Electronic structure of Fe- vs. Ru-based dye molecules

Abstract

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.

Crystal fields of porphyrins and phthalocyanines from polarization-dependent 2p-to-3d multiplets

“…Sample integrity was monitored by checking N 1s spectra of each sample for a characteristic peak just below 400 eV which corresponds to a broken phthalocyanine or porphyrin ring. 4 No such peaks were observed for the sublimed samples. Typical N 1s spectra are shown in Figure 1 and the supplementary material.…”

“…1 The N 1s spectra were calibrated as in Ref. 4. Radiation damage was minimized by using the narrowest possible exit slits.…”

“…Typical dye molecules, such as porphyrins and phthalocyanines, contain a central 3d or 4d metal ion surrounded by an organic π system. In previous work we have used a combination of X-ray absorption spectroscopy (XAS) and first principles density functional theory (DFT) calculations to systematically investigate their energy level structure, 1,2 to detect the influence of axial and peripheral ligands on the energy levels, 3 to compare the level structure of Ru-and Fe-based dye molecules, 4 and to investigate the energy levels in different parts of donor-π -acceptor complexes. 5 There is a substantial amount of literature on the characteristic multiplet structure of the metal 2p-to-3d transitions in such molecules.…”

A direct Fe–O coordination at the FePc/MoOxinterface investigated by XPS and NEXAFS spectroscopies

“…In this temperature range, the FePc molecules will not decompose. 23,24 The SRPES experiments were carried out at the 4B9B beamline in the Beijing Synchrotron Radiation Facility (BSRF), Institute of High Energy Physics. The photon energy of 4B9B beamline ranges from 10 to 1000 eV with an energy resolution power (E/DE) of about 1500.…”

High-performance Co9Se8/CoSe counter electrode for dye-sensitized solar cells

“…Typical DSSC consists of a nanocrystalline TiO 2 film sensitized by dye molecules, an electrolyte composed of the I À =I À 3 redox couple, and a platinized counter electrode (CE) in a sandwich structure. The performance of DSSCs can be further improved by modifying various aspects of sandwich structure, such as, modification of the TiO 2 film, dye molecules, electrolyte, and CE [5][6][7][8]. Generally, Pt CE is fabricated on the F-doped tin oxide coated glass substrate and used as the standard CE of DSSCs, due to its high electrocatalytic activity, excellent conductivity, outstanding chemical stability, etc.…”