Improving Average Electron Population in Quantum-Dot Emissive Layer via Core-Shell ZnO@ZnMgO Nanoparticles for QLEDs with Efficiency Exceeding 30%
Quantum dot light-emitting diodes (QLEDs) are emerging as a leader in next-generation display technology. In principle, the efficiency of QLEDs is highly reliant on the radiative recombination rate of injected electrons and holes in the QD emissive layer. Within a solitary light-emitting cycle, a pre-negative-charged QD bursts into a fleeting sparkle upon encountering a hole, much like a lighted piston within a roaring engine. More pistons bring higher horsepower. The challenge of achieving highly efficient QLED lies in how to increase the number of pre-negatively charged QDs. To address these limitations, we developed a ZnO@ZnMgO core-shell nanoparticle (NP)-based electron transport layer (ETL). This design synergistically combines the high conductivity of ZnO core and the low defect density of the ZnMgO shell. Measured by electron-excited transient absorption, the average electron population (<N_e>) in the emissive layer for ZnO@ZnMgO and ZnMgO-based QLEDs was 0.61 and 0.33 at 4 V, respectively, which greatly increases the carrier recombination efficiency. As a result, green QLEDs achieve a peak EQE of 30.66%, maximum luminance of 1,615,039.85 cd/m2, and a low turn-on voltage of approximately 2 V. The T95 operational lifetime exceeded 29,000 h at 1,000 cd/m2. Currently, all parameters are at the top level within the QLED region.