Enhancing Efficiency and Stability of ZnSe Pure Blue Quantum Dot Light-Emitting Diodes via Ionic Liquid Doping

Abstract

Quantum dot light-emitting diodes (QLEDs) are emerging as promising candidates for next-generation displays, with the current efficiency and stability of both red and green QLEDs meeting display requirements. However, the efficiency and stability of blue QLEDs, particularly pure blue iterations, significantly lag behind their red and green counterparts, thus hindering the widespread adoption of full-color QLEDs. Here, we introduce a strategy to improve the efficiency and stability of pure blue zinc selenide (ZnSe) QLEDs by adding a new ionic liquid (IL) salt, 1-butyl-3-methylimidazolium phosphorous hexafluoride (BMIMPF6), into the hole transport layer (HTL). This IL salt acts as an effective p-dopant, enhancing charge mobility while also increasing the surface potentials of the HTL for better alignment of energy bands at the interface. This results in a significant improvement in device performance, with the external quantum efficiency (EQE) increasing from 4.90% to 7.02%, setting a new record for cadmium-free pure-blue ZnSe QLEDs. Additionally, the device's operational lifetime, measured as the time taken for luminance to drop to 50% (T50) at 100 cd m⁻², sees a remarkable six-fold increase, reaching 177 hours. Our work represents a significant advancement in developing cadmium-free pure-blue ZnSe QLEDs and offers valuable insights for designing efficient and stable quantum dot-based displays.