Bandgap Tunable Zn1-xMgxO Thin Films as Electron Transport Layer for High Performance Quantum Dot Light-emitting Diodes
Since the introduction of inorganic ZnO nanoparticles as electron transport layer (ETL) material, the device performance of colloidal quantum dot light-emitting diodes (QLEDs) has been rapidly improved. Although there have been rapid advances in luminance, efficiency and lifetime, device performance is still limited by balanced electron/hole injection into the quantum dot layer. In this paper, solution processed Zn1-xMgxO (ZMO) films with tunable bandgaps are designed as ETL for high performance QLEDs. It is evidently found that the band gap of ZMO broadens as well as the energy level varies with increasing of Mg concentration. As a consequence, the energy barrier between the Al cathode and ZMO ETL are tuned for balancing the electron/hole injection towards a better device performance. The luminance intensity increases from 20,229 to 36,685 cd m-2, meanwhile the current efficiencies increase from 3.74 to 13.73 cd A-1 and the power efficiencies increases from 4.65 to 12.94 lm W-1 with 0.05% Mg doping ratio, respectively. Especially, the optimized device based on ZMO exhibits enhanced external quantum efficiency (EQE）of 9.46% which is 3.67-fold compared with that of pure ZnO nanoparticles (2.58%). The proposed approach provides a new method for the design and fabrication of high performance QLEDs by incorporating multielement semiconductors with variable bandgaps as ETL.