Hitoshi Kusama

TiO2 Band Shift by Nitrogen-Containing Heterocycles in Dye-Sensitized Solar Cells: a Periodic Density Functional Theory Study

A density functional theory (DFT) method (periodic DMol3) with full geometry optimization was used to study the adsorption of nitrogen-containing heterocycles such as pyrazole, imidazole, 1,2,4-triazole, pyridine, pyrimidine, pyrazine, and 4-t-butylpyridine (TBP) on TiO2 anatase (101), (100), and (001) surfaces. All structures displayed a negative shift in the TiO2 Fermi level upon adsorption of N-containing heterocycles. Additionally, the heterocycles were examined as an additive in an I-/I3- redox electrolyte solution of dye-sensitized TiO2 solar cell. The DFT results indicated that the negative shift of TiO2 Fermi level was due to the adsorbate dipole moment component normal to the TiO2 surface plane, and corresponded to the enhanced open-circuit photovoltage (Voc) and the reduced short-circuit photocurrent density (Jsc) in a dye-sensitized solar cell.

Influence of benzimidazole additives in electrolytic solution on dye-sensitized solar cell performance

Abstract The influence of benzimidazole additives on the performance of a bis(tetrabutylammonium)- cis -bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) dye-sensitized TiO 2 solar cell with an I − /I 3 − redox electrolyte in acetonitrile was investigated by measuring the current–voltage characteristics of more than 20 different benzimidazole derivatives under AM 1.5 (100xa0mW/cm 2 ). The benzimidazole additives tested had varying effects on the cell performance. Adding benzimidazole drastically enhanced the open-circuit photovoltage ( V oc ) and the fill factor (ff), but reduced the short-circuit photocurrent density ( J sc ) of the solar cell. In order to determine the reasons for the additive effects on cell performance the physical and chemical properties of the benzimidazoles were computationally calculated. Consequently, the greater the calculated partial charge of the nitrogen atoms in position 3 of the benzimidazole groups, the larger the V oc , but the smaller the J sc values. The V oc values also increased as the molecular size of the benzimidazole derivatives decreased. Moreover, the greater the absolute difference between the calculated dipole moment of the benzimidazole and acetonitrile, the larger the J sc value. These results suggest that these properties of the benzimidazoles influenced the extent of interaction between the TiO 2 electrode and electrolyte solvent, which changed the dye-sensitized solar cell performance.

Theoretical study of quinolines–I2 intermolecular interaction and implications on dye‐sensitized solar cell performance

The monomer and intermolecular charge‐transfer complexes of 13 different quinoline derivatives with diiodine were studied using ab initio molecular orbital (MO) and density functional theory (DFT) methods. Calculations revealed that the σ* orbital of iodine interacts with the nitrogen lone pair in the quinoline ring. The open‐circuit photovoltage (Voc) values of an Ru(II) complex dye‐sensitized nanocrystalline TiO2 solar cell with an I−/I u20093− redox electrolyte in acetonitrile using quinoline additives were compared to the computational calculations on the intermolecular interaction between quinolines and I2. The optimized geometries, frequency analyses, Mulliken population analyses, natural bond orbital (NBO) analyses, and interaction energies indicate that the Voc value of the solar cell is higher when quinoline complexes more favorably interact with I2. Therefore, the interaction between the quinoline additives and iodine redox electrolyte is an important factor for controlling dye‐sensitized solar cell performance.