See Through Solar Cells

Tuesday, July 30, 2013 @ 02:07 PM gHale

Nearly doubling the efficiency of a breakthrough photovoltaic cell they created last year, a new two-layer, see-through solar film is now in development that could end up on windows, sunroofs, smartphone displays and other surfaces to harvest energy from the sun.

The new device consists of two thin polymer solar cells that collect sunlight and convert it to power. It’s more efficient than previous devices because its two cells absorb more light than single-layer solar devices, because it uses light from a wider portion of the solar spectrum, and because it incorporates a layer of novel materials between the two cells to reduce energy loss, said researchers from UCLA.

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While a tandem-structure transparent organic photovoltaic (TOPV) device developed at UCLA in 2012 converts about 4 percent of the energy it receives from the sun into electric power (its “conversion rate”), the new tandem device, which uses a combination of transparent and semi-transparent cells, achieves a conversion rate of 7.3 percent.

The new cells could serve as a power-generating layer on windows and smartphone displays without compromising users’ ability to see through the surface, said Yang Yang, the Carol and Lawrence E. Tannas, Jr., professor of engineering at the UCLA Henry Samueli School of Engineering and Applied Science. The cells work so they appear light gray, green or brown, and so can blend with the color and design features of buildings and surfaces.

“Using two solar cells with the new interfacial materials in between produces close to two times the energy we originally observed,” said Yang, who is also director of the Nano Renewable Energy Center at the California NanoSystems Institute at UCLA. “We anticipate this device will offer new directions for solar cells, including the creation of solar windows on homes and office buildings.”

The tandem polymer solar cells consist of a photoactive plastic. A single-cell device absorbs only about 40 percent of the infrared light that passes through. The tandem device, which includes a cell composed of a new infrared-sensitive polymer developed by UCLA researchers, absorbs up to 80 percent of infrared light plus a small amount of visible light.

Using transparent and semi-transparent cells together increases the device’s efficiency, and the materials ended up processed at low temperatures, making them relatively easy to manufacture, said Chun-Chao Chen, a graduate student in the UCLA materials science and engineering department who is the primary author of a paper on the subject.

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