Review of Two‐Step Method for Lead Halide Perovskite Solar Cells

The quality of the perovskite film is crucial to the technological breakthrough of perovskite solar cells (PSCs). The two‐step method can facilitate the formation of a perovskite film with high quality and reproducibility. Many milestones have been made in the development of hybrid lead halide PSCs by using the two‐step method, which has a significant impact on their practical application. Herein, the reaction mechanism of the two‐step method including two‐step immersion method and two‐step spin coating method is summarized. The strategies such as component engineering, solvent engineering, and additive engineering of the two‐step method in preparing high‐quality films are introduced systematically and in detail. In addition, current issues of the two‐step method and its applications in lead‐free PSCs, all‐inorganic PSCs, large areas, and tandems are introduced and some suggestions are put forward for future research.