Implanting Crystal Nuclei at the Buried Interface to Regulate the Growth of Inorganic Perovskite for High‐Performance Solar Cells

The substitution of organic cations with inorganic Cs + in metal halide perovskites provides a broad chance for the development of high‐performance tandem solar cells due to excellent thermal stability and ideal bandgaps of inorganic perovskites. However, the buried interface that governs interfacial charge transport and initialization of perovskite film crystallization is often overlooked due to difficulties in tailoring it. Herein, a strategy of modifying TiO 2 surface with 2‐(4‐aminobutyl) guanidine sulfate (AGS) is proposed to tackle these issues. It is found that the introduction of AGS induces in situ formation of PbSO 4 dots and interaction with perovskite precursors, which rigorously regulate the crystallization of inorganic perovskite, featuring fast nucleation and acceleration of the phase transition process. This results in more uniform films, enlarged grain size, with reduced defects. The modified buried interface exhibits alleviated strain, suppressed ion migration, fewer voids, and better contact. Together with improved interfacial energy level match between perovskite and TiO 2 , the power conversion efficiency of modified inorganic perovskite solar cells (PSCs) increases from 19.84% to 22.22%, with a voltage deficit of only 0.44 V. Furthermore, PSCs still maintain 91.5% of its initial value after continuous operation at maximum power point tracking and illumination for 800 h.