Surface Oxidation of Quantum Dots to Improve the Device Performance of Quantum Dot Light-Emitting Diodes

Insulating alumina (Al2O3) prevents charge transport, which is often considered to be profitless for the performance of a photoelectric device. However, in this study, we report a strategy to improve the device performance of a CdSe/CdS/ZnS quantum dot light-emitting diode (QLED) by aluminum doping in quantum dot (QD) shells and the subsequent controllable surface oxidation, which produces Al2O3 on the QD surface. Compared with the QLED based on CdSe/CdS/ZnS QDs, the QLED based on CdSe/CdS:Al/ZnS:Al QDs with controllable oxidation shows significant improvement of the device performance, including the luminance and external quantum efficiency, resulting from better charge transport balance. The maximum external quantum efficiency is 13.9%, which is nearly 2.8-fold increase in comparison with that of the QLED based on CdSe/CdS/ZnS QDs without Al doping and surface treatment. What is more, the device lifetime also shows an enhancement factor of about 10 times that of the counterpart based on CdSe/CdS/ZnS QDs, which is attributed to the protection from the surface oxide layer and improved radiation recombination efficiency. The results have deepened the understanding of the mechanism of insulating metal oxide on the QD surface in the QLED device and prove to be a simple and ingenious strategy to successfully improve the performance of the QLED.