Control of secondary phases and disorder degree in Cu2ZnSnS4 films by sulfurization at varied subatmospheric pressures

Cu2ZnSnS4 (CZTS)thin films deposited using direct current magnetron sputtering and sulfurized at different argon atmosphere pressures of 950, 460 and 50 mbar are studied focusing on the control of disorder degree and secondary phases. The films are in detail characterized employing X-ray diffraction, scanning electron and conductive atomic force microscopies, energy dispersive X-ray, μ-Raman spectroscopies and mappings. Such a comprehensive approach shows how the pressure variation influences morphology, structural and electrical properties of the films in submicron scale. The films sulfurized at the lowest applied pressure of 50 mbar are found to be single-phase CZTS with low disordering degree. Nevertheless, in those sulfurized at 950 and 460 mbar, Cu2-xS and ZnS secondary phases with concomitant spatial inhomogeneities are detected. At the same time, sulfurization at higher pressures enlarges the grains, which however demonstrate wide size distribution. Formation of CZTS crystal structure and secondary phases as well as acceleration of grain growth depending on pressure are interpreted and discussed ; The authors would like to express their sincere thanks to Prof. M. Valakh, Prof. N. Klyui for sample fabrication and helpful discussions. This research was supported in part by National Natural Science Foundation of China [ 61525503 , 61620106016 , 61835009 , 81727804 , 61722508 , 61604098 ]; Guangdong Natural Science Foundation Innovation Team, China [ 2014A030312008 ]; National Academy of Sciences of Ukraine [ 8/19-Н ]; and Ministry of Education and Science of Ukraine [ 19BF051-02 ].