Fabrication of (Cu,Ag)2SnS3 thin films by sulfurization for solar cells

In this paper, we fabricated thin films composed of (Cu,Ag)2SnS3 using a sulfurization process for photovoltaic devices. The stacked NaF / Sn / (Ag + Cu) precursor was deposited by sequential evaporation of Ag, Cu, and Sn elements and NaF followed by crystallization in a mixed sulfur/tin atmosphere for 30 min at 530 °C and 570 °C, respectively. The X-ray diffraction patterns in all samples exhibited several peaks near the diffraction line of the monoclinic Cu2SnS3 (CTS) structure. Moreover, the lattice spacing increased according to Vegard's law as the [Ag] / ([Ag] + [Cu]) molar ratio in the films increased up to a value of approximately 0.05. Based on the results of scanning electron microscopy studies, the grain sizes for the produced thin films increased as the [Ag] / ([Ag] + [Cu]) molar ratio increased in the evaporation materials, while the performance of the solar cell fabricated with [Ag] / ([Ag] + [Cu]) = 0.05 and a sulfurization temperature of 570 °C corresponded to an open-circuit voltage of 244 mV, a short-circuit current density of 36.9 mA/cm2, a fill factor of 0.45, and an efficiency of 4.07%.