TiO2/TNO homojunction introduced in a dye-sensitized solar cell with a novel TNO transparent conductive oxide film

In this study, niobium-doped titanium oxide (TNO) was employed for a novel transparent conductive oxide (TCO) film to construct a porous-TiO2/TNO homojunction in a dye-sensitized solar cell (DSSC). However, considering a balance between the electrical and optical properties of the TCO film, the sheet resistance in TNO was tuned to be higher than that in a typical fluorine-doped tin oxide (FTO). The photovoltaic performance of the cell with the TNO film (TNO cell) was optimized to be almost comparable to that with a conventional FTO film (FTO cell) by coating the surface of the porous-TiO2 layer with a thin alumina or magnesia film to block a back reaction within the cell. An electrochemical impedance measurement was conducted to determine the detailed photovoltaic performance from the viewpoint of electron transportation in the cell. R-1, the real part of (1), indicated that electron transportation at the porous-TiO2/TNO interface was more favorable than that at the porous-TiO2/FTO interface, which was supported by AC phase change in the cell at a high-frequency range. We found that the homojunction newly introduced in the cell is one of the key concepts for developing a DSSC into a high-performance photovoltaic device.