmente la capa absorbente CIGS. En nuestro caso, las técnicas utilizadas son la galvanoplastia y la pirólisis por pulverización para la deposición de películas CIGS. Estas técnicas son más baratas, prácticamente alcanzables en cualquier laboratorio y dan un buen rendimiento. Por lo tanto, mediante técnicas de deposición de bajo coste hemos estudiado el comportamiento de la célula solar con una capa de MoSe2 como capa interfacial y el efecto de la banda prohibida de la capa formada y la capa tampón utilizada sobre los parámetros de las células solares CIGS. Los resultados de este estudio podrían ayudar a mejorar el rendimiento de las células solares CIGS utilizando técnicas de bajo coste. / [CA] Aquest projecte de recerca es centra en el camp de les energies renovables i més concretament en l'energia solar fotovoltaica. La tesi s'ha centrat en el desenvolupament de pel·lícules primes de Coure-Indi-Gali-Seleni o Sulfur (CuIn1-xGax(Se,S)2) amb tècniques de baix cost. La majoria de les cel·les basades en CIGS utilitzen el CdS com a capa de búfer. En el nostre experiment, farem servir una altra capa de tampó com ara SnS2 o ZnO1-xSx com a alternativa al CdS per millorar la nostra cel·la. L'estudi es centrarà en el contacte tampó/absorbidor per reduir la recombinació. En aquest treball, reportem la recerca experimental del desenvolupament i la caracterització de la calcopirita de coure, indi, gali i seleni (CIGS) mitjançant la tècnica d'electrodeposició i pulverització. A més, ens hem centrat en el contacte entre la capa generadora que és l'absorbidor i el circuit extern. Les propietats elèctriques d'aquest contacte depenen principalment del procés de deposició de la capa absorbent en el contacte posterior utilitzat. Per tant, serà necessari controlar el creixement de la capa interfacial de MoSe2 entre l'absorbidor i el contacte posterior en el cas del molibdè per obtenir un rendiment òptim. És clar que l'eficiència de la cel·la depèn d'un gran nombre de paràmetres experimentals i varia segons els mètodes de fabricació, especialment la capa absorbent CIGS. En el nostre cas, les tècniques utilitzades són la galvanoplàstia i la piròlisi per pulverització per a la deposició de pel·lícules CIGS. Aquestes tècniques són més econòmiques, pràcticament assolibles en qualsevol laboratori i proporcionen un bon rendiment. Per tant, mitjançant tècniques de deposició de baix cost hem estudiat el comportament de la cel·la solar amb una capa de MoSe2 com a capa interfacial i l'efecte de la banda prohibida de la capa formada i la capa tampó utilitzada sobre els paràmetres de les cel·les solars CIGS. Els resultats d'aquest estudi podrien ajudar a millorar el rendiment de les cel·les solars CIGS utilitzant tècniques de baix cost. / [EN] Our research project aims at the field of renewable energies and more specifically, photovoltaic solar energy, i.e. solar cells, our study focuses on the elaboration of Copper-Indium-Gallium-Selenium or Sulfide (CuIn1-xGax(Se,S)2 thin films for solar cells with low-cost techniques also to develop the performance of the typical solar cell structure: n-ZnO/i-ZnO/n-tampon/p-CIGS/p+-MoSe2/back contact. Most of the CIGS based cells use CdS as a buffer layer. In our experiment, we will make use of another buffer layer such as SnS2 or ZnO1-xSx as an alternative to CdS to improve our cell. The investigation will be carried out on the buffer/absorber contact to reduce recombination. In addition, we will focus on the contact between the generating layer which is the absorber and the external circuit. The electrical properties of this contact depend essentially on the deposition process of the absorber layer on the back contact used. It will thus be necessary to control the growth of the MoSe2 interfacial layer between the absorber and the back contact in the case of Molybdenum in order to obtain an optimal yield. Obviously, the yield of the cell depends on a large number of experimental parameters and varies according to the fabrication methods, especially of the CIGS absorber layer. In our case the techniques used are electrodeposition and spray pyrolysis for the deposition of CIGS films, there techniques are cheaper, practically feasible in the laboratory and give good performance. Therefore, we will investigate, using low-cost deposition techniques, the performance of the cell with a MoSe2 layer as an interfacial layer and the effect of the bandgap of the formed layer and the buffer layer used on the parameters of the CIGS solar cells. The results of this study could help to improve the performance of the CIGS solar cell using low-cost techniques. / Armel Ignace, N. (2024). Elaboration et caractérisation de couches minces de cuivre, indium, gallium et sélénium (CIGS) pour cellules solaires [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/203613