Highly Efficient, Stable Exciplex-Based OLEDs with Narrowband Emission via Multiple Resonance Effect.

Color purity, device lifetime, and external quantum efficiency (EQE) serve as critical performance metrics for high-quality organic light-emitting diodes (OLEDs), yet these remain the primary bottlenecks in the development of exciplex-based OLEDs. Here, we developed a construction strategy for efficient thermally activated delayed fluorescence (TADF) exciplexes with narrowband emission by introducing a multiresonance TADF (MR-TADF) donor. The highly planar MR-TADF molecule SYBN and derivatives of 2,4,6-triphenyl-1,3,5-triazine (3N) are employed, resulting in driving forces of the exciplex formation (ΔGCS) up to 1.2 eV and strong intermolecular charge-transfer characteristics. These features enable the resulting exciplexes to exhibit high photoluminescence quantum yield (PLQY) up to 89% with narrow full-width at half-maximum (FWHM) down to 60 nm and fast reverse intersystem crossing rate (). Device performance characterization reveals that OLED devices based on this system demonstrate excellent comprehensive performance: the optimal device achieves a high EQE of 27.28%, a narrow FWHM of only 60 nm, and an extrapolated LT operational lifetime exceeding 6,000 h at an initial luminance of 1,000 cd m. This research not only breaks the performance records of exciplex-based OLEDs but also provides a new paradigm for the design and development of ideal exciplex luminescent materials.