Eutectic Urea Phosphate Suppresses Phase Segregation in Wide‐Bandgap Photovoltaic Perovskites

Compositional segregation resulting from non-uniform crystallization remains a critical bottleneck limiting the performance of wide-bandgap (WBG) mixed-halide perovskite photovoltaics. Herein, we report a halide-specific coordination strategy by employing a eutectic molecule to stop the phase segregation in WBG perovskites. Owing to the differential affinity of stronger for bromine-based octahedra than iodine-based ones, the urea phosphate molecule acts as a molecular pacemaker synchronizing the crystallization of disparate perovskite phases. This strategy successfully eliminates vertical and lateral phase segregation within the films, leading to a substantial reduction in non-radiative recombination and charge transport losses. Consequently, the champion perovskite photovoltaic devices present a power conversion efficiency (PCE) of 22.27% under AM 1.5G illumination and a promising indoor PCE of 42.64% under 1000 lux. The finding offers a robust paradigm to fabricate high-quality WBG photovoltaic perovskites for indoor energy harvesting in the Internet of Things.