Modulating Residual Lead Iodide via Functionalized Buried Interface for Efficient and Stable Perovskite Solar Cells

Sufficient lead iodide (PbI₂) in perovskite films effectively passivates defects and enhances device performance. However, excess large-grained PbI₂ clusters tend to be randomly distributed in the perovskite layer, which mitigate the positive effect of the PbI₂. Here, we first modulated the distribution and size of PbI₂ clusters by functionalizing the buried interface of 4,4′-diaminodiphenyl sulfone hydroiodide (DDSI₂). As a multifunctional modifier, DDSI₂ can optimize the energy level of tin oxide (SnO₂) and passivate the buried interface defects via −NH₃⁺ and SO functional groups. Moreover, the hydrogen bonding and coordination between DDSI₂ and perovskite retard the crystal growth rate and alleviate the lattice stress, thereby improving the quality of the perovskite and modulating the distribution of PbI₂. Consequently, the DDSI₂-modified device displays a power conversion efficiency of 24.10% and a storage stability of 1800 h. We demonstrate a unique strategy for the rational control of PbI₂ for efficient and stable perovskite solar cells.