Developments and challenges ahead in blue perovskite light-emitting devices

Recently, perovskite light-emitting diodes (PeLEDs) have developed rapidly in the green, red, and near-infrared light emissions, owing to the unique optoelectronic characteristics of halide perovskites, such as high carrier mobility, narrow emission linewidths, high photoluminescence quantum yield, as well as bandgap tunability. However, the efficiency improvement in blue (especially deep-blue) PeLEDs is still inferior to other analogs, which severely restricts the PeLED applications. Here, we systematically summarize the substantial progress in the performance of blue PeLEDs based on different blue perovskite candidates, and recent advances from three aspects (i.e., the sky-blue, pure-blue, and deep-blue light emissions). Then, we point out several challenges existing in deep-blue PeLEDs, such as the effect of Cl- ions incorporation, spectral instability, ion migration, and the difficulty of charge injection, and highlight the strategies to improve device efficiency, to motivate further research and development of blue PeLEDs.