27 Nov 2008
A green dopant is set to help move OLEDs into emerging large-market applications.
Kodak has developed a new OLED dopant that could help green OLEDs achieve luminous efficiencies greater than 31 cd/A and lifetimes in excess of 65,000 hours, resulting in an external quantum efficiency of 8.7%. Such advances in OLED device architecture and materials are crucial to wide adoption of the technology in the displays sector, a market expected to grow by more than $17 billion annually.
"This new dopant is designated Kodak OLED Material EK-GD403," Sundaram Krishnamurthy, director of Materials R&D at Kodak OLED Systems, told optics.org. "It is the result of a comprehensive study of the modelling and degradation mechanisms involved, driven by the need to devise materials which work well others in the OLED stack."
According to Krishnamurthy, OLED materials need to demonstrate teamwork, with each material needing to work within the device's layer structure. "This dopant works with a particular host like a hand in a glove," he said. "In the future, as OLED usage increases and applications grow in solid-state lighting (SSL), that concept is going to be a very critical factor. We have achieved our high luminance efficiencies and lifetimes across a common technology platform for displays and SSL. That is the beauty of it."
The new dopant can be used in isolation, or as part a white OLED formulation. Kodak expects white OLEDs to play an important part in the wider acceptance of OLED materials, and has developed systems using colour filters and four sub-pixels (in red, green, blue and white) to dramatically increase the performance of such materials.
"For white OLEDs in particular we have improved luminance efficiency by 50% every year for the last three years," said James Buntaine, CTO of Kodak OLED Systems and vice president of its Display Group. "The most recent situation is that we have achieved a little over 35 cd/A white luminance efficiency, and that is just using fluorescent materials. With hybrid structures, combining fluorescent and phosphorescent materials, we have achieved over 50 cd/A."
Kodak expects the economic and environmental advantages of white OLED formulations to become more attractive as display sizes increase. "OLED screens are most compelling as they become larger," commented Buntaine. "To achieve a practical cost structure, large glass manufacturing is required, which in practice means Gen 5 panels or above. The only practical approach at that scale is to use white OLED technology."
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