Organic LEDs Get Chlorine Boost

A simple chlorine treatment is being used to improve OLEDs, which could make manufacturing this light display technology faster, easier and cheaper than current methods.

Professor Zheng-Hong Lu of the department of materials science and engineering at the University of Toronto and PhD candidates Michael G. Helander and Zhibin Wang have found a simple method of using chlorine to drastically reduce traditional OLED device complexity and dramatically improve its efficiency all at the same time.

Prototype large-area red, green and blue OLEDs fabricated using chlorinated indium tin oxide transparent electrodes. (Images: Department of Materials Science and Engineering, University of Toronto)

By engineering a one-atom-thick sheet of chlorine onto the surface of an existing industry-standard electrode material (indium tin oxide, or ITO) found in today's flat-panel displays, these researchers have created a medium that allows for efficient electrical transport while eliminating the need for the several costly layers found in traditional OLED devices.

"It turns out that it's remarkably easy to engineer this one-atom-thick layer of chlorine onto the surface of ITO," said Helander. "We developed a UV-light-assisted process to achieve chlorination, which negates the need for chlorine gas, making the entire procedure safe and reliable."

Prototype large-area OLEDs fabricated using chlorinated indium tin oxide transparent electrodes.

The team tested its green-emitting "Cl-OLED" against a conventional OLED and found that the efficiency was more than doubled at very high brightness.

"OLEDs are known for their high efficiency," Helander said. "However, the challenge in conventional OLEDs is that as you increase the brightness, the efficiency drops off rapidly."

UV treatment process to functionalize the surface of the transparent indium tin oxide electrode with a layer of chlorine one atom thick.

Using chlorinated ITO, this team of advanced materials researchers was able to prevent this dropoff and achieve a record efficiency of 50 percent at 10,000 cd/m2 (a standard florescent light has a brightness of approximately 8,000 cd/m2), which is at least two times more efficient than the conventional OLED.

"Our Cl-ITO eliminates the need for several stacked layers found in traditional OLEDs, reducing the number of manufacturing steps and equipment, which ultimately cuts down on the costs associated with setting up a production line," said Zheng-Hong Lu. "This effectively lowers barriers for mass production and thereby accelerates the adoption of OLED devices into mainstream flat panel displays and other lighting technologies."

For more information, visit: www.utoronto.ca