High‐Performance Rb–Cs0.14FA0.86Pb(BrxI1−x)3 Perovskite Solar Cells Achieved by Regulating the Halogen Exchange in Vapor–Solid Reaction Process

Despite tremendous progress in efficiency and stability, perovskite solar cells are still facing the challenge of scalability and reproducibility. Vapor–solid reaction methods that derived from the chemical vapor deposition have been regarded as facile approaches to prepare perovskite films with large size. However, different from the precise control of compounding ratio by weighting in the solution process, the perovskite films deposited by vapor–solid reaction methods always suffer from undesired I − /Br − ratio, leading to poor performance of the solar device. Thus, controllable halogen exchange in the vapor–solid reaction process is significant for the further development of this technique. Herein, different alkali‐metal ions (such as Na + , K + , and Rb + ) are added into the inorganic CsBr/PbI 2 framework, and it is found that the halogen exchange in the vapor–solid reaction process can be regulated by these ions. After optimization, high‐quality Rb‐Cs 0.14 FA 0.86 Pb(Br x I 1‐ x ) 3 films with proper I − /Br − ratio are successfully obtained. Perovskite solar cells based on the as‐prepared perovskite films exhibit a significant enhancement on V oc and the champion power conversion efficiency reaches 19.6% with a V oc of 1.13 V.