Dual-Interfacial Engineering of Charge-Transport Layers for Efficient Low-Current-Density Quantum Dot Light-Emitting Diodes

Abstract Quantum dot light-emitting diodes (QLEDs), employing nanoscale colloidal quantum dots as emissive materials, have emerged as strong contenders for next-generation lighting and display technologies owing to their advantages of simple fabrication, high brightness, and excellent color purity. However, conventional QLEDs suffer from severe nanoscale charge imbalance caused by excessive electron injection from the ZnMgO nanoparticle-based electron transport layer (ETL) relative to hole injection, which significantly limits both efficiency and operational lifetime. Moreover, excessive electrons can accumulate in the hole transport layer (HTL), inducing unwanted emission from the HTL and thereby reducing color purity. To address the charge imbalance, we introduced a molecular-scale self-assembled monolayer (2PACz) onto the hole injection layer (PEDOT: PSS), forming an interfacial dipole that improves contact with the HTL and reduces carrier leakage. The self-assembled monolayer also modulates the energy level alignment, reducing the hole injection barrier and enhancing hole transport capability. In addition, 18-Crown-6 was incorporated into the ZnMgO nanoparticle electron transport layer (ETL) to increase the electron injection barrier. Through this dual nanoscale interfacial engineering of both electron and hole transport layers, the red-emitting QLEDs achieved an external quantum efficiency (EQE) exceeding 20% at a low current density (10−2 mA/cm2), with a maximum EQE of 30.63% at 100 mA/cm2. Furthermore, the devices exhibited a T95 operational lifetime of 9289.8 h at 1000 cd/m2. This study provides a practical nanoscale interfacial engineering approach for fabricating low-power, high-performance red QLEDs with enhanced stability and longevity.