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This paper concerns the microstructure of the anodic titanium oxide ͑ATO, TiO 2 ͒ nanotube ͑NT͒ and its use for the dye-sensitized solar cell ͑DSSC͒ device. The ATO length was controlled by various electrolytes and anodic time at various constant applied voltages. The lengths of the NTs at 0.3-0.5 and 0.9-22 m were controlled by 0.5 vol % HF and 0.58 wt % KF aqueous solutions for varied periods of anodization ͑1-24 h͒. The 0.5 wt % NH 4 F electrolyte in ethylene glycol can produce 4-41 m for varied periods of anodization ͑0.5-8 h͒. ATO made of 0.3 ͑0.5 vol % HF͒, 12 ͑0.5 wt % KF͒, and 18 m ͑0.5 wt % NH 4 F͒ was used for the DSSC anode; the best cell performance attained 0.13, 3.76, and 6.18%. The DSSC made of 18 m ATO has a short-circuit current density ͑J sc ͒ of 13.45 mA/cm 2 , a fill factor of 0.64, an open voltage ͑V oc ͒ of 0.72 V, and a photocurrent efficiency of 6.18% under an air mass 1.5 illumination test.

The effect of ethanol on the photoelectrochemical fabrication of macroporous n-type Si͑100͒ ͑pore diameter Ͼ 50 nm͒ in 2.0 M hydrofluoric acid was investigated. A cross-sectional scanning electron microscope examination revealed the formation of rough bigger pores ͑diameter Ϸ 7-8 m͒ in the absence of ethanol but smooth smaller ones ͑diameter Ϸ 3-4 m͒ in the presence of ethanol when the silicon was etched at 0.250 V ͑vs saturated calomel electrode͒ under 50 W illumination for 3 h. Characteristic electrochemical properties, such as limiting current density ͑i limit ͒, half-wave current density ͑i l/2 ͒, transition potential ͑E trans ͒, and half-wave potential ͑E p/2 ͒ were derived from dc polarization. Electrochemical impedance spectroscopy conducted at E trans and E p/2 was helpful to illustrate the kinetics of the photoelectrochemical reaction. An additional inductive loop in the Nyquist plot occasioned at low frequencies in the presence of ethanol was attributed to the relaxation of the adsorption of ethanol in the pores. Addition of ethanol in the etching solution led to a decrease of contact angle between the solution and the silicon. Wetting behavior of ethanol plays an important role in the formation of smooth and small macropores.

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