Highly Efficient Near‐Infrared Electrofluorescence from a Thermally Activated Delayed Fluorescence Molecule

Near‐IR organic light‐emitting diodes (NIR‐OLEDs) are potential light‐sources for various sensing applications as OLEDs have unique features such as ultra‐flexibility and low‐cost fabrication. However, the low external electroluminescence (EL) quantum efficiency (EQE) of NIR‐OLEDs is a critical obstacle for potential applications. Here, we demonstrate a highly efficient NIR emitter with thermally activated delayed fluorescence (TADF) and its application to NIR‐OLEDs. The NIR‐TADF emitter, TPA‐PZTCN, has a high photoluminescence quantum yield of over 40 % with a peak wavelength at 729 nm even in a highly doped co‐deposited film. The EL peak wavelength of the NIR‐OLED is 734 nm with an EQE of 13.4 %, unprecedented among rare‐metal‐free NIR‐OLEDs in this spectral range. TPA‐PZTCN can sensitize a deeper NIR fluorophore to achieve a peak wavelength of approximately 900 nm, resulting in an EQE of over 1 % in a TADF‐sensitized NIR‐OLED with high operational device durability (LT95>600 h.). A highly efficient NIR‐TADF emitter with high kRISC is developed for NIR‐OLEDs. The NIR‐TADF‐OLED showed a significantly high EQE of 13.4 % with an EL peak at 734 nm. Notably, the NIR‐TADF molecule can sensitize a deeper‐NIR‐fluorophore, resulting in an EQE of 1.1 % at over 900 nm in the TADF‐sensitized NIR‐OLED.