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.

Surface Planarization of Low-Temperature Flowable Silicon Oxide for Atomic Layer Deposition Al2O3 Thin Film Encapsulation.

In this research, a flowable chemical vapor deposition (FCVD) process was developed to planarize particle-scattered surfaces for thin film encapsulation by atomic layer deposition (ALD). Nanometer-thick ALD layers are known to have good barrier properties owing to the conformal deposition of the films and their high density, but those barrier properties are vulnerable to degradation because of surface particles on the substrates. In this study, FCVD silicon oxide layer was applied to particlescattered surfaces as a planarization interlayer. Flowable silicon oxide thin films were deposited with tetrabutoxysiline and O2 in an inductively coupled plasmas reactor. The chemical bonding structure of the flowable silicon oxide was verified with Fourier transform infrared spectroscopy. To confirm the planarization effect, particles 2 µm in diameter were intentionally spread on the substrates by electrospray processing and nanometer-thick Al2O3 layers were deposited on top of the planarization interlayers. With the flowable silicon oxide interlayer and the same particle density on flexible substrates, the water vapor transmission rate was reduced to 1.2×10-3 g/(m² day) from 2.0×10-3 g/(m² day). The flowable silicon oxide layers are thus demonstrated to be effective interlayers to reduce the influence of particle contamination for ALD barrier films.