DFT investigation of the TiO2 band shift by nitrogen-containing heterocycle adsorption and implications on dye-sensitized solar cell performance

A density functional theory (DFT) method (periodic DMol3) with full geometry optimization was used to investigate the adsorption of nitrogen-containing heterocycles such as 4-t-butylpyridine (TBP) and imidazole on a TiO2 anatase (1 0 1) surface. Negative shifts of the TiO2 Fermi level by N-containing heterocycle adsorption were observed. Imidazole adsorption shifted the Fermi level of TiO2 more negatively than TBP. This shift corresponded to the enhancement of the open-circuit photovoltage (Voc) and the reduction of the short-circuit photocurrent density (Jsc) in a dye-sensitized TiO2 solar cell. We are the first to theoretically discover a TiO2 band shift upon N-containing heterocycles adsorption, and have successfully related this shift to the effect as an additive in an electrolyte solution on dye-sensitized solar cell performance.