Self-aggregation of the Interfacial Passivation Layer from Ionic Additive-Stabilized PbI₂ Film for High-Performance Perovskite Solar Cells

Lead halide perovskites (LHPs) face challenges in commercialization due to the instability of their thin films during the fabrication process. During the continuous spin-coating process of formamidinium/methylammonium (FA+/MA+) organic ammonium salts, the degradation and densification of the lead iodide (PbI2) layer frequently result in incomplete conversion of the perovskite, which severely impacts the performance of perovskite solar cells. In this work, we introduced the organic ion compound tetrabutylammonium hexafluorophosphate (TBAPF6) into the PbI2 precursor solution. TBAPF6 promotes the pre-expansion of the PbI2 layer, resulting in a uniform nanoporous morphology on the surface of the PbI2 film. The adsorption interaction between TBAPF6 and lead iodide stabilizes the morphology of the lead iodide film, thereby extending its storage time and further delaying the crystallization rate of the perovskite. The TBA+ cations can react with excess lead iodide to form two-dimensional perovskites, thereby enhancing the stability of the perovskite layers. Additionally, TBAPF6, as an ionic compound, can spontaneously diffuse into the buried interfaces of the perovskite to form an interfacial passivation layer. The power conversion efficiency of perovskite devices based on TBAPF6 was ultimately improved from 21.53% to 24.62%. Furthermore, these devices exhibit excellent environmental and operational stability.