Fully Planarized Donor Enables Record-High Efficiency for Blue Through-Space Charge Transfer Emission

Through-space charge transfer (TSCT) emitters featuring spatially separated donor-acceptor architecture offer a promising strategy for designing thermally activated delayed fluorescence materials. However, developing high-performance blue TSCT emitter remains challenging due to the intrinsic trade-off between a wide bandgap and sufficient spatial electronic interactions. Herein, a fully planarized donor, in favor of strengthening spatial interactions and suppressing non-radiative decay, is proposed to construct blue TSCT emitter. The resulting emitter exhibits an emission peak of 467 nm, a high photoluminescence quantum yield of 98% and a large reverse intersystem crossing (RISC) rate of 1.8×10⁶ s^-1. Organic light-emitting diodes based on the emitter achieve a maximum external quantum efficiency (EQE_max) of 34.0% with Commission Internationale de L'Eclairage (CIE) coordinates of (0.16, 0.29) and a maximum luminance of 21560 cd m^-2, which, to the best of our knowledge, represents the state-of-the-art performances for blue TSCT emitters. Furthermore, hyperfluorescent devices employing the emitter as sensitizer demonstrate a high EQE_max of 35.8% with a narrow full width at half maximum of 20 nm and CIE coordinates of (0.12, 0.14). This work demonstrates the critical importance of the fully planarized donor for developing high-efficiency blue TSCT emitter.