Efficient Thermally Activated Delayed Fluorescence Conjugated Polymeric Emitters with Tunable Nature of Excited States Regulated via Carbazole Derivatives for Solution-Processed OLEDs

Abstract

For main-chain-type thermally activated delayed fluorescence (TADF) polymeric emitters, conjugated or nonconjugated monomers are generally copolymerized as the spacers to suppress the inter- and intramolecular exciton concentration quenching. In this work, carbazole derivatives are introduced into the main chains of the conjugated polymers based on the TADF unit, 2-(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide (DBTO2-PTZ). It is found that the content of carbazole derivatives units could not only effectively suppress exciton quenching and nonradiative transition but also manipulate the distribution of molecular orbits and ΔEST values and even regulate the nature of excited states. Therefore, the upconversion of triplet exciton from triplet to singlet excited state could be regulated by introducing the different contents of carbazole derivatives. Among three synthesized polymers, COP-10 displays a relatively higher kRISC and PLQY in the film state. The optimized OLED device without any TADF assistant dopant could reach to an EQEmax of 15.7% with a lower turn-on voltage of 3.2 V.