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Blue electroluminescent metal halide perovskites

Bright and color-pure electroluminescent materials are of great commercial interest for advanced lighting and display technology. The emergence of metal halide perovskites has given rise to full coverage of the recommendation 2020 standard, the newly defined color gamut in next-generation displays. Despite the recent development of perovskite-based red and green light-emitting diodes (LEDs) that already reach the maximum external quantum efficiency of 20%, it remains challenging to build deep-blue LEDs with comparable device performance. In this Perspective, we review and comment on the synthesis, progress, and challenges toward stable blue electroluminescence (EL), with a focus on (i) anion-exchanged, (ii) quantum-confined colloidal, and (iii) quasi-two-dimensional perovskites. A perspective outlook discussing the strategies of reducing the non-radiative losses and device interface engineering is given at the end.