Realizing Record‐High Electroluminescence Efficiency of 31.5 % for Red Thermally Activated Delayed Fluorescence Molecules

Abstract

Tailor‐made red thermally activated delayed fluorescence (TADF) molecules comprised of an electron‐withdrawing pyrazino[2,3‐f][1,10]phenanthroline‐2,3‐dicarbonitrile core and various electron‐donating triarylamines are developed. They can form intramolecular hydrogen‐bonding, which is conducive to improving emission efficiency and promoting horizontal orientation and show near infrared (NIR) emissions (692–710 nm) in neat films and red delayed fluorescence (606–630 nm) with high photoluminescence quantum yields (73–90%) in doped films. They prefer horizontal orientation with large horizontal dipole ratios in films, rendering high optical out‐coupling factors (0.39–0.41). Their non‐doped OLEDs exhibit NIR lights (716–748 nm) with maximum external quantum efficiencies (ηext,max) of 1.0–1.9%. And their doped OLEDs radiate red lights (606–648 nm) and achieve record‐beating ηext,max of up to 31.5%. These new red TADF materials should have great potentials in display and lighting devices.

Molecular Design Strategy for Orange Red Thermally Activated Delayed Fluorescence Emitters in Organic Light‐Emitting Diodes (OLEDs)

“…To surpass the EQE over 30 % by considering molecular orientation, in 2021, Tang et al reported a series of cyano-fused pyrazinophenanthroline acceptor-based four emitters, DCPPr-α-NDPA, DCPPr-β-NDPA, DCPPr-TPA, and DCPPr-DBPPA were designed and synthesized. [34] The PL emissions in toluene solvents were around 598-620 nm, and the ~EST of emitters were maintained below 0.08 eV. On the other hand, the PLQY of all four emitters was enhanced by over 72 %.…”

Deep-Red and Near-Infrared Iridium Complexes with Fine-Tuned Emission Colors by Adjusting Trifluoromethyl Substitution on Cyclometalated Ligands Combined with Matched Ancillary Ligands for Highly Efficient Phosphorescent Organic Light-Emitting Diodes

“…This is in favor of balanced charge fluxes and broader recombination zones within the series of EMLs, effectively reducing triplet–triplet annihilation (TTA) processes, which are considered responsible for emitting state quenching, leading to unwanted EL efficiency roll-off [ 26 ]. These procedures ensure all these devices achieve, in general, high efficiency levels for deep-red and NIR emission OLEDs [ 2 , 8 , 19 ], especially under the practical luminance range of 100–1000 nit.…”

“…Organic near-infrared (NIR) materials and their light-emitting devices were developed rapidly since they are widely used in information-secured displays and night-vision/photodynamic therapy/signal processing devices [ 1 , 2 , 3 ]. Among them, thermally activated delayed fluorescence (TADF) organics [ 2 ] and phosphorescent transition-metal complexes based on the platinum (II) and osmium (II) family [ 3 ] seem to be ideal candidates for efficient NIR organic light-emitting diodes (OLEDs) due to both 25% singlet and 75% triplet excited states being converted into light emissions, which can generally achieve external quantum efficiencies (EQEs) of over 10%.…”

“…Organic near-infrared (NIR) materials and their light-emitting devices were developed rapidly since they are widely used in information-secured displays and night-vision/photodynamic therapy/signal processing devices [ 1 , 2 , 3 ]. Among them, thermally activated delayed fluorescence (TADF) organics [ 2 ] and phosphorescent transition-metal complexes based on the platinum (II) and osmium (II) family [ 3 ] seem to be ideal candidates for efficient NIR organic light-emitting diodes (OLEDs) due to both 25% singlet and 75% triplet excited states being converted into light emissions, which can generally achieve external quantum efficiencies (EQEs) of over 10%. Nevertheless, some negative factors related to these above-mentioned materials (or devices), such as expensive raw materials, several additional auxiliary layers required, adopting mixed host systems based on precise-control concentrations, etc., restrict their further application in NIR-electroluminescent (EL) devices [ 4 , 5 ].…”

New aggregation-induced delayed fluorescent materials for efficient OLEDs with high stabilities of emission color and efficiency

“…26–30 Therefore, OLEDs based on low cost TADF materials can realize high electroluminescence (EL) efficiencies, comparable to those based on noble metal-containing phosphorescence materials. 31–36 However, many TADF materials suffer from serious concentration quenching and exciton annihilation because of the long lifetimes of the triplet excited states. 37–40 Although this situation can be addressed to some extent by employing a blend film containing the host and the dopant as an emitting layer (EML) to reduce concentration quenching, the doped devices still encounter drastic efficiency roll-offs at high voltages, which becomes a troublesome obstacle for the commercial application of TADF materials.…”