For this project, Chris Giebink, associate professor of electrical engineering at Penn State, has been awarded a two-year, $1.1 million grant from the U.S. Department of Energy (DOE). The research, which is being conducted in conjunction with Michael Hickner, professor of materials science and engineering, chemical engineering, and chemistry, is focused on increasing the efficiency of OLEDs used for room lighting.
“Because this is a two-year grant, the research is fast-paced and intense,” Giebink said. “The product of this particular grant ideally will be something that we translate into commercial production with our industry partner, OLEDWorks. This gives us the chance to have real-world impact in the near term, which would be gratifying.”
“Right now, only about 20 percent of the light that’s generated in OLEDs gets out,” explains Giebink. “The rest is trapped in the device and wasted.” Overcoming this challenge could make OLEDs more than twice as efficient as the fluorescent lamps currently used in buildings. Over the past 10 years, there have been many approaches for extracting the remaining light out of OLEDs, but so far, no one has been able to do so in a way that’s manufacturable.
“We can implement solutions in the lab at a size of about a millimeter by a millimeter, but doing it on a scale of meters in a way that’s actually compatible with manufacturing is the real challenge,” Giebink said. “That’s where our project comes in. We’re not trying to scatter the light out. We’re actually changing the makeup of the organic semiconductors to change their refractive index, which is an indication of how fast light propagates in a material. What we’re trying to do is lower that value in the organic materials that make up the OLED because, if we can, it’ll avoid much of the problem to begin with.”
The difficulty with this approach is that trying to change the refractive index of the materials themselves may negate the molecules’ electrical and luminescent properties, which took 10 to 15 years of design work to achieve. An alternative being investigated is to blend in other molecules, to decrease the refractive index of the entire OLED film without adversely affecting the properties of the original molecules. If Giebink and his fellow researchers can blend these molecules effectively, they will work with OLEDWorks to see if they can scale up the work to be manufactured.
“The efficiency of organic LEDs commercially right now is something like 70 to 80 lumens per watt. For comparison, your standard incandescent lightbulb is a little bit less than 20. So, we’re talking about four times the efficiency,” Giebink said. “That’s a big opportunity for energy savings that complements what inorganic LEDs are able to provide.”
Penn State University – www.psu.edu
OLEDWorks – www.oledworks.com