Charge balance control of quantum dot light emitting diodes with atomic layer deposited aluminum oxide interlayers.

We developed a 1.0 nm thick aluminum oxide (AlO) interlayer as an electron blocking layer to reduce leakage current and suppress exciton quenching induced by charge imbalance in inverted quantum dot light emitting diodes (QLEDs). The AlO interlayer was deposited by an atomic layer deposition (ALD) process that allows precise thickness control. The AlO interlayer lowers the mobility of electrons and reduces Auger recombination which causes the degradation of device performance. A maximum current efficiency of 51.2 cd A and an external quantum efficiency (EQE) of 12.2% were achieved in the inverted QLEDs with the AlO interlayer. The AlO interlayer increased device efficiency by 1.1 times, increased device lifetime by 6 times, and contributed to reducing efficiency roll-off from 38.6% to 19.6% at a current density up to 150 mA cm. The improvement of device performance by the AlO interlayer is attributed to the reduction of electron injection and exciton quenching induced by zinc oxide (ZnO) nanoparticles (NPs). This work demonstrates that the AlO interlayer is a promising solution for charge control in QLEDs and that the ALD process is a reliable approach for atomic scale thickness control for QLEDs.