Study of interface properties between Cu2ZnSnS4 thin films and metal substrates

Abstract

In this study, the effects of various metal substrates on the interface properties of Cu2ZnSnS4 (CZTS)/metal structures were investigated. The crystal phases, morphologies, and element distributions at the interfaces between CZTS thin films and various metal substrates (Mo, W, Ti, and Al foils) were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and secondary ion mass spectroscopy. MoS2 and WS2 phases were formed at the CZTS/Mo and CZTS/W interfaces, respectively. No Ti-S and Al-S compounds were formed at the CZTS/Ti and CZTS/Al interfaces. The formation of these phases was dependent on the lowest reaction temperature between the metal foil and S vapor. The size of particles at the back surface of the CZTS thin film on the Ti substrate was larger than that on the other substrates, because the Ti element improved the crystallinity of CZTS. The presence of a thick WS2 layer at the CZTS/W interface was attributed to the fact that the (211) plane of the W foil caused exposure of a greater number of W atoms in the sulfurization process because of the body-centered cubic crystal structure of W. The diffusion of Ti atoms into the CZTS thin film was due to the large average hop distance of defects in the CZTS thin film and the relatively low activation energy of Ti atoms. Current–voltage curves and energy band diagrams revealed that the ohmic contacts formed at the CZTS/Mo and CZTS/Ti interfaces were better than those formed at the CZTS/W interface and that a Schottky contact was formed at the CZTS/Al interface.