An interfacial layer (IL) between the CdS quantum dot (QD) and dye is necessary in the CdS-dye co-sensitized solar cell (CSC) to prevent the corrosion of CdS and the damage of electrolyte. In this study, the simple method of using a TiO2 sol–gel solution is suggested to fabricate the IL. An air exposure process after dipping into the TiO2 sol–gel solution facilitates formation of the anatase TiO2 thin film. To confirm the effect of TiO2 IL, the performance of CdS-dye CSC is analyzed and compared to the conventional CdS QD sensitized solar cell (QDSC). The formed TiO2 IL effectively prevents the corrosion of CdS and the damage of electrolyte. In addition, this suppresses the electron recombination from the CdS to the electrolyte, resulting in the enhanced electron transport at the TiO2/CdS QD-dye/electrolyte interface. As a result, the overall photovoltaic performance is much increased from 1.33% to 2.77%, compared to the conventional CdS QDSC.