The chemical stability of dye-sensitized solar cells (DSSC) determines both the cell performance and the cell life-time. The presence of water in the solar cell from surrounding leakage through the imperfection packaging sealants causes the decrease in life-time of photogenerated electrons on the working electrodes, which induces the occurrence of the dark current to the electrolytes and thus leakage current significantly deteriorated the life-time of the DSSC. Reliable electrolyte additives diminishing the influences of water to the DSSCs degradation process becomes a critical issue in maintaining an acceptable cell life-time. In this work, the effects of four benzimidazole derivatives a-d as the electrolyte additives in the presence of water were comprehensively examined by time-dependent photovoltaic performance of the cells. As a result, open-circuit voltage (V(oc)), short-circuit current (J(sc)), efficiency (eta), and fill factor (FF) collected from I-V curves were studied. In addition, electrochemical impedance spectroscopy (EIS) technique was implemented to evaluate the effects of the charge-transfer resistance (R(ct)) at the interfaces between TiO(2)/dye/electrolyte. Results showed that the bis-benzimidazole derivative c gives significant improvement in the long-term stability due to the effective protection of the ligands between dye and working electrodes from the attack by environmental water molecules. (C) 2010 Elsevier B.V. All rights reserved.