Characterization on Highly Efficient Perovskite Solar Cells Made from One‐Step and Two‐Step Solution Processes

One‐step and two‐step methods are regarded as the main solution processes for preparing organic metal halide perovskite (PVSK) films. Both of them are also reported to produce high‐quality PVSK films and high‐performance devices. Herein, two highly efficient perovskite solar cells (PSCs) made by one‐step (19.91%) and two‐step (20.63%) methods are analyzed in detail. Particularly, the nucleation mechanism and structural characteristics of the PVSK films made from different methods are systematically discussed. Characterizations from field‐emission scanning electron microscopy (FE‐SEM), atomic force microscopy (AFM), Kelvin probe force microscopy (KPFM), and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) show that the ion distribution in the PVSK film made by the one‐step method is less uniform horizontally, while the PVSK film made by the two‐step method is less uniform vertically. Both films contain a considerable amount of unreacted species, including PbI₂, cations, and halides, which are relics from their parental fabricating process. Despite these significant differences, both films are capable to deliver nearly 20% conversion efficiency. This study depicts a clear picture of the PVSK film properties made by one‐step and two‐step methods and provides plentiful information for further improvement in the future.