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 DMol(3)) 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 (101) 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 (V-oc) and the reduction of the short-circuit photocurrent density (J(sc)) 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 dyesensitized solar cell performance. (c) 2007 Elsevier B.V. All rights reserved.