Two-channel singlet exciton harvesting for high efficiency fluorescent organic light-emitting diodes using dual thermally activated delayed fluorescence mechanism

Abstract

A two-channel singlet exciton harvesting device was developed to improve the external quantum efficiency (EQE) of the fluorescent organic light-emitting diodes (OLEDs) using a dual, thermally activated delayed fluorescence (TADF) mechanism. The emitting layer consisted of two TADF materials, the 10,10'-(sulfonylbis(4,1-phenylene))bis(9,9-dimethyl-9,10-dihydroacridine) (DMAC-DPS) TADF emitter and the TADF exciplex formed between DMAC-DPS and ((1,3,5-triazine-2,4,6-triyl)tris(benzene-3,1-diyl))tris(diphenylphosphine oxide) (POT2T), and a green fluorophore. The DMAC-DPS serves as the main TADF matrix, which transports carriers, forms excitons, and harvests the singlet excitons of the fluorophore, whereas the DMAC-DPS:POT2T exciplex played a role of a second TADF material harvesting the singlet excitons of the fluorophore while suppressing the Dexter energy transfer. The exciplex was dispersed in the DMAC-DPS by managing the POT2T content, which reduced triplet-triplet-annihilation of the exciplex while suppressing Dexter energy transfer to the fluorophore. The two-channel singlet exciton harvesting mechanism maximized the singlet exciton formation, which enhanced the EQE of the fluorescent OLEDs from 10.3% to 15.0% compared to the conventional singlet exciton harvesting device using either TADF compound or TADF exciplex.