Cu2ZnSnS4 films with Cu-poor composition prepared by spin coating from a nontoxic methanol-based solution: the effect of annealing temperature

In comparison with the stoichiometry and Zn-rich/Cu-poor compositions of Cu 2 ZnSnS 4 (CZTS) photovoltaic material, the properties of Cu-poor films have not been explored adequately. In this study, Cu-poor films were spin-coated from a non-hazardous methanol-based solution. Films were subject to a brief annealing process in the temperature range of 350-550 °C. As-grown and annealed films were uniform, compact, photosensitive, and free from secondary phases. As the annealing temperature increased, the size of crystallites increased and the film dislocation density decreased steadily. Films had a direct bandgap of 1.4-1.5 eV. The presence of three sub-bandgap transitions were detected and identified. By varying the annealing temperature, hole concentration, hole mobility, and film resistivity varied systematically in the range of 10 16- 10 18 cm −3 , 1-140 cm 2 /V-s, and 0.02-64 Ωcm, respectively. Cu-poor films showed structural and optoelectronic properties similar to the Zn-rich/Cu-poor and stoichiometric films and, thus, have the potential for device applications.