Dye Sensitization of Four Low Index TiO₂ Single Crystal Photoelectrodes with a Series of Dicarboxylated Cyanine Dyes

Abstract

Four dicarboxylated cyanine dyes were used to sensitize single-crystal anatase (001), anatase (101), rutile (001), and rutile (100) surfaces. Incident photon to current efficiencies (IPCE) spectra and isotherms were gathered for the different combination of dyes and surfaces. The maximum coverage of the surface-bound dyes on the TiO2 crystal surfaces was determined by photochronocoulometric measurements. The IPCE spectra of the surface-bound dyes revealed that both the dye monomers and H-aggregates were both present and generated photocurrent. The relative abundance of dye monomers and H-aggregates was found to be strongly dependent on the crystallographic face used as the substrate for sensitization. The ratio of dye monomer to H-aggregate was quantified by fitting the IPCE spectra with a sum of the dye monomer and H-aggregate solution spectra. The trends in surface coverage were explained using a simple "lattice matching" model where the distance between the coordinatively unsaturated Ti binding sites on the various TiO2 crystallographic surfaces was compared with the distance between the carboxylate groups on the dyes. The rutile (100) surface had the highest coverage for all the dyes in agreement with the predictions of the lattice-matching model. Absorbed photon-to-current-efficiencies (APCEs) were calculated from the incident photon current efficiencies, the extinction coefficients and the measured surface coverages. The factors that affect the APCE values such as the relative injection yield for monomers and aggregate, the relative surface coverage values for monomers and aggregates, and semiconductor doping levels are discussed.

Change in spectral properties of dyes upon immobilization on silicon surfaces: a combined theoretical and experimental study

“…b Spectra of dye A in the immobilised state involving experimental and theoretical spectra of (i) non-interacting dye molecule with both linkers (ii) interacting and non-interacting dye molecules with APTES linker (iii) interacting and non-interacting dye molecules with PEI linker ◂ Considering that the theoretical spectra indicates that only covalent bond formation does not cause such magnitude of red shift in absorption maxima, a possible reason is formation of aggregates [28] which was indicated in the case of dye A. Formation of such aggregates upon immobilization of carboxylate dyes on different surfaces has been reported by Mulhern et al [28] and Choi et al [53]. So formation of aggregates on the surface in our case is not an exception.…”

Probing the Relative Photoinjection Yields of Monomer and Aggregated Dyes into ZnO Crystals

“…1. R8 has a red shifted absorption maximum and is known to aggregate much more readily than G15, 30 allowing further investigation of aggregation effects on photoinjection yields.…”

“…32 The structural difference is an additional two carbons in the bridging carbon chain between the two cyanine groups extending the conjugation length from three to five carbons, as shown in Figure 1. R8 has a red-shifted absorption maximum and is known to aggregate much more readily than G15, 30 allowing for further investigation of aggregation effects on photoinjection yields.…”

8-Hydroxylquinoline-conjugated porphyrins as broadband light absorbers for dye-sensitized solar cells

“…Multiple BZA groups were introduced into porphyrin dyes in order to increase their binding capability. [10][11][12][13][14][15] However, a compromise in solar cell efficiency was observed. Imahori et al 16 found that energy conversion efficiency decreased when a second BZA group was introduced into the porphyrin.…”