W(VI) is doped into TiO 2 via a solÀgel method, and the crystalline anatase structure is well preserved with the W content ranging from 0.1% to 5%. The conduction band (CB) of TiO 2 moves downward (i.e., positive shift) gradually with increasing the W content from 0.1% to 2% and then stays almost unchanged with increasing the W content from 2% to 5%. Dye-sensitized solar cells (DSSCs) based on the W-doped anatase TiO 2 show an advantage in repressing the charge recombination. The electron lifetime in the DSSC is significantly improved by the W-doping. As a result of the positive shift of the CB and repressed charge recombination, the short-circuit photocurrent (J sc ) of the DSSC is improved remarkably. The collective effect of the positive shift of the CB and the enhanced electron lifetime caused by the W-doping makes the open-circuit photovoltage (V oc ) remain almost unchanged below 0.5% W-doping and decrease above 0.5% W-doping. The highest power conversion efficiency (η = 9.1%) is obtained at 0.2% W-doping, which shows increases by 17% in J sc and by 20% in η, as compared with the undoped DSSC.

A series of oriented rutile TiO 2 nanorod-array films are in-situ grown on fluorine-doped tin oxide (FTO) coated glass substrates from a mixed acid solution containing titanium tetraisopropoxide (TTIP), hydrochloric acid (HCl), acetic acid (HOAc), and water (H 2 O) by means of hydrothermal reaction at 150 C. The effect of HOAc in the titania growth solution on the structure and micromorphology of TiO 2 nanorod array films, as well as the photoelectric conversion properties in dyesensitized solar cells (DSSCs) has been fully investigated. It is found that HOAc can facilitate the formation of uniform, dense, and vertically oriented TiO 2 nanorods and hence improves the dye adsorption, electron diffusion coefficient, and the photovoltaic performance of DSSCs, typically in short-circuit photocurrent and power conversion efficiency. A power conversion efficiency of 4.03% has been achieved on a DSSC based on a 2.3 mm-long nanorod array film obtained from a mixed acid solution with the TTIP:HCl:HOAc:H 2 O ratio of 0.8:4:8:8 by volume.

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