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.