Structural engineering using rubidium iodide as a dopant under excess lead iodide conditions for high efficiency and stable perovskites

•The effect of rubidium doping on the mixed-perovskite was investigated under different amounts of excess PbI2.•The rubidium doping eliminates the yellow non-perovskite phase, improves the crystallinity of the black perovskite phase.•Cathodoluminescence reveals the segregation and spatial distribution of different phases on the perovskite films.•We achieved an efficiency of 18.8% for perovskite cells with rubidium doping and improvements in thermal/photo stability.