Computer simulations of charge transport in dye-sensitized nanocrystalline photovoltaic cells

Charge transport in dye-sensitized nanocrystalline TiO2 electrodes was studied by a theoretical model. For studies of recombination processes through trap states, a Shockley-Read model, which represents electron transfer through an effective trap level, was used as a recombination term in the model. The simulation results have demonstrated that thermal release of the electrons trapped in shallow tail states to the conduction band contributes to effective electron diffusion in the nanocrystalline electrodes. However, the electrons captured in the tail states at the lowest energy may recombine with oxidized ions in electrolytes. Short-range screening of externally applied biases in the nanocrystalline electrodes was taken into account as a boundary condition in the model. Calculations of current-voltage characteristics have indicated that relatively high open-circuit voltages can be attained under the boundary condition.