Electron Transport Layer Engineering Induced Carrier Dynamics Optimization for Efficient Cd‐Free Sb₂Se₃ Thin‐Film Solar Cells

Abstract Antimony selenide (Sb₂Se₃) is a highly promising photovoltaic material thanks to its outstanding optoelectronic properties, as well as its cost‐effective and eco‐friendly merits. However, toxic CdS is widely used as an electron transport layer (ETL) in efficient Sb₂Se₃ solar cells, which largely limit their development toward market commercialization. Herein, an effective green Cd‐free ETL of SnO_x is introduced and deposited by atomic layer deposition method. Additionally, an important post‐annealing treatment is designed to further optimize the functional layers and the heterojunction interface properties. Such engineering strategy can optimize SnO_x ETL with higher nano‐crystallinity, higher carrier density, and less defect groups, modify Sb₂Se₃/SnO_x heterojunction with better interface performance and much desirable “spike‐like” band alignment, and also improve the Sb₂Se₃ light absorber layer quality with passivated bulk defects and prolonged carrier lifetime, and therefore to enhance carrier separation and transport while suppressing non‐radiative recombination. Finally, the as‐fabricated Cd‐free Mo/Sb₂Se₃/SnO_x/ITO/Ag thin‐film solar cell exhibits a stimulating efficiency of 7.39%, contributing a record value for Cd‐free substrate structured Sb₂Se₃ solar cells reported to date. This work provides a viable strategy for developing and broadening practical applications of environmental‐friendly Sb₂Se₃ photovoltaic devices.