Sep
13
New Solar Tech Harvests 85 Percent of Light
September 13, 2018 | Leave a Comment
Hokkaido University scientists have developed a photoelectrode that can harvest 85% of visible light. It is built in a 30 nanometers-thin semiconductor layer sandwiched between gold layers, converting light energy 11 times more efficiently than previous methods.
The research team, led by Professor Hiroaki Misawa of the Research Institute for Electronic Science at Hokkaido University, has been aiming to develop a photoelectrode that can harvest visible light across a wide spectral range by using gold nanoparticles loaded on a semiconductor. But merely applying a layer of gold nanoparticles did not lead to a sufficient amount of light absorption, because they took in light with only a narrow spectral range.
Left: The newly developed photoelectrode, a sandwich of semiconductor layer (TiO2) between gold film (Au film) and gold nanoparticles (Au NPs). The gold nanoparticles were partially inlaid onto the surface of the titanium dioxide thin-film to enhance light absorption. Right: The photoelectrode (Au-NP/TiO2/Au-film) with 7nm of inlaid depth traps light making it nontransparent (top). An Au-NP/TiO2 structure without the Au film are shown for comparison (bottom). Image Credit: Hiroaki Misawa of the Research Institute for Electronic Science at Hokkaido University. Click image for the largest view.
In the study published in Nature Nanotechnology, the research team sandwiched a semiconductor, a 30-nanometer titanium dioxide thin-film, between a 100-nanometer gold film and gold nanoparticles to enhance light absorption. When the system is irradiated by light from the gold nanoparticle side, the gold film worked as a mirror, trapping the light in a cavity between two gold layers and helping the nanoparticles absorb more light.
To their surprise, more than 85 percent of all visible light was harvested by the photoelectrode, which was far more efficient than previous methods. Gold nanoparticles are known to exhibit a phenomenon called localized plasmon resonance which absorbs a certain wavelength of light. “Our photoelectrode successfully created a new condition in which plasmon and visible light trapped in the titanium oxide layer strongly interact, allowing light with a broad range of wavelengths to be absorbed by gold nanoparticles,” says Hiroaki Misawa.
When gold nanoparticles absorb light, the additional energy triggers electron excitation in the gold, which transfers electrons to the semiconductor. “The light energy conversion efficiency is 11 times higher than those without light-trapping functions,” Misawa explained. The boosted efficiency also led to an enhanced water splitting: the electrons reduced hydrogen ions to hydrogen, while the remaining electron holes oxidized water to produce oxygen – a promising process to yield clean energy.
“Using very small amounts of material, this photoelectrode enables an efficient conversion of sunlight into renewable energy, further contributing to the realization of a sustainable society,” the researchers concluded.
This march to high efficiency solar cells is not going to stop. Yet this research looks like quite a jump forward, except for the gold, a rare element. Gold isn’t as high priced as platinum, but surely isn’t cheap. Your humble writer hopes the team seeks a substitute that isn’t over a thousand dollars an once. They might find a substitute that is way less costly and maybe better.
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