Highly Stable and Scalable Blue QD-LED via an Evaporated TiO₂ Thin Film as an Electron Transport Layer

Quantum dot-based light-emitting diodes (QD-LEDs) have excellent optical properties; however, their limitations of stability, reproducibility, and scalability due to the solution process are the major drawback. Herein, blue QD-LEDs fabricated with the conventional vacuum process using an e-beam-evaporated TiO₂ thin film as an electron transport layer (ETL) are demonstrated. CdZnS/ZnS-based blue LEDs with a TiO₂ thin film are fabricated under ambient conditions. They exhibit maximum external quantum efficiencies of 3.53% and a peak luminance of 2847 cd m⁻². These values are retained, which minimizes performance degradation under high potential bias. In addition, the optimized evaporated TiO₂ thin film has a negligible red shift (0.5 nm) of the peak wavelength between the photoluminescence spectrum and electroluminescence spectrum with stable full-width at half-maximum changing by less than 2 nm at high voltage. Finally, a blue QD-LED is fabricated on a scalable emission area of 2 × 2 in. with a patterned cathode accompanied by an evaporated TiO₂ thin film, which allows to perform conventional photolithography. A highly stable and reproducible vaporized inorganic thin film as the ETL supports the multilayer architecture to minimize the process damage.