Electron Transport Layer Engineering Induced Carrier Dynamics Optimization for Efficient Cd-Free Sb 2 Se 3 Thin-Film Solar Cells.

Antimony selenide (Sb 2 Se 3 ) 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 Sb 2 Se 3 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 Sb 2 Se 3 /SnO x heterojunction with better interface performance and much desirable "spike-like" band alignment, and also improve the Sb 2 Se 3 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/Sb 2 Se 3 /SnO x /ITO/Ag thin-film solar cell exhibits a stimulating efficiency of 7.39%, contributing a record value for Cd-free substrate structured Sb 2 Se 3 solar cells reported to date. This work provides a viable strategy for developing and broadening practical applications of environmental-friendly Sb 2 Se 3 photovoltaic devices.