Japan Broadcasting Corp (NHK) and Nippon Shokubai Co Ltd announced that they drastically improved the oxygen and moisture resistances of their OLED device.
The announcement was made at SID 2013, an academic conference on display technologies (lecture number: P.140L). Also, a display made by using the new technology was demonstrated at a press preview of Open House 2013 May 28, 2013.
As the development of flexible OLED displays and OLED lighting devices is recently advancing, their durabilities remain as a big issue to be solved for commercialization. To solve this problem, the barrier capability of the sealing layer located outside of an OLED device is being strengthened. But it requires special materials and potentially increases costs.
The new technology developed by NHK and Nippon Shokubai proved that it is possible to significantly improve durability just by changing the structure inside an OLED device and its materials.
According to the announcement, while the light-emitting area of the previous OLED device prototyped by the two companies decreases by half in 100 days in the air due to the oxidation of their negative electrodes, the latest OLED device hardly deteriorates under the same conditions, they said. Therefore, the cost of sealing materials to be used outside of an OLED device can potentially be lowered.
The new OLED device developed by NHK and Nippon Shokubai has the "inversed OLED (iOLED)" structure, in which the structure between the electrodes of a bottom-emission device is inverted. Specifically, an electron-injection layer, electron-transport layer, light-emitting layer, hole-transport layer and positive electrodes (such as titanium and gold) are formed in this order on a transparent substrate/transparent negative electrodes (ITO).
For normal bottom-emission OLED devices, a hole-transport layer (such as PEDOT:PSS), light-emitting layer, electron-transport layer and electron-injection layer are formed in this order on a transparent substrate (such as glass)/transparent positive electrodes (such as ITO), and, then, negative electrodes (such as aluminum) are formed.