Technical / Research - Page 21

The Fraunhofer FEP institute in Germany first unveiled its bi-directional OLED microdisplays in 2012 with the novel idea of embedding photo detectors between the OLED pixels. Since then the instituted demonstrated its second-generation microdisplay that supported a resolution of 800x600 (SVGA), up from VGA in the first generation prototypes.

The Fraunhofer FEP now announced that it developed a new generation of these displays, that employ an extra-think encapsulation layer, which can turn these new displays into fingerprint sensors. The idea is that the OLED display illuminates the fingers and then the reflected light is used to detect and analyze the fingerprint with excellent accuracy.

The EU launched a new project called HyperOLED with an aim to develop materials and matching device architectures for high-performance, hyperfluorescence TADF OLED emitters. HyperOLED is coordinated by Merck, and the project partners include MicroOLED and the Fraunhofer IOF institute. This three years project received a €4 million grant from the EU.

These OLED emitters will be realized by combining TADF molecular hosts with novel shielded fluorescence emitters, targeting saturated blue emission of very high efficiency at high brightness. The project will also achieve efficiency gains through molecular alignment to enhance light outcoupling.

TADF are getting a lot of attention now, as a promising new emitter type that could finally enable efficient blue emission, and also efficient alternative to red and green phosphorescent emitters.

Several new TADF research papers have been announced by SID and will be presented at DisplayWeek 2017. Below you will find a list of these recent achievements, at no particular order.

Researchers from the Korea-based ETRI (Electronics and Telecommunications Research Institute) produced the largest OLED panel to date (370 x 470 mm) that use graphene electrodes.

From the photo above (and image below) it seems that this panel is actually made from 12 small OLEDs - but it seems that the graphene deposition itself was done on the whole substrate.

Researchers from the Technical University in Dresden have developed a method to produce polymer TADF emitting molecules. Up until now most TADF materials are based on small molecules or chromophores linked to a polymer network.

This research focused on actual polymer TADF, and using a controlled extension of the conjugation of the monomers HOMO wavefunction, the researchers were able to to increase thephotoluminescence quantum yield from about 3% to about 71%. The reseachers say that this is an encouraging first step towards polymer TADF emitters.

Researchers from the University of Cambridge, the University of East Anglia and the University of Eastern Finland developed soluble carbene-metal-amides light emitting materials that were found to be very efficient and reach an internal quantum efficiency of nearly 100% at high brightness.

The new materials look like propellers and the rotation of the molecules changes the light emitting efficiency. Those materials are made from copper or gold, but the researchers aim to find similarly-shaped materials that are free from rare elements.

According to the Korea Herald, Samsung Electronics demonstrated several new display technologies in a private room during the Mobile World Congress last month. All of these technologies are expected to enter production within the next year or two, according to the source quoted by the report.

1,200 PPI AMOLED for VR

The report claims that Samsung demonstrated a high-resolution AMOLED panel for VR applications. The AMOLED on display featured a 1,200 PPI - much higher than Samsung's current highest density displays which are 577 PPI. Samsung's aim is to reach 1,500 PPI which will greatly enhance the VR experience.

In November 2016 Sunic Systems announced that it developed an plane-source evaporation-FMM based AMOLED production process that can reach very high densities. The 100um mask announced in November can achieve a PPI of 1,500. This may be the system that Samsung is now testing. Sunic says that eventually this technology will enable even 2,250 PPI.

Researchers from Osaka University managed to create multi-color Mechanochromic Luminescent (MCL) materials. The materials were found to exhibit efficient TADF emission, and the researchers developed an efficient OLED device based on these new materials.

MCL materials change their color in response to a change in their environment - for example pressure or temperature. Most MCL materials can only change between two colors, but the new materials can switch between yellow, red and orange. The color shift occurs in response to heating, fuming, and grinding.

Researchers from the Tokyo Institute of Technology developed new electron injection layer and electron transport layer materials suitable for OLED displays produced on IGZO backplanes. The new materials, based on transparent amorphous oxides, were found to increase the stability of the OLED device.

The new materials are transparent, and chemically stable. The can be adopted for use in web processes - which means that low-cost production processes are possible.

Researchers from Michigan State University (MSU) developed a stretchable circuit that includes an OLED display, produced entirely using an ink-jet printer.

The researchers used special developed inks to produce both the circuits and the organic elements - and they say that the ink was also used to produce the substrate, but that seems rather unlikely.