The Zn_1−xMg_xO electron transport layer for charge balance in high-brightness inverted quantum-dot light-emitting diodes

Colloidal quantum-dot light-emitting diodes (QLEDs) are rapidly gaining recognition as formidable contenders in the realm of next-generation lighting and display devices. Notwithstanding, the journey to commercialization of QLED devices encounters a roadblock in the form of inadequate flexibility exhibited by the electron transport layer, which is typically made of ZnO nanoparticles. The hindrance stems from the substantial specific surface area, existence of surface defect states, and the fixed ZnO bandgap. To surmount these obstacles, we delved into the potential of integrating Mg element as a dopant in ZnO, aiming to enhance the surface chemistry, electrical characteristics, and film morphology of colloidal ZnO nanoparticles. The results clearly indicated that Mg doping played a critical role in diminishing surface defects in ZnO, while simultaneously reducing the density of oxygen vacancies, thereby regulating its electron mobility. Through modulation of the Mg doping concentration, the bandgap width of ZnO can be fine-tuned, leading to the creation of a more suitable electron transport layer. The inverted QLED devices based on Zn_1−xMg_xO electron transport layers exhibited remarkable advancements, with a peak external quantum efficiency and current efficiency of 6.7% and 29 cd A⁻¹, respectively. These values surpassed those of reference devices by 35 and 28%, underscoring the efficacy of Zn_1−xMg_xO as a viable approach for enhancing the efficiency of QLED devices.