Crystallization management of CsPbI2Br perovskites by PbAc2-incorporated twice spin-coating process for efficient and stable CsPbI2Br perovskite solar cells

CsPbI2Br perovskite solar cell has been extensively studied due to its exceptional thermal stability and relatively stable perovskite phase structure. However, the presence of bromine leads to a rapid crystallization rate of CsPbI2Br films, resulting in small grain size and high defect density. Additionally, CsPbI2Br demonstrates poor light absorption due to its wide bandgap. Therefore, it is crucial to control the crystallization rate and increase the film thickness to reduce defect density, enhance light absorption, and improve photovoltaic performance. In this study, we utilized a PbAc2-incorporated twice spin-coating (PTS) process to address these issues. Initially, PbAc2 was added to the CsPbI2Br precursor solution to form a CsPbI2Br film, which was then coated with the CsPbI2Br precursor solution to produce the PTS film. Ac− can delay the perovskite crystallization, leading to the formation of thicker and denser CsPbI2Br films. Moreover, lone-pair electrons of the oxygen atom provided by Ac− formed coordination bonds with under-coordinated Pb2+ ions to fill halogen ion vacancies, thereby reducing the defect density. Ultimately, the PTS CsPbI2Br device achieved a peak power conversion efficiency (PCE) of 16.19% and maintained 96.7% of its initial PCE over 1500 h at room temperature under 25% relative humidity without any encapsulation.