Utilizing Novel Exciplex for Narrowband OLEDs with High‐Efficiency and Low‐Efficiency Roll‐Off

Abstract Exciplexes formed by electron donor (D) and electron acceptor (A) demonstrate significant potential for enhancing the performance of organic light‐emitting diodes (OLEDs) due to their thermally activated delayed fluorescence (TADF) characteristics. However, conventional exciplex systems suffer from severe spectral broadening, which makes it difficult to achieve high‐purity monochromatic emission for exciplex‐based OLEDs. Here, a novel design strategy for an exciplex system is proposed by utilizing the D‐A‐D type multi‐resonance TADF (MR‐TADF) molecule t ‐DABNA as the electron donor and 1,3,5‐triazine (TRZ) derivatives as the electron acceptor. Owing to introducing intramolecular short‐range charge transfer (SRCT) features while preserving the intermolecular long‐range charge transfer (LRCT) characteristics, green exciplex (SFTRZ: t ‐DABNA) exhibits a narrow full‐width at half‐maximum (FWHM ∼ 63 nm), a rapid reverse intersystem crossing rate constant ( k RISC ∼ 10 6 s −1 ), and an enhanced radiative decay rate constant ( k r ∼ 10 7 s −1 ). The green OLED based on SFTRZ: t ‐DABNA (9:1) emitter is successfully fabricated with a record‐breaking external quantum efficiency (EQE) of 31.38%, an exceptionally narrow FWHM of 57 nm, and an ultralow efficiency roll‐off of 18.8% at 1000 cd m −2 . Furthermore, employing the novel exciplex as host, maximum EQEs of 13.4% and 23.95% are achieved for Rubrene‐ and TBRb‐doped orange hyperfluorescence OLEDs, respectively.