Supercycle Al-Doped ZnMgO Alloys via Atomic Layer Deposition for Quantum Dot Light-Emitting Diodes

Colloidal quantum-dot light-emitting diodes (QD-LEDs) have been significantly improved in terms of device performance and lifetime by employing zinc oxide (ZnO) as an electron transport layer (ETL). Although atomic layer deposition (ALD) allows fabrication of uniform, high-quality ZnO films with minimal defects, the high conductivity of ZnO has hindered its straightforward application as an ETL in QD-LEDs. Herein, we propose fabrication of Al-doped ZnMgO (Al:ZnMgO) ETLs for QD-LEDs through a supercycle ALD, with alternating depositions of various metal oxides. The supercycle ALD allows for extensive control of compositions, which is not possible in typical hydrolysis-based approaches. ZnMgO alloys produced by ALD adjust the band gap to match the QDs and suppress the electron injection. However, Mg compositions of >10% lead to a reduction in electron conductivity, limiting the charge balance in the QDs. The Al doping provides Al³⁺ ions, oxygen vacancies, and zinc interstitials to compensate for the reduced conductivity of ZnMgO. Composition tuning based on the supercycle ALD enables to realize the ETLs offering optimal electron injection capability without compromising the electrical conductivity. QD-LEDs with the Al:ZnMgO ETLs exhibit a peak external quantum efficiency of 15.7% and peak luminance of 167,000 cd m^-2, on par with typical devices using ZnMgO nanocrystal-based ETLs.