Technology for CZTS-Silicon Tandem Solar Cells

Silicon-based tandem solar cells will play a major role in the future of the photovoltaics (PV) industry due to their very high efficiency potential. However, the sensitive nature of silicon bulk material, particularly to contamination, has restricted the top absorber's choice for monolithic integration to a few candidates with a limited thermal budget and mild fabrication processes. In this thesis, we chose Cu2ZnSnS₄, a quaternary compound semiconductor, as a promising non-toxic, earth-abundant, and cheap candidate from emerging thin-film technologies and systematically studied the integration challenges with silicon. For this purpose, we developed a thermally resilient silicon cell structure protected with an ultrathin nitride-based diffusion barrier at the interface of the two cells. By engineering the interfacial layers, we managed to keep the silicon cell intact during the full top cell fabrication and demonstrated a world-record efficiency for a CZTS-Si tandem solar cell. The developed technology enables not only the growth of a wide range of materials on silicon but also provides new insights to the PV community for future silicon-based tandem cell architectures.