Thermal annealing induced modification on structural and optical properties of Cu2ZnSnS4 thin films for solar cell application

The influence of thermal annealing on sol-gel derived Cu2ZnSnS4 (CZTS) thin films was carried out in quartz tubular furnace at different temperature (300-600 °C) for 1 h in the presence of elemental sulfur. The structural studies confirm the formation of tetragonal kesterite CZTS structure along (112) plane and indicate the presence of impurity phases at lower sulfurization temperature. CZTS films revealed high dense morphology with large grain size at 500 °C. The optical band-gap energy decreased from 1.8 to 1.52 eV with the increase in sulfurization temperature. The electrical measurements show p-type conductivity of the films with carrier mobility of 13.12 cm2/V.s. The sulfurized CZTS thin film at 500 °C was used for superstrate solar cell structure with Cd-free buffer layer. The solar cell exhibited short-circuit current density of 4.8 mA/cm2, open-circuit voltage of 140 mV, fill factor of 0.31 and power conversion efficiency of 0.208% under 100 mW/cm2 illumination.