Abstract
AbstractThe endeavor to develop high‐performance narrowband blue organic light‐emitting diodes (OLEDs) with low efficiency roll‐off represents an attractive challenge. Herein, we introduce a hetero‐acceptor design strategy centered around the heptagonal diimide (BPI) building block to create an efficient thermally activated delayed fluorescence (TADF) sensitizer. The alignment of a twisted BPI unit and a planar diphenyltriazine (TRZ) fragment imparts remarkable exciton dynamic properties to 26tCz‐TRZBPI, including a fast radiative decay rate (kR) of 1.0×107 s−1 and a swift reverse intersystem crossing rate (kRISC) of 1.8×106 s−1, complemented by a slow non‐radiative decay rate (kNR) of 6.0×103 s−1. Consequently, 26tCz‐TRZBPI facilitates the fabrication of high‐performance narrowband pure‐blue TADF‐sensitized fluorescence OLEDs (TSF‐OLEDs) with a maximum external quantum efficiency (EQEmax) of 24.3 % and low efficiency roll‐off even at a high brightness level of 10000 cd m−2 (EQE10000: 16.8 %). This showcases a record‐breaking external quantum efficiency at a high luminance level of 10000 cd m−2 for narrowband blue TSF‐OLEDs.
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