Hole Injection Barrier-Driven Positive Aging Mechanism in Inverted QLEDs

Positive aging is usually observed during the operation of quantum dot-light-emitting diodes (QLEDs), which introduces significant challenges for accurate performance assessment and industrial standardization. However, the mechanism of positive aging remains unclear and has long been attributed to the instability of the ZnO-based electron transport layer. Here, a new operational positive aging mechanism in inverted-structure QLEDs is reported, primarily driven by trap states at the interface of the hole transport layer (HTL). An elevated hole injection barrier can promote the accumulation of holes and their trapping via defect states, resulting in subsequent non-radiative recombination. Operational aging induces a progressive reduction in defect-mediated charge trapping, leading to a marked enhancement in radiative recombination efficiency and the device manifests as positive aging. By employing an insulating layer to spatially isolate the interface between quantum dots and HTL, the non-radiative recombination of electrons and accumulated holes can be effectively mitigated. Consequently, the positive aging phenomenon is significantly suppressed, and the current efficiency of the fresh device is improved by 240%. These findings elucidate the critical effects of interface properties on carrier dynamics and provide a strategy for achieving optimal device efficiency at the early stage of operation.