Suppression of phase segregation in wide-bandgap perovskites with thiocyanate ions for perovskite/organic tandems with 25.06% efficiency

Mixed halide wide-bandgap perovskites are suitable for integration in tandem photovoltaics such as perovskite/organic tandem solar cells. However, halide phase segregation originating from halogen vacancy-assisted ion migration in wide-bandgap perovskites limits the device efficiency and lifetime. Here we incorporate pseudo-halogen thiocyanate (SCN) ions in iodide/bromide mixed halide perovskites and show that they enhance crystallization and reduce grain boundaries. Trace amount of SCN ions in the bulk enter the perovskite lattice, forming an I/Br/SCN alloy, and occupy iodine vacancies, blocking halide ion migration via steric hindrance. Taken together, these effects retard halide phase segregation under operation and reduce energy loss in the wide-bandgap perovskite cells. The resulting perovskite/organic tandem solar cell achieves a power conversion efficiency of 25.82% (certified 25.06%) and an operational stability of 1,000 h. Wide-bandgap perovskite solar cells suffer from phase segregation. Zhang et al. show that thiocyanate ions overcome the issue by occupying iodide vacancies while regulating crystallization, enabling perovskite/organic tandem cells with 25.06% efficiency.