A low cost mesoporous carbon/SnO2/TiO2 nanocomposite counter electrode for dye-sensitized solar cells

Highly porous carbon/SnO2/TiO2 nanocomposite films that can be used as counter electrodes in dye-sensitized solar cells (DSSCs) are fabricated by coating a homogeneous and viscous carbon paste on F-doped tin oxide conducting glass. The carbon paste is prepared by ball-milling a mixture of carbon, SnO2 powder and TiO2 hydrosol in an organic solution. The composite films are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscope, Brunauer-Emmett-Teller and Form Talysruf Profiler. The results indicate that the photovoltaic performances of the composite DSSCs are influenced by the content of SnO2. When the content is increased to 30%, SnO2 not only acts as "framework" to strengthen the mechanical stability of the composite film but also increases the specific surface area and root-mean-square roughness, which improve fill factor and short-circuit current, finally increasing power conversion efficiency from 5.12% to 6.15%. Cyclic voltammetry analysis and electronic impedance spectroscopy of the optimum composite film display higher catalytic activity for I3-/I- redox reactions and much lower charge-transfer resistance compared with Pt, respectively. Dye-sensitized solar cells based on this nanocomposite counter electrode achieve efficiency as high as 6.15% which is comparable to that of the cells using sputtering Pt as counter electrode at similar conditions.