Electron Transport Layer Engineering Induced Carrier Dynamics Optimization for Efficient Cd-Free Sb₂ Se₃ Thin-Film...

Antimony selenide (Sb₂ Se₃ ) 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 Sb₂ Se₃ 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 Sb₂ Se₃ /SnO_x heterojunction with better interface performance and much desirable "spike-like" band alignment, and also improve the Sb₂ Se₃ 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/Sb₂ Se₃ /SnO_x /ITO/Ag thin-film solar cell exhibits a stimulating efficiency of 7.39%, contributing a record value for Cd-free substrate structured Sb₂ Se₃ solar cells reported to date. This work provides a viable strategy for developing and broadening practical applications of environmental-friendly Sb₂ Se₃ photovoltaic devices.