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 1.8×10 6 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.