High open-circuit voltage CuSbS₂ solar cells achieved through the formation of epitaxial growth of CdS/CuSbS₂ hetero-interface by post-annealing treatment

The earth-abundant and environmentally-friendly CuSbS₂ solar cells have been struggling with low device performance, especially poor open circuit voltage (V_oc). In this work, post-annealing treatment of the CuSbS₂/CdS heterojunction performed on CuSbS₂-based solar cells was firstly reported. With this treatment, we demonstrated CuSbS₂ solar cells with a record V_oc of 622 mV. The improvement of device performance was found peaked at 250°C post-annealing which mainly benefits from the significantly boosted open-circuit voltage and short-circuit current. The study of microstructure by high-resolution transmission electron microscopy revealed that such improvement could be attributed to the formation of epitaxial CuSbS₂/CdS hetero-interface upon heat treatment, which reduces the interface defect density that may lead to reduced V_oc deficit. Besides, results of photoluminescence and time-resolved photoluminescence measurements also indicated improved electrical properties of completed devices with higher photoluminescence intensity and longer minority carrier lifetime.