Tin disulfide segregation on CZTS films sulfurized at high pressure

CZTS thin films were synthesized by annealing of Zn, Cu, and Sn stacked layers under sulfur atmosphere. Pressure was controlled by varying the mass of the sulfur charges introduced into the closed annealing chamber. Films sulfurized at higher pressure show clear segregation of hexagonal SnS2, suggesting that Sn reacts with gaseous sulfur to form a solid-state phase, leading to an inhomogeneous 3D film morphology. Lower pressure synthesis yields uniform layers mainly composed of CZTS. Variations in film morphology suggest that different reaction pathways take place as the pressure is raised. Formation of gaseous SnS is favored at lower pressure, while nucleation of solid SnS2 preferentially occurs at higher pressure. Influence of the cooling rate after annealing was also studied. We have found that this strongly affects the film stoichiometry, while the film morphology did not show relevant dependence on this parameter.