Alignment of Heptagonal Diimide and Triazine Enables Narrowband Pure-Blue Organic Light-Emitting Diodes with Low Efficiency Roll-Off

Abstract

The 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 (k_R ) of 1.0×10⁷ s^-1 and a swift reverse intersystem crossing rate (k_RISC ) of 1.8×10⁶ s^-1 , complemented by a slow non-radiative decay rate (k_NR ) 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 (EQE_max ) 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.

Keywords: Heptagonal Diimide; Hyperfluorescence; Narrowband Pure-Blue Emission; Organic Light-Emitting Diode; Thermally Activated Delayed Fluorescence.