High‐Efficiency and High Color Purity Solution‐Processable Deep‐Blue OLEDs Enabled by Linearly Fully Fused Acceptor‐Donor‐Acceptor Molecular Design

Abstract Solution‐processable organic light‐emitting diodes (OLEDs) have attracted much attention from academia and industry because of their advantages such as low production cost and suitability for large‐scale production. However, solution‐processable deep‐blue OLEDs that simultaneously have high efficiencies and satisfy the BT.2020 standard remain still a great challenge. To address this issue, here a tetraboron multiresonance thermally activated delayed fluorescence (MR‐TADF) emitter, tBO‐4B, embedded with two soluble 2,12‐di‐tert‐butyl‐5,9‐dioxa‐13b‐boranaphtho[3,2,1‐de]anthracene groups is designed and synthesized with a linearly fully fused acceptor–donor–acceptor‐type molecular structure. tBO‐4B not only achieves an ultranarrow full width at half maximum of 12 nm but also has a negligibly small singlet‐triplet energy gap and large spin‒orbit coupling, eventually leading to very fast reverse intersystem crossing rate (4.23 × 10⁶ s⁻¹). The sensitizer‐free solution‐processed OLED exploiting tBO‐4B as the emitter achieves an ultrahigh maximum external quantum efficiency (EQE_max) of 30.3%, with Commission Internationale de l’Éclairage (CIE) coordinates of (0.147, 0.042) meeting the BT.2020 blue standard. In addition, the corresponding sensitizer‐free vacuum‐processed deep‐blue devices also exhibit an impressive EQE_max of 39.6% and mild efficiency roll‐off with CIE coordinates of (0.147, 0.043). This work will facilitate the development of high‐efficiency ultrapure deep‐blue MR‐TADF materials for solution‐ and vacuum‐processed OLEDs.