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Left: the recently developed photoelectrode, a semiconductor layer sandwich (TiO2) between gold film (Au film) and gold nanoparticles (NP Au). The gold nanoparticles have been partially embedded on the surface of the titanium dioxide thin film to enhance the absorption of light. Right: The photoelectrode (Au-NP / TiO2 / Au-film) with 7 nm of light-inset traps making it non-transparent (top). An Au-NP / TiO2 structure without the Au film is presented for comparison (bottom). Credit: Misawa H. et al., Nature Nanotechnology, July 30, 2018
Scientists have developed a photoelectrode capable of collecting 85% of visible light in a thin 30 nanometer semiconductor layer between the gold layers, converting light energy 11 times more efficiently than methods preceding.
In order to achieve a sustainable society, there is a growing demand to develop revolutionary solar cells or artificial photosynthesis systems that utilize the visible light energy of the sun while using as few materials as possible.
The research team, led by Professor Hiroaki Misawa of the Institute for Research in Electronic Science at Hokkaido University, aims to develop a photoelectrode capable of capturing visible light over a wide spectral range using nanoparticles of gold loaded on a semiconductor. But the simple application of a layer of gold nanoparticles does not result in sufficient absorption of light because they only absorb light in a narrow spectral range.
In the study published in Nature Nanotechnology, the research team sandwiched a semiconductor, a 30-nanometer thin titanium dioxide film, between a 100-nanometer gold film and gold nanoparticles to enhance the Absorption of light. When the system is irradiated with light from gold nanoparticles, the gold film serves as a mirror, trapping light in a cavity between two layers of gold and helping the nanoparticles to absorb more light.
To their surprise, more than 85% of all visible light was harvested by the photoelectrode, which was much more efficient than the previous methods. Gold nanoparticles are known to present a phenomenon called localized plasmon resonance that absorbs a certain wavelength of light. "Our photoelectrode has successfully created a new condition in which plasmon and visible light trapped in the titanium oxide layer interact strongly, allowing light of a wide range of wavelengths. to be absorbed by the gold nanoparticles, "says Hiroaki Misawa.
When gold nanoparticles absorb light, the extra energy triggers an electronic excitation in the gold, which transfers the electrons to the semiconductor. "The efficiency of the conversion of light energy is 11 times higher than that without the function of light trapping," said Misawa. Increased efficiency also led to better water splitting: the electrons reduced the hydrogen ions to hydrogen, while the remaining electron holes oxidized the water to produce oxygen – a promising process to produce clean energy.
"By using very small amounts of material, this photoelectrode enables efficient conversion of sunlight into renewable energy, thus contributing to the achievement of a sustainable society," the researchers concluded.
Explore more:
How gold nanoparticles could improve the storage of solar energy
More information:
Xu Shi et al. Splitting of water improved under modal coupling conditions, Nature Nanotechnology (2018). DOI: 10.1038 / s41565-018-0208-x
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