Phase transition behavior and defect analysis of CuSbS2 thin films for photovoltaic application prepared by hybrid inks

CuSbS2 (CAS) thin films were deposited via a non-vacuum hybrid ink method onto a Mo/soda lime glass (SLG) substrate. To fabricate the CAS films, Cu-Sb precursors were spin coated and then annealed with sulfur powder. During annealing, different amounts of sulfur powder were used to control the crystal orientation of the films. X-ray diffraction (XRD) patterns were employed to examine the crystal orientation by calculating the texture coefficient and Lotgering factor. It was found that the S-flux amount during sulfurization was a critical parameter for controlling the crystal orientation and phase transition of the CAS structure. Originally, CAS has an orthorhombic structure; however, if the S-flux was higher than the optimum, a pseudo-phase transition from orthorhombic to cubic was observed. In addition, the electrical characteristics and defect properties were conducted for the solar cells prepared with various S-flux to understand the difference in the photovoltaic performances affected by the structural change. Admittance spectroscopy revealed that the defect levels were shallower in the CAS solar cell with an orthorhombic structure, which could have contributed to the better photovoltaic performance than that of the cubic structure. The CAS solar cell deposited with low S-flux exhibited dominant V-S(2+) defects; however, for excessive S-flux, Cu-Sb(2-) became prominent.