Blue quantum dot-based electroluminescent light-emitting diodes

Quantum dot light-emitting diodes (QD-LEDs) have been considered as one of the promising candidates for light sources in display applications owing to their good color saturation, high brightness, spectral tunability, and low processing cost. Thus far, the performance of red and green QD-LEDs has been significantly improved by optimizing QD materials and device architectures and by gaining a further understanding of their luminescence mechanism. However, as one of the three primary color sources, the performance of blue QD-LEDs still lags behind that of red and green QD-LEDs. Herein, we review the recent research progress in blue QD-LEDs, including Cd-based QD-LEDs, perovskite-based LEDs (PeLEDs), and heavy-metal-free QD-LEDs. The advances in Cd-based blue QD-LEDs are firstly introduced, and the efficiency has been improved from less than 0.1% to similar to 20% through the optimization of the components and surface ligands of QDs as well as the optimization of device architecture and interfacial engineering, and the aging mechanism of blue QD-LEDs is also discussed. Next, we review PeLEDs based on different types of perovskite materials, including two-dimensional (2D)/quasi-2D perovskites included in organic-inorganic halide perovskites and all inorganic perovskites. Currently, state-of-the-art PeLEDs fabricated from quasi-2D organic-inorganic perovskites exhibit the maximum external quantum efficiency (eta(EQE)) exceeding 11%. Furthermore, we summarize the research progress in heavy-metal-free blue QD-LEDs, which are fabricated from ZnSe, InP, Cu-based QDs and carbon dots. Although there is a huge gap in the device performance of heavy-metal-free LEDs as compared to the other two types of blue LEDs, the heavy-metal-free blue LEDs stand for a promising achievement toward their practical application. Finally, some challenges and possible development directions of blue QD-LEDs are suggested, which may speed up the further progress.