Effects of 5-Membered Heteroaromatic Spacers on Structures of Porphyrin Films and Photovoltaic Properties of Porphyrin-Sensitized TiO₂ Cells

Abstract

Novel 5-(5-carboxy-2-thienyl)-10,15,20-tris(2,4,6-trimethylphenyl)-porphyrinatozinc(II) (Zn5S), 5-(5-carboxy-2-furyl)-10,15,20-tris(2,4,6-trimethylphenyl)porphyrinatozinc(II) (Zn5O), and 5-(4-carboxy-2-thienyl)-10,15,20-tris(2,4,6-trimethylphenyl)porphyrinatozinc(II) (Zn4S) were synthesized to evaluate the spacer effects on the structures of the porphyrin films and the photovoltaic properties of the porphyrin-sensitized TiO2 solar cells. Each of the porphyrins showed different adsorption behavior and saturated coverage on the TiO2 surface and photovoltaic properties depending on the identity of heteroatoms in the bridge and the position of carboxylic acid. Specifically, Zn5S-sensitized TiO2 cell displayed larger, maximum incident photon-to-current efficiency of 65% and maximum power conversion efficiency of 3.1% than Zn5O-sensitized TiO2 cell by ∼20% and ∼40%, respectively. We interpret that these results are stemmed from ancillary electron-transfer pathway through specific interaction between a sulfur atom in the bridge of Zn5S and the TiO2 surface. Optical spectroscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, density functional theory calculations, and photovoltaic measurements under standard AM 1.5 conditions were employed to support our proposal.

Meso-Substituted Porphyrins for Dye-Sensitized Solar Cells

“…These results are in agreement with the work reported earlier in 2007 by Imahori and co-workers, who studied the influence of five-membered ring spacers on the structure of porphyrin films and their photovoltaic performances in TiO 2 -DSSCs ( Figure 35 and Table 14). 255 The dye Zn5S linked through a 5-carboxythien-2-yl anchoring group surpasses clearly the performances in DSSCs of both Zn5O with a 5-carboxyfuran-2-yl and the regiosiomer Zn4S with a 4-carboxythien-2-yl. Interestingly, DFT calculations predict that the electronic structure of the porphyrin core is almost unchanged for the three dyes, but that the nature of the heteroatom (S or O), as well as the substitution position, causes considerable variations in the electron densities of the spacers, increasing in the order Zn5S < Zn4S < Zn5O.…”

Novel meso-substituted porphyrins: Synthesis, characterization and photocatalytic activity of their TiO2-based composites

“…Diverse functional groups anchored to the macrocycle were reported to influence the efficiency of TiO 2 -Pp systems, depending on the position of the substituent and spacer length [30], occurrence of strong polar groups (e.g. -OH, -SO 3 , RCOO-) [31][32][33][34][35] and also highly electronegative atoms, e.g. O or Cl, combined with the pyrrole units [36,37].…”

Strategic Synthetic Approaches to Porphyrin-Based Artificial Light-Harvesting Systems for Solar Energy Utilization

“…120 One carboxylic group as an anchoring group was attached on the meso-5-membered heteroaromatic moiety to guarantee the single anchorage of the porphyrin molecule on the TiO 2 . Modifications in spacers including switching one element (i.e., sulfur vs. oxygen) in the bridge or changing the position of the anchoring group (i.e., 4-vs. 5-position) were found to have significant effects on the dye coverage and the structures of the porphyrin monolayers on the TiO 2 surface, and photovoltaic properties of the porphyrin-sensitized TiO 2 cells.…”