Trap States Comparison of Mesoporous TiO2 Photoanodes with Different Particle Sizes

For the dye-sensitized solar cells (DSSCs), trap states exist in the TiO2 based photoanode and play an important role on the dynamic process of charge transport and recombination in the DSSCs. Generally, trap states mainly result from impurities, interface adsorption of ions, the breakdown of the lattice periodicity in the semiconductor, dangling bonds and/or the rearrangement of surface atoms. In this paper, we compare trap states of different nanoparticles based TiO2 photoanode films. The result of X-ray photoelectron spectroscopy (XPS) indicates that Ti3+ and the content of oxygen vacancies in the porous films decrease with the increase of particle sizes. Furthermore, to confirm the difference of trap states in these photoanodes, the measurements of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed. It is found that compared with the larger particle size, the TiO2 photoanode films based on the smaller nanoparticles possess more trap states. This research provides a useful description of microscopic mechanism for the effect of porous films with different sizes on cell photovoltaic performances.