Effect of supporting electrolyte concentration on one-step electrodeposited CuInS2 films for ZnS/CuInS2 solar cell applications

摘要

A one-step electrodeposition process was used to obtain CuInS2 (CIS) films on a molybdenum substrate by varying the supporting electrolyte (lithium chloride, LiCl) concentration. The as-deposited samples were characterized by scanning electron microscopy, energy-dispersive spectroscopy, profilometry, and diffuse reflectance spectroscopy. From characterization, it was found that different concentrations of LiCl mainly lead to a morphological change in the obtained CIS films. Moreover, their chemical composition shifted to the stoichiometric composition for high concentrations of the supporting electrolyte. After annealing, the structural analysis from X-ray diffraction revealed that all samples crystallized in the tetragonal phase of CIS. In addition, it was found that the crystallite size increased for samples grown at higher concentrations of LiCl. Optical studies carried out by diffuse reflectance spectroscopy revealed that the band gap values increased from 1.40 to 1.45 eV (average) after the annealing process. Finally, zinc sulfide (ZnS) thin films were chemically deposited onto electrodeposited CIS films in order to evaluate the photovoltaic response of ZnS/CIS bilayer systems. We discovered that ZnS thin films covered the surface of CIS more effectively for the highest concentration of LiCl and that only the ZnS/CIS bilayer with the CIS film obtained at the highest concentration of LiCl showed a photovoltaic response.