3D and 2D Metal Halide Perovskites for Blue Light-Emitting Diodes

Metal halide perovskites (MHPs) are emerging next-generation light emitters that have attracted attention in academia and industry owing to their low material cost, simple synthesis, and wide color gamut. Efficient strategies for MHP modification are being actively studied to attain high performance demonstrated by commercial light-emitting diodes (LEDs) based on organic emitters. Active studies have overcome the limitations of the external quantum efficiencies (EQEs) of green and red MHP LEDs (PeLEDs); therefore, the EQEs of PeLEDs (red: 21.3% at 649 nm; green: 23.4% at 530 nm) have nearly reached the theoretical limit for the light outcoupling of single-structured planar LEDs. However, the EQEs of blue PeLEDs (12.1% at 488 nm and 1.12% at 445 nm) are still lower than approximately half of those of green and red PeLEDs. To commercialize PeLEDs for future full-color displays, the EQEs of blue MHP emitters should be improved by approximately 2 times for sky-blue and more than 20 times for deep-blue MHP emitters to attain values comparable to the EQEs of red and green PeLEDs. Therefore, based on the reported effective approaches for the preparation of blue PeLEDs, a synergistic strategy for boosting the EQE of blue PeLEDs can be devised for commercialization in future full-color displays. This review covers efficient strategies for improving blue PeLEDs using fundamental approaches of material engineering, including compositional or dimensional engineering, thereby providing inspiration for researchers.