Two‐Step Vapor‐Solid Reaction for the Growth of High‐Quality CsFA‐Based Lead Halide Perovskite Thin Films

Thin‐film solar cells based on organic–inorganic hybrid perovskite light absorbers have attracted intense attention both from the scientific and industrial communities in recent years. Researchers worldwide have developed various strategies for depositing high‐quality perovskite thin films including composition optimization, surface modification, and solvent engineering. However, these strategies are mainly based on the perovskite thin films which are deposited via solution processes. Though vacuum and vapor‐based techniques have been widely used in the modern thin‐film industry, these technologies still need further developments for the deposition of high‐quality organic–inorganic hybrid perovskite thin films. Herein, a novel two‐step vapor–solid reaction procedure for the deposition of high‐quality methylamine‐free hybrid perovskite thin films is proposed. The first vapor–solid reaction step gives the perovskite a proper chemical stoichiometric ratio, and the second step can refine the crystallinity of the film. Therefore, by utilizing this method, it is possible to obtain high‐quality perovskite thin films with larger grain sizes and lower tap densities. Consequently, perovskite solar cells based on these films have achieved a high power conversion efficiency of 20.79%.