Interface Engineering by Small Molecules toward Efficient Hole Transport Layer-Free Sn–Pb Perovskite Solar Cells with High Fill Factors
Yu Xu, Jiayu You, Jingwei Zhu, Yuliang Xu, Jialun Jin, Peng Jiang, Qinfei Gao, Zhiyu Gao, Juncheng Wang, Wenbo Jiao, Yi Luo, Tianshu Ma, Kai Wu, Shengqiang Ren, Cong Chen, Changlei Wang, Dewei Zhao
Abstract
Low-bandgap (LBG) tin–lead (Sn–Pb) perovskites are essential for tandem solar cells but face challenges because the use of a hygroscopic PEDOT:PSS hole transport layer (HTL) reduces device stability. A HTL-free structure can overcome these issues but introduces new drawbacks like imbalanced carrier transport and severe recombination. This study introduces 3-amino-5-mercapto-1,2,4-triazole (AMTZ) as a rear interface passivator to simultaneously mitigate defects and stabilize Sn–Pb perovskite films. The aromatic triazole group of AMTZ coordinates with dangling Pb 2+ /Sn 2+ cations to reduce interface trap states, while the reducing thiol (–SH) group suppresses Sn 2+ oxidation. In addition, AMTZ post-treatment also modulates the energy-level alignments, promoting fluent charge transfer in HTL-free perovskite solar cells (PSCs). Consequently, we achieved efficient HTL-free LBG PSCs with a champion efficiency of 21.87% and an impressive fill factor of over 80%. Moreover, the optimized device maintained 80% of the initial efficiency upon 550 h of storage. This work demonstrates a viable strategy for developing efficient and stable HTL-free LBG PSCs through interfacial engineering.