Deep-blue organic light-emitting diodes (OLEDs) featuring thermally activated delayed fluorescence (TADF) are experiencing growing demand, especially for full-color display applications, as they can harvest both singlet and triplet excitons to achieve high electron-to-photon conversion efficiencies. However, deep-blue TADF materials that can achieve sufficiently high electroluminescence (EL) efficiencies at a practical luminance and high emission color purity remain exceedingly rare. Herein, two deep-blue TADF emitters are reported, OBO-I and OBO-II, combining a polycyclic organoboron and phenazasiline as weak electron acceptor and donor units, respectively. Both emitters exhibit efficient deep-blue TADF, with high photoluminescence quantum yields of 81% and 98%, respectively, along with rather short emission lifetimes of ≈1 µs in their doped films. TADF-OLEDs incorporating OBO-II achieve extremely high maximum external EL quantum efficiencies of up to 33.8% in the blue color gamut. Furthermore, high EL efficiencies far exceeding 20% are retained, even at a high luminance of over 1000 cd m−2, indicating highly suppressed efficiency roll-offs. The importance of the proposed fluorophore design, which combines proper weak donor and acceptor units possessing high triplet excited energies for ideal deep-blue TADF, is highlighted by this study.
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