Fabrication of solar cells based on Cu₂ZnSnS₄ prepared from Cu₂SnS₃ synthesized using a novel chemical procedure

¹ Department of Mechanical Engineering, Universidad Nacional de Colombia, Bogotá, Colombia
² Department of Chemistry, Universidad Nacional de Colombia, Bogotá, Colombia
³ Department of Chemistry Engineering, Universidad Nacional de Colombia, Bogotá, Colombia
⁴ Department of Physics, Universidad Nacional de Colombia, Bogotá, Colombia

^a e-mail: ggordillog@unal.edu.co

Received: 1 July 2016
Received in final form: 17 September 2016
Accepted: 26 September 2016
Published online: 9 November 2016

Abstract

Solar cells based on kesterite-type Cu₂ZnSnS₄ (CZTS) thin films were fabricated using a chemical route to prepare the CZTS films, consisting in sequential deposition of Cu₂SnS₃ (CTS) and ZnS thin films followed by annealing at 550 °C in nitrogen atmosphere. The CTS compound was prepared in a one-step process using a novel chemical procedure consisting of simultaneous precipitation of Cu₂S and SnS₂ performed by diffusion membranes assisted CBD (chemical bath deposition) technique. Diffusion membranes were used to optimize the kinetic growth through a moderate control of release of metal ions into the work solution. As the conditions for the formation in one step of the Cu₂SnS₃ compound have not yet been reported in literature, special emphasis was put on finding the parameters that allow growing the Cu₂SnS₃ thin films by simultaneous precipitation of Cu₂S and SnS₂. For that, we propose a methodology that includes numerical solution of the equilibrium equations that were established through a study of the chemical equilibrium of the system SnCl₂, Na₃C₆H₅O₇·2H₂O, CuCl₂ and Na₂S₂O₃·5H₂O. The formation of thin films of CTS and CZTS free of secondary phases grown with a stoichiometry close to that corresponding to the Cu₂SnS₃ and Cu₂ZnSnS₄ phases, was verified through measurements of X-ray diffraction (XRD) and Raman spectroscopy. Solar cell with an efficiency of 4.2%, short circuit current of 16.2 mA/cm² and open-circuit voltage of 0.49 V was obtained.