Covalent modification of photoanodes for stable dye-sensitized solar cells

This paper describes the surface modification of TiO2 with 3-aminopropyltriethoxysilane (APTES) followed by covalent attachment of Ru-based N719 dye molecules to TiO2 through an amide linkage for use as photoanodes (PAs) in dye-sensitized solar cells (DSSCs). Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) confirms the surface chemistry between the TiO2 and dye. The photovoltaic efficiency of DSSCs with covalently linked dye is very similar (6-7%) to that of traditionally prepared DSSCs prepared by direct immersion when both have similar dye coverage. Importantly, the efficiency of PAs with covalently linked dye did not change after storage for more than 60 days in air, whereas the traditionally prepared PAs decreased dramatically after 1 day and lost most of their efficiency after a week. FTIR and UV-vis characterization of the dye suggests that covalent linkage improves stability by preventing the loss of the thiocyanato ligands and/or tetrabutylammonium cations on the dye. PAs with covalently linked dye are also more stable toward water, acid, heat, and UV light compared to traditionally prepared PAs and are more stable compared to other modified PAs with dye attached through electrostatic or hydrogen-bonding interactions.