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08 May 2006
Incorporating salmon DNA into the structure of a conventional OLED makes it ten times more efficient and thirty times brighter, say researchers in the US.
Salmon DNA could hold the key to more efficient and brighter OLEDs, according to researchers in the US. By incorporating a thin layer of DNA into the OLED structure, the team says its BioLEDs are as much as ten times more efficient and thirty times brighter than their conventional counterparts. (Applied Physics Letters 88 171109)
The team's idea involves using the DNA as an electron-blocking layer. This improves the probability of electrons and holes recombining and emitting photons, which in turn enhances the device's luminance.
"It turns out that DNA has nearly ideal energy levels that allow hole transport to proceed unimpeded while it prevents electrons being transported too quickly," Andrew Steckl from the University of Cincinnati told optics.org. "This gives both electrons and holes a greater opportunity to recombine and emit photons."
Steckl and colleagues used DNA from Japan. "Salmon fishing is a very large industry in Hokkaido, Japan, some 200 000 tons per year," explained Steckl. "While the meat and eggs are edible, the male roe is normally a waste product but it is very rich in DNA."
DNA is normally soluble in water making it very difficult to process into thin films. To overcome this, the team used a reaction with a surfactant to convert the DNA into a water insoluble form, but soluble in selected alcohols. This allowed the group to spin coat a 20 nm thick electron blocking layer of DNA on top of the BioLED's hole injection layer.
The team tested a green- and blue-emitting BioLED against conventional OLEDs and found that the DNA electron blocking layer improved the luminance in both cases. For a current density of 200 mA/cm2, the green BioLED achieved 15000 cd/m2, whereas the baseline device reached just 4500 cd/m2. On the other hand, the blue BioLED had a luminance of 1500 cd/m2 at 200 mA/cm2, while the corresponding baseline device reached around 800 cd/m2.
Conventional OLEDs are renowned for having lifetime issues but Steckl and colleagues believe the DNA could also play a role here. "Our preliminary results show that the lifetime of the BioLEDs are significantly longer than that of equivalent OLEDs without the DNA layer," said Steckl. "We are working on understanding the difference in degradation mechanisms."
"We are trying to improve the control of the DNA layer thickness and properties," he continued. "We are also working on introducing lumophores in the DNA layer to obtain combined photoemission from multiple layers in the device. So far we have only used salmon DNA for BioLED fabrication, but are considering other sources of DNA such as mammalian and plant DNA."
Author
Jacqueline Hewett is editor of Optics & Laser Europe magazine.
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