Strategies for improving luminescence efficiencies of blue-emitting metal halide perovskites

Lead halide perovskites (LHPs) are suitable as the emissive layers in light-emitting diodes (LEDs). The external quantum efficiency of green LEDs based on LHPs is now over 20%. Nevertheless, the blue LHP LEDs lag behind the green ones in terms of efficiency. Photoluminescence (PL) quantum yield (QY) and stability of the NCs under various operating conditions are two major factors that influence the LED performance. Therefore, to promote the efforts towards achieving improved LED efficiencies, herein, we summarize several synthetic methods that produce blue-emitting LHP NC, followed by several approaches devised to boost their PL QYs up to near unity. Light-induced anion segregation is one of the limitations of using blue-emitting mixed-halide LHPs, which triggers the attention to single halide, quantum-confined LHP nanoplatelets (NPLs). Syntheses, structure, and luminescent properties of organic–inorganic and all-inorganic blue-emitting LHP NPLs are discussed elaborately. In the last portion, the luminescent properties of lead-free metal halides, which are of current interest, are discussed, followed by an outlook and future directions. In conclusion, our review discusses various literature attempts to obtain stable blue-emitting LHP NCs, which can be helpful in a better design of the blue-emitting LHP NCs towards various light-emitting applications.