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 EU launched two TADF related collaborative research projects to focus on TADF emitters, Project HyperOLED and the 2015 project Phebe.
The latest TADF news:
Researchers develop an efficient stretchable TADF OLED emitter
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.
Wisechip announces its second TADF/HF PMOLED device
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.
Nanomatch announces a novel class of emitters for efficient and stable blue OLEDs
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.
Is current OLED architecture obsolete? An interview with the head of Germany's Max Planck Institute
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 suggest using the dipole moments of TADF host materials to increase emission performance
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 Shenzhen University designed efficient selenium-integrated TADF OLED emitters
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.
Researchers develop new highly-efficient cyanopyrazine-enhanced fluorophores OLED emitters
Researchers from Russia's Ural Federal University developed a new OLED emitters based on cyanopyrazine-enhanced fluorophores. The presence of cyanogroup substance in the composition of fluorophores significantly increases the efficiency of the OLED emitters.
The researchers say that they have modified the pyrazine-based push-pull system with cyanogroup and studied how this affected the photophysical properties of the fluorophores and the performance of OLED devices based on these materials.
Samsung Display acquires TADF material developer Cynora
According to reports, Samsung Display acquired OLED material developer Cynora, for about $300 million. Samsung acquires just the IP and technology, and Cynora terminated its entire workforce a couple of weeks ago. Samsung is already an investor in Cynora, and so is LGD.
Cynora has been low on cash (its last financing round was in 2019), according to reports, and did not manage to find new investors, and so the company opted to be sold to Samsung. The reported sum seems to be rather high for an emergency exit, and some later reports quotes much lower sums, perhaps even around $30 million or so.
Researchers developed promising N-doped PAH OLED emitters
Researchers from the Polish Academy of Sciences (PAS) and from the Silesian University of Technology have developed new OLED emitter materials based on aromatic electron-donating and -accepting moieties bridged by an antiaromatic seven-membered ring.
The researchers say that the new design of its N-doped PAHs is very flexible, and their properties are very responsive to the choice of the electron-accepting group. The researchers can thus can tune the emission mechanism between TADF emission and room temperature phosphorescence (RTP) emission, which gives high degree of control over the emission profile.
Kyulux explains how narrow-spectrum Hyperfluorescence emission is more efficient than PHOLED emission
Second-generation OLED phosphorescence emission features an internal quantum efficiency of almost 100% - which would normally mean you cannot get more efficient than that.
As Kyulux explains in a recent post, though, phosphorescent suffers from a wide emission spectrum. In order to achieve a good color gamut (for which as narrow-spectrum emission as possible is best) display makers have to filter out the "tail" of the emission. This results in reduced brightness and efficiency.
