Secondary phases and disorder degree investigation of Cu₂ZnSnS₄ films

In this study, Cu₂ZnSnS₄ (CZTS) thin films are deposited onto the glass slides via the radio frequency (RF) magnetron sputtering, and subsequently sulfurized at different heating rates of 5 °C/min, 20 °C/min, 35 °C/min and 50 °C/min, respectively. The disorder degrees and the secondary phases of finally obtained CZTS thin films are then systematically investigated by using scanning electron microscopy, X-ray diffraction, energy dispersive X-ray, Raman spectroscopy, Raman mapping, UV–vis–NIR spectroscopy, and the Hall effect measurement system. The morphological, structural, and electrical properties of fabricated CZTS films affected by the heating rate are subsequently evaluated. The heating rate of 20 °C/min during the sulfurization process is found to produce a nearly single-phase kesterite CZTS with a substantially low disorder degree. However, more Cu_2-xS and Cu₃SnS₃ secondary phases are found in samples that are annealed at other heating rates. The effect of heating rate on the decomposition during the sulfurization process is also studied and then elaborated. This study provides an optimal condition for minimizing the secondary phases and disorders, in other words, providing the idea process condition to manufacture the high-quality CZTS thin films for solar cells with high conversion efficiency.