Ultra‐Deep‐Blue Aggregation‐Induced Delayed Fluorescence Emitters: Achieving Nearly 16% EQE in Solution‐Processed Nondoped and Doped OLEDs with CIE<i>_y</i> &lt; 0.1

Abstract Ultra‐deep‐blue aggregation‐induced delayed fluorescence (AIDF) emitters (TB‐tCz and TB‐tPCz) bearing organoboron‐based cores as acceptors and 3,6‐substituted carbazoles as donors are presented. The thermally activated delayed fluorescence (TADF) properties of the two emitters are confirmed by theoretical calculations and time‐resolved photoluminescence experiments. TB‐tCz and TB‐tPCz exhibit fast reverse intersystem crossing rate constants owing to efficient spin–orbit coupling between the singlet and triplet states. When applied in solution‐processed organic light‐emitting diodes (OLEDs), the TB‐tCz‐ and TB‐tPCz‐based nondoped devices exhibit ultra‐deep‐blue emissions of 416–428 nm and high color purity owing to their narrow bandwidths of 42.2–44.4 nm, corresponding to the Commission International de l´Eclairage color coordinates of ( x = 0.16–0.17, y = 0.05–0.06). They show a maximum external quantum efficiency (EQE max ) of 8.21% and 15.8%, respectively, exhibiting an unprecedented high performance in solution‐processed deep‐blue TADF‐OLEDs. Furthermore, both emitters exhibit excellent device performances (EQE max = 14.1–15.9%) and color purity in solution‐processed doped OLEDs. The current study provides an AIDF emitter design strategy to implement high‐efficiency deep‐blue OLEDs in the future.