Finely Controlled Synthesis of Zn_1–xMg_xO Nanoparticles with Uniform Size Distribution Used as Electron Transport Materials for Red QLEDs

In this work, we report the finely controlled synthesis of Zn1–xMgxO nanoparticles (NPs) by a Corning advanced-flow reactor (AFR), which produced a uniform size distribution with 75% NPs in the range 3–4 nm with good reproducibility. The Zn1–xMgxO NPs have been applied as an electron transport layer (ETL) in red quantum light-emitting diodes (QLEDs). Different from the traditional method of one-pot synthesis which needs several hours to finish a synthetic cycle, the synthesis by AFR is much faster due to the fast heat and mass transport in the reaction chamber, and a typical synthetic cycle in the AFR needs only a few minutes. Optical properties of the NPs indicate that the Mg ion that substitutes the Zn ion in the ZnO matrix is almost linear with the doping concentration in the solution, which is consistent with the first-principles calculations. The Zn1–xMgxO NPs synthesized with the AFR were subsequently used as the ETL in fabricating red QLEDs, and the resultant performance exceeded that of the device based on the traditional one-pot synthesized NPs. For example, the external quantum efficiency, current efficiency, and power efficiency improved by 25.1%, 21.6%, and 26.9%, respectively. Moreover, better luminescence uniformity was observed in the QLED using the ZnMgO NPs synthesized with the AFR. The device reached an optimal performance when x is 15% in Zn1–xMgxO. The finely controlled synthesis of stable Zn1–xMgxO NPs has the potential in industry application to solve the critical issues of ETLs that impede progress in the mass production of QLEDs.