Current-voltage characteristics were formulated on the basis of the clear dependence of open-circuit voltages and fill factors on short-circuit current densities found in dye-sensitized nanocrystalline solar cells of 2-4% efficiency. A survey of the highest efficiency cells has demonstrated applicability of this model to these cells as well, and made clear the necessary conditions for these efficiencies. An estimation of a theoretical maximum efficiency in dye-sensitized TiO2 solar cells of the I-/I-3(-) redox couple has revealed that 13% efficiency is attainable with improvement of short-circuit current density. Nonnegligible influences of drift current and trap states on energy conversion processes are suggested. (C) 2003 The Electrochemical Society.