Enhanced incident photon-to-electron conversion efficiency of tungsten trioxide photoanodes based on 3D-photonic crystal design.

In this study, 3D-photonic crystal design was utilized to enhance incident photon-to-electron conversion efficiency (IPCE) of WO(3) photoanodes. Large-area and high-quality WO(3) photonic crystal photoanodes with inverse opal structure were prepared. The photonic stop-bands of these WO(3) photoanodes were tuned experimentally by variation of the pore size of inverse opal structures. It was found that when the red-edge of the photonic stop-band of WO(3) inverse opals overlapped with the WO(3) electronic absorption edge at E(g) = 2.6-2.8 eV, a maximum of 100% increase in photocurrent intensity was observed under visible light irradiation (λ > 400 nm) in comparison with a disordered porous WO(3) photoanode. When the red-edge of the stop-band was tuned well within the electronic absorption range of WO(3), noticeable but less amplitude of enhancement in the photocurrent intensity was observed. It was further shown that the spectral region with a selective IPCE enhancement of the WO(3) inverse opals exhibited a blue-shift in wavelength under off-normal incidence of light, in agreement with the calculated stop-band edge locations. The enhancement could be attributed to a longer photon-matter interaction length as a result of the slow-light effect at the photonic stop-band edge, thus leading to a remarkable improvement in the light-harvesting efficiency. The present method can provide a potential and promising approach to effectively utilize solar energy in visible-light-responsive photoanodes.