Improved Crystallization and Stability of Mixed-Cation Tin Iodide for Lead-Free Perovskite Solar Cells
Xin Xu, Kun Cao, Wenjing Zhu, Wenwen Gu, Ben Ma, Minchao Qin, Jie Qian, Yao Lu, Ziwei Liu, Shufen Chen, Xinhui Lu, Wei Huang
Abstract
Formamidinium tin iodide (FASnI3) perovskite is a promising light harvester for lead-free perovskite solar cells (PSCs). However, the poor quality of the solution-processed FASnI3 film always leads to an inferior efficiency and poor stability. Herein, we demonstrate a mixed-cation strategy by trace-doping of highly hydrophobic cations to construct high-quality three-dimensional (3D) perovskite films. Tin halide perovskites with FA and 3,3-diphenylpropylammonium (DPPA) hybrid cations were fabricated, and the trace-doping of DPPA cations can greatly enhance the stability of 3D perovskites by suppressing the oxidation of Sn2+ to Sn4+. After optimization of DPPAI/FAI ratios, the DPPA0.02FA0.98SnI3 perovskite achieves better film crystallinity and morphology. Our champion device based on DPPA0.02FA0.98SnI3 perovskite shows the highest power conversion efficiency of 6.75% with all improved device parameters. Moreover, the corresponding unencapsulated device retains 70% of its initial efficiency after aging over 600 h in N2 environment. This work provides a feasible approach to fabricate high-quality 3D perovskites for lead-free PSCs applications.