Enhanced Carrier Dynamics Resulted from Non-Volatile Chloride Additive for Improved Average Efficiency of PSCs

Abstract Chlorine additives are commonly used to optimize perovskite solar cells (PSCs). However, due to strong volatility, organic chlorine additives often result in poor stability and residual lead iodide (PbI2). Here, we report a method to improve perovskite film crystallization via the formation of lead chloride (PbCl2)-induced intermediate phase in a two-step process. Results show that non-volatile PbCl2 not only creates a porous structure favorable for solid-liquid reactions during the second step deposition but also forms a MAPbCl3 intermediate phase with methylammonium chloride (MACl), which greatly promotes the crystallization quality of perovskite (PVK) films. Additionally, transient absorption (TA) spectroscopy indicates that an appropriate amount of PbCl2 can improve the carrier dynamics, while excess additives would deteriorate the charge activity. As a result, the average power conversion efficiency (PCE) of the optimal modified devices is promoted from 18.79% to 21.34% with a champion efficiency of 23.15%. And the hysteresis index (HI) reduced from 17.48% to 6.09%. PbCl2 added PSCs can retain 78% of its initial PCE after 1000 hours under 50% relative humidity (RH) in ambient air. Our work provides a novel approach to precisely control the carrier dynamics and clarifies the mechanism of PbCl2 in the growth process of perovskite films.