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

Abstract

Near-IR organic light-emitting diodes (NIR-OLEDs) are potential light-sources for various sensing applications as OLEDs have unique features such as ultraflexibility 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 codeposited film. The EL peak wavelength of the NIR-OLED is 734 nm with an EQE of 13.4 %, unprecedented among raremetal-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 (LT 95 > 600 h.).

Three-dimensional sensing of surfaces by projection of invisible electroluminescence from organic light-emitting diodes

“…Figure 1 (A and B) shows the molecular structures and related energy level diagrams of the molecules designed as host materials for the NIR hyperfluorescence system ( 15 , 16 ) used in this study. In this hyperfluorescence system, the thermally activated delayed fluorescent (TADF) assistant dopant 11,12-bis(4-(diphenylamino)phenyl)dibenzo[ a , c ]phenazine-2,3,6,7-tetracarbonitrile (TPA-PZTCN) ( 17 ) converts triplets into singlets, which are transferred to the NIR fluorescence emitter 4,8- bis[4-( N , N -diphenylamino)phenyl]benzo[1,2- c :4,5- c ′]bis[1,2,5]thiadiazole (BBT-TPA) ( 18 , 19 ) for converting into emission. To reduce the driving voltage, carrier injection barriers—particularly at interfaces between carrier transporting layers and the emissive material layer (EML)—and carrier trapping in the EML must be eliminated.…”

Thermally Activated Delayed Fluorescence and Room‐Temperature Phosphorescence in Materials with Imidazo‐pyrazine‐5,6‐dicarbonitrile Acceptors

“…Acceptors for deep red/NIR TADF materials are commonly assembled from a handful of strongly electron‐withdrawing moieties easily incorporated through established synthetic procedures. In particular, numerous literature reports have combined pyrazine and cyano groups to create strong electron acceptors [14–17] . (Scheme 1) For example, Tang and coworkers demonstrated red TADF materials constructed from the strong electron acceptor pyrazino[2,3‐f][1,10]phenanthroline‐2,3‐dicarbonitrile (DCPPr) and triarylamines, with PLQY up to 90 % in doped films and external quantum efficiency (EQE) of doped OLEDs reaching 31.5 % [18] .…”

Integrating Asymmetric O−B−N Unit in Multi‐Resonance Thermally Activated Delayed Fluorescence Emitters towards High‐Performance Deep‐Blue Organic Light‐Emitting Diodes

“…However, such a molecular design enhances the structural relaxation in the excited states, resulting in an increased Stokes shift and a broad emission profile, whose FWHM typically exceeds 70 nm [24] . Moreover, their intrinsic character of intramolecular charge transfer (ICT) would be stabilized by strong intra/inter‐molecular interactions, leading to a red‐shifted emission, making a great difficulty to obtain deep blue TADF emission [25–27] . Therefore, the molecular design overcoming the above issues of the traditional TADF compounds has been pursued, especially in the deep‐blue region [28]…”