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

Nidhi Sharma, Michael Yin Wong, David Hall, Eduard Spuling, Francisco Tenopala-Carmona, Alberto Privitera, Graeme Copley, David B. Cordes, Alexandra M.Z. Slawin, Caroline Murawski, Malte C. Gather, David Beljonne, Yoann Olivier, Ifor D.W. Samuel, Eli Zysman-Colman

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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.

Original languageEnglish
Pages (from-to)3773-3783
Number of pages11
JournalJournal of Materials Chemistry C
Volume8
Issue number11
DOIs
Publication statusPublished - 21 Mar 2020

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