NREL Scientists Re-envision LED as “Solar Cell in Reverse”

Scientists at the National Renewable Energy Laboratory recently devised an innovative way to generate generate green-colored light that could prove to be a major advance in LED lighting technology.

LED lights, which unlike conventional bulbs and CFLs lose very little of their energy as heat, are expected to become the lighting technology of choice by the end of the next decade.

True white light is a combination of all the colors in the spectrum. At minimum, red, green and blue light are needed in combination to create white-appearing light for use in homes and offices.

Researchers have had success generating red and blue lights in LEDs, but have been unable to generate green. The green light in today’s LED bulbs is the result of aiming blue light at a phosphor that then emits green light. This workaround, while effective, represents a loss of efficiency.

NREL has to date been on the cutting edge of solar cell design. One of its researchers, Angelo Mascarenhas, had the insight that an LED is effectively a solar cell in reverse, since it converts electricity into light while a solar cell does the opposite.

NREL had already been examining the challenges involved in capturing green-spectrum sunlight. In fact, they had been working with the same material as the LED researchers: gallium indium nitride—a material that was causing problems in solar cells, too.

For the solar cells, NREL researchers developed a technique to layer lattices of atoms that resulted in a firmly bonded cell with almost no impurities. At Mascarenhas’s suggestion they endeavored to reverse the process to create a green-generating LED. Their very first effort was a success.

Now the NREL team wants to try to create a fourth color, which would make the white light appear even whiter.

Mascarenhas said he expected that in three years the lab will have succeeded in creating a mosaic-patterned blue and green device that could help produce LED lights with a color rendering index over 90.

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