Performance simulation for dye-sensitized solar cells: Toward high efficiency and solid state

We have carried out performance simulations for the dye-sensitized solar cells which consist of a mesoporous TiO2 semiconductor film coated with photosensitizing dyes and a charge transport layer which is either a liquid electrolyte or a solid hole conductor. The calculations for the current-voltage characteristics and the energy conversion efficiency have been made, and the dependence of the efficiency on the material parameters has been discussed. In the case of liquid-state cells, the improvement in the sunlight absorption ability through the enhancement of molar extinction coefficient of the dye sensitizer or of roughness factor of the nanocrystalline TiO2 is essential for achieving very high efficiencies. The effects on the efficiency caused by other factors such as the resistance of transparent conducting oxide electrode, the cell area and the diffusion constants of redox ions are also investigated. In the case of solid-state cells, some specific factors such as the detachment of the hole transport layer from the TiO2 electrode and the decrease of the shunt resistance associated with internal leakages are suggested as possible causes of the significant suppression of the efficiency.