Optimizing ZnO-Quantum Dot Interface with Thiol as Ligand Modification for High-Performance Quantum Dot Light-Emitting Diodes.

As the electron transport layer in quantum dot light-emitting diodes (QLEDs), ZnO suffers from excessive electrons that lead to luminescence quenching of the quantum dots (QDs) and charge-imbalance in QLEDs. Therefore, the interplay between ZnO and QDs requires an in-depth understanding. In this study, DFT and COSMOSL simulations are employed to investigate the effect of sulfur atoms on ZnO. Based on the simulations, thiol ligands (specifically 2-hydroxy-1-ethanethiol) to modify the ZnO nanocrystals are adopted. This modification alleviates the excess electrons without causing any additional issues in the charge injection in QLEDs. This modification strategy proves to be effective in improving the performance of red-emitting QLEDs, achieving an external quantum efficiency of over 23% and a remarkably long lifetime T of >12 000 h at 1000 cd m. Importantly, the relationship between ZnO layers with different electronic properties and their effect on the adjacent QDs through a single QD measurement is investigated. These findings show that the ZnO surface defects and electronic properties can significantly impact the device performance, highlighting the importance of optimizing the ZnO-QD interface, and showcasing a promising ligand strategy for the development of highly efficient QLEDs.