In situ micro- and macro-Raman investigation of the redox couple behavior in DSSCS

Solar cells based on nanocrystalline TiO2 sensitized by dyes that contain poly-pyridyne rings have been examined by in situ micro- and macro-Raman spectroscopy under positive and negative bias. Four modes in the low frequency range appear for nearly short-circuit conditions and are attributed to the vibrations of triiodide, bound on the oxidized form of the dye. The intensity and frequency of these modes depend on the applied potential and their behavior is correlated with characteristic regions of the current–potential curves. Our results are supported by polarized Raman experiments and basic theoretical simulations.