Impact of High Charge-Collection Efficiencies and Dark Energy-Loss Processes on Transport, Recombination, and Photovoltaic Properties of Dye-Sensitized Solar Cells

We report on the relationships between the energy-loss processes in the dark, charge-collection efficiency and photocurrent density–voltage characteristics of dye-sensitized solar cells (DSSCs). The charge-collection efficiencies (η cc ) of the DSSCs with different electrolytes were close to 100%. Despite the high η cc values, the DSSCs showed significant loss of photocurrent density and power density resulting from dark processes associated with the exchange current density J 0 at the TiO 2 /electrolyte interface, series resistance of the cells, and diode ideality factor. Even in DSSCs with high η cc values, making recombination slower and transport faster in the dark would reduce these losses. The opposing effects of J 0 and light absorption properties of DSSCs were found to determine the optimum film thickness ( L opt ) for the highest output power density. These effects also explain why L opt is generally much less than the electron diffusion length.