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.
Exciton efficiency beyond the spin statistical limit in organic light emitting diodes based on anthracene derivatives / Sharma N.; Wong M.Y.; Hall D.; Spuling E.; Tenopala-Carmona F.; Privitera A.; Copley G.; Cordes D.B.; Slawin A.M.Z.; Murawski C.; Gather M.C.; Beljonne D.; Olivier Y.; Samuel I.D.W.; Zysman-Colman E.. - In: JOURNAL OF MATERIALS CHEMISTRY. C. - ISSN 2050-7534. - ELETTRONICO. - 8:(2020), pp. 3773-3783. [10.1039/c9tc06356k]
Exciton efficiency beyond the spin statistical limit in organic light emitting diodes based on anthracene derivatives
Privitera A.;
2020
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.
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