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.