Creation of thin film CuSbSe2 through closed space vapor transportdeposition

Abstract: With an increasing demand for fossil-free energy the development of efficient solar cells made from sustainable and abundant materials is needed. A promising group of new absorber materials are the chalcogenide materials, including the chalcostibnite compounds copper antimony selenide, CuSbSe2. The few studies that have been carried out on this material show promising properties with an absorption coefficient higher than 7 x 104 cm-1 in the visible region and a band gap around 1.5-1.1 eV, which theoretically can be tuned by creating an alloy with the more studied and higher band gap material CuSbS2. This project has focused on creating CuSbSe2 using closed space vapor transport (CSVT) depositions. Three different approaches have been used; deposition of antimony selenide, Sb2Se3, on pre-sputtered copper films, deposition of antimony and selenium in two steps on pre-sputtered copper films and deposition of selenium on pre-sputtered stacked films of copper and antimony. The films were analyzed using optical imaging, SEM, EDS, XRD, and UV-Vis spectroscopy. It was found that the Cu-Sb-Se system is complicated, containing numerous phases with low crystallographic symmetry compared with chalcopyrite materials. The sublimation data found in the literature for Sb2Se3 is not applicable for the pressures used in this project. Created samples did not contain enough antimony and further studies on Sb2Se3 are needed if CuSbSe2 is to be created in the CSVT system using Sb2Se3 as source. In the three different experimental procedures used in the project, the phases CuSbSe2, Cu3SbSe3, Cu3SbSe4, Sb2Se3 and an unknown phase were observed in the samples. The composition of the unknown phase could not be identified but its XRD pattern has been revealed. The window in ratio of Cu:Sb for creating CuSbSe2 seems to be very narrow and needs to be close to 1:1. If so the phase can be formed by annealing samples consisting of  Cu3SbSe4 or Sb2Se3. A more refined approach where the deposition and reaction with selenium can be better controlled thus needs to be developed in order to form films with single phase CuSbSe2.