Dye-sensitized solar cells(DSSCs) have a FTO/TiO2/Dye/Electrolyte/Pt-counter electrode structure, but a more than 10% electron loss occurs at each interface. A passivating layer between the Electrolyte/FTO glass interface can prevent the recombination of electrons. FTO glass was coated with ZnO thin films by RF-magnetron sputtering. Each film was deposited under different O-2(Oxide) pressures. Under each pressure, the passivating layer showed a difference in thickness. The optical transmittance of the ZnO thin film depends on the thickness and grain size of ZnO thin film. A TiO2-nanoparticle upper layer was coated on the ZnO passivating layer by screen-printing. FTO showed relatively high intensity but the X-ray diffraction pattern revealed the presence of ZnO thin films. The conversion efficiency of the DSSCs were strongly affected by the passivating layer. The conversion efficiency measured the maximum conversion efficiency of 4.29% at O-2 5 mTorr, which is due to the effective prevention of electron recombination with the electrolyte.