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

¹Electronics and Materials Science Course, Department of Engineering, Graduate School of Integrated Science and Technology, Shizuoka University, 3-5-1 Johoku, Hamamatsu, Shizuoka 432-8561, Japan
²Institute of General and Analytical Chemistry, Budapest University of Technology
and Economics, Szt. Gellért tér 4, Budapest 1521, Hungary
³Kanagawa Academy of Science and Technology (KAST), 3-2-1 Sakado, Kawasaki, Kanagawa 213-0012, Japan
⁴Department of Chemistry, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan

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. R₁, the real part of ω₁, 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.

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