Using Guest–Host Interactions To Optimize the Efficiency of TADF OLEDs

Santos, Paloma L. dos and Ward, Jonathan S. and Bryce, Martin R. and Monkman, Andrew P. (2016) Using Guest–Host Interactions To Optimize the Efficiency of TADF OLEDs. The Journal of Physical Chemistry Letters, 7 (17). p. 334103346. ISSN 1948-7185

Abstract

We show that the emitter and host combination must be optimized to minimize the reverse intersystem crossing (rISC) barrier and maximize thermally activated delayed fluorescence (TADF). The blue TADF emitter, 2,7-bis(9,9-dimethyl-acridin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DDMA-TXO2), has strong TADF character due to efficient charge transfer (CT) state formation. By combining DDMA-TXO2 with a host of correct polarity (DPEPO) that relaxes the CT manifolds’ energy to become resonant with the lowest-energy local triplet state of DDMA-TXO2, the emitter and host combination produce a minimum rISC barrier (ΔEST), which maximizes TADF efficiency. We show that the sensitivity of these splittings is highly dependent on emitter environment and must be carefully tuned to optimize device performance. Devices utilizing DDMA-TXO2 in the DPEPO host show blue electroluminescence (EL), with commission internationale de l’éclairage (CIE) chromaticity coordinates of CIE (0.16, 0.24), with a maximum external quantum efficiency of 22.4%. This high device performance is a direct consequence of optimizing the TADF efficiency by this “host tuning”.