May 17, 2006 – Scientists from the U. of Cincinnati claim to have developed a method to make organic light-emitting diodes (OLED) as much as 10x more efficient and 30x brighter — with a little help from the humble salmon fish.
Incorporating a thin layer of salmon DNA into the OLED structure as an electron-blocking layer improves the chance for electrons and holes to recombine and emit photons, thus enhancing the device’s luminance, the researchers claim. Tests showed that a green “BioLED” with the DNA electron blocking layer (current density of 200 mA/cm2) achieved luminance of 15000 cd/m2, vs. 4500 cd/m2 for conventional OLEDs. A similarly enhanced blue BioLED produced 1500 cd/m2 luminance, nearly twice as much as the baseline device.
“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,” explained U. of Cincinnati researcher Andrew Steckl. The BioLEDs’ lifetime also appears to be significantly longer than that of equivalent OLEDs without the DNA layer — the team is still trying to understand the difference in degradation mechanisms. Also, Steckl said the team is working to introduce lumophores into the DNA layer to obtain combined photoemission from multiple layers in the device, and are exploring other types of DNA for OLED fabrication, including mammalian and plant DNA.
The water-soluble DNA was difficult to process into thin films, so the researchers utilized a surfactant to convert the DNA into a form insoluble with water, but soluble in selected alcohols. It was then spin-coated into a 20µm-thick electron blocking layer on top of the BioLED’s hole injection layer.
Should the process prove viable for production of OLEDs, availability of salmon DNA is another bonus. Salmon fishing is a 200,000 tons/year industry in Hokkaido, Japan, and normally the male roe is a waste product, but is very rich in DNA.
Full details of the process were published in the May 8 edition of the journal Applied Physics Letters.