New Oled Device Water/oxygen - Resistant, Long - Life, Energy - Efficient


New OLED Device Water/oxygen-resistant, Long-life, Energy-efficientJapan Broadcasting Corp (NHK) announced May 24, 2016, that it has drastically extended the service life of a red OLED device for flexible displays and drastically reduced its power consumption.
Also, NHK exhibited a full-color display that was prototyped in 2015 by using a film substrate and the previous-generation technology at Open House 2016, which NHK Science & Technology Research Laboratories (STRL) organized from May 26 to 29, 2016. In other words, NHK proved that the film substrate-based display with almost no sealing can continuously display video for more than one year after it was made.

One problem after another

The latest OLED device is based on the "inversed OLED (iOLED)" technology, which NHK STRL first announced in 2013 (See related article). The key to this technology (structure) is the material of its electron injection layer.

While many of OLED devices having a conventional structure use lithium fluoride (LiF), which is easily oxidized, NHK STRL used an organic material called "polyethyleneimine" for the iOLED that was prototyped in 2013.

Though its electron injection layer was resistant to moisture and oxygen, it was deteriorated by driving current. And its emission lifetime (the time it takes for the initial brightness of 1,000cd/m2 to be halved) was 1,000 hours or less, which is 1/10 that of commonly-used materials, even when it was sealed by glass.

In 2015, NHK STRL developed an iOLED device with an improved emission lifetime and a film substrate-based display using it. However, the driving voltage increased from 3.9V in 2013 to 5.6V in 2015, lowering internal quantum efficiency from 100% to 70%.

High oxygen/moisture resistance, long emission lifetime, low driving voltage realized at same time

This time, NHK STRL used a new organic material and additive for the electron injection layer of the red iOLED device. As a result, the driving voltage was lowered to 3.7V, the internal efficiency returned to 100%, and the emission lifetime was drastically increased to 10,000 hours or longer.

"This is the world's first OLED device that has a long service life, high energy-saving capability (because of the low driving voltage) and resistance to oxygen and moisture," NHK said.

For the future, NHK STRL plans to accelerate the development of green and blue OLED devices that have the same high energy-saving capability and long service life as the latest red OLED device.