TADF, 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 TADF emitters are expected to become commercial by 2018.
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 TADF technology. Germany-based Cynora is focusing on a blue TADF emitter. Both companies aim to release their first commercial materials in late 2017 or early 2018.
Idemitsu Kosan also considers TADF as one of the key OLED technologies and intends to focus on TADF in the future (although Idemitsu's actual TADF plans are not clear yet). 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:
Kyulux announced that it has developed a new blue Hyperfluoresence/TADF OLED emitter. Kyulux managed to extend the lifetime of the material and reached 100 hours at LT95 (@ 750 cd/m2) while maintaining a high EQE of 26% - 22% at 1,000 cd/m2. The emission wavelength is 470 nm.
Kyulux says that its blue Hyperfluorescence emitter is the world’s top performing material at the moment. Kyulux now aims to work together with OLED panel makers to improve the systems further by optimizing the device structure and the rest of the OLED stack in pilot production lines.
Kyulux and Wisechip unveiled a flexible PMOLED display that uses Kyulux’s Hyperfluoresence yellow emitter. Wisechip says that the power consumption of this display is almost half of Wisechip's regular fluorescent yellow PMOLED.
The first flexible HF PMOLED is a 1.71″ 256x64 display, that is now ready to be produced (Wisechip says this will enter mass production before the end of 2018). Wisechip originally aimed to introduce its first glass-based HF yellow emitter PMOLED by the end of 2017, but it seems they decided to jump straight to a flexible panel.
Researchers from the Universitat Autònoma de Barcelona and TU-Dresden have demonstrated that ultra-stable film formation can be used to to improve the performance of OLED devices.
The researchers grew (using evaporation) the organic materials as ultrastable glasses - a growth condition that allows for thermodynamically most stable amorphous solids. Testing four different phosphorescent emitters, the researchers show significant (over 15%) increases of efficiency and operational stability. The researchers also say that these growing conditions are expected to even be more useful for TADF materials.
Thermal activation sensitized fluorescence, or TASF, is a new type of TADF OLED emitter material developed at China's Tsinghua University. During SID Displayweek, Visionox demonstrated the first TASF prototype display.
We do not have a lot of information on this new emitter technology, except what Visionox provided at the conference: a sky-blue color (468 nm, CIE: 0.153, 0.201), a luminous efficiency of 26.6 cd/A and an external quantum efficiency of over 17%. The brightness of this OLED PMOLED display was 800 nits.
The following is a sponsored post by Cynora
CYNORA, a leader in TADF (thermally activated delayed fluorescence) materials for OLEDs, presents its newest high-performing blue emitting materials at the SID Display Week 2018 in Los Angeles. The company is currently working with the key display makers to finish the commercialization of the industry’s first blue high-efficiency emitter.
OLED displays have become standard for premium mobile and TV displays in the last couple of years. However, those OLED displays have not yet reached their fullest potential. High-efficiency blue OLED emitters are needed to reduce power consumption and increase the display resolution further. Despite urgent requests by the OLED display panel makers for a high-efficiency blue emitter in the last few years, no material supplier has yet been able to produce such an emitter.
Researchers from Taiwan's National Tsing Hua University (NTHU) developed a new TADF OLED emitter material that maintains its high efficiency at high luminance. The researchers say that this new material is the world's most efficient TADF emitter at high brightness.
The new material is made from two diboron-based molecules, CzDBA and tBuCzDBA. These donor–acceptor–donor (D–A–D) type and rod-like compounds concurrently generate TADF with a photoluminescence quantum yield of ~100% and an 84% horizontal dipole ratio in the thin film. The researchers synthesized a green TADF emitter that achieved a a high external quantum efficiency of about 37.8% with an efficiency roll-off of only 0.3% at 1,000 cd/m2.
Display Supply Chain Consultants (DSCC) says that OLED material revenues grew 43% to reach $869 million in 2017. DSCC expects the OLED material market to grow at a 24% CAGR until 2022, when the market will reach $2.56 billion.
The small/medium display market accounts to about 59% of the total OLED material market, and this will continue until 2022. For the TV market, DSCC expects ink-jet printing to enable producers to make lower the material costs of OLED TV production, and OLED TV materials will grow at a rate of 23%, from $344 in 2017 to $963 million in 2022.
Japan-based chemical producer Nagase announced that it invested ¥500 million Yen ($4.6 million USD) in Hyperfluoresence TADF materials developer Kyulux. Nagase is currently offering materials for LCD producers, so this is likely to be a strategic investment for the company.
Kyulux’s first aim is to develop commercial red, green and yellow hyperfluorescence emitter/host combinations, to replace the 2nd-Gen phosphorescent emitters currently used in OLED displays and lighting panels. In 2017 Kyulux announced a collaboration with PMOLED maker WiseChip to bring Hyperfluoresence TADF emitter based displays to the market by the year's end.
German TADF developer Cynora recently participated in the international OLED summit in China, and the company presented its latest blue TADF material that features a CIEy of 0.18, EQE of 21% and a lifetime of 10 hours LT97 at 700 nits. This is an improvement of the material shown in September 2017 (which had the same specification but with a lower EQE of 14%).
Cynora reports that during the last 24 months, the company achieved its most important goals - high efficiency and a satisfying color point. It has made "tremendous progress" in the last year on the lifetime front and is now close to commercial lifetime specification.
Many OLED producers believe that Ink-Jet printing of OLED emissive materials is the best way to achieve lower-cost OLED TV production, and to enable OLEDs to compete in the medium part of the TV market. Ink-Jet printing is an efficient process (less material waste compared to evaporation) and it can be very quick as well. The main drawbacks of inkjet are the limited resolution and the need for soluble emissive materials which are less efficient compared to evaporation ones.
A Kateeva OLED ink-jet printing system
These challenges are being overcome, and it seems that at least four groups (in Korea, Japan and China) are charging forward towards mass production of ink-jet printed OLEDs. Ink-jet printer makers and soluble material suppliers are also optimistic ink-jet printing commercialization will soon be here as the material performance gap is diminishing.