Investigation of operation and degradation mechanisms in ZnTeSe blue quantum-dot light-emitting diodes by identifying recombination zone

ZnTeSe quantum dots (QDs), recognized as promising eco-friendly blue electroluminescent emitters, remain under-explored in light-emitting diode (LED) applications. Here, to elucidate the operation and degradation mechanisms of ZnTeSe blue QD-LEDs, stacked ZnTeSe QD layers with discernable luminescence are designed by varying Te doping concentrations, and the recombination zones (RZs) of the blue QD-LEDs are investigated. The RZs are identified near the hole-transport layer (HTL), confirmed by angular-dependent electroluminescence measurements and optical simulations. In addition, in order to investigate carrier dynamics in the process of recombination, the transient electroluminescence (tr-EL) signals of the dichromatic QD-LEDs are analyzed. As a result, it is inferred that the RZ initially formed near the electron-transport layer (ETL) due to the high injection barriers of electrons. However, due to the fast electron mobility, the RZ shifts toward the HTL as the operating current increases. After the device lifetime tests, the RZ remains stationary while the photoluminescence (PL) corresponding to the RZ undergoes a substantial decrease, indicating that the degradation is accelerated by the concentrated RZ. Thus this study contributes to a deeper understanding of the operational mechanisms of ZnTeSe blue QD-LEDs.