An ZnMgO:PVP inorganic–organic hybrid electron transport layer: towards efficient bottom-emission and transparent quantum dot light-emitting diodes

Abstract

ZnO-based nanoparticles (NPs) are widely used as electron transport layers (ETLs) in quantum dot light-emitting diodes (QLEDs) because of their advantages of high electron mobility and appropriate energy levels. However, QLEDs with ZnO ETLs suffer from unbalanced charge injection and interfacial exciton quenching. To address these issues, ZnMgO NPs are mixed with polyvinylpyrrolidone (PVP), which improves the morphology, reduces the conductivity and decreases the surface quenching sites of ZnMgO ETLs. As a consequence, QLEDs with ZnMgO:PVP hybrid ETLs exhibit a high current efficiency (CE) of 56.70 cd A⁻¹ and a peak EQE of 13.36%, which are about 1.33-fold higher than those of the devices with ZnMgO ETLs. In addition, the ZnMgO NPs are effectively densified by mixing with PVP. Because of the improved compactness, the hybrid ETL can even withstand the plasma damage during indium-tin-oxide (ITO) sputtering, which thus enables the fabrication of transparent QLEDs. With ZnMgO:PVP, the resulting transparent QLEDs exhibit a high transparency of 80% and a record CE of 44.23 cd A⁻¹, which is 7.2-fold higher than that of the devices with ZnMgO ETLs. The developed ZnMgO:PVP composite, with improved compactness, tunable conductivity and reduced quenching sites, could be the ideal ETL for efficient bottom-emission and transparent QLEDs.