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

Abstract

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 30min 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 244mV, a short-circuit current density of 36.9mA/cm2, a fill factor of 0.45, and an efficiency of 4.07%.