A novel deep-blue fluorescent emitter employed as an identical exciplex acceptor for solution-processed multi-color OLEDs

Abstract

Currently, exciplex-type thermally activated delayed fluorescence (TADF) materials are emerging as a promising strategy for optimizing organic light-emitting devices (OLEDs). However, achieving highly efficient multi-color OLEDs based on exciplexes remains a formidable challenge. Herein, a deep-blue fluorescent emitter, named BOBTFB, endowed with a benzene (B), 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen (BO) and trifluoromethylbenzene (TFB) as the bridged core, electron-acceptor moiety, and π-spacer, respectively, was designed and synthesized. Employing BOBTFB as an identical exciplex acceptor and pairing it with distinct electron donors (TCTA, TAPC and m-MTDATA), blue, green and yellow exciplex-based solution-processed OLEDs have been obtained for the first time with emission peaks located at 470 nm, 510 and 564 nm, respectively. Notably, the yellow device exhibited an exceptionally low turn-on voltage (V_on) of 2.2 V, a maximum current efficiency (CE_max) of 38.83 cd A⁻¹, and a maximum external quantum efficiency (EQE_max) of 12.18%, respectively, which results from the low non-radiative transition rate and fast radiative transition rate of the BOBTFB:m-MTDATA forming exciplex. Moreover, the combination of TCTA:m-MTDAT:BOBTFB results in an exciplex white OLED with an EQE_max of 1.49%, a maximum color rendering index (CRI) of 82 and CIE coordinates of (0.23, 0.33), respectively. As far as we know, this work is the first reported utilization of an identical electron acceptor for solution-processed multi-color OLEDs.