Studies on the Interfacial Electric Field and Stark Effect at the TiO₂/Dye/Electrolyte Interface

Interfaces of dye-sensitized TiO 2 nanoparticles with electrolytes or hole conductors have been widely applied in photoelectrochemical cells. However, the fundamental understanding of their properties and function is still poor. Herein, we demonstrate that the spectral changes that occur in the visible spectrum of dye-sensitized TiO 2 films upon (a) Li + titration, (b) potentiostatic electron accumulation in mesoporous TiO 2, and (c) photoinduced electron injection into TiO 2 can be explained by the Stark effect, which can then be used to characterize the change in the local electric field at the TiO 2 /dye/electrolyte interface. A quantitative analysis of the Stark effect indicates that the compact (Helmholtz) layer capacitance at the TiO 2 /dye/electrolyte interface strongly affects the strength of the local electric field. Systematic studies show that the Helmholtz layer capacitance depends strongly on the Li + concentration and surface dye coverage but is independent of the concentrations of other electrolytic species and the light intensity. These results illustrate the potential of Stark spectroscopy for the in situ study of the TiO 2 /dye/electrolyte interfaces and provide substantial new insights into these widely applied interfaces related to photoelectrochemistry and other research fields.