Suppressing intermolecular interactions for enhancing the performance of exciplex‐based OLEDs

Abstract

AbstractIn this study, a new triazatruxene‐based donor Tr‐iBu bearing branched alkyl groups is reported to suppress the aggregation found in a previously reported methyl‐substituted counterpart Tr‐Me. The effects of a steric factor on the propensity of exciplex formation were examined by respectively mixing these triazatruxene‐based donors with PO‐T2T and two new acceptors PO‐T2P and PO‐Pyr, all bearing phosphine oxide as the peripheral groups and N‐heteroarene cores with different numbers of nitrogen. Based on the steric hindrance of side groups and their corresponding molecular orbitals alignments of donors and acceptors, the characteristics of exciplex‐forming systems were analyzed. Among them, the exciplex‐forming blends Tr‐iBu:PO‐T2P and Tr‐iBu:PO‐Pyr were selected to serve as the emitting layer (EML) to achieve OLED devices with a moderate maximum external quantum efficiency (EQEmax) of 8.27 and 7.54%, respectively. Adopting the Förster resonance energy transfer strategy, the exciplex cohost was doped with a fluorescence emitter, DPy2CN, to realize a deep‐red OLED device with the emission peak centered at 674 nm while retaining EQEmax of 6.28%. Our results highlight the importance of suppressing the donor aggregation, adequate donor: acceptor combination, and a suitable triplet state of composing the materials for giving efficient exciplex‐based OLEDs.