New multi-functional chalcogenides for photovoltaic and thermoelectric materials

The subject of this PhD thesis is part of a research domain of great present interest in new semiconductor materials for photovoltaic and thermoelectric applications. This domain contains the elaboration and the study of both Cu-based chalcogenides bulk and thin-film samples, driven by materials design principles. One of the most research semiconductor materials is the synthetic mineral tetrahedrite, typified by Cu₁₂Sb₄S₁₃. Optical, electrical, and thermal properties have been tuned via chemical substitutions, allowing optimization of performance toward the realizations of high-efficiency devices. Chapter 2 and 3 detail exploration of several tetrahedrite-derivatives for PV and TE applications, respectively. This work demonstrates that this exceptional multi-functionality is related to the unique structural building blocks of these materials. In the context of similar structural features, Cu₃-V-VI4 (V = P, As, Sb; VI = S, Se) has been discovered as new absorbers in Chapter 4. Chapter 5 attempts to find the missing Co₂GeS₄ compound through (Fe,Co)₂GeS₄ and (Co,Zn)₂GeS₄ solid solutions by a systematic investigation between theoretical prediction and experimental results. More generally, this fundamental research creates a practical framework for future design principles based search and discovery of effective materials.