Advancing Chalcogenide Solar Cells with Numerical Simulations: From Device Physics to Color Engineering

This doctoral thesis investigates, through advanced numerical simulations, the physical mechanisms and optimization strategies of chalcogenide solar cells, with particular focus on Cu(In,Ga)Se₂ (CIGS) and CuGaSe₂ (CGS)–based devices. The adopted approach combines electro–optical modeling and simulated electrical characterization, providing a coherent and comprehensive understanding of the processes that determine the efficiency and reliability of thin-film photovoltaics. In the first part, CIGS solar cells with alternative non-toxic buffer layers, such as Zn(O,S) and Zn₀.₇₅Mg₀.₂₅O, are investigated, highlighting the combined influence of bulk recombination, band offsets, and interface defects. The results provide design guidelines for the development of high-performance cadmium-free heterojunctions. Subsequently, the study focuses on the wide-bandgap CuGaSe₂ absorber, of particular interest for tandem solar cells, emphasizing the role of bulk defects and band alignment in open-circuit voltage losses. The use of Zn₁₋ₓSnₓO as a buffer layer emerges as a promising, environmentally friendly alternative to CdS. The central part of the thesis is devoted to the optical and color engineering of CIGS solar cells for building-integrated applications. Self-consistent electro-optical simulations demonstrate how the layer thicknesses and optical constants simultaneously affect efficiency and perceived color, enabling a wide range of hues with only minor efficiency trade-offs. The resulting performance–color maps provide a valuable design tool for the development of aesthetically integrated photovoltaic modules for building applications. Finally, the limits of capacitance-based characterization techniques (CV, DLCP, and Fast-CV) are analyzed for silicon, CIGS, and perovskite solar cells. The study highlights how bulk and interface defects, doping levels, band offsets, and device geometry influence the apparent charge densities extracted from these measurements. Overall, this work demonstrates that TCAD numerical simulation is a key tool for understanding, optimizing, and innovating chalcogenide photovoltaic technologies, contributing to the development of more efficient, sustainable, and versatile solar devices.