Controlled solid‐state Phase Transition of Formamidinium Dominated Perovskite Layers Fabricated Through Magnetron Sputtering for Photovoltaics

Abstract Perovskite solar cells (PSCs) based on formamidinium lead iodide (FAPbI 3 ) have demonstrated the highest power conversion efficiencies. Typically fabricated through solution‐processing, FAPbI 3 films necessitate intricate crystallization control to avoid the formation of a more stable non‐perovskite phase. Magnetron sputtering, an effective solvent‐free technique, has gained attention for producing large‐area perovskite films. Here, a novel approach to create high‐quality FAPbI 3 ‐based perovskite thin films by employing magnetron sputtering is presented. Specifically, a mechanosynthesized blend of (FA 1‐ x MA x )Pb(I 1‐ x Br x ) 3 (MA = methylammonium) is used as a single‐source target for sputtering, and a post‐annealing transforms various phases in the initial deposited film into coherent FAPbI 3 ‐based films with an ultra‐long and controlled crystallization process. Despite minimal residual MABr after post‐annealing, its presence is crucial in the formation of perovskite film, as evidenced by a distinct solid‐state phase transformation process is presented. A comprehensive investigation of the films' structural, compositional, and optical properties, with respect to varying MABr doping ratios, reveals details of perovskite phase development and the pivotal influence of MABr. PSCs fabricated with the optimized films display a substantial increase in the power conversion efficiency, reaching 20.1%. These results underscore the potential of combining magnetron sputtering and post‐annealing in the scalable production of high‐efficiency PSCs.