Highly Efficient and Spectrally Narrow Near‐Infrared Fluorescent OLEDs Using a TADF‐Sensitized Cyanine Dye

Abstract Through various triplet‐harvesting approaches, fluorescent organic light‐emitting diodes (OLEDs) that emit in the visible spectrum can now be fabricated with efficiencies rivaling those of their phosphorescent counterparts. However, achieving high efficiencies in the near‐infrared (NIR) is considerably more challenging. This is in part due to the low quantum yield of most fluorescent NIR emitters and inefficient triplet exciton harvesting in such devices. Here, fluorescent NIR OLEDs with an external quantum efficiency of 5.4% and a peak emission wavelength of 790 nm are demonstrated. The OLEDs are fabricated by combining a deep‐red host that undergoes thermally assisted delayed fluorescence with a near‐infrared cyanine dye that emits with high efficiency. The devices show nearly pure NIR emission with a NIR cut‐on wavelength of 749 nm and >90% emitted power at wavelengths above 750 nm. It is also shown that the host polarity strongly affects the device performance.