Treatment of solution-processed magnesium-doped zinc oxide with 4-methylthiophenol for efficient and stable full-color quantum dot light-emitting devices

Solution-processed zinc oxide nanoparticles (NPs) films are recognized as efficient electron transport layers (ETLs) for quantum dot light-emitting diodes (QLEDs), offering both good stability and high efficiency. However, due to the inherently high work function of such films, exciton quenching occurs at the QDs/ZnO interface in these QLEDs, thereby compromising performance. In this study, we propose a simple surface modification method for solution-processed magnesium-doped ZnO (ZnMgO) ETLs treated with 4-methylthiophenol (MTP). The effects of MTP treatment on the chemical, morphological, and electrical properties of thin films based on colloidal ZnMgO NPs were meticulously analyzed. For the first time, the proposed MTP-modified ZnMgO films were applied in QLEDs to investigate the impact of surface modification of the ETLs on device performance. The optimization of charge balance and the prevention of QD emission quenching were successfully decoupled. Full-color QLEDs utilizing the MTP-modified ZnMgO ETLs demonstrated impressive peak external quantum efficiencies: 10.27 % for blue-QLEDs, 21.03 % for green-QLEDs, and 17.41 % for red-QLEDs. Moreover, by modifying the surface of ZnMgO with MTP, the sensitivity of ZnMgO to water molecules was significantly reduced, thereby enhancing the stability of ZnMgO NPs. Consequently, these QLEDs featuring more stable ZnMgO exhibit extended lifetimes with T 50 values of 105,422 h (red), 48,071 h (green), and 187 h (blue). This discovery offers a novel strategy for improving the efficiency and lifetime of QLEDs by employing MTP-treated ZnMgO NPs as the ETLs.