Structurally Tolerance-Factor-Tuned Metal Halide Nanocrystals for Environmentally Stable and Efficient Red Light-Emitting Diodes

Black phase CsPbI₃, naturally possessing the superiority of high radiative recombination efficiency and narrow emission line width, shows promise for commercial applications of red perovskite light-emitting diodes (PeLEDs). However, the metastable black phase CsPbI₃ with a marginal tolerance factor (t) of 0.81 would easily convert to the nonoptical yellow phase. Herein, we demonstrate the strategy of partial substitution of larger dimethylammonium cation (DMA⁺) for Cs⁺ to achieve the stable tolerance factor of 0.903 for greatly improved Cs_0.7DMA_0.3PbI₃ nanocrystals. These NCs present a superior ultraviolet (UV) irradiation stability by retaining 80% of the initial photoluminescence intensity after 5 h, which is much better than that of its counterparts (retaining 30%). Based on this, the as-developed red PeLEDs demonstrate remarkable luminance of 1258 cd/m² and external quantum efficiency of 3.39%, which are almost 6 times and 3 times that of its counterparts, respectively (203 cd/m² and 1.28%). This strategy may pave the way to improving the stability and efficiency of PeLEDs.