Narrow‐Band Dibenzoselenophene‐Based Emitter with Rapid Triplet Conversion for Versatile OLED Applications with Superior Roll‐Off Suppression

Abstract Selenium‐containing multiple resonance thermally activated delayed fluorescence (MR‐TADF) materials with ultra‐fast reverse intersystem crossing (RISC) have emerged as a promising solution for mitigating efficiency roll‐off in organic light‐emitting diodes (OLEDs). In this work, we introduce DBSeBN, the first MR‐TADF emitter incorporating a rigid five‐membered dibenzoselenophene unit. This design simultaneously achieves a narrow full width at half maximum of 23 nm across a wide range of doping concentrations in films, along with an ultra‐fast RISC rate of 1.1 × 10 7 s −1 , which is two orders higher than that of its sulfur‐containing counterpart, DBTBN, due to the enhanced spin‐orbit coupling via the heavy atom effect of selenium. As an OLED emitter, DBSeBN demonstrates exceptional performance, achieving a maximum external quantum efficiency of 31.6% and retaining 23.3% at 1000 cd m −2 , surpassing DBTBN in suppressing efficiency roll‐off. Its remarkably fast RISC and insensitivity to doping concentration enable unprecedented versatility in advanced OLED architectures. As a sensitizer in sensitized green‐fluorescent OLEDs, it surpasses Ir‐based complex sensitizers in reducing efficiency roll‐off. As a blue emitter in bi‐color white OLEDs, it effectively harnesses high‐energy triplet excitons to minimize efficiency roll‐off. DBSeBN thus expands the scope of MR‐TADF materials across various kinds of OLED applications while suppressing efficiency roll‐off.