Johnson, Phillip S.4; Cook, Peter L.4; Zegkinoglou, Ioannis4; García Lastra, Juan Maria5; Rubio, Angel6; Ruther, Rose E.7; Hamers, Robert J.4; Himpsel, F. J.4
1 Atomic scale modelling and materials, Department of Energy Conversion and Storage, Technical University of Denmark2 Department of Physics, Technical University of Denmark3 Theoretical Atomic-scale Physics, Department of Physics, Technical University of Denmark4 University of Wisconsin-Madison5 Department of Energy Conversion and Storage, Technical University of Denmark6 Universidad del Pais Vasco7 Oregon State University
In order to explore whether Ru can be replaced by inexpensive Fe in dye molecules for solar cells, the differences in the electronic structure of Fe- and Ru-based dyes are investigated by X-ray absorption spectroscopy and first-principles calculations. Molecules with the metal in a sixfold, octahedral N cage, such as tris(bipyridines) and tris(phenanthrolines), exhibit a systematic downward shift of the N 1s-to-π* transition when Ru is replaced by Fe. This shift is explained by an extra transfer of negative charge from the metal to the N ligands in the case of Fe, which reduces the binding energy of the N 1s core level. The C 1s-to-π* transitions show the opposite trend, with an increase in the transition energy when replacing Ru by Fe. Molecules with the metal in a fourfold, planar N cage (porphyrins) exhibit a more complex behavior due to a subtle competition between the crystal field, axial ligands, and the 2+ vs. 3+ oxidation states.
Journal of Chemical Physics, 2013, Vol 138, Issue 4