Self-assembled Nanometer-Scale ZnS Structure at the CZTS/ZnCdS Heterointerface for High-Efficiency Wide Band Gap Cu2ZnSnS4 Solar Cells

Despite remarkable progress in the performance of kesterite Cu2ZnSnS4 (CZTS)-based photovoltaic technology has been achieved, the interface recombination and associated open-circuit voltage (Voc) deficit still dominate the loss mechanism in this technology. To alleviate heterojunction interface recombination in pure sulfide thin film solar cells, passivation structure at the interface is required. In this work, we developed an ultrathin nanometer-scale ZnS dielectric passivation layer which is readily formed in situ at the CZTS/ZnCdS heterointerface during the ZnCdS buffer deposition process via Zn diffusion from the ZnCdS bulk to the interface. With this nanoscale structure, a remarkable open-circuit voltage and fill factor improvement is illustrated, and a total area efficiency of 9.25% is obtained. The formation and features of the nanoscale ZnS layer are investigated by high-resolution scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. This self-assembled ZnS layer wit...