AsianScientist (Jan. 27, 2017) – Using a nanostructured thermal emitter, researchers at Kyoto University have doubled the peak conversion rate of solar cells to 40 percent. Their work has been published in Science Advances.
Harnessing the energy of the Sun is a promising way to meet the world’s growing demand for energy. However, the efficiency of energy conversion remains a key limiting factor.
“Current solar cells are not good at converting visible light to electrical power. The best efficiency is only around 20 percent,” explained study first author Takashi Asano, an associate professor at Kyoto University who uses optical technologies to improve energy production.
Higher temperatures emit light at shorter wavelengths, which is why the flame of a gas burner will shift from red to blue as the heat increases. Higher heat offers more energy for conversion, making short wavelengths an important target in the design of solar cells.
“The problem,” continued Asano, “is that heat dissipates light of all wavelengths, but a solar cell will only work in a narrow range.”
“To solve this, we built a new nano-sized semiconductor that narrows the wavelength bandwidth to concentrate the energy.”
Previously, Asano and his colleagues at the Susumu Noda lab had taken a different approach.
“Our first device worked at high wavelengths, but to narrow output for visible light required a new strategy, which is why we shifted to intrinsic silicon in this current collaboration with Osaka Gas,” said Asano.
To emit visible wavelengths, a temperature of 1,000°C was needed. Conveniently, silicon has a melting temperature of over 1,400°C. The scientists etched silicon plates to have a large number of identical and equidistantly-spaced rods, the height, radii, and spacing of which was optimized for the target bandwidth.
Using this material, the team has shown in that their nanoscale semiconductor raises the energy conversion rate of solar cells to at least 40 percent.
“Our technology has two important benefits,” adds lab head Noda. The first is energy efficiency: we can convert heat into electricity much more efficiently than before. Secondly is design. We can now create much smaller and more robust transducers, which will be beneficial in a wide range of applications.”
The article can be found at: Asano et al. (2016) Near-infrared–to–visible Highly Selective Thermal Emitters Based on an Intrinsic Semiconductor.
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Source: Kyoto University.
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