Resonant Raman study of dye instability in dye‐sensitized TiO 2 system: The effect of surface states

The most critical problem in commercialization of the dye‐sensitized solar cell (DSSC) is its long‐term stability. Many factors contribute to the instability of a DSSC. In order to clarify the role of the surface defects on the cell instability, we modified the TiO 2 surface chemical states, fabricated DSSCs with a very simple structure, and carried out resonant Raman scattering to monitor the dye degradation under open‐circuit condition. The results showed that the dye stability was very sensitive to the TiO 2 surface states. The dye degradation can be described by an exponential decay law. The oxygen vacancy–Ti 3+ chemical state enhanced the recombination of electron with the oxidized electrolyte, i.e ., the electron in the TiO 2 conduction band injected back to the electrolyte, and consequently enhanced the dye regeneration rate by I − , which came from the reduction of ${\rm I}_{3}^{- } $ with electrons. Under the open‐circuit condition the dye stability was increased when it was attached to a TiO 2 surface with a relatively high percentage of oxygen vacancy–Ti 3+ chemical state. The increased electron recombination occurred at the TiO 2 /electrolyte interface resulted in a much decreased open‐circuit voltage and short‐circuit current in a DSSC.