Impedance Spectroscopy on Pristine and Degraded Quantum Dot Light-Emitting Diodes

Quantum dot light-emitting diodes (QLEDs) continue to pose significant challenges for investigating their internal physical processes due to complex multilayer structures. In this study, impedance spectroscopy is employed to investigate QLEDs with varying thicknesses of functional layers, enabling the establishment of an equivalent circuit model for QLEDs. According to the fitting parameters extracted from the Nyquist plots based on this model, it can be indicated that holes preferentially accumulate in the poly((9,9-dioctylfluorenyl-2,7-diyl)-co-{4,4′-[N-(4-s-butylphenyl) diphenylamine]}) (TFB) hole transport layer, and the hole injection into the quantum dots (QDs) layer is enhanced during operation. Moreover, the formation of carrier traps in the QD layer under electrical stress induces an increase in resistance and additional nonradiative recombination, serving as the primary mechanism responsible for the degradation of QLEDs.