The present technology relates to a method for evaluation of an oxide semiconductor electrode, an apparatus for evaluation of an oxide semiconductor electrode, and an apparatus for production of an oxide semiconductor electrode. More particularly, the present technology relates to a method for evaluation of an oxide semiconductor electrode, an apparatus for evaluation of an oxide semiconductor electrode, and an apparatus for production of an oxide semiconductor electrode, the oxide semiconductor electrode being intended for use in a dye-sensitized solar cell.
Dye-sensitized solar cells are now under intensive research and development owing to their characteristic property that they employ an electrolytic solution, they are produced from cheap raw materials at a low production cost, and they utilize a dye which serves for decoration. An ordinary dye-sensitized solar cell is composed of a substrate with a conductive film formed thereon, an oxide semiconductor electrode formed on the substrate from an oxide semiconductor film (such as TiO2 film) and a dye in combination, an electron transporting material such as iodine, and a counter electrode.
The dye-sensitized solar cell contains a dye (derived from ruthenium complex, for example) which effectively absorbs visible light. Upon light absorption, the dye in excited state injects electrons into the conduction band of TiO2. The electrons injected into TiO2 reach the cathode through the anode and the external circuit. On the other hand, the dye which has donated electrons to TiO2 and is in an oxidized state receives electrons from I− in the electrolytic solution and then returns to a neutral molecule. In this step, I− changes into I3−. The I3− receives electrons coming from the counter electrode through the external circuit and then returns to I−. The foregoing cycles are repeated for photoelectric conversion.
The oxide semiconductor electrode is usually a thin film of TiO2 which is formed on the substrate having a conductive film formed thereon. To form the thin film of TiO2, the substrate is coated with a paste of TiO2 particles of nano size, followed by baking at about 450° C. The resulting TiO2 film abounds with pores of nano size, and the interstices of pores adsorb the dye of ruthenium complex. The adsorption of the dye is accomplished by immersion of the TiO2 film in a dye solution.
The dye adsorbed to the oxide semiconductor electrode affects the characteristic properties of the dye-sensitized solar cell differently depending on its amount. The amount of the dye adsorbed to the oxide semiconductor electrode is determined by desorption of the dye in an alkaline solution, followed by colorimetry, as disclosed in Japanese Patent Laid-open No. 2004-79610 (hereinafter referred to as Patent Document 1).