Sol-Gel Derived CZTS/ZnSnO Thin Film Heterojunction

Kesterite (Cu2ZnSnS4)-based thin-film heterojunctions were fabricated using a solution-processed sol–gel spin coating method with Zn0.85Sn0.15O (ZTO) as an n-type layer. The device structure Ag/FTO/ZTO/CZTS/Ag was fabricated under non-vacuum conditions and characterized for structural, optical, and interfacial properties. X-ray diffraction and Raman spectroscopy revealed the formation of Cu2ZnSnS4 (CZTS) with a dominant (112) orientation and a wurtzite ZnO structure with Sn incorporation. X-ray photoelectron spectroscopy (XPS) confirmed stable Cu+, Zn2+, Sn4+, and S2– oxidation states. Field-emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX) revealed a compact grain morphology, smooth surface coverage, and a near-stoichiometric elemental composition. UV–vis spectroscopy showed a direct band gap of approximately 1.62 eV, while ZTO exhibited transparency and a wide band gap of 3.22 eV. Photoluminescence indicated near-band-edge emission with defect-related recombination in CZTS. Hall measurements confirmed p-type CZTS and n-type ZTO, enabling carrier transport across the heterojunction. The current–voltage characteristics exhibited rectifying behavior, with a barrier height of 0.73 eV and an ideality factor of 1.84, confirming the formation of a rectifying heterojunction. The results demonstrate the fabrication of solution-processed CZTS/ZTO heterojunctions employing ZTO as an n-type layer.