TADF OLED emitters, introduction and market status
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. While a blue HyperFluoresence emitter is not here yet, in late 2019 Kyulux and Wisechip brought to market the first OLED with a yellow HF emitter. Kyulux believes it will be able to commercialize its AMOLED Hyperfluorescence materials by 2025.
Another company involved with TADF development was Germany-based Cynora. In 2022, Cynora was acquired by Samsung. Other companies include Noctiluca, and beeOLED.
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.
Researchers combine blue TADF emitters and yellow MR-TADF emitters to create high efficiency and long-lasting white OLED devices
Researchers from Shenzhen University and Wuhan University have designed new white OLED devices that exhibit exceptional power efficiency (over 190 lm/W, 39% EQE) and extended operational lifetime (LT80 446 hours at 1,000 cd/m2).
The new device uses a blue TADF emitter emitter combined with a yellow MR-TADF emitter. The light is a warm white light. The researchers also used the same technique to create a standard white emission device, that still achieves a high EQE of 35.6%, thus further validating the strategy.
Researchers design a highly promising host material for blue TADF OLED devices
Researchers from National Taiwan University, together with colleagues from Yuan Ze University, National Dong Hwa University and Academia Sinica, have developed a very high efficiency blue TADF OLED device, by adopting a favorable horizontal oriented host material.
The researcher designed a new host material (4Ac26CzBz) that is made from acridan and carbazole moieties linked to a benzimidazole core. The host material exhibits a wide optical gap (Eg) and high triplet energy (T1) of 3.3 and 3.0 eV, respectively. The researchers used 4TCzBN as the blue-light TADF dopant, and report a remarkably high device external quantum efficiency of 35.8 % (59.8 cd/A and 62.8 lm/W) and a low turn-on voltage (<3 eV). The device features with significant suppression of the efficiency roll-off, maintaining a high efficiency of 29.7 % as luminance at 1000 cd/m2.
BOE shows a TADF-sensitized Tandem AMOLED device prototype
During the company's Innovation Partner Conference, BOE demonstrated a new 6.55" OLED panel prototype that utilizes TADF-sensitized materials and a tandem stack architecture. The company says that the TADF materials offer significantly improved color gamut, and it achieve 95% BT.2020 coverage, this in addition to the high power efficiency and long lifetime.
It is our understanding that BOE's TADF-Sensitized material platform combines a deep green Hyperfluorescence emitter and a standard deep-red phosphorescence material. The blue emitter is likely a standard fluorescence bluet emitter.
Samsung Display: we develop blue OLED emitter technologies, both PHOLED and TADF based
Samsung Display's Lee Chang-hee, VP and head of SDC's research center, gave a talk during K-Display 2024, and updated that Samsung is progressing towards a next-generation blue OLED emitter technology in two tracks.
SDC is working with Universal Display, to adopt the company's blue PHOLED system. This is progressing, but SDC says that the pace is slow - indeed we heard from UDC lately that the introduction of a commercial material will take longer than expected.
Next generation OLED emitter development - industry update
OLED emitter materials are the heart of the OLED device, and the materials that make the most impact on the performance of the OLED display. Most OLED displays utilize red, green and blue emitters.
The efficiency of the current state-of-the-art commercial red and green OLED emitters is excellent - it is in fact close to 100% internal quantum efficiency (IQE) which means that you cannot improve much on the efficiency of the emitter itself (there's still work to be done on getting the light out of the device). Blue OLED emission is a completely different story - current commercial blue emitters suffer from very low efficiency, around 25%. This means that three quarters of the energy goes to waste. Changing to a 100% IQE blue emitter could end up improving the total display efficiency by 20-30%.
Next-generation OLED technologies that will enable brighter and more efficient displays
OLED displays have been gaining popularity rapidly, and are already the dominant smartphone display technology. OLEDs are also the display technology of choice in the smartwatch market, making inroads into the TV, monitor, laptop and tablet markets. The future of the OLED industry looks bright.
In recent years, the focus of the industry, beyond increasing capacity and reducing production costs, has been improving the performance of OLEDs in the areas of display brightness, efficiency, and lifetime. Brightness is required in many applications - from TVs (for HDR and to view in ambient lighting) through smartphones (outdoor viewing) to automotive, and efficiency is a plus in any scenario (but mostly in mobile displays). Display lifetime is already good enough for many applications, but in some cases (like automotive, and IT displays) it is critical. These three properties usually go together - if you can make more efficient OLED displays, you can drive them at a lower current to achieve the same brightness, and so lifetime increases, or you can achieve higher brightness, etc.
Kyulux announces a new CFO as the company progresses towards Hyperfluorescence commercialization
Japan-based Hyperfluorescence materials developer Kyulux announced that Jimyeong Yu will join its executive management team, as the company's new Chief Financial Officer (CFO).
Jimyeong Yu will take over as Kyulux’s CFO, replacing Akira Minakuchi, who passed away in September 2023. As CFO of Kyulux, Jimyeong Yu will oversee financial accounting operations including procurement activities, and as a member of the management team, will be involved in formulating and implementing future business plans.
Researchers develop the longest lasting deep-blue CMA TADF OLED emitters
Researchers from the University of Manchester, University of Cambridge and University of Eastern Finland, led by Dr. Alexander Romanov have developed a new deep-blue Carbene-Metal-Amide (CMA) OLED emitter material with promising operating lifetime.
The emitter is based on a a new CMA complex with a rigid amide donor, benzoguanidine. The researcher say that the new design unlocks bright charge-transfer deep-blue emission with 100% photoluminescence quantum yields. The excited state lifetimes of the new CMA complexes are among the lowest reported to date among all TADF emitters
(down to 213 ns), resulting in remarkably fast radiative rates of up to 4.7 × 10 6 s−1 .
Two research groups show that it is possible to produce a high-performance pure blue MR-TADF OLED emitter without the need for an assistant dopant
Researchers from the Universities of St Andrews, Kyoto and Kyushu have coincidentally developed state-of-the-art multi-resonant TADF (MR-TADF) OLED emitters, based on a helical boron-nitrogen-oxygen doped nanographene design.
In these multiple studies, the researchers have shown that it is possible to obtain deep blue, narrowband emission, very fast reverse intersystem crossing rates constants, and high-efficiency vacuum-deposited OLEDs.
Researchers explain TADF efficiency roll off, to assist material developers in optimizing TADF emitters
Researchers from the University of St. Andrews in the UK, led by Professor Ifor Samuel and Professor Eli Zysman-Colman, identified the key processes controlling the efficiency of TADF OLED emitters under high brightness. This could assist material develops on their quest to design materials that maintain high efficiency at high brightness.
The researchers explain that OLEDs have lower efficiency at higher brightness, and in many TADF materials, the efficiency roll-off is severe, so that the high efficiencies achieved at very low brightness are not maintained at higher brightnesses needed for displays or lighting applications. For the first time, the researcher identified the key processes controlling the triplet population, and propose a figure of merit for efficiency roll-off.
