The photovoltage-determining mechanism in dye-sensitized solar cells

We attempt to distinguish between two competing models of the photovoltage- determining mechanism in dye-sensitized solar cells. One model does not con sider the equilibrium potential difference at the TiO2/substrate interface to be a significant factor in determining the photovoltage; the other claim s that this potential difference sets the upper limit to the achievable pho tovoltage. We deposit dye-sensitized TiO2 films on four different substrate s that have vacuum work functions spanning a 1.4 eV range and measure the p hotovoltage obtained from these films in three different redox electrolyte solutions. No significant differences in photovoltage are obtained on the d ifferent substrates, not even on Pt where the interfacial potential should oppose electron transfer. We suggest that the interfacial potential barrier may be smaller than expected and/or too thin to have a significant influen ce on cell performance. We conclude that the photovoltage is determined by photoinduced chemical potential gradients, not by equilibrium electric fiel ds.