TiO 2 / 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‐TiO 2 / 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‐TiO 2 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 ω 1 , indicated that electron transportation at the porous‐TiO 2 / TNO interface was more favorable than that at the porous‐TiO 2 / 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.