Standing Wave Enhancement of Red Absorbance and Photocurrent in Dye-Sensitized Titanium Dioxide Photoelectrodes Coupled to Photonic Crystals

The light harvesting efficiency of dye-sensitized photoelectrodes was enhanced by coupling a TiO₂ photonic crystal layer to a conventional film of TiO₂ nanoparticles. In addition to acting as a dielectric mirror, the inverse opal photonic crystal caused a significant change in dye absorbance which depended on the position of the stop band. Absorbance was suppressed at wavelengths shorter than the stop band maximum and was enhanced at longer wavelengths. This effect arises from the slow group velocity of light in the vicinity of the stop band, and the consequent localization of light intensity in the voids (to the blue) or in the dye-sensitized TiO₂ (to the red) portions of the photonic crystal. By coupling a photonic crystal to a film of TiO₂ nanoparticles, the short circuit photocurrent efficiency across the visible spectrum (400-750 nm) could be increased by about 26%, relative to an ordinary dye-sensitized nanocrystalline TiO₂ photoelectrode.