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Meshed surface extracts more light

15 Mar 2007

A textured polymer film that suits both large and small emitters can enhance the outcoupling efficiency of an OLED by 46% say its inventors.

A dense mesh of tangled microwires could be ideal for extracting more light from emitters such as LEDs and OLEDs, according to researchers in Taiwan. Trapped light is a problem for the industry as it impairs device performance and can lead to overheating. (Appl. Phys. Lett. 90 091102)

"The surface not only enhances light extraction by destroying the total internal reflection condition, but it also allows light to diffuse through the mesh structure," Yu-Hung Cheng of National Tsing Hua University told optics.org. "We believe that our thin film is a potential candidate to replace the diffusive optics found in backlight modules."

The structured film is created by embedding polydimethylsiloxane in porous anodic aluminium oxide. The aluminium "template" is etched away using strong alkali solution to reveal a 20 micron thick film that can then be applied to various emitters and optical components.

To test the material, scientists glued a section of film to an OLED and compared the output with a bare reference device. The outcoupling enhancement was calculated to be 46% and was shown to be insensitive to optical wavelength, which helps to preserve the color spectrum of the emitter.

The group is evaluating several application areas, including LEDs, OLEDs and solar cells. "The casting process is simple and low-cost," said Cheng. "With this technology you could actually monolithically integrate all of the optics in a backlight module into a film." Ultimately, the team hopes to turn its idea into a product by co-operating with key industrial partners.

Author

James Tyrrell is News Editor of Optics & Laser Europe magazine and a contributor to optics.org.

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