Carrier Generation and Recombination in AC–QLEDs with a Synergistic Capacitance Effect of ZnO/PVDF Heterofunction Layers

The alternating current-driven electroluminescence (AC-EL) of Cd-based quantum dots is garnering increasing attention due to advantages such as high efficiency and an extended operating lifetime. However, the generation and transport mechanisms of charge carriers within devices still need to be more understood. Here, we construct a simple device and investigate its luminance mechanisms within a single cycle using time-resolved spectroscopy. We tested the luminance-voltage and luminance-frequency characteristics of the device as the thickness of the insulating layer varied, finding that they both exhibited a trend of initially increasing and then decreasing as the voltage or frequency increased. We subsequently investigated the transient electroluminescent characteristics of the device, which featured a P(VDF-TrFE-CFE) layer as the insulator. This layer prevents carrier injection from the Al electrode, while the ZnO layer acts as a charge-generating layer to provide additional carriers. We observed that with an increase in AC voltage, the strongest luminance peak is advanced in the cycle compared to when lower voltages were applied. The position of the strongest luminance peak is delayed with an increasing AC frequency. The C-V characteristics demonstrated that the synergistic P(VDF-TrFE-CFE)/ZnO exhibited a displacement current transforming to a conduct current, which activates the forward operation of the QLED and enables it to emit light. The mechanism we present may serve as a benchmark for improving the luminance and longevity of such devices.