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

Abstract The earth‐abundant and environmentally‐friendly CuSbS 2 solar cells have been struggling with low device performance, especially poor open circuit voltage (V oc ). In this work, post‐annealing treatment of the CuSbS 2 /CdS heterojunction performed on CuSbS 2 ‐based solar cells was firstly reported. With this treatment, we demonstrated CuSbS 2 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 CuSbS 2 /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.