Using green light materials to emit blue light, successfully extending OLED lifespan

　　White light is the rising star of lighting technology. The U.S. Department of Energy (DOE) predicts that by 2020, OLED lighting will be on par with LED in terms of cost, efficiency, and lifespan metrics!

　　However, the industry is currently facing the dilemma that organic blue phosphorescent materials have too short a lifespan. The OLED emitting layer is mainly composed of red fluorescent materials, green light materials, and blue phosphorescent materials mixed together to form white light. If any one of these materials suffers lifespan degradation, the entire OLED will fail. How to overcome the inconsistent lifespans of materials has become a challenging issue for the industry.

　　Taiwan's ITRI (Industrial Technology Research Institute) has developed the "OLED Surface Plasmon Coupling Gain Technology," which converts the emission spectrum of green light materials into blue light, breaking through the bottleneck of the short lifespan of organic blue light emitting materials. (All images courtesy of ITRI)

Taiwan ITRI's solution to the 'blue flash' phenomenon is to not use any blue light materials at all, but to use technology to make green light materials become the source of blue light, thereby developing the OLED surface plasmon-coupled gain technology PCOLED (Plasmon-Coupled Organic LED).

Initially, when Taiwan ITRI was conducting experiments on the light-emitting structure of green light materials, it was unexpectedly discovered that the green light material emitted seemingly impossible blue light. This led ITRI to open up a new research direction. Later, by applying physics thinking, they designed a special structure for the green light material and continuously adjusted parameters, finally identifying and summarizing the reasons and methods by which the green light material emitted blue light.

Finally, by using the DML structure to generate a planar plasmon-coupled effect (Plasmon-Coupled), the emission spectrum of the green light material can be converted into blue light. This allows white-light OLED to use green light materials to replace the traditional blue light material layer, which not only solves the problem of an overly short lifespan, but even extends it by as much as 20 times compared to traditional OLED.

In terms of efficiency, through continuous R&D and device optimization, the blue light emission efficiency of DML has been able to surpass the level of existing blue fluorescent materials and most known blue phosphorescent materials, reaching 35 cd/A. After verification, the OLED DML white light technology can emit white light with a color rendering index (CRI) of 77 and a color temperature of 2039 K, suitable for indoor lighting use. In addition, ITRI has successfully lit up a large-area white light module measuring 10 cm × 10 cm.

Currently, the ITRI team has applied for patents on related technologies in Taiwan, Germany, the United States, and mainland China, and has collaborated with private companies to further master key OLED materials and process technologies, moving toward industrialization.