In situ gel formation of high quality kesterite thin films

Thin photovoltaics based on chalcopyrite film, Cu(In,Ga)Se2 (CIGS) and related alloys, have established a record efficiency over 22,3% on the laboratory scale, but the scale-up is hindered because of the In low availability. Moreover, conventional methods for fabricating chalcogenide-based solar cells involve vacuum processes, e.g. co-evaporation and sputtering. On the other hand, Kesterite photovoltaics utilizing Cu2ZnSnS4, Cu2ZnSnSe4 and Cu2ZnSn(S,Se)4, composed by earth-abundant elements, can be successfully realized using solution-based methodologies. Non-vacuum processes present significant advantages as lower production costs, higher productivity and uniformity of the final stoichiometry composition. In Nature, kesterite is a mineral with a formula Cu2(Zn,Fe)SnS4, in which zinc and iron share the same lattice sites. Therefore, in this context, we present a new chemical procedure to obtain a high quality Cu2ZnSnS4, Cu2(Zn1-xFex)SnS4, and Cu2FeSnS4 thin films composed by highly soluble and inexpensive precursors in a non-toxic solvent. The films were prepared by a Sol-Gel method and the deposition was carried out by in situ gel formation on fluorine doped tin oxide coated glass. The films obtained were characterized by Raman spectroscopy, X-ray diffraction, energy dispersive X-ray analysis, and by electronic scanning microscopy. The developed methodology has successfully identified an innovative way to achieve high quality kesterite thin films for optoelectronic applications.