Science: Simple, Inexpensive Solar Energy from Light-Absorbing Dyes

Glass panels collect different colors of sunlight and have solar cells attached to their edges. Stacking the plates improves how much power is generated.

Photo by and © Donna Coveney, MIT

MIT engineers say they have developed a more efficient way to capture energy from the sun, increasing solar power up to 10 times more than conventional solar panels. The simple, inexpensive technology described in the 10 July issue of Science could make solar power more viable around the world.

Typically, solar energy is obtained by large mirrors that reposition themselves as the sun moves and focus the solar energy onto solar cells, which transform sunlight into electricity. But the set-up of these so-called solar concentrators takes up a lot of space as the mirrors must have ample room between so that some cells don't cast shadows on others. And the mirrors generate a lot of heat and need to be cooled.

Researchers have tried using colored dyes—as opposed to mirrors—to absorb light and then transfer the energy to solar cells. The dyes were attached to plastic sheets attached to solar cells, a device called luminescent solar concentrator. But a lot of energy was lost in the transfer.

Researchers Marc Baldo and Shalom Goffri

Photo by and © Donna Coveney, MIT

Graduate student Michael Currie and his collaborators found a way to increase the amount of energy transferred from the panel to the solar cell, a system they call "organic solar concentrators." They coated glass panels with a thin layer of light-absorbing organic dyes. Each panel had a different type of dye on it which absorbed a different wavelength of sunlight.

The panels were positioned on top of each other. As sunlight travels through the glass layers, short wavelength light is captured first while longer wavelengths travel through the first panel and then are collected by later panels coated with dyes that absorb longer wavelengths of light. Solar cells attached to the edges of the panels capture the solar energy.

The researchers tinkered with the dyes to boost how much light was absorbed, what types of wavelengths could be absorbed and how thin the dye coating could be. They also studied how stable over time the dyes were when exposed to light. Their preliminary measurements show that the efficiency of the dye decreased by 8% "after the equivalent of three months outside," the authors wrote in their Science report. When packaged and protected by ultraviolet filters, the authors expect that dyes will last even longer.

In essence, the system is cost-effective because it increases the efficiency of less efficient—yet less expensive—solar cells by increasing how much light the cells take in.

Luminescent solar concentrators are simple to produce, and the researchers predict that they could be put into practice within three years, according to an MIT news release. Simply adding the inexpensive system to existing solar panels could increase efficiency by 50%.

Brandon Bryn and Molly McElroy

10 July 2008