Effect of annealing on the morphology and compositions of Cu2ZnSnSe4 thin films fabricated by thermal evaporation for solar cells

Cu2ZnSnSe4 thin films for photovoltaic devices have been fabricated by a single-step thermal evaporation process from synthesized Cu2ZnSnSe4 ingots and Na2Se powder. The obtained X-ray diffraction patterns revealed the presence of Cu2ZnSnSe4 and SnSe phases in all studied samples; however, the second phase disappeared after sample annealing at 500 °C for 30 min under mixed Sn/Se atmosphere. According to the results of scanning electron microscopy studies, the grain sizes for the produced thin films increased with annealing, while the best performance of the solar cells fabricated by the single-step evaporation process corresponded to an open-circuit voltage of 240 mV, short-circuit current of 27.6 mA/cm2, fill factor of 0.41, and efficiency of 2.76%.