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Ionic Liquid Induced Band Shift of Titanium Dioxide
Author(s) -
Weber Henry,
Kirchner Barbara
Publication year - 2016
Publication title -
chemsuschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.412
H-Index - 157
eISSN - 1864-564X
pISSN - 1864-5631
DOI - 10.1002/cssc.201600844
Subject(s) - ionic liquid , electrolyte , chemical physics , dipole , titanium dioxide , dye sensitized solar cell , ion , adsorption , ionic bonding , semiconductor , chemistry , materials science , optoelectronics , organic chemistry , catalysis , electrode , metallurgy
Ionic liquids (ILs) have become an established option for the use as electrolytes in dye‐sensitized solar cells. In the present study, the adsorption of a multitude of different ILs on a TiO 2 surface is studied systematically, focusing on the energetic modifications of the semiconductor. The cation was found to generally cause an energetic downward shift of the TiO 2 band levels by accepting electron density from the surface, and the anions were observed to function in the opposite direction, raising the energy levels by donating electron density. Both effects counterbalance each other, leaving the desired outcome dependent on the choice of the specific IL, i.e., the choice of the cation/anion combination. The correlation of the band levels with the properties of the IL was successfully achieved. The dipole moment of the adsorbed ionic liquid species showed little to no correlation with the semiconductor energetics, but the charge transfer calculated by radical Voronoi tessellation revealed a high correlation. The current findings contribute to a deeper understanding of the role of the electrolyte in dye‐sensitized solar cells, and ILs in general, and help with choosing and tuning of the electrolyte solutions in existing applications.