We investigated the electrical characteristics of ZnO nanoparticles (NPs) with air exposure that is a widely used electrontransport layer for quantum dot light-emitting diodes (QLEDs). Upon air exposure, we observed changes in the densityof states (DOS) of the trap levels of ZnO NPs. In particular, with air exposure, the concentration of deep trap energylevels in ZnO NPs decreased and electron mobility significantly improved. Consequently, the air-exposed ZnO reducedleakage current by approximately one order of magnitude and enhanced the external quantum efficiency at the low drivingvoltage region of the QLED. In addition, based on the excellent conductivity properties, high-brightness QLEDs couldbe achieved.