Exciton efficiency beyond the spin statistical limit in organic light emitting diodes based on anthracene derivatives†‡
Michael Yin Wong,Eduard Spuling,Francisco Tenopala-Carmona,Alberto Privitera,Graeme Copley,David B. Cordes,Alexandra M. Z. Slawin,Caroline Murawski,Malte C. Gather,David Beljonne,Ifor D. W. Samuel,Eli Zysman-Colman
Journal of Materials Chemistry C Pub Date : 01/28/2020 00:00:00 , DOI:10.1039/C9TC06356K
Abstract

We report two donor–acceptor (D–A) materials based on a cyanoanthracene acceptor paired with diphenylamine (DPAAnCN) and carbazole (CzAnCN) donor moieties. These compounds show hybrid locally excited (LE) charge-transfer (CT) excited states (HLCT), which we demonstrated through a combined photophysical and computational study. Vacuum-deposited organic light emitting diodes (OLEDs) using these HLCT emitters exhibit maximum external quantum efficiencies (EQEmax) close to 6%, with impressive exciton utilization efficiency (Φs) of >50%, far exceeding the spin statistic limit of 25%. We rule out triplet–triplet annihilation and thermally activated delayed fluorescence as triplet harvesting mechanisms along with horizontal orientation of emitters to enhance light outcoupling and, instead, propose a “hot exciton” channel involving the nearly isoenergetic T2 and S1 states.

Graphical abstract: Exciton efficiency beyond the spin statistical limit in organic light emitting diodes based on anthracene derivatives