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 (Al₂O₃) 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 Al₂O₃ interlayer was deposited by an atomic layer deposition (ALD) process that allows precise thickness control. The Al₂O₃ 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^-1 and an external quantum efficiency (EQE) of 12.2% were achieved in the inverted QLEDs with the Al₂O₃ interlayer. The Al₂O₃ 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^-2. The improvement of device performance by the Al₂O₃ interlayer is attributed to the reduction of electron injection and exciton quenching induced by zinc oxide (ZnO) nanoparticles (NPs). This work demonstrates that the Al₂O₃ 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.