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In this study, we demonstrate a photovoltachromic cell (PVCC) which is a solar cell and able to take solar energy to stimulate chromic behavior with the characteristic of tunable transmittance. The cell is composed of a patterned WO(3)/Pt electrochromic electrode and a dye-sensitized TiO(2) nanoparticle photoanode. Compared to reported photoelectrochromic cells (PECC) with nonpatterned WO(3) electrochromic electrodes, PVCC achieves a much faster bleaching time of only 60 s by blocking the light at short circuit. When PVCC is bleached under illumination at open circuit, an exceedingly short bleaching time of 4 s is achieved. Furthermore, PVCC has photovoltaic characteristics comparable to those of dye-sensitized solar cells (with Pt as the counter-electrode). In contrast to conventional photochromic devices, the transmittance of PVCC under a constant illumination can be adjusted by the resistance of a load in series with the cell. These characteristics are a result of the patterned WO(3)/Pt electrode, which provides effective charge transfer pathways to facilitate the charging/discharging of Li ions and electrons via the photovoltaic potential and the Pt-electrolyte catalytic route, respectively.

TiO(2) nanowire (NW)/nanoparticle (NP) composite films have been fabricated by hybridizing various ratios of hydrothermal anatase NWs and TiO(2) NPs for use in dye-sensitized solar cells (DSSCs). Scanning electron microscopy (SEM) images reveal that uniform NW/NP composite films were formed on fluorine-doped tin oxide (FTO) substrates by the dip-coating method. The NWs are randomly but neither vertically nor horizontally oriented within the composite film. The TiO(2) NP DSSC possesses superior performance to those of the NW/NP composite and the pure NW cells, and the efficiency of the NW/NP composite DSSC increases on increasing the NP/NW ratio in the composite anode. All types of DSSC possess the same dependence of performance on the anode thickness that the efficiency increases with the anode thickness to a maximum value, then it decreases when the anode is thickened further. Electrochemical impedance spectroscopy analyses reveal that the NP DSSCs possess larger effective electron diffusion coefficients (D(eff)) in the photoanodes and smaller diffusion resistances of I(3)(-) in electrolytes compared to those in the NW/NP and the NW DSSCs. D(eff) decreases when NWs are added into the photoanode. These results suggest that the vertical feature of the NWs within the anodes is crucial for achieving a high electron transport rate in the anode.

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The in-situ X-ray absorption spectroscopy of three tungsten oxide films was performed to study the electronic and atomic structures following repeated cycles of coloration and bleaching processes. The transparent tungsten oxide films become deep blue upon intercalation of Li + ions in the WO 6 octahedra when an external electrical bias was applied. These films reverted to transparent when a reverse external electrical bias was applied. W L 3 -edge X-ray absorption near-edge structure (XANES) measurements of the nanocrystalline and crystalline tungsten oxide films revealed that the intensity of the white-line feature decreases after coloration and recoverably increases after bleaching owing to the filling and unfilling of the W 5d-O 2p conduction band states. The second derivative of the W L 3 -edge XANES spectra indicated an increase in structural disordering following repeated cycles of coloration and bleaching. However, the extended X-ray absorption fine structure analysis showed that the nearestneighbor W-O bond distances in the samples overall remain unchanged by coloration and bleaching.The nanocrystalline tungsten oxide film exhibited more effective recovery ($97% after first cycle) of the electronic structures than the other two crystalline samples in terms of the filling and unfilling of the W 5d-O 2p conduction band states after repeated coloration and bleaching. These results show that the nanocrystalline tungsten oxide sample has superior electrochromic properties to the crystalline samples.