Low‐Temperature Processed CsPbI₃ for Flexible Perovskite Solar Cells Through Cs─I bond Weakening

Abstract All‐inorganic triiodide cesium lead (CsPbI 3 ) exhibits huge potential in perovskite solar cells (PSCs). However, the high‐temperature crystallization process (≈340 or 180 °C) limits their further development, especially in flexible PSCs. Here, a Cs─I bond weakening approach is proposed to realize the low‐temperature crystallization of CsPbI 3 by introducing organic sulfonate of 1‐propylsulfonate‐3‐methylimidazolium chloride (SMCl). SMCl can strongly interact with CsI and weaken the Cs─I bond to dissociate free I − ions for the effective transition of initial PbI 2 to [PbI 6 ] 4− , which greatly decreases the crystallization temperature of black CsPbI 3 to 90 °C. As a result, flexible PSCs are realized with efficiency of 13.86%, which is the highest efficiency of flexible CsPbI 3 devices. Besides, SMCl will also help to release the tensile strain and stabilize CsPbI 3 phase, leading to good thermal and mechanical stability. Almost no efficiency loss is observed in flexible PSCs after 36000 bending cycles with a curvature radius of 5 mm.