Dye-sensitized solar cell (DSC) modules are most likely to work for long time under negative bias due to the mismatch in the outdoor usage, which can obviously influence the cell performance. In this paper, the interface property of DSC under negative bias is investigated by Raman spectroscopy, electrochemical impedance spectroscopy and incident-photon-to-electron conversion efficiency (IPCE). The results of Raman spectroscopy indicate that the decreased peak intensity at 167 cm-1 (the oxidized state of N719 (D+)/ I3-) after 1000 h could be due to Li+ ions diffusing into the TiO2 electrode and partially being intercalated into the TiO2 film. It is also found that the increased recombination resistance in the interface of TiO2/electrolyte resultes in the improved open-circuit voltage and the decreased IPCE values, leading to reduced short-circuit current for DSC with base electrolyte under the long-term negative bias. However, when BI is added into the base electrolyte, the Raman spectrum shows no significant change and that the cell efficiency remains stable after 1000 h. The reason is that BI could prevent Li+ ions from being intercalated into the TiO2 film. It is proven by the further experiments where the DSC with BI exhibits better stability under different negative biases.