TADF OLED emitters, or Thermally Activated Delayed Fluorescence, is a relatively new class of OLED emitter materials that promise efficient and long-lifetime performance without any heavy metals. TADF research started in earnest in 2012, and the first TADF emitters reached commercial status at the end of 2019.
There are currently three main challenges with OLED emitters that TADF aims to solve - an efficient and long-lasting blue color emitter, low cost alternatives current red and green emitters and the development of soluble OLEDs that can be deposited using low cost ink-jet printing or other "wet" methods.
TADF is being developed by several companies. Japan-based Kyulux was established to commercialize Prof. Adachi's HyperFluoresence technology, which combines two emitter systems, TADF and Fluorescence. Germany-based Cynora is focusing on a blue TADF emitter. Both companies are working hard to achieve commercial-ready materials. While a blue TADF (or HyperFluoresence) emitter is not here yet, in late 2019 Kyulux and Wisechip brought to market the first OLED with a yellow HF emitter.
Idemitsu Kosan also considers TADF as one of the key OLED technologies and intends to focus on TADF in the future. In late 2019 Idemitsu together with Toray announced the world's most efficient red OLED emitter - based on Idemitsu's TADF/HF material. UDC has been recently awarded a patent on TADF materials, although the company says that TADF is not in its focus.
The latest TADF news:
Researchers from the University of Manchester, led by Prof. Alexander Romanov, developed a promising new Carbene-Gold-Arylacetylide (CMAc) OLED near UV emitter type. The researchers also detail a strategy to develop longer device lifetimes for such emitters.
The new emitter exhibits an efficiency of 1% EQE, and a lifetime of 20 minutes at a practical brightness of 10 nits (LT50). This is low compared to commercial OLEDs - but it is actually quite outstanding for such an emitter, and the researchers say that this is among the longest lifetimes for a near UV-OLED at a practical brightness ever reported. In addition, organic fluorescent and TADF emitters rarely exceed 1% EQE at practical brightness.
Poland-based TADF OLED emitter developer Noctiluca announced that it has signed an Evaluation License Agreement with a leading consumer electronics maker, based in California. In fact, Noctiluca says that its partner is the world's largest consumer electronics company, that has several products that utilize OLED displays.
It's likely that Noctiluca's partner is Apple, that is interested in testing the company's emitters. According to Noctiluca, its partner will test the materials at its R&D facility and laboratory in Taiwan. This is likely to be an early stage testing agreement, but still a very interesting development.
Researchers from Korea's KAIST institute, in collaboration with Gyeongsang National University developed a new TADF OLED deep-blue emitter molecule that achieves an EQE of 33%. Combined with a fluorescent emitter to create a hyperfluorescence system, the researchers achieved an EQE of 35.4%, with mitigated efficiency roll-off. The researchers say that this is the world's highest-efficiency narrow-band deep-blue TADF OLED emitter.
To develop the new emitter the researchers introduced sterically hindered peripheral phenyl groups to boron-based TADF emitter. The resulting material, o-Tol-ν-DABNA-Me, offers a pure narrowband emission that is far less sensitive to concentration compared to standard TADF emitters.
A few months ago we reported on research conducted at Germany's Max Planck Institute, led by Prof. Paul W.M. Blom, that looks into single-layer OLED devices. In such devices, a single TADF OLED emitter layer is sandwiched between two electrode - a much simpler design compared to commercial OLED devices that use multilayer stacks, sometimes with 10 or more layers.
The researchers the the MPI say that in fact it is possible to develop highly efficient OLEDs with just the TADF emitter, as there's no fundamental reason or major benefits that arise from multilayer OLEDs. The researchers continue their work, and now they have developed a new single-layer blue OLED in which every injected electron is converted into a photon - or 100% IQE. This is the first time that such a single-layer OLED device was demonstrated (see image above).
Researchers at the University of Chicago, led by Sihong Wang (above) and Juan de Pablo, developed a stretchable OLED device that uses TADF emitters to enable high efficiency and high stretchability.
The researchers say that this is the highest-efficiency stretchable display demonstrated to date, as all previous designs used fluorescent OLED emitters. The TADF stretchable device achieves 10% EQE and a stretchability of 125%. The substrate of this new device is a newly synthesized polymer.
PMOLED display maker Wisechip has launched its second TADF/HF OLED display, a 5.5" 256x64 yellow PMOLED device. The company says that by using Kyulux's Hyperfluoresence™ OLED technology it offers double the brightness compared to its standard OLEDs.
Wisechip is the first and only company to commercialize TADF/HF device. The company's first device was launched in 2020, a 2.7" yellow PMOLED.
This is a sponsored post by Nanomatch
Using their in-house virtual design tools, Nanomatch developed a new class of emitters that enables the production of stable, fluorescent OLED devices with close to 100% internal quantum efficiency also in the blue color range.
The specific class of fluorescent emitters facilitates the generation of only singlets with radiative decay of the order of 10-8s, thereby eliminating quenching processes induced by long-lived triplets. Having filed the patent end of February 2023, Nanomatch is now looking for partners to commercialize this new concept in order to realize efficient, stable blue OLEDs on an industrial level.
Researchers from Germany's Max Planck Institute, led by Prof. Paul W.M. Blom, are looking into single-layer OLED devices (in which a single emitting layer is sandwiched between two electrodes), with an aim to match their efficiencies to those of common multilayer OLED stacks, like the ones used in commercial OLED displays.
Current OLED architectures utilize multilayer stacks of materials, in order to increase the performance and lifetime of OLED devices. But according to the latest findings by Prof. Blom, equal efficiencies can indeed be met with single-layer TADF OLED emitters - and there's no fundamental reason or major benefits that arise from multilayer OLEDs.
Researchers from the University of Cambridge, led by Dr Alex Gillett, have studied the effect of host materials (the dielectric environment) on the performance of TADF OLED emitters, and specifically how the dipole moment of the host material can affect the rISC rate of the TADF component.
The impact of the toluene solvent dynamics on the riSC process of TXO-TPA (left: TXO-TPA in an explicit toluene solvent environment, right: TXO-TPA in vacuum)
The researchers tested several TADF OLED materials, and in some of these materials, the effect of different host materials can be quite dramatic. It is believed that commercial TADF devices could benefit from tuning the host and emitter combination to achieve higher performance, including a better efficiency roll-off as conversion of triplets into singlets can be accelerated.
Researchers from China's Shenzhen University are working towards efficient selenium-integrated TADF OLED emitters.
The researchers latest work detailed the structure-activity relationship between heavy atom effects and multiple resonance TADF performance. The researchers say that their new emitters effectively solve some of the issues inherent in TADF emission technology, specifically the sharp drop in emission at high brightness, what is called the emission roll-off.