Metamorphosis from Quantum Dots to Quantum Shells and Highly Efficient Quantum Shell Light–Emitting Diodes

Abstract The bottom‐up design of chemical structure affords 0D nanocrystals (NCs) with tunable band structures and unexpected optical properties. Herein, an example of alloyed quantum shell (QS) is demonstrated by tailoring the chemical compositions in its core/shell structure. In the CdZnSe/ZnSeS/CdSeS/CdS (C/S₁/S₂/S₃, in which C is the CdZnSe core and S represents the shells) structure, there is an intriguing metamorphosis from quantum dot (QD) to QS (that is, C and C/S₁ belong to QDs, meanwhile C/S₁/S₂ and C/S₁/S₂/S₃ are in the QS regime). Due to uniform morphology, perfect nanostructure, negligible defects, and unique energy level alignment, the C/S₁/S₂/S₃ QS exhibits a high photoluminescence quantum yield of 90.9%, an ultra‐long fluorescence lifetime of 215.2 ns, and a slow radiative transition rate. It enables QS‐based light–emitting diodes (QS‐LEDs) with the state‐of‐the‐art performance, such as high external quantum efficiency (EQE of 22.16%) and excellent stability. Meanwhile, the investigation of charge carrier dynamics reveals the difference between the QD‐ and QS‐LEDs, showing that the charge carriers inside the QS‐LEDs need more time to recombine with each other. Based on these findings, this study believes that the emerging QSs can be attractive and efficient light–emitting materials used in lighting and displays.