Stress Relaxation for Lead Iodide Nucleation in Efficient Perovskite Solar Cells
Zhimiao Zheng, Yansong Ge, Xiangfeng Yang, Wenlong Shao, Haibing Wang, Zhenhua Yu, Chen Tao, Hua‐Hua Fu, Weijun Ke, Guojia Fang
Abstract
Abstract Porous lead iodide (PbI 2 ) film is crucial for the complete reaction between PbI 2 and ammonium salts in sequential‐deposition technology so as to achieve high crystallinity perovskite film. Herein, it is found that the tensile stress in tin (IV) oxide (SnO 2 ) electron transport layer (ETL) is a key factor influencing the morphology and crystallization of PbI 2 films. Focusing on this, lithium trifluoromethanesulfonate (LiOTf) is used as an interfacial modifier in the SnO 2 /PbI 2 interface to decrease the tensile stress to reduce the necessary critical Gibbs free energy for PbI 2 nuclei formation. The relaxed tensile stress facilitates the more porous PbI 2 generation with larger particles and higher roughness, resulting in superior‐quality perovskite films. Besides, this strategy effectively passivates the inherent electron traps of SnO 2 and smooths the interfacial energy levels, boosting the charge extraction and transfer. As a result, a champion power conversion efficiency (PCE) of 25.33% (25.10% stabilized for 600 s) is achieved. Furthermore, the device demonstrates exceptional stability, retaining 90% of its initial PCE at its maximum power point tracking measurement (under 100 mW cm −2 white light illumination at ≈55 °C temperature, in N 2 atmosphere) after 600 h.