Mixed halide wide-bandgap (WBG) perovskites, widely used as a top-cell absorber in tandem solar cells, exhibit severe photoinduced halide phase segregation. A feasible solution is to exploit pure-iodide WBG perovskites, essentially increasing Cs content instead of Br to achieve bandgap widening. However, the efficiency of pure-iodine WBG perovskite solar cells (PSCs) reported so far has been inferior to that of the typical mixed halide WBG PSCs due to complex nucleation and phase transition processes, leading to poor crystallization quality and a high density of defect states in pure-iodine WBG perovskites. Here, by combining lead thiocyanate (Pb(SCN)