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.