Temperature‐Reliable Low‐Dimensional Perovskites Passivated Black‐Phase CsPbI3 toward Stable and Efficient Photovoltaics

Abstract Low‐dimensional (LD) perovskites can effectively passivate and stabilize 3D perovskites for high‐performance perovskite solar cells (PSCs). Regards CsPbI 3 ‐based PSCs, the influence of high‐temperature annealing on the LD perovskite passivation effect has to be taken into account due to fact the black‐phase CsPbI 3 crystallization requires high‐temperature treatment, however, which has been rarely concerned so far. Here, the thermal stability of LD perovskites based on three hydrophobic organic ammonium salts and their passivation effect toward CsPbI 3 and the whole device performance, have been investigated. It is found that, phenyltrimethylammonium iodide (PTAI) and its corresponding LD perovskites exhibit excellent thermal stability. Further investigation reveals that PTAI‐based LD perovskites are mainly distributed at grain boundaries, which not only enhances the phase stability of CsPbI 3 but also effectively suppresses non‐radiative recombination. As a consequence, the champion PSC device based on CsPbI 3 exhibits a record efficiency of 21.0 % with high stability.