Spectroscopic studies of electrochemical reactions of adsorbed dye layers

Abstract

Dye reactions at transparent electrodes were studied by spectroscopic investigations using the attenuated total reflection technique. All experiments were performed by modulating the concentration and consequently the absorption itself (potential modulation). The applicability of this method has been demonstrated by studying the distribution of monomers and dimers in adsorbed dye layers (viologene) or in the vicinity of the electrode. Measurements at higher modulation frequencies have shown that unstable semiquinones in adsorbed dye layers (methylene blue, thionine) involved in the oxidation-reduction cycle could be detected.

Potential Distribution and Photovoltage Origin in Nanostructured TiO2 Sensitization Solar Cells: An Interference Reflection Study

“…The real and imaginary parts of ε in eq 6 are Since N e can be modulated under application of the AC potential bias, according to eq 6 a change in N e will produce a change in n̂ . Therefore, the V AC induced changes in the spatial distribution of the electric field within the FTO layer, and therefore in N e , will also produce changes in the absorption coefficient, α(λ, x ; V AC ) = (4π/λ) k and so in Im( ε ).…”

“…The process taking place in all these electromodulation experiments can be described as follows: the internal electric field distribution in the thin film, E ( x ; V AC ) is modified by under application of an alternative potential, V AC , which affects the spatial distribution of the thin film absorption coefficient, α 2 (λ, x ; V AC ). Essentially, the incident light beam undergoes multiple reflections in the thin film, giving rise to an interference phenomenon because of the difference of the refraction index of the thin film (FTO in our case) and the glass substrate. − The ratio of the field-modulated reflectance to the total reflectance, d R / R , is then directly recorded as a function of wavelength. Here we show that the modulation reflection spectrum (d R / R vs λ) of the FTO layer at the back contact of a DSSC can be used in order to evaluate the potential distribution at the FTO/TiO 2 /electrolyte interface and its dependence on the voltage and illumination bias.…”

“…Essentially, the incident light beam undergoes multiple reflections in the thin film, giving rise to an interference phenomenon because of the difference of the refraction index of the thin film (FTO in our case) and the glass substrate. [8][9][10][11][12][13][14] The ratio of the field-modulated reflectance to the total reflectance, dR/R, is then directly recorded as a function of wavelength. Here we show that the modulation reflection spectrum (dR/R vs λ) of the FTO layer at the back contact of a DSSC can be used in order to evaluate the potential distribution at the FTO/TiO 2 /electrolyte interface and its dependence on the voltage and illumination bias.…”