Deposition of Porous Photocatalytic TiO₂ Film for Dye-Sensitized Solar Cells by Low-Powered Atmospheric Plasma Spray Equipment

Abstract

Oxide films have been used for corrosion resistance, abrasion resistance and thermal barrier coatings of bridges, semiconductor manufacturing equipment, engines and so on. Besides they start to be utilized as functional film such as photovoltaic device, solid electrolyte and gas sensor. However, because of its excellent chemical stability, alumina film has been practically used. Recently, because of its excellent photocatalytic properties, TiO₂ film was successfully applied to antimicrobial coating and photovoltaic device for dye-sensitized solar cell (DSSC).

Authors have been developing electric power generating systems using renewable energy devices such as small-scale hydro and DSSC (Ando et al., Vacuum 80:1278–1283, 2006). For lifetime elongation of the small-scale hydro and low-cost DSSC manufacturing in this area, development of alumina film and TiO₂ film deposition process using atmospheric plasma spray (APS) is thought to be effective. However, since solid materials such as powder and wires are used as feedstock in the case of thermal spray, the flame should have enough thermal energy to melt the feedstock during flight (Ando et al., Front Appl Plasma Technol 7:75–80, 2014).

Therefore, high-power (over 30 kW class) APS equipment has been thought to be demanded so far. In our previous study, in order to achieve a low-cost APS system, we developed a 1 kW class APS equipment; it is very difficult for small company to introduce APS equipment because of its high initial cost.

The purpose of this study is to create TiO₂ film which is suitable for DSSC. In this study, to develop a deposition process for oxide film with practical strength, 1 kW class APS equipment was carried out. To increase the power conversion efficiency of DSSC, a porous titanium dioxide with a wide band gap is typically used; the large surface area of the TiO₂ ensures the absorption of sufficiently large number of dye molecules for efficient harvesting of radiant energy. Surface morphologies of the TiO₂/NaCl film was evaluated using optical micrographs.

Consequently, it was confirmed that the photocatalytic porous TiO₂ film could be deposited and its conversion efficiency was high in comparison with the film deposited with our conventional dense TiO₂ film without addition and removal of NaCl particles. Additionally, it was confirmed that conversion efficiency of the DSSC using the porous TiO₂ film was high in comparison with our previous study using dense TiO₂ film.