Realization of highly efficient organic emitting diodes using thermally activated delayed fluorescence (TADF) materials with fast reverse intersystem crossing

Abstract

Considering the essential role of intramolecular interactions in engineering the photophysical properties of thermally activated delayed fluorescent (TADF) materials for organic light-emitting diode (OLED) applications, we designed and synthesized three blue TADF molecules using benzophenone, 2-benzoylpyridine, and 3-benzoylpyridine as acceptors and 3,6-di-tert-butylcarbazole as a donor, which were denoted as BTC, B2-TC, and B3-TC, respectively. H-bonding was introduced between the benzene and pyridine of 2-benzoylpyridine for B2-TC and between the donor and acceptor for B3-TC. The formation of intramolecular H-bonds greatly increased oscillator strength and simultaneously decreased the energy gap between the lowest singlet and triplet states, thus accelerating reverse intersystem crossing. Owing to this, the OLED employing B2-TC as an emitter achieved a maximum current efficiency of 51.6 cd A⁻¹ and a maximum external quantum efficiency of 25.1% with the electroluminescent peak at 480 nm. Thus, our work demonstrates an effective method to design blue TADF materials for high-performance OLEDs.