Pure-Blue OLED

Present OLED displays have a problem when it comes to blue light sources. While high-performance red and green organic light-emitting diodes exist, the existence of equally performing sources of blue light is lacking. A new mix of emitter molecules has been used by researchers in Japan and a new method has been demonstrated which may overcome this challenge.

The pure-blue OLED separates the processes of energy conversion and emission into two distinct molecules. Using this technique, the researchers could create a high-efficiency pure-blue emission that can sustain brightness for relatively long periods. There are no costly metal atoms that the device uses.

Researchers say that while red and green OLEDs have an increasing number of choices, systems that emit high-energy blue light have become a challenge. Trade-offs have always occurred with efficiency, colour purity, cost, and lifetime. Generally, blue emitters have shorter operating lifetimes and use costly metals such as iridium or platinum.

Researchers from the Center for Organic Photonics and Electronics Research (OPERA) of Kyushu University have produced molecules that emit light based on the thermally triggered activated delayed fluorescence. Without a metal atom, the process can attain performance and often shows emissions comprising a wide variety of colours.

A two-molecule technique called hyperfluorescence was used by the researchers. Using that method, the team obtained longer operating lifetimes, at a higher brightness than previously recorded for highly effective OLEDs of similar colour purity. To practically double the emission of the same electrical current, their solution basically stacks two systems on top of each other. The result was a life expectancy that almost doubled at high brightness. Researchers predict that at more modest intensity, the system could retain 50% of its brightness for over 10,000 hours. The team expects that their OLEDs in the future will replace the existing blue OLEDs used in displays.


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