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 PbI ₂ . Although excess PbI ₂ can reduce the internal defects of the perovskites and promote charge transfer, excess PbI ₂ is unevenly distributed in the perovskites and easily decomposed into the composite center of charge. Therefore, the growth and distribution of PbI ₂ crystals can be regulated by introducing 4-fluoroaniline (4-FLA) as an additive into the precursor of PbI ₂ . 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 PbI ₂ layer structures, thereby facilitating the uniform dispersion of excess PbI ₂ within the perovskites. Additionally, 4-FLA is restricted from being embedded in the PbI ₂ layer due to the steric hindrance of 4-FLA and the hydrogen bond interaction between nitrogen atoms and PbI ₂ . Therefore, it leads to better dispersion of PbI ₂ , 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 PbI ₂ to achieve efficient and stable PSCs.