The role of sulphur in the sulfurization of CZTS layer prepared by DC magnetron sputtering from a single quaternary ceramic target

The influence of sulphur vapour pressure, controlled by its mass, on the grain growth and optoelectronic properties of Cu2ZnSnS4 (CZTS) films prepared by a two-step procedure based on sputtering was studied. It was found that both the crystallinity and grain size of the films were promoted with the increase of the sulphur vapour pressure, indicating that the crystal growth was controlled by the sulphur vapour pressure. In addition, the crystal growth process of CZTS was investigated by analysing the microstructure and elemental composition of the sulfurized films with different masses of sulphur. It was also found that the content of Sn in the sulfurized films decreased after high-temperature annealing. However, the second phase SnS2 was observed on the sample surface, which led to the increase of the optical band gap of the film. Moreover, we proposed the regulatory mechanism of sulphur vapour pressure in the grain growth of CZTS film. Finally, a highly crystalline p-type kieserite Cu2ZnSnS4 film with carrier concentration of 8.16 × 1017 cm−3, mobility of 1.24 cm2/V s and optical bandgap of 1.54 eV was obtained. This CZTS layers are expected to fabricate high efficiency thin film solar cells.