Mg-Doped NiO Hole Transport Layers with Ultrathin ALD-MgO Diffusion Barriers for All-Inorganic Quantum Dot Light-Emitting Diodes

Although hybrid quantum dot (QD) light-emitting diodes (QLEDs) commonly rely on organic hole transport layers, their vulnerability to oxygen and moisture severely limits their long-term stability. Replacing these organics with p-type transparent oxide semiconductors such as NiO offers a chemically and electronically robust alternative; however, the large valence band offset (∼0.6 eV) between the pristine NiO and the 1S_h state of QDs restricts efficient hole injection. In this study, we engineered Mg-doped NiO thin films via a sol–gel process for simultaneously improving p-type conductivity and tailoring valence band alignment with the QD layer. We employed few-cycle atomic layer deposition (ALD) to conformally coat indium tin oxide with an ultrathin (∼1 nm) MgO layer as a diffusion barrier, which suppressed indium ion migration during annealing at 430 °C, thereby preserving interfacial integrity and enhancing device stability. The combination of dopant-modulated NiO and ALD-based diffusion blocking yielded QLEDs with a markedly improved luminance and external quantum efficiency. These results present a viable interface-engineering strategy for developing stable, optimal-performance, and all-inorganic QLED architectures.