[Click to enlarge image]
[Click to enlarge image]

NHK Science & Technology Research Laboratories (STRL) offered a private view of Open House 2013 May 28, 2013, to mass media and unveiled an 8-inch full-color flexible OLED display.

For the display, STRL formed bottom-emission OLED devices on a plastic sheet. Its pixel count is equivalent to VGA (640 x 480 pixels), and its resolution is 100ppi (pixels per inch).

STRL has been engaged in the development of flexible OLED displays for several years. But this is the first time in two years that it has announced one at Open House. In 2011, the size of its flexible OLED display was five inches.

Red color realized with platinum-based phosphorescent material

In addition to the larger size, STRL added three features for the new display. First, it used a red phosphorescent material that has a low power consumption and a long life and was developed by the company in 2012. Second, it employed an amorphous InGaZnO (a-IGZO) TFT for driving pixels. Third, the protective layer for OLEDs, etc was formed by applying a polymer material.

Many phosphorescent materials use an iridium (Ir) complex. But the red phosphorescent material is made by combining (1) a guest material developed by using a platinum (Pt) complex and (2) a host material (benzoquinoline derivative).

STRL employed the a-IGZO TFT because it is highly flexible and suited for large displays, the company said. For the 5-inch display announced in 2011, the company used organic TFTs. It did not disclose the details of the third feature.