New approach to low-cost dye-sensitized solar cells with back contact electrodes

Much attention has been paid to the development of dye-sensitized solar cells (DSCs) owing to a possibility of low production cost. One of the main factors that has hampered the practical application of DSCs is the use of a transparent conducting oxide (TCO) substrate of very high cost. Here we introduce a newly structured DSC back contact dye-sensitized solar cell (BCDSC) in which the TCO is omitted and a porous Ti electrode for electron collection, called a back contact electrode (BCE), is placed on the side opposite to the side of light irradiation. We succeeded in fabricating on the TiO2 film a BCE with large enough pore size for both efficient dye adsorption onto the film and smooth I(-)/I(3)(-) redox couple transportation through the film. Electrochemical impedance spectroscopy study showed that increase in the BCE thickness causes increase in the I(-)/I(3)(-) redox couple transport resistance at the same time as reduction of BCE resistance. Under standard air mass (AM) 1.5 irradiation (100 mW cm(-2)), a BCDSC with N719 dye yielded an overall conversion efficiency of 8.4%. An intensity modulated photovoltage spectroscopy (IMVS) study indicated that the lifetime of electrons in the TiO(2) film of the BCDSC is long enough for them to reach the BCE. The BCDSC therefore has the potential for high photovoltaic performance even though the TiO(2) film contains many interfaces between TiO(2) Particles such as the grain boundary in the polycrystalline silicon. The high-efficiency BCDSC achieved in the present study brings a low-cost DSC one step closer to practical use.