A highly efficient violet-blue OLED with Rec.2020 CIEy based on an orthogonal phenanthroimidazole-substituted 1,2,4-triazole derivative

Abstract

It has been challenging to achieve high efficiency and low roll-off violet-blue OLEDs with the Commission Internationale de l’Eclairage (CIE) coordinates matching the blue-light standard of ultra-high definition televisions (UHDTVs) ITU-R BT.2020. Herein, a novel triazole (TAZ)-based hybrid local and charge transfer (HLCT) fluorophore, PI-TAZ-tbuCZ, has been successfully designed and synthesized by introducing the bulky phenanthroimidazole unit at the sp³ hybrid N4 atom of TAZ. This not only improves the thermal stability, showing a high thermal decomposition temperature of 459 °C, but also limits the molecular conjugation length and intramolecular charge transfer, effectively guaranteeing short-wavelength emission. The resulting device exhibits a violet-blue electroluminescence emission with the peak wavelength of 407 nm, narrow full width at half-maximum of 52 nm and CIE coordinates of (0.160, 0.043). Notably, a maximum external quantum efficiency of 6.01% is achieved, and the value still keeps as high as 5.10% at 500 cd m⁻², showing a small efficiency roll-off. These results illustrate that PI-TAZ-tbuCZ should be a promising fluorophore for violet-blue OLEDs.