Dye-sensitized photoelectrochemical and solid-state solar cells: charge separation, transport and recombination mechanisms

Experiments on dye-sensitized (DS) photoelectrochemical cells made from SnO2, ZnO and comparison with similar cells based on TiO2 gives much insight into the nature of charge separation, transport and recombinations. It is shown that the trap mediated recombinations are sensitive to the effective electron mass and therefore explains difference between the cells made from TiO2 and SnO2 or ZnO. Considering the trap mediated electron leakage from nanocrystallites, a theoretical model is constructed to explain quantitatively the effect of trapping on static and transient behavior of the cells. The model clearly demonstrate that trapping seriously affects the performance of the cell, when the electron leakage from traps is significant. The predictions of the model are compared with experimental data on transient measurements. The paper will also comment on the problem of recombinations in DS solid-state cells.