Dispersive precipitation of PbI2 for the optoelectronic properties preferred α-FAPbI3 solar cells

Abstract

Abstract text: Formamidinium lead triiodide (α-FAPbI3) is a critical component in the development of highly efficient and stable organic-inorganic metal halide perovskite solar cells (PSCs). α-FAPbI3 exhibits unique optoelectronic property changes during its phase transition, making it a material of significant interest. In this study, we investigate the characteristics and byproducts of the α-FAPbI3 phase transition. Our findings reveal that polar gases act as a key factor in triggering the transformation of α-FAPbI3 into yellow-phase formamidinium lead triiodide (δ-FAPbI3), while polar solvents facilitate the precipitation of PbI2 from α-FAPbI3. The phase evolution and precipitation processes of δ-FAPbI3 and PbI2 from α-FAPbI3 demonstrate four distinct degradation pathways. Throughout these degradation pathways, the power conversion efficiency (PCE), absorption edges, absorption intensity and photoluminescence spectroscopy (PL) of the devices and films exhibit a unique unimodal variation. Our research indicates that the -dispersive precipitation of PbI2 during the phase transition can significantly optimize the photoelectric properties and enhance the performance of PSCs. Leveraging this phenomenon, we achieved an increase in the PCE of devices undergoing the phase transition process, from 22.41% to 25.12%. These results highlight the potential of controlled phase transitions in improving the efficiency and stability of perovskite-based solar cells.