Abstarct: Cu2(Zn,Sn)S4 is a quaternary semiconductor compound of the I2-II-IV-VI4 group, which is formed of non-toxic, inexpensive and available materials. It has an absorption coefficient of about 104 cm-1 in the visible range, and also a direct band gap of about 1.50 eV at the room temperature. These features have transformed this compound into an absorber laxyer suitable for use in solar cells. In this dissertation, at first, pure and doped-Cu2ZnSnS4 (CZTS) thin films with potassium and sodium elements were prepared under different growth conditions with spin coating method and then the structural, optical and electrical properties of them were studied. Also, several photovoltaic devices were made using CZTS laxyers and their photovoltaic parameters were investigated. The results of the structural analysis of the prepared samples (pure and doped) showed that all samples have a kesterite structure. Comparison of the crystal structure of pure samples showed that the annealed sample at a temperature of 500°C for 40 min and the sulfurized sample at 500 °C for 20 min have a bigger crystalline size than other samples. Comparison of the results for the samples prepared with different molar ratio of zinc (Zn) and copper (Cu) showed that the samples prepared with molar ratio of Zn/Sn= 1.13 and Cu/(Zn+Sn)= 0.90 have a greater crystalline size and its band gap (1.53eV) is closer to the optimum value. Investigation of optical properties of all samples (pure and doped) showed that their band gaps changes in the range of 1.33-1.96 eV. The comparison of the band gap of pure samples showed that the sulfurization process reduced band gap by 9%. Study of electrical properties of the pure and doped- samples showed that all samples have p-type conductivity, and doping increases the carrier concentrations. Also, the carrier concentration of potassium doped-samples was higher (ten times) than the sodium doped- samples. Investigating of the effect of change in copper and zinc salts type (chloride or acetate) on the electrical properties of the samples showed that the carrier concentrations in the samples prepared by chloride salts, are more than 5%. All photovoltaic devices that made of CZTS thin films showed a diode behavior. The comparison of the results showed that the best fill factor (49%) has related to the sulfurized and annealed samples in 500oC for 20 min.