Abstract
A surprising yet highly practical approach to improve the performance of a TADF exciplex blend is reported. Using the TSBPA donor and PO-T2T acceptor to form an exciplex, we are able to blue shift the emission, increase PLQY from 58 to 80%, and increase the device EQE from 14.8 to 19.2% by simply diluting the exciplex with an inert high triplet energy host material—here either UGH-3 or DPEPO. These effects are explained in terms of an increasing donor–acceptor distance and associated charge separation, while different behaviors observed in the different hosts are attributed to different energy barriers to electron transfer through the host. We expect that the observed performance-enhancing effects of dilution will be general to different exciplex blends and host materials and offer a new way to optimize the electrical properties of exciplex emission layers with narrow blue emission.
Highlights
A surprising yet highly practical approach to improve the performance of a thermally activated delayed fluorescence (TADF) exciplex blend is reported
While the donor (D) and acceptor (A) spacing is rigidly set by the chemical structures of molecular TADF materials, D−A spacing in exciplexes has only gained limited attention as a design parameter until recently
Low temperatures decrease the reverse intersystem crossing (rISC) rate, this is outcompeted by a simultaneous increase in the exciplex photoluminescence quantum yield (PLQY) as nonradiative singlet decay channels are suppressed at low temperatures
Summary
A surprising yet highly practical approach to improve the performance of a TADF exciplex blend is reported.
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