Resonant Raman study of dye instability in dye‐sensitized TiO2 system: The effect of surface states

Abstract

AbstractThe 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 TiO2 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 TiO2 surface states. The dye degradation can be described by an exponential decay law. The oxygen vacancy–Ti3+ chemical state enhanced the recombination of electron with the oxidized electrolyte, i.e., the electron in the TiO2 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 TiO2 surface with a relatively high percentage of oxygen vacancy–Ti3+ chemical state. The increased electron recombination occurred at the TiO2/electrolyte interface resulted in a much decreased open‐circuit voltage and short‐circuit current in a DSSC.