Researchers from RIES, Japan (Research Institute for Electronic Science at Hokkaido University) have developed a photoelectrode that is able to pick about 85% of visible light and it’s efficiency compared to previous methods is 11 times better. Scientists’ intention was to develop a photoelectrode, which could harvest visible light spectrum across a wide spectral range by applying very small particles (nanoparticles) of gold loaded on top of the semiconductor. Unfortunately, this layer of nanoparticles did not lead to a reasonable amount of light absorption, because they were only absorbing it’s narrow spectral range.
During its illumination process from the top side (the gold nanoparticle side), the gold film worked as a mirror, which trapped the light in a Titanium Dioxide layer between two other layers. This helped aforementioned nanoparticles in better light absorbtion – surprisingly, more than 85 percent of the visible light was picked by the photoelectrode. This was possible due to phenomenon, which gold nanoparticles exhibit, so-called localized plasmon resonance, which allows them to absorb a certain wavelength of light.
Researchers say, that this photoelectrode has successfully created a new condition, in which plasmon and visible light trapped in the Titanium Dioxide layer strongly interact. That allows to absorb a broad range of light wavelengths by gold nanoparticles.
When gold nanoparticles absorb the light, the additional energy triggers electron excitation (transfer of a bound electron to a more energetic state) in the gold, which transfers electrons to the semiconductor.
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. This new photoelectrode doesn’t require much amounts of certain materials to make, thus producing it could contribute to further realization of a sustainable society – the researchers concluded.