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.