Highly Efficient Near-Infrared Delayed Fluorescence Organic Light Emitting Diodes Using a Phenanthrene-Based Charge-Transfer Compound

Significant efforts have been made to develop high-efficiency organic light-emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) emitters with blue, green, yellow, and orange-red colors. However, efficient TADF materials with colors ranging from red, to deep-red, to near-infrared (NIR) have been rarely reported owing to the difficulty in molecular design. Herein, we report the first NIR TADF molecule TPA-DCPP (TPA=triphenylamine; DCPP=2,3-dicyanopyrazino phenanthrene) which has a small singlet-triplet splitting (E-ST) of 0.13eV. Its nondoped OLED device exhibits a maximum external quantum efficiency (EQE) of 2.1% with a Commission International de LEclairage (CIE) coordinate of (0.70, 0.29). Moreover, an extremely high EQE of nearly 10% with an emission band at =668nm has been achieved in the doped device, which is comparable to the most-efficient deep-red/NIR phosphorescent OLEDs with similar electroluminescent spectra.