In OLED, 2 Blue LEDs Better Than One, Suggests LG Display Patent

In an OLED display, two blue LEDs are better than one, suggests LG Display in a U.S. patent (9,305,979) granted April 5 for an “organic light emitting diode display device and method of fabricating the same.” That deceptively simple title is for a patent that covers LG Display’s discovery that OLED displays look and work better if two blue LEDs are used in each pixel -- one for handling light-blue light, the other deep-blue -- but with the same fluorescent material used to make both diodes. This improves power efficiency because materials conventionally needed to produce deep-blue light were inefficient, the patent said. The method also reduces production costs because constructing each pixel from four different fluorescent sub-pixel materials (red, green, light-blue and deep-blue) is more difficult that using three materials -- red, green and single-blue -- to produce the four sub-pixels (red, green, light-blue and deep-blue), it said. Making one type of blue fluorescent material generate two quite different shades of blue is done by depositing a very thin extra metal layer over just half the area of the blue material, the patent said. This extra layer creates a “micro-cavity effect,” which bounces the blue light repeatedly to amplify it at a specific wavelength, it said. The wavelength depends on the thickness of the reflective layer (on the order of 100 angstroms) and its distance from the blue fluorescent material, it said. Essentially, this means half the blue pixel is tuned to a deeper blue, it said. The result is a display with four sub-pixels, instead of three, for better blue light balance, the patent said. The method also creates a display that's easier and less costly to produce, has better power consumption and lasts longer because of lower wear and tear, it said. LG Display representatives didn’t comment Tuesday on commercialization plans.