Carrier Generation\nand Recombination in AC–QLEDs\nwith a Synergistic Capacitance Effect of ZnO/PVDF Heterofunction Layers

The alternating current-driven electroluminescence\n(AC-EL)\nof Cd-based\nquantum dots is garnering increasing attention due to advantages such\nas high efficiency and an extended operating lifetime. However, the\ngeneration and transport mechanisms of charge carriers within devices\nstill need to be more understood. Here, we construct a simple device\nand investigate its luminance mechanisms within a single cycle using\ntime-resolved spectroscopy. We tested the luminance–voltage\nand luminance–frequency characteristics of the device as the\nthickness of the insulating layer varied, finding that they both exhibited\na trend of initially increasing and then decreasing as the voltage\nor frequency increased. We subsequently investigated the transient\nelectroluminescent characteristics of the device, which featured a\nP(VDF-TrFE-CFE) layer as the insulator. This layer prevents carrier\ninjection from the Al electrode, while the ZnO layer acts as a charge-generating\nlayer to provide additional carriers. We observed that with an increase\nin AC voltage, the strongest luminance peak is advanced in the cycle\ncompared to when lower voltages were applied. The position of the\nstrongest luminance peak is delayed with an increasing AC frequency.\nThe C–V characteristics demonstrated that the synergistic P(VDF-TrFE-CFE)/ZnO\nexhibited a displacement current transforming to a conduct current,\nwhich activates the forward operation of the QLED and enables it to\nemit light. The mechanism we present may serve as a benchmark for\nimproving the luminance and longevity of such devices.