Technical / Research - Page 24

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.

Researchers from Turkey demonstrated a display prototype that is printed on paper (using graphene inks). This was a very simple device, but potentially such a technology could be used to create a foldable display with interesting optoelectronic properties.

To create this display, the researchers used electro-modulation of the optical properties of the multilayer graphene via blocking the interband electronic transitions. The researcher report that the paper display has high optical contrast and a fast response time.

In 2011 the University of Florida announced a new organic-TFT backplane/emitter technology called CN-VOLET. The University spun-off the technology into a company called nVerPix, with funding from Nanoholdings.

We have talked to nVerPix in the past and updated on the technology back in 2013. The nVerPix team presented their technology at SID's DisplayWeek - and it won the "best prototype" awarded. nVerPix demonstrate a working mono-color (green) 320x240 2.5" display. The aperture ratio is 70% and the brightness is over 500 nits.

Samsung Display developed a new high-resolution OLED display, specifically for VR applications. The 5.5" panel, on display at SID DisplayWeek, sported a 3840x2160 resolution - or 806 PPI. The panel offered a brightness of 350 nits and a color gamut of 97% adobe RGB.

This is the highest resolution mobile phone sized OLED ever demonstrated, and it exactly matches the highest resolution LCD - Sharp's 5.5" 806 PPI IGZO panel unveiled in 2015. Samsung's display probably uses some sort of PenTile architecture, though, so actual sub-pixel count is smaller.

Researchers from Korea's KAIST institute developed a rollable OLED device that uses graphene-based electrodes. The researchers say that the new OLED is much more durable when bent compared to current devices made with ITO electrodes.

The electrodes were made from a stack of materials - titanium oxides, graphene and conductive polymers. The new OLEDs were also brighter than current devices, and with a higher color gamut. This was achieved by maximizing the resonance within the OLED.

GJM developed a new 300mm roll-to-roll deposition system that can directly deposit both organic and inorganic materials on plastic materials - and be used to mass produce flexible OLEDs. The system was developed in collaboration with the Korea Institute of Machinery & Materials.

GJM says that its R2R system can speed up production times compared to current systems - by about 50% (GJM says that production amount can be improved by 1.5 times) - and so contribute to lower cost production. The system can be used to produce both OLED display and lighting panels.

Japan Display (JDI) announced that it has signed a technology development agreement with Semiconductor Energy Laboratory (SEL) regarding the development of Oxide-semiconductor backplane technology for next-generation displays, including OLED displays.

SEL's backplane technology is called c-axis aligned crystal (CAAC), which has been co-developed with Sharp. CAAC is based on an IGZO thin-film that has a novel crystal structure.

Universal Display developed a new AMOLED structure that is a sort of WOLED - RGB hybrid structure. The idea is to use a large blue sub-pixel and a large yellow sub-pixel that is split into three areas - unfiltered and red and green filtered.

This structure is easier to deposit compared to a true RGB AMOLED (that requires very fine patterning of red, green and blue subpixels) but increase the aperture ratio compared to a WOLED architecture (which LG for example uses in its OLED TVs) - which increases the lifetime and color gamut of the display.