Insights into meso-structured photoanodes based on titanium oxide thin film with high dye adsorption ability

In this work, the absorption of N719 dye on titania films with significantly different morphologies has been investigated. By changing the synthetic approach, we have prepared sol-gel titania films with a flat surface (TiSG), mesoporous films with an ordered porous structure (TiMS) and a reference film from commercial titania P25 using the well-known doctor-blade technique (TiDB). The surface roughness and grain size distribution of titania films has been explored by atomic force microscopy. The effectiveness of the various type of titania films to absorb the N719 dye has been investigated by UV-vis spectroscopy, whereas the dye-titania interaction was examined by Raman spectroscopy. Further information on the structural and morphological properties of titania films were obtained by small angle X-ray diffraction and scanning electron microscopy. Both sol-gel and mesoporous titania films were deposited by spin-coating the solution of titania precursor, which produces films of about 300 nm, much thinner than those afforded by the doctor-blade technique (similar to 6.8 mu m). When the thickness of TiMS film was increased up to 1 mu m, the absorbance of dye-sensitized titania became also higher, reaching levels similar to those of the reference N719-TiDB film in spite of its lower thickness. Our findings show that the morphological properties of titania substrates affect their ability to adsorb the N719 dye and, in particular, it was observed an enhanced dye adsorption onto meso-structured titania. N719 absorbance normalized to titania film thickness reveals that both the roughness and porosity of titania promote the dye adsorption. The much higher ability of meso-structured photoanodes to adsorb the dye can be attributed to the ordered and highly porous structure of TiMS. The photocurrent-voltage measurements of TiMS and TiDB dye sensitized films with similar thickness (similar to 500 nm) have shown the superiority of N719-TiMS thus suggesting the key role of the mesoporous structure.