Production and characterization of Cu2SnS3 films for solar cell applications: The effect of the sulfurization temperature on CuS secondary phase

Cu2SnS3 is a good alternative to solve the problems related to CdTe and CIGS absorber layers having toxic, expensive and rare-earth elements. In this study, CTS films were obtained by a two-stage process that includes sulfurization of Sn-Cu metallic precursors stacked by thermal evaporation. Sulfurization process was carried out in the temperature range of 400-550 degrees C, and the role of the sulfurization temperature on secondary phases of CTS films was reported. XRD and Raman analyzes revealed that CTS film sulfurized at 550 degrees C has a highly crystalline tetragonal-CTS phase, and undesirable CuS secondary phase can be significantly minimized due to increased sulfurization temperature. Elemental analyses showed that desired Cu-poor stoichiometry was reached at 550 degrees C and 550 degrees C. Optical analyzes indicated that optical band gap values approached the optimum value for photovoltaic applications, and 1.39 eV was reached especially for CTS-550 film. Thickness and optical constants of the films were determined using spectroscopic ellipsometry. CuS secondary phase in Cu-rich CTS-400 and CTS-450 films brought metallic behavior to the materials, and electrical resistivity of the Cu-poor CTS-550 film approached the appropriate value for photovoltaic applications. Besides, surface analyzes proved that sulfurization temperature has a strong effect on the surface properties and the film surface became more compact at 550 degrees C. As a result, this study showed that higher sulfurization temperatures (especially 550 degrees C) contribute to the solution of the CuS secondary phase problem, which limits the performance of CTS-based solar cells.

Automated summary

This study investigated the influence of sulfurization temperature on Cu2SnS3 films, and the results showed that sulfurization at 550 degrees Celsius significantly reduced undesired CuS secondary phases, enhancing the photovoltaic performance of the films.