Freestanding CdS nanotube films as efficient photoanodes for photoelectrochemical cells

Recently, freestanding lms have attracted much attention because they are highly useful in the fabrication of various nanodevices. Freestanding lms can be used on any substrate without deterioration of their own unique properties. Layerby-layer (LBL) deposition has been used widely in the synthesis of freestanding lms, especially of polymer lms with specic physical and mechanical properties. As the demand for photoelectrical devices has increased, the focus of attention has moved recently to freestanding light harvesting lms. Although some conjugated polymers have been applied as light harvesting materials in photovoltaics, most of them are made as solution types or nanoparticles to coat on the substrates and hardly made as freestanding lms for light harvesting. Semiconductors are appropriate light absorbing materials for fabrication of freestanding lms. By using a narrow band gap semiconductor, visible light absorption can be enhanced. However, there has not been much research into semiconducting freestanding lms owing to the difficulty of growing semiconductors without substrates, thus most freestanding semiconductor lms consist of a freestanding organic/inorganic support with attached semiconductor quantum dots rather than of a composite freestanding lm. In the present study, we have developed a novel synthesis route for the fabrication of a large scale, highly uniform, freestanding CdS nanotube lm that uses an array of ZnO nanorods as a sacricial template. This route requires only simple