Losing the blues: why organic LEDs are turning pink too fast

by Guy Kewney | posted on 17 November 2004

Still on course for seeing the roll-up electronic newspaper inside a couple of years, the makers of organic LED screens are suffering from a problem: the blues go away too soon.

Guy Kewney

According to an Electronics Weekly analysis, huge investment is going into organic LEDs, with the objective of having thin, flexible screens which use very little power, for both portable and full-screen use.

"Imagine a TV that is not just thin like a plasma screen, but thin like a birthday card. That lives in a narrow box near the ceiling and has a string you pull to unroll it," writes Steve Bush enthusiastically - but he goes on to admit that there are problems. Particularly, ageing problems.

"Absolute life expectance is not actually the biggest issue with OLED as, unlike LCDs which use colour filters over identical pixels, OLEDs are vulnerable to differential aging," Bush writes. He quotes a source: "The big problem for colour is red, green and blue emitters degrade at different rates."

In particular, the blue fades long before the red and green.

"Two years ago, one firm was getting through four displays a day on their stand at a show. They had to swap displays as colour-shift was obvious within hours of switch-on even though the life of its weakest OLED material was rated at 2,000 hours."

A full analysis of these, and other OLED problems - barrier layers, active matrix designs, and so on, is given in the full article

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