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May 03, 2007

Solar cells make OLEDS luminous enough for mobile devices

Organic light-emitting diodes (OLEDs) offer an alternative to conventional electronic displays (such as LCDs) and have advantages generally including wide viewing angles, rapid response and thin shapes. However, one area that scientists would like to improve is achieving better contrast, especially under strong lighting environments. A low-power, high-contrast OLED could provide higher quality displays for mobile electronics, and also result in longer battery lifetimes.

When the scientists placed a solar cell in the back of the OLED, the solar cell absorbed the incident light and internal OLED emission and then converted the light to electrical power for reuse via photovoltaic action. Although the power recycling efficiency achieved in this trial was a modest 0.26%, the scientists explained that there is much room for improvement beyond this initial demonstration, simply by using more efficient OLEDs and solar cells.

“The solar cell stack put behind the OLED actually play two roles,” said Wu. “First, it functions as a black absorbing material. Second, it also functions as an optical coating to induce destructive interference of incident ambient light, so that the ambient light reflection can be much suppressed.”

Overall, this arrangement could reduce the reflectance of the OLED from 70% in a conventional OLED to about 1.4%, without compromising the electroluminescence efficiency. The device even improves upon the OLED polarizer approach, which has a reflectance of about 5%. By getting the reflectance down to that level, the scientists are helping to prepare OLEDs to be highly competitive with current light displays.


OLED costs are higher than high volume LCDs but they are catching up.

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