Improving the Dynamic Stability of High‐Efficiency Quantum Dot Light‐Emitting Diodes by Core–shell Engineering

Quantum dot light-emitting diodes (QD-LEDs) hold great potential for enabling ultra-clear and ultra-bright display technologies. Although the operational life of QD-LEDs under static conditions has reached commercial standards, their dynamic stability, i.e., performance consistency while being switched on and off, remains largely behind that of state-of-the-art III-V inorganic LEDs. In this work, the degradation mechanism of red-emitting CdZnSe/ZnSe QD-LEDs with high external quantum efficiency (EQE) and long static operating lifetime is studied. Surprisingly, it is found that the accelerated EQE decline is mainly due to the fast-increasing electron leakage into the organic hole transport layer (HTL) under continuous voltage scans. To improve the dynamic stability of QD-LEDs, these findings inspired us to refine the size and architecture of CdZnSe/ZnSe QDs by introducing a ZnSeS/ZnS outer shell, where the ZnS shell improves the electron confinement and the ZnSeS mitigates the lattice mismatch between ZnSe and ZnS. Consequently, the electron leakage into the HTL is significantly inhibited, leading to QD-LEDs with minimal EQE drop of <4% after >5000 voltage cycles within a 0 - 4.5 V voltage range, while the devices still possessed excellent static stability, as their T₉₅ at 1000 cd m^-2 for over 61 000 h.