Influence of substrate temperature on the properties of electrodeposited kesterite Cu2ZnSnS4 (CZTS) thin films for photovoltaic applications

We prepared Cu2ZnSnS4 (CZTS) films on Mo-coated glass substrates by using electrodeposition in an acidic electrolyte containing Cu, Zn, and Sn species. We examined how the substrate temperature influenced the compositional, structural, morphological, and electrical properties of the CZTS films by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), Raman spectroscopy, energy dispersive spectroscopy, and ultraviolet-visible absorption spectroscopy. The film sulfurized at a substrate temperature of 580 A degrees C exhibited the best characteristics because of its large grain size and low number of voids. At a sufficiently high temperature, this fabrication process yielded single-phase CZTS with no secondary phases. The grain size increased with deposition temperature: the size at 580 A degrees C was about twice that at 460 A degrees C. All the CZTS films were Cu-rich and S-poor, with the composition changing at 580 A degrees C. XRD revealed that the films had nanocrystalline kesterite structures, indicated by intense, sharp (112), (200), (220), and (312) diffraction peaks. The crystallite size was 34.6-57.3 nm, increasing with substrate temperature. FESEM indicated that the morphology improved with substrate temperature. The optical band gaps of the films were 1.36-1.49 eV, and their absorption coefficients were on the order of 10(-4) cm(-1), making them quite suitable for use in solar cells. We fabricated solar cells with a structure of soda-lime glass/Mo/Cu2ZnSnS4/CdS/i-ZnO/ZnO:Al/Al and achieved a maximum conversion efficiency of similar to 2.69 %.