Technical / Research - Page 24

Korea equipment maker DAWONSIS developed a new OLED deposition process that is based on FMM but according to the company can be scalable to large-area deposition. This could theoretically enable efficient evaporation-based OLED TV production.

The so-called Joule Heating Deposition process use a large area material source (as opposed to point-sources or line-sources currently used) using a conductive film that is efficiency heated using voltage induction. According to DAWONSIS this process is scalable and also efficient in terms of material usage (which is about 70%-80%).

Exactly one year ago at IFA 2016, Panasonic unveiled its first OLED TV, the 65" curved 4K TX-65CZ950. Now Panasonic unveiled a new "reference" OLED TV prototype, with an aim to show what is possible with next-gen OLED technology.

Panasonic said that it achieved significant progress with near-black reproduction, by applying its plasma self-illuminating experience. It's not clear what is meant exactly, but this probably related to software algorithms Panasonic is developing to increase the quality of the OLED TV image. The panel, of course, is supplied by LG Display.

The Fraunhofer Institute is working on alternative light sources for photo therapy, and Flexible OLED technology is prime candidate because it is light weight, can be flexed and does not produce almost any heat (unlike LED-based lighting).

Before flexible OLEDs are actually used in such treatment, though, it is important to know if OLEDs carry any potential toxic risks. The Fraunhofer FEP performed an initial study on in vitro cell cultures afflicted by defined damage. The researchers used flexible 10x10 cm green OLEDs, and found that the OLEDs positively stimulated the damaged cells, as expected. The tests showed now cytotoxity in the material systems, including when the OLEDs were bent (this increases the chance of material leakage from the OLEDs).

Researchers from Japan's Semiconductor Energy Laboratory (SEL) developed a new OLED device architecture that enables efficient, long-lasting and low-drive voltage OLEDs, at practical brightness levels.

The researchers call the new device architecture exciplex-triplet energy transfer, or ExTET. The image above shows the elementary process and its energy state diagram. To create the emissive layer of the ExTET, the researcher took a film with an electron-transporting material (ETM) and a hole-transporting material (HTM) and doped it with a phosphorescent dopant. Direct recombination between the electrons at the LUMO level and the hole at the HUMO level forms a charge-transfer excited complex (exciplex) - and the phosphorescent emission occurs via energy transfer from the exciplex to the dopant.

Reports from China suggest that LG Display is considering changing the basic structure of its white OLED panels (WOLED) used in LGD's OLED TVs. LGD is currently using yellow and blue OLED materials to create a white OLED, but now LGD may switch to an RGB based mix.

It's not clear from the Chinese reports (which are unverified yet, of course) - but it's likely that LGD will not switch to a direct-emission RGB structure, but rather use the RGB materials to create a white OLED and remain with a color-filter based design. Switching from Y/W to R/G/B may enable LGD to achieve higher color purity - and so a larger color gamut, and may also be more efficient.

Last week we reported about a new large-scale computer-driven material screening process that was developed by Researchers from Harvard University, MIT and Samsung.

The so-called Molecular Space Shuttle system combines theoretical and experimental chemistry, machine learning and cheminformatics, with an aim to quickly identify new OLED molecules (the system was already used to deisgn more than a 1,000 new high-performance blue-light emitting molecules). Today Kyulux announced that it secured a license to Harvard University’s Molecular Space Shuttle deep learning system.

Researchers from Harvard University, MIT and Samsung developed a large-scale computer-driven material screening process that incorporates theoretical and experimental chemistry, machine learning and cheminformatics, with an aim to quickly identify new OLED molecules.

The so-called Molecular Space Shuttle system was used to design more than 1,000 new high-performance blue-light emitting molecules. It seems that there is still a lot of work ahead to find the best new candidates and actually test these molecules, but this may be a promising new direction in OLED molecule research.

Researchers from Japan developed a new method that can be used to change the color and fluorescence of compounds using oxygen and hydrogen gases. This is a reversible method that is environmentally friendly. The technique can find applications in sensors and control of organic semiconductors and OLED devices.

The researchers explain that they were able to perform a molecular switch in aromatic compounds that are commonly used in OLEDs, OPVs and other applications. The switch was performed using an orthoquinone moiety.

In 2013, the Japan Broadcasting Corp (NHK) and Nippon Shokubai developed a new OLED structure called inverted OLED, or iOLED, that drastically improves oxygen and moisture resistances. The basic idea behind iOLED is to invert the structure between the electrodes of a bottom-emission OLED. The electrodes are based on an organic material (polyethyleneimine) and not Lithium-based like most electrodes.

NHK iOLED (2015)

In 2015, NHK demonstrated a full-color iOLED display that uses a film substrate. The company now demonstrated the same display - more than one year after it was fabricated - still working even though there is almost no encapsulation.

In April 2016, Japan's Semiconductor Energy Laboratory (SEL) and Advanced Film Device announced they have developed a hybrid OLED - reflective LCD display, that can switch between an OLED mode (for dark environments) and reflective LCD mode (for sunlight visibility). Such a display could be very power efficient.

TR-Hybrid in OLED mode

SEL demonstrated a prototype display at SID 2016, and provided more information. SEL calls these displays TR-Hybrid displays (TR means Transmissive OLED and Reflective LC). To create this display, SEL introduced holes into the reflecting electrodes of a reflective LCD, and the OLED layer beneath transmitted light through these holes in OLED mode.