AVS 56th International Symposium & Exhibition
    Surface Science Tuesday Sessions
       Session SS2-TuA

Paper SS2-TuA11
Electronic Structure of Zinc and Free-Base Tetraphenylporphyrin Derivatives Adsorbed on TiO2(110) and ZnO(11-20) Surfaces for Application in Dye Sensitized Solar Cells

Tuesday, November 10, 2009, 5:20 pm, Room M

Session: Wide Band Gap Semiconductors
Presenter: S. Katalinic, Rutgers University
Authors: S. Katalinic, Rutgers University
S. Rangan, Rutgers University
R. Thorpe, Rutgers University
R.A. Bartynski, Rutgers University
J. Rochford, Rutgers University
K. Chitre, Rutgers University
E. Galoppini, Rutgers University
Correspondent: Click to Email
Metalloporphyrins play an essential role in photosynthetic mechanisms and therefore are natural candidates for electron transfer mediator in dye sensitized solar cells (DSSCs). Among the possible metalloprophyrins, the zinc tetraphenylporphyrins (ZnTPP) derivatives have been found to have similar electron injection and charge recombination properties as the important standard ruthenium dye N3 for DSSCs, as well as reasonable performances using TiO2 or ZnO as substrates.

Due to a strong decoupling of the meso-phenyls from the main porphyrin macrocycle, the optical absorption properties of the ZnTPP derivatives are found relatively insensitive to the meso-phenyls functionnalization. As a consequence, the adsorption geometry on the surface, as well as the molecule-molecule interaction, can be altered independently of the absorption properties.

Using direct and inverse photoemission spectroscopy we have measured the occupied and unoccupied electronic states of several zinc (and free-base for comparison) tetraphenyporphyrin derivatives adsorbed on single crystals TiO2 and ZnO surfaces. From this, the alignment of the molecular levels (in particular the frontier orbitals) with respect to the substrate band edges can be directly determined. For a full interpretation of the electronic structure of such molecular adsorbates, we have compared our measurements to ab-initio calculations of the density of states. In addition to spectroscopic surface averaged probes, we have used scanning tunneling microscopy to study the local bonding geometries at the surface of the semiconductors. Recent results will be presented and compared to those available in the literature.