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Materials scientist lights the way with new generation technology

Nigel Shepherd, associate professor of materials science and engineeringOrganic light emitting diodes (OLEDs) can potentially revolutionize lighting technology by providing solid-state light sources that are considerably more efficient than traditional incandescent or fluorescent lighting. 

UNT researchers have been at the forefront of OLED technology development with help from the U.S. Department of Energy and the National Science Foundation (NSF).

Nigel Shepherd, left, has been awarded an NSF grant of nearly $300,000 for his project, “Workfunction Modification of ZnO Anodes for Second Generation OLEDs.”  This research builds on work begun in 2010 with an NSF EAGER grant (Early-Concept Grant for Exploratory Research.)

In the current project, Shepherd looks to new materials to improve efficiency while significantly reducing the cost of OLEDs. 

He is assisted by his team at the Optoelectronics and Thin Films Laboratory and also by co-investigator Jincheng Du, associate professor of materials science and engineering, who will use computational modeling to assist the experimental work.

“The first generation goal was to understand the basic mechanisms, and improve brightness, color, and efficiency of OLEDs,” Shepherd said.  “The goal with the second generation is to obtain high efficiency at significantly reduced cost so that the technology can transition from research labs to widespread use.

The commonly used positive electrode in OLEDs is indium-tin oxide (ITO), which is a transparent conducting oxide (TCO).  Transparency is necessary so that generated light can escape the device.  However, indium is expensive, and the earth’s reserve is relatively small.  The researchers are investigating zinc oxide (ZnO) as an alternative because zinc is considerably more abundant and less expensive than both indium and tin. 

To be successfully used in this application, the ZnO must be processed to have the correct balance of transparency, electrical conductivity, and electrical band alignment with the organic layer next to it. While the optical transparency and electrical conductivity of ZnO can be comparable to ITO, its workfunction is typically smaller.   

This means that more voltage is needed to turn on an OLED with a ZnO anode, which translates to higher power consumption and lower efficiency.  Tuning the ZnO workfunction by modifying its surface properties to obtain device performance comparable to OLEDs with ITO is the core of the study.

The group will research how the workfunction modifications influence outcomes such as device threshold voltage, current, luminance, power efficiency, and external quantum efficiency of OLEDs.  Zinc oxide could lower the cost of OLEDs, which with widespread use would significantly reduce the amount of fossil fuel consumed by general lighting. 

— Amelia Jaycen, Publications Intern, Office of Research and Economic Development

 

Posted on: Tue 07 May 2013

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