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

Abstract

We report two donor&ndash;acceptor (D&ndash;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 (&Phi;s) of &gt;50%, far exceeding the spin statistic limit of 25%. We rule out triplet&ndash;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 &ldquo;hot exciton&rdquo; channel involving the nearly isoenergetic T2&nbsp;and S1&nbsp;states.</p

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