Blue color - Page 2

NHK Science & Technology Research Laboratories (STRL), in collaboration with Professor Hirohiko Fukagawa from Chiba University, has developed an OLED display device that can emit light while simultaneously harvest solar energy. NHK says that this is the first time that such a device has been developed, where it is capable of blue light emission.

The basic idea behind the new device is that it is capable of quickly alternating between emitting light and generating electricity. The device is also quite efficient in both its light emission and energy generation.

Researchers from the University of Michigan and The Pennsylvania State University, in collaboration with OLEDWorks, has managed to create high aspect ratio OLED devices, by fabricating the OLEDs on substrates with sub-millimeter, high aspect ratio surface textures. This design increases the active OLED area per panel, reducing the local current density needed to achieve a given luminance.

The researchers report that this approach can extend the lifetime by up to 2.7X, this was verified on a blue fluorescent OLED device. These devices also offer up to 40% higher light extraction efficiency, as the corrugated substrates scatter the trapped light, significantly boosting EQE.

Japan-based TSK Corporation announced that it is collaborating with Samsung Display for the full-scale development of blue OLED display materials, based on the company's iron catalyst technology. The two companies are developing host and electron blocking materials.

TSK explains that in most OLED synthesis, palladium catalysts are used. But palladium is a rare metal primarily sourced from Russia and South Africa, and it is also expensive and polluting. TSK developed a proprietary, environmentally friendly chemical process that uses iron, a naturally abundant metal, as a catalyst in place of the palladium.

Researchers from the South China University of Technology, in collaboration with colleagues from Jihua Laboratory, and Jilin University, have managed to increase the efficiency of deep-blue MR-TADF 5-DABNA OLED emitters, by replacing a single molecule - swapping a phenyl for a tiny methyl group. The researchers say that the new material reached a world-leading 32.48% EQE, and an ultrahigh brightness of 11,619 cd/m².

This one material change made a big difference - the researcher report that it has tripled the reverse intersystem crossing rate (known as kRISC) which improves the light output, while the delayed fluorescence time was shortened by more than half, helping maintain brightness at high power. And the emitter still maintained its 457 nm deep-blue emission with exceptionally narrow (22 nm) spectrum.

Researchers from South China University of Technology, with colleagues from the Chinese University of Hong Kong and the Hong Kong University of Science and Technology, have applied a crossed long-short axis (CLSA) molecular design strategy to design new deep-blue OLED emitters.

The researchers developed two emitters that achieve excellent maximum EQE of 11% (at CIE coordinates of 0.155, 0.039) and 11.3% (at CIE coordinates of 0.155, 0.041). Even at ultrahigh luminance (10,000 nits), the emitters maintain EQEs of 9.3% and 9.1% - which the researchers say is the best performance reported to date for deep-blue OLEDs with CIEy ≤ 0.046.

In 2023, 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 say that in fact it is possible to develop highly efficient OLEDs with just the TADF emitter - and have demonstrated 100% IQE single-layer devices, with an EQE of 27.7%. In 2024, the reported the highest performance TADF system.

The researchers now report that they have designed a single-layer hyperfluorescence OLED device, which is both efficient and stable. This new research was led by Prof. Blom and Prof. Wetzelaer at the Max Planck Institute.

Researchers from the University of Toyama have discovered that by adding a tiny 3-nanometer wide spacer between donor and acceptor layers in exciplex OLEDs improves the energy transfer and boosts the light emission.

The researchers report that adding this spacer resulted in a 77-fold increase in EQE in exciplex upconversion OLEDs (ExUC-OLEDs), that usually suffer from poor energy transfer. ExUC-OLEDs can be driven at ultra-low voltages, which make them attractive for next-generation OLED displays.

The UK's Engineering and Physical Sciences Research Council  (EPSRC) has awarded 2.9 million GBP (around $3.9 million USD) to a research group at the University of St Andrews led by Prof. Eli Zysman-Colman, to develop solution-processable stable and efficient blue OLED emitters, based on Prof. Zysman-Colman TADF OLED emitters research.

The research group will establish a 5-year open fellowship, that will form a team of 6 researchers. The final objective is to develop an automated film formation and characterization platform. While the grant is academic, this technology may end up being commercialized by SolOLED. 

Researchers at Kyushu University, and Soochow University, led by Prof. Chihaya Adachi, have designed a new strategy to develop MR (multiple resonance) TADF OLED emitters that offer both a narrowband emission and adequate FMOs energy levels, by manipulating the frontier orbital levels.

The researchers explain that the energy level alignment of frontier molecular orbital (FMO) is essential for controlling charge carrier and exciton dynamics in OLED devices. Current MR emitters mostly suffer from inadequate FMO levels. In this research, which used a blue (459 nm) MR OLED emitter, a wavefunction perturbation strategy was proposed by incorporating cyano motifs at peripheral sites of MR backbone to adjust the energy levels. The approach significantly shifted the HOMO levels without compromising the color purity. The researcher report that detrimental carrier trapping effect was eliminated, enhancing external quantum efficiency to exceeding 23%, maintaining around 20% at 1000 cd m−2, and improving the device stability.