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.