Final Report Summary - NFESEC (Nanophotonics for Efficient Solar-to-H2 Energy Conversion)
Photo-electrochemical water splitting is a very promising and environmentally friendly route for the conversion of solar energy into hydrogen. However, the solar-to-H2 conversion efficiency is still very low due to rapid bulk recombination of charge carriers. In this project we have developed a photonic nano-architecture to improve charge carrier generation and separation by manipulating and confining light absorption in a visible-light-active photoanode constructed from BiVO4 photonic crystal and plasmonic nanostructures.
The main reason for the dominant electron-hole recombination in the bulk is the short diffusion length of photoexcited minority charge carriers. To address this problem, nanostructuring has been extensively studied, reducing bulk recombination by shortening the travel length for charge carriers. However, nanostructuring can also increase surface recombination and lower the surface photovoltage. Nanophotonic structures, manipulating and confining light on the nanometer scale, provides new opportunities to improve the efficiency. Photonic crystals show great potential in manipulating light based on photonic band structure concepts, in which near-bandgap resonant scattering and slow photon effects can enhance the interaction of light with a semiconductor. Plasmonic metal nanostructures with surface plasmon resonances can act as antennas to localize optical energy and control the location of charge carrier generation. The interaction of localized electric fields surrounding the plasmonic metal particles with a neighbouring semiconductor provides a pathway for the selective formation of electron-hole pairs in the near-surface region of the semiconductor.
We have designed photonic nanostructured BiVO4 as highly-efficient photoanodes for solar water splitting. The superior performance obtained is attributed to a coupling of an inverse opal photonic crystal with localized surface plasmons from Au NPs that enhances the light absorption and charge carrier separation. The plasmonic effect of Au NPs is significantly amplified in the inverse opal structure due to a strong coupling with the photonic Bragg resonance. The reflection loss of light due to the photonic stop band in an inverse opal structure of visible-light-active semiconductor is avoided by simply adding an un-patterned semiconductor underlayer. Our nanophotonic photoanodes show AM 1.5 photocurrent densities of 3.1 ± 0.1 mA cm-2 at 1.23 V vs. RHE, which is among the highest for oxide-based photoanodes and over 4 times higher than the unstructured planar photoanode. The nano-architecture of such photoelectrodes opens new opportunities to increase overall solar-to-H2 conversion efficiencies toward industrial viability by manipulating and confining light in the photoelectrode.
The main reason for the dominant electron-hole recombination in the bulk is the short diffusion length of photoexcited minority charge carriers. To address this problem, nanostructuring has been extensively studied, reducing bulk recombination by shortening the travel length for charge carriers. However, nanostructuring can also increase surface recombination and lower the surface photovoltage. Nanophotonic structures, manipulating and confining light on the nanometer scale, provides new opportunities to improve the efficiency. Photonic crystals show great potential in manipulating light based on photonic band structure concepts, in which near-bandgap resonant scattering and slow photon effects can enhance the interaction of light with a semiconductor. Plasmonic metal nanostructures with surface plasmon resonances can act as antennas to localize optical energy and control the location of charge carrier generation. The interaction of localized electric fields surrounding the plasmonic metal particles with a neighbouring semiconductor provides a pathway for the selective formation of electron-hole pairs in the near-surface region of the semiconductor.
We have designed photonic nanostructured BiVO4 as highly-efficient photoanodes for solar water splitting. The superior performance obtained is attributed to a coupling of an inverse opal photonic crystal with localized surface plasmons from Au NPs that enhances the light absorption and charge carrier separation. The plasmonic effect of Au NPs is significantly amplified in the inverse opal structure due to a strong coupling with the photonic Bragg resonance. The reflection loss of light due to the photonic stop band in an inverse opal structure of visible-light-active semiconductor is avoided by simply adding an un-patterned semiconductor underlayer. Our nanophotonic photoanodes show AM 1.5 photocurrent densities of 3.1 ± 0.1 mA cm-2 at 1.23 V vs. RHE, which is among the highest for oxide-based photoanodes and over 4 times higher than the unstructured planar photoanode. The nano-architecture of such photoelectrodes opens new opportunities to increase overall solar-to-H2 conversion efficiencies toward industrial viability by manipulating and confining light in the photoelectrode.