Hetero‐Nucleation Induced [111]‐Oriented Mixed Halide Perovskite for Stable Pure Red Light‐Emitting Diodes

Abstract Mixed halide 3D perovskites are promising for bright, efficient, and wide‐color gamut light‐emitting diodes (LEDs) due to their excellent carrier transport, high luminescence, and easily tunable bandgaps. However, serious halide ion migration inside mixed halide 3D perovskite results in poor operational and spectral stability of the as‐fabricated LEDs. Here, a hetero‐nucleation crystallization strategy is reported to grow [111]‐orientation preferred mixed halide 3D perovskite CsPbI 3‐x Br x thin films for stable pure red LEDs. This hetero‐nucleation crystallization is enabled by the addition of phosphoric acid (H 3 PO 4 ) complexation, which promotes the growth of small perovskite grains into large grains with uniform [111]‐orientation. The obtained [111]‐orientation preferred film exhibits excellent stability under light or electric field stimulus as revealed by model analysis and experimental results compared to that of [001]‐orientation preferred film. Thus, based on the [111]‐orientation preferred film, the fabricated LED exhibits an external quantum efficiency of 22.8%, a maximum brightness of 12 000 cd m −2 , and a half‐life time of 4080 min under 1.5 mA cm −2 . More importantly, the electroluminescence spectrum of the device remains stable during the continuous operation of 4080 min, showcasing the significant spectral stability improvement enabled by the hetero‐nucleation induced [111]‐orientation strategy.