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Materials scientists make solar energy chip 100 times more efficient

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Posted March 21, 2013
Part of a 2-inch-diameter gallium-arsenide wafer used as a base for photon-enhanced thermionic emission chips. Credit: Brad Plummer / SLAC

Part of a 2-inch-diameter gallium-arsenide wafer used as a base for photon-enhanced thermionic emission chips. Credit: Brad Plummer / SLAC

(Phys.org) —Scientists working at the Stanford Institute for Materials and Energy Sciences (SIMES) have improved an innovative solar-energy device to be about 100 times more efficient than its previous design in converting the sun’s light and heat into electricity.

“This is a major step toward making practical devices based on our technique for harnessing both the light and heat energy provided by the sun,” said Nicholas Melosh, associate professor of materials science and engineering at Stanford and a researcher with SIMES, a joint SLAC/Stanford institute. The new device is based on the photon-enhanced thermionic emission (PETE) process first demonstrated in 2010 by a group led by Melosh and SIMES colleague Zhi-Xun Shen, who is SLAC’s advisor for science and technology. In a report last week in Nature Communications, the group described how they improved the device’s efficiency from a few hundredths of a percent to nearly 2 percent, and said they expect to achieve at least another 10-fold gain in the future.

Concentrated sunlight (red arrows at the top) heats up the device's semiconductor cathode (beige and grey upper plate) to more than 400 degrees Centigrade. Photoexcited hot electrons (blue dots) stream out of the cathode's nanotextured underside down to the anode (white/gray surface), where they are collected as direct electrical current. Additional solar and device heat is collected below the anode (arrow shows the cool-to-hot, blue-to-red flow) to run electricity-generating steam turbines or Stirling engines. Credit: Nick Melosh

Concentrated sunlight (red arrows at the top) heats up the device’s semiconductor cathode (beige and grey upper plate) to more than 400 degrees Centigrade. Photoexcited hot electrons (blue dots) stream out of the cathode’s nanotextured underside down to the anode (white/gray surface), where they are collected as direct electrical current. Additional solar and device heat is collected below the anode (arrow shows the cool-to-hot, blue-to-red flow) to run electricity-generating steam turbines or Stirling engines. Credit: Nick Melosh

Conventional photovoltaic cells use a portion of the sun’s spectrum of wavelengths to generate electricity. But PETE uses a special semiconductor chip to make electricity by using the entire spectrum of sunlight, including wavelengths that generate heat. In fact, the efficiency of thermionic emission improves dramatically at high temperatures, so adding PETE to utility-scale concentrating solar power plants, such as multi-megawatt power tower and parabolic trough projects in California’s Mojave Desert, may increase their electrical output by 50 percent. Those systems use mirrors to focus sunlight into superbright, blazingly hot regions that boil water into steam, which then spins an electrical generator.

Read more at: Phys.org

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