Photoelectrochemical Analysis of the Dyed TiO₂/Electrolyte Interface in Long-Term Stability of Dye-Sensitized Solar Cells

Abstract

The interface structure induced by electrolyte cations was found to play a significant role in determining the performance and stability of dye-sensitized solar cells. The trap state density in the nanostructure TiO 2 electrodes was affected by the adsorbed 1,2-dimethyl-3-propylimidazolium cation (DMPI + ) or alkali cations, such as Li +, Na +, K +, and Cs +, on the dyed TiO 2 electrode and was found to increase with the order of decreasing cation radius DMPI + < Cs + < K + < Na + < Li + . The change in interface structure resulted from the accumulation of the adsorbed cations to increase trap states in the nanostructure TiO 2 electrodes during long-term accelerated aging tests. The size effect of electrolyte cations on the cell performance suggested that the reduced surface cations, when small cations penetrated into titania lattice, resulted in a negative shift of the TiO 2 conduction band edge and a weaker interaction of Li + with dyes to obtain the decline in photocurrent and efficiency. The overall efficiency of dye-sensitized solar cells with large DMPI + in the electrolyte retained over 110% of its initial value after 2100 h. Also, no obvious differences in the efficiency for dye-sensitized solar cells with electrolyte cations, such as Li +, Cs +, and DMPI +, were observed after 1270 h under one sun light soaking in our experiment. The results suggested that large DMPI + chemisorbed on TiO 2 surface could not intercalate into the TiO 2 lattice for the enhanced stability of dye-sensitized solar cells in practical application.