A Catalyst‐Like System Enables Efficient Perovskite Solar Cells

High‐quality perovskite films are essential for achieving high performance of optoelectronic devices; However, solution‐processed perovskite films are known to suffer from compositional and structural inhomogeneity due to lack of systematic control over the kinetics during the formation. Here, the microscopic homogeneity of perovskite films is successfully enhanced by modulating the conversion reaction kinetics using a catalyst‐like system generated by a foaming agent. The chemical and structural evolution during this catalytic conversion is revealed by a multimodal synchrotron toolkit with spatial resolutions spanning many length scales. Combining these insights with computational investigations, a cyclic conversion pathway model is developed that yields exceptional perovskite homogeneity due to enhanced conversion, having a power conversion efficiency of 24.51% for photovoltaic devices. This work establishes a systematic link between processing of precursor and homogeneity of the perovskite films. A cyclic reaction pathway in perovskite conversion facilitated by catalytic PbI2‐mesylate anion complexes is explored. This approach yields a remarkably homogeneous perovskite film, resulting in a remarkable power conversion efficiency of 24.51% and excellent maximum‐power‐point‐tracking stability in the corresponding perovskite solar cells.