Delocalizing Electron Distribution in Thermally Activated Delayed Fluorophors for High-efficiency, Long-lifetime Blue Electroluminescence

Abstract

Thermally activated delayed fluorescent (TADF) emitters are promising for the next generation organic light-emitting diodes (OLEDs), yet their efficiency and stability still cannot meet the requirements for commercialization. Here, we establish a design rule for highly efficient and stable TADF emitters by introducing an auxiliary acceptor to delocalize electron distributions, not only enhancing the molecular stability in the negative polaron state but also accelerating the triplet-to-singlet up-conversion and the singlet radiative processes simultaneously. Proof-of-the-concept TADF compounds, based on a multi-carbazole-benzonitrile structure, exhibit near-unity photoluminescent quantum yields, short-lived delays, and improved photo- and electroluminescent stabilities. Deep-blue OLED utilizing one of these molecules as the sensitizer for a multi-resonance emitter achieves a remarkable LT95 (time to 95% of initial luminance) of 221 h at an initial luminance of 1000 cd m-2, together with a maximum external quantum efficiency of 30.8% and Commission Internationale de l'Eclairage coordinates of (0.14, 0.17). This work would unlock the potential of TADF emitters for practical applications.