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 consider the equilibrium potential difference at the TiO2/substrate interface to be a significant factor in determining the photovoltage; the other claims that this potential difference sets the upper limit to the achievable photovoltage. We deposit dye-sensitized TiO2 films on four different substrates that have vacuum work functions spanning a 1.4 eV range and measure the photovoltage obtained from these films in three different redox electrolyte solutions. No significant differences in photovoltage are obtained on the different 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 influence on cell performance. We conclude that the photovoltage is determined by photoinduced chemical potential gradients, not by equilibrium electric fields.