Regulation of Lead Iodide Crystallization and Distribution for Efficient Perovskite Solar Cells.

At present, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has reached 26.1%. Polycrystalline perovskite films prepared by sequential deposition are often accompanied by excess PbI2. Although excess PbI2 can reduce the internal defects of the perovskites and promote charge transfer, excess PbI2 is unevenly distributed in the perovskites and easily decomposed into the composite center of charge. Therefore, the growth and distribution of PbI2 crystals can be regulated by introducing 4-fluoroaniline (4-FLA) as an additive into the precursor of PbI2. We observe that the presence of an amino group in 4-FLA leads to a reduction in the strength of van der Waals forces between PbI2 layer structures, thereby facilitating the uniform dispersion of excess PbI2 within the perovskites. Additionally, 4-FLA is restricted from being embedded in the PbI2 layer due to the steric hindrance of 4-FLA and the hydrogen bond interaction between nitrogen atoms and PbI2. Therefore, it leads to better dispersion of PbI2, resulting in better passivation and device efficiency. Based on the hydrophobicity of the benzene ring, the modified perovskite film shows excellent hydrophobicity. Ultimately, we achieved 21.63% PCE and 1.16V VOC. This provides an effective strategy for regulating excess PbI2 to achieve efficient and stable PSCs.