High‐Performance Solution Processable Red TADF‐OLED with External Quantum Efficiency Exceeding 28% Using a Multi‐Resonance Emitter Host

Achieving high-efficiency soluble red thermally activated delayed fluorescence (TADF) emitters remains a substantial challenge owing to the constraints imposed by the energy-gap law. In this study, an asymmetric pyrene-azaacene derivative, named PBCNT, is prepared and characterized, featuring a strong electron-donating tert-butyl diphenylamine moiety and an electron-withdrawing cyano group. PBCNT exhibits intense red emission with a peak wavelength of 664 nm in a toluene solution. It demonstrates an evident TADF character in the solid state, attributed to a small energy difference of 0.04 eV between its lowest singlet and triplet states. By employing a multi resonance-type TADF molecule as the host matrix, a solution-processed organic light-emitting diode (OLED) based on PBCNT achieved a record-high maximum external quantum efficiency (EQE) of 28.5%, with a red emission peak at 608 nm, facilitated by effective Förster energy transfer, good horizontal emitting dipole orientation and managed intermolecular interactions between the host and dopant. This represents one of the highest EQE values reported among solution-processed red TADF OLEDs emitting electroluminescence at wavelengths greater than 600 nm. This paper introduces a promising pathway for developing efficient red TADF emitters that overcome the limitations of the energy-gap law.