Study of the Electrical Properties of Cu₂ZnSnS₄ (CZTS) Thin Film Using Atomic Force Microscopy (AFM) Techniques

CZTS is a compound semiconductor made from elements which are plainly available and nonpoisonous having favorable optoelectronic properties for thin film solar cell (TFSC) applications. In this study, Cu-poor CZTS thin film was fabricated on soda lime glass (SLG)/Mo-deposited substrate using cosputtering followed by post sulfurization in H₂S atmosphere. Local electrical transport study was carried out by using conductive atomic force microscopy (C-AFM) for small bias voltage (100 mV). Here we observed that most of the dark current (I_dark) flow through grain boundaries (GBs) than grain interiors. The positive high current about 3.4 nA and sharp C-AFM signal at the GBs, dips to the zero (0) value at the grain interior. Local surface potential (V_surface) study was carried out using kelvin probe force microscopy (KPFM), which showed that the positive V_surface potential about 175 mV in the vicinity of GBs in a Cu-poor CZTS sample. On the basis of these results we inferred a potential landscape (V_L) around the GBs. All result shows that due to variation in elemental composition which creates Cu-deficit or Cu_Zn anti site defects at GBs, leads reduced effective band gap (E_eff) than the bulk towards grain inner to GBs.[-2pt].