Non-Negligible Intrinsic Nonradiative Recombination in Ideal Wide-Bandgap Mixed-Halide Perovskites

Wide-bandgap mixed-halide perovskites are promising top subcell absorbers for tandem photovoltaics, yet they suffer from severe open-circuit voltage losses. The prevailing view attributes these losses to nonradiative recombination caused by halide phase segregation, and research efforts have thus far focused primarily on improving halide homogeneity. Here, through rigorous first-principles calculations, we reveal that substantial nonradiative recombination persists even in an ideal, phase-segregation-free wide-bandgap perovskite CsPbI1.5Br1.5. This recombination is dominated by iodine interstitial defects, which exhibit a nonradiative capture coefficient on the order of 10-9 cm3 s-1. This finding explains why persistent open-circuit voltage losses remain prevalent in wide-bandgap perovskites even when halide segregation is effectively suppressed. This study highlights the critical need to move beyond halide segregation engineering and to develop targeted passivation strategies for iodine interstitial defects, providing a clear pathway to unlock the full potential of wide-bandgap perovskite solar cells.