Atomic Layer Deposition Stabilizes Nanocrystals, Enabling Reliably High-Performance Quantum Dot LEDs

Quantum dot light-emitting diodes (QD-LEDs) with stable high efficiencies are crucial for next-generation displays. However, uncontrollable aging, where efficiency initially increases during storage (positive aging) but is entirely lost upon extended aging (negative aging), hinders further device development. It is uncovered that it is chemical changes to nanocrystal (NC)-based electron transport layer (ETL) that give rise to positive aging, their drift in structure and morphology leading to transiently improved charge injection balance. Using grazing-incidence small-angle X-ray scattering, it is found that ZnMgO NCs undergo size-focusing ripening during aging, improving size uniformity and creating a smoother energy landscape. Electron-only device measurements reveal a sevenfold reduction in trap states, indicating enhanced surface passivation of ZnMgO. These insights, combined with density functional theory calculations of ZnMgO surface binding, inspire an atomic layer deposition (ALD) strategy with Al₂O₃ to permanently suppress surface traps and inhibit NC growth, effectively eliminating aging-induced efficiency loss. This ALD-engineered ZnMgO ETL enables reproducible external quantum efficiencies (EQEs) of 17% across 30 batches of LEDs with a T₆₀ of 60 h at an initial luminance of 4500 cd m^-2, representing a 1.6-fold increase in EQE and a tenfold improvement in operating stability compared to control devices.