“…Quasi-two-dimensional (quasi-2D) perovskites have been extensively studied for high-performance solar cells and light-emitting diodes, due to the easily modulated film properties such as the hydrophobicity, energy band gap, energy and charge transfer, and nonradiative recombination. − Especially for perovskite light-emitting diodes (PeLEDs), the external quantum efficiencies (EQEs) of the red and green quasi-2D PeLEDs are already higher than those of three-dimensional PeLEDs, exceeding 25% and 28%, respectively. − However, for lighting and display applications, the efficiencies of blue PeLEDs (including deep blue, blue, and sky blue) need to be further elevated. , Generally, the inefficient blue light emission is mainly related to strong nonradiative recombination, inefficient energy transfer, and unbalanced charge transport. , Compared to the perovskites with mixed halides of bromide and chloride, which are prone to form defects due to halide segregation, pure bromide quasi-2D perovskites show a greater potential for high-efficiency blue PeLEDs. , Notably, the phase distribution of quasi-2D perovskite films can be effectively modulated to significantly improve the energy transfer and in turn suppress the energy losses of the related nonradiative recombination. , …”