J. Heyrovsky Institute of Physical Chemistry of the ASCR, v. v. i.
Dolejškova 2155/3, 182 23 Prague 8, Czech Republic
In the framework of ORION project JHIPC, LCPO-CNRS and SOLVIONIC explored a potential use of ionic liquids as a template in the synthesis of TiO2 films.
The work showed an important pathway to better utilizing the space within the nano-TiO2 network. If confirmed, this might increase the efficiency of the Dye Sensitized Solar Cell.
We also conducted systematic research on the precursors used for dip coating in the preparation of TiO2 films and of the parameters utilized. A variety of solutions with organic templates supplied from our partners were modified by using aqueous or non-aqueous solvents, adjusting the pH, or addition of H3PO4.
Although all data have not been analyzed yet, there is an apparent and very consistent difference in the film quality after addition of very small amounts of phosphoric acid to the solutions. A significant improvement after H3PO4 addition was observed for all ionic liquids and co-polymers used in the study. Phosphoric acid also significantly reduced hydrolysis of Ti-precursors, stabilizing them.
Picture 1. Templated TiO2 precursors (from the left)
Traditional recipes:
IL) MOIC = methyl-3-octylimidazolium chloride, A) PIL: PEO-PIL 1 (imidazolium acrylate, short block), B) BMIC = 1-butyl-3-methylimidazolium chloride SOLVIONIC, C) PEO-PIL 3 (imidazolium acrylate, long block), D) PEO-PIL 1 (N-vinyl imidazolium, long-block), E) PIL-PVP 1 (short N-vinyl imidazolium block), F) PIL-PVP 2 (long N-vinyl imidazolium block), G) DIB = dodecyl imidazolium bromide
Modified recipes:
M) 1) BMIC in Ethanol → 2) + HCl, → 3) + H3PO4
I) 1) DIB in Butanol → 2) + HCl, → 3) + H3PO4
II) 1) PEO-PIL 1 in Butanol→ 2) + HCl, → 3) + H3PO4
III) 1) BMIC in Butanol → 2) + HCl, → 3) + H3PO4
IIIA) 1) BMIC in Butanol → 2) + H2O
IIIB) 1) BMIC in Butanol → 2) + H2O → 3) + H3PO4
Phosphoric acid provided better optical transparency and mechanical properties to the TiO2 films and better characteristics to the ionic liquid and copolymer templated organometallic precursors.
This effect can be directly used in the production of solar cells and preparation of TiO2 films for variety of uses.
