Stable and efficient QLEDs with crystallographic TiO2 as the electron transportation layer and improved carrier transportation by chlorination

Abstract

In order to obtain improvement in efficiency and stability of quantum dot light-emitting diodes (QLEDs), it is essential to seek carrier transport layer with higher carrier transport efficiency and better air stability. In terms of the high-performance carrier transport layer, solution-processed inorganic metal oxides show promise for efficient QLEDs because of their suitable energy band, high carrier mobility, especially their outstanding air stability. In this study, we employed high-quality oleic acid-capped TiO2 nanocrystals as the electron transportation layer to fabricate air-stable inverted QLEDs. These TiO2 nanocrystals have narrow size distribution, outstanding crystalline property, especially excellent air stability. To improve the interfacial carrier transportation performance of oleic acid-capped TiO2 nanocrystals, we introduce a thionyl chloride (SOCl2) post-ligand exchange process that replaces organic long-chain ligands with single inorganic ligands efficiently. The stability of oleic acid-capped TiO2-based QLEDs were evaluated by comparing with the traditional ZnO-based QLEDs. As a result, oleic acid-capped TiO2 nanoparticles show excellent long-term air stability. This study offers an alternative strategy to deal with the stability issue of optoelectronic devices.