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 V_OC. This provides an effective strategy for regulating excess PbI₂ to achieve efficient and stable PSCs.