UCLA

Chalcopyrite solar cells have attracted a lot of attention due to their highest power conversion efficiency among all thin film solar cells. However, significant cost reductions as well as large scale production are necessary to compete with conventional electrical power generation. The development of new deposition technologies for the absorber layer as well as the conducting window layer that are compatible with atmospheric deposition on a manufacturing-scale are urgently required to significantly offset production costs. This dissertation demonstrates the development of fully solution-processed high performance CuIn(Se,S)2 photovoltaic devices based on a hydrazine processed absorber layer and metal nanowire composite window layer. Furthermore, the included studies present a deep understanding of the materials chemistry involved in the formation of the CuIn(Se,S)2 precursor molecules and thin films, as well as material design for metal nanowire composite window layers, and the charge transport mechanism in the fully solution-processed high performance CuIn(Se,S)2 photovoltaic devices. Chapter 2 presents the identification of the molecular precursor species present in hydrazine CuIn(Se,S)2 solutions, and precise control of energy band gap of CuIn(Se,S)2 by tailoring the bonding environment of the molecular species present in precursor solutions. Chapter 3 investigates secondary phase formation at the Mo/CuIn(Se,S)2 interface as well as a strategy for achieving a large grained CuIn(Se,S)2 film structure with demonstrated photovoltaic device performance using a sputtered metal oxide window layer. Chapter 4 focuses on the development of transparent conductors composed of solution processed silver nanowires composite window layers demonstrating better optoelectronic and mechanical properties than conventionally sputtered indium tin oxide films. Chapter 5 centers on the complete replacement of sputtered metal oxides by metal nanowires embedded in conductive nanoparticle window layer without any sacrifices in device performance, elucidate the role of each component of the window layers by probing spatially resolved carrier collection, and presents a detailed study of band alignment in fully solution-processed high performance CuIn(Se,S)2 photovoltaic devices by investigating current-voltage characteristics in the dark and under illumination from several controlled wavelength ranges. Thin film chalcopyrite solar cells employing solution-processed absorber layers combined with metal nanowire-metal oxide nanoparticle composite window layers are anticipated to effectively serve as a renewable energy source with reduced fabrication costs and competitive device performance.