Sensitization of wide band-gap semiconductors with light harvesting chromophores has achieved enormous interests in the past decade mostly because of its wide application in the solar energy related research fields, e.g. dye-sensitized solar cells (DSSCs) and solar fuels. However, the fundamental understanding of semiconductor/chromophores/electrolyte interface is still poor. Recently, Stark effect, i.e., spectral shifts that occur under the influence of an electric field, have been identified in dye-sensitized TiO2 surfaces after electron injection into the mesoporous TiO21,2. Consequently, the presence of this local electric field has shown important impacts on the ionic charge movement in the electrolyte. A reversible and slow charge compensation process (t1/2>0.1 s) has been recently suggested at this interface mainly characterized by use of electro- and photo-induced absorption spectroscopy3. These results reveal important charge uptake and release processes during the electron accumulation and release within the TiO2 nanoparticles. In the following studies, we further investigate the factors affecting the initial Stark bleach amplitude, an indicator of the local electric field strength. The surface adsorption of cations, e.g. Li+, has shown significant impacts on the electric field strength. The electron conductivity within the TiO2 film is also investigated in order to evaluate the possible impacts of the local electric field on the electron transport within the TiO2 mesoporous structure. Preliminary results have indicated that the charge compensation could also be coupled with a reduction of the electron conductivity within the mesoporous structure. Finally, the effects of the interfacial electrical field on the charge transfer processes, e.g. recombination processes, at this interface are studied using nanosecond laser spectroscopy. These results illustrate the potential of Stark spectroscopy for in-situ study of the TiO2/dye/electrolyte interface, and provide substantial new insights about the impacts of the local electric field on the charge carriers transport and interfacial electron transfer at these widely applied interfaces in photoelectrochemical systems.

References:

1.U. B. Cappel, S. M. Feldt, J. Schöneboom, A. Hagfeldt and G. Boschloo, J. Am. Chem. Soc., 2010, 132, 9096–101.2

2. S. Ardo, Y. Sun, A. Staniszewski, F. N. Castellano and G. J. Meyer, J. Am. Chem. Soc., 2010, 132, 6696–709.3        

3. W. Yang, M. Pazoki, A. I. K. Eriksson, Y. Hao and G. Boschloo, Phys. Chem. Chem. Phys., 2015, 17, 16744–16751.