Enhancing the efficiency of inverted quantum-dot light-emitting diodes by using red carbon dot blended ZnO as an electron transport layer

Abstract

Zinc oxide nanoparticles (ZnO NPs) are widely utilized as an electron transport layer (ETL) in quantum dot light-emitting diodes (QLEDs) due to their low cost, high electron mobility, and stability. However, their surface defects can trap electrons, resulting in an imbalance in charge injection. This study introduces red carbon dot-passivated ZnO NPs as an ETL in inverted QLEDs. The results show significant enhancements in maximum brightness (from 21 741 to 63 476 cd m⁻²), maximum current efficiency (from 19.45 to 25.40 cd A⁻¹), and maximum external quantum efficiency (EQE, from 13.90% to 18.20%). These improvements are attributed to the passivation of ZnO surface defects by functional groups of the red carbon dots (RCDs), which suppress exciton quenching at the interface. Additionally, the higher lowest unoccupied molecular orbital (LUMO) of RCDs effectively blocks excessive electron injection into ZnO. This approach demonstrates the potential for RCD-modified ZnO to enhance QLED performance.