In this study, a solar cell with ITO/ZnO/P3HT:PCBM/MoO 3 /Ag structure was produced. Then, the effect of ZnO, which was synthesized with different methods, on device efficiency was investigated. As the synthesis method, solgel, nanocrystal and solution processes were used. First of all, XRD characterization has been made for each different synthesis method. Later, the devices were produced by coating with the obtained ZnO solutions. The efficiency of the devices was determined under 100 mw/cm 2 solar irradiance using Keithley 2400 sourcemeter. According to the obtained findings, the highest efficiency (2.90%) was achieved with ZnO synthesized by sol-gel method. In addition, the sol-gel method has extra advantages as it requires cheaper equipment and relatively harmless chemicals compared to other methods. As a result, it was determined that the most suitable synthesis method for ZnO to be used in organic solar cells is the sol-gel method.