Phase evolution of Cu₂ZnSnS₄ (CZTS) kesterite thin films during the sulfurization process

The development of high efficiency Cu₂ZnSnS₄ (CZTS) thin film solar cells depends on the synthesis of phase pure CZTS films. Due to the narrow phase window, it is difficult to prepare CZTS films with a pure kesterite phase (i.e., a film that lacks traces of detrimental secondary phases). For this, phase evolution of kesterite CZTS in films must be systematically studied. In the present study detailed phase evolution of kesterite CZTS via the sulfurization of stacked Cu/SnS₂/ZnS precursor was examined. The phase evolution of kesterite CZTS was analyzed during the temperature-dependent sulfurization of stacked precursors. In addition to traditional X-ray diffraction and Raman analysis, transmission electron microscopy (TEM) characterization was used to study the phase evolution and trace locations of secondary phases in the sulfurized films. Furthermore, based on the experimental evidences the reaction pathways for the formation of CZTS kesterite phase and plausible phase evolution mechanism are proposed.