Adsorption geometry of mono and tetra phosphonate functionalized porphyrin molecules on TiO2(110) surfaces

FERNÁNDEZ, CYNTHIA C.; WECHSLER, DANIEL; STEINRÜCK, HANS-PETER; LYTKEN, OLE; WILLIAMS, F. J.

Regensburg, Germany,

Conferencia; DPG Spring Meeting of the Condensed Matter Section; 2019

Deutsche Physikalische Gesellschaft

Solar energy technologies at the forefront of renewable energy research include dye-sensitized solar cells and water-splitting dye-sensitized photoelectrochemical cells. These devices are constructed attaching molecular chromophores to semiconducting materials. The most extensively studied systems are based on porphyrin molecules bonded to TiO2 surfaces using carboxylates and phosphonates as anchoring groups. One of the critical factors affecting the performance of the device is the adsorption geometry of the molecules. Therefore, fundamental studies aiming at understanding the interaction of functionalized porphyrin molecules with TiO2 surfaces are of great importance. In this work, we studied the bonding and adsorption geometry of tetraphenyl porphyrin molecules containing one or four phosphonate groups. The investigation was carried out by means of synchrotron radiation X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) measurements. Our results show that the number of linker groups have a great influence on the adsorption geometry. Molecules with one phosphonate group adsorb with the macrocycle tilted away from the surface whereas molecules with four phosphonate groups adsorb with the macrocycle close to the surface. This is an important finding for the design of dye-sensitized solar and photoelectrochemical cells. This project is supported by the DFG through FOR 1878 (funCOS).