An Al-doped TiO2 interfacial layer for effective hole injection characteristics of quantum-dot light-emitting diodes

Abstract

The charge imbalance in quantum-dot light-emitting diodes (QLEDs) is a major hindrance in improving the performance of related devices. To realize high efficiency and stability of QLEDs with a high luminance behavior, the charge balance optimization of QLEDs should be achieved by introducing interfacial layers such as hole-transporting and electron-blocking layers. In this paper, we report an Al-doped TiO₂ (ATO) interfacial layer to improve the charge balance for enhancing the luminance and efficiency of QLEDs. We focused on Al doping modulation in TiO₂ for increasing the number of defect sites, which was confirmed through X-ray photoelectron spectroscopy (XPS). The photoluminescence spectra were analyzed to locate the oxygen vacancies and defect sites inside the ATO film. These findings suggested that a better interfacial energy level alignment can be achieved by both intrinsic defect sites related to oxygen vacancies and the induced titanium defect sites in TiO₂. QLEDs with an optimized ATO interfacial layer showed a luminance and current efficiency of 119 516 Cd m⁻² and 18.46 Cd A⁻¹, respectively. The lifetime of the device was 12 hours, which was almost four times greater than that of the device without the ATO interfacial layer. This study shows that the enhanced hole injection from the ITO anode into the V₂O₅ hole injection layer (HIL) can be achieved by inserting an ATO interfacial layer. Also, a well-aligned energy level in QLEDs can help to improve the performance of the device.