TiO2 Composites for Efficient Poly(3-thiophene acetic acid) Sensitized Solar Cells

The effect of TiO2 mesoporous structures sensitized with poly (3-thiophene acetic acid) (PTAA) on the photovoltaic performance was investigated. In contrast to conventional Ru-complex dye-sensitized solar cells (DSCs), the cell efficiency(eta) of PTAA-sensitized solar cells exhibited strong dependence on the TiO2 pore structures. Incorporation of up to 40 wt % large TiO2 nanoparticles (L-TiO2) into small TiO2 nanoparticles (S-TiO2) increased eta, in spite of a reduction in dye loading due to a decrease in surface area. The highest eta of 2.36 +/- 0.04% was obtained for a TiO2 film comprised of S-TiO2 (60 wt %) and L-TiO2 (40 wt %). Electrochemical impedance measurements suggested that the 25% increase in eta for the DSC comprised of 40 wt % L-TiO2 resulted not from rapid diffusion of the redox electrolyte through the larger pores, but instead was due to the higher electron density in the conduction band of TiO2. It was inferred, therefore, that the highest eta obtained for the DSC comprised of 40 wt % L-TiO2 was due to the high degree of anchoring of COOH groups. This inference was further confirmed by obtaining an eta of 2.92 +/- 0.06%, the highest eta ever reported for a polymer-dye based DSC, using a low-molecular weight PTAA sensitizer. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3519305] All rights reserved.