A dual-site additive mediated crystallization strategy for homogenized FA–Cs based perovskite solar cells

Although the coordinatively stabilized lattice and the ease of solution processability render mixed A-site perovskites an ideal material for high-efficiency and stable perovskite photovoltaics, the spontaneous cation segregation between formamidinium (FA) and cesium (Cs) poses a critical threat to device performance. This study demonstrates that the divergent coordination capabilities among components, in conjunction with non-equilibrium crystallization kinetics, are the underlying causes of interfacial phase separation. Such a phenomenon leads to lattice mismatch and non-radiative recombination, which severely compromise the performance and operational stability of devices. To address this challenge, we developed a dual-site additive mediated crystallization strategy employing bifunctional molecular design, which enables film homogenization and minimizes interfacial loss. The resulting inverted devices demonstrate impressive efficiencies of 26.68% (0.057 cm² aperture area, certified: 26.51%) and 25.14% (1 cm² aperture area), highlighting exceptional scalability. Crucially, the dual-site cooperative modulation mechanism suppresses degradation pathways, allowing devices to retain >94% initial efficiency after operating for over 1100 hours at the maximum power point under 1 sun. Our findings provide transformative insights into solution chemistry design, crystallization control, and manufacturing scalability, establishing a robust and comprehensive framework for the commercialization of perovskite photovoltaics.