In a study published in Nature Nanotechnology, scientists in Japan have developed a ‘golden sandwich’ photoelectrode that can harvest 85 percent of visible light. In pursuit of a sustainable society, there is an ever-increasing demand to develop solar cells or artificial photosynthesis systems that use visible light energy from the sun.
To meet this demand, researchers led by Professor Hiroaki Misawa of the Research Institute for Electronic Science at Hokkaido University, Japan, sought to create a photoelectrode that can harvest visible light across a wide range of wavelengths.
One possible strategy to achieve this is to load gold nanoparticles on a semiconductor, but this only led to light absorption in a narrow spectral range.
The research team thus sandwiched a 30-nanometer titanium dioxide thin-film semiconductor between a 100-nanometer gold film and gold nanoparticles to enhance light absorption. When the system was irradiated by light from the gold nanoparticle side, the gold film functioned as a mirror, trapping light in a cavity between the two gold layers, thereby allowing the nanoparticles to 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. This is due to a property of gold nanoparticles known as localized plasmon resonance.
When gold nanoparticles absorb light, the additional energy triggers electron excitation in the gold film, which then transfers electrons to the semiconductor. “Our photoelectrode successfully created a new condition in which plasmons and visible light trapped in the titanium oxide layer strongly interact, allowing light with a broad range of wavelengths to be absorbed by the gold nanoparticles,” said Misawa.
“The light energy conversion efficiency is 11 times higher than those without light-trapping functions.” The boosted efficiency of light capture also enhanced the water splitting capability of the photoelectrode. 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.