Why Sb₂Se₃/CdS Interface Produces Higher Power Conversion Efficiency

Developing the Cd-free electron transport layer (ETL) is a crucial subject in the field of antimony selenide (Sb₂Se₃) solar cells. At present, the power conversion efficiency (PCE) of the Cd-free Sb₂Se₃ solar cell is still substantially lower than that of CdS-based devices. It is significant to reveal the electron transfer features in Sb₂Se₃/CdS heterojunction and Sb₂Se₃/Cd-free ETL heterojunction for development of a Cd-free Sb₂Se₃ solar cell with high PCE. In this work, Sb₂Se₃/Cd heterojunction and Sb₂Se₃/ZnO heterojunction were systematically investigated from the view of PCE, trap state passivation, interface charge separation, and carrier kinetics on a picosecond time scale. Experimental results demonstrate that electron transfer at Sb₂Se₃/CdS and Sb₂Se₃/ZnO occurs on a comparable time scale with time constants of 1.38-3.42 and 1.91-3.17 ps, respectively. The PCE gap between the Cd-based device and the Cd-free device is mainly determined by the passivation effect. The excellent passivation effect of CdS on Sb₂Se₃ ensure the high electron transfer efficiency at Sb₂Se₃/CdS heterojunction. Our results reveal the key challenges in improving the performance of Cd-free Sb₂Se₃ solar cells.