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

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 × 10⁷ 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.