CZTS: a non-vacuum deposition method

The research in thin film solar cells has been dominated by light absorber materials based on chalcogenides CdTe and Cu(In,Ga)Se2 in the last decades. Both the toxicity of cadmium and the scarce availability of indium lead towards the development of a material which constituents are earth-abundant and relatively harmless. Polycrystalline Cu2ZnSnS4 (CZTS) is a semiconductor with a bandgap between 1,40 and 1,50 eV and an absorption coefficient higher than 104 cm-1, thus suitable for being employed as a thin film light absorber. Kesterite-type CZTS material showing the highest energy conversion efficiency (η) is synthesized mostly via vacuum-based methods such as sputtering or evaporation of metals (or metal sulphides) onto the suitable substrate. These techniques have the advantage of easily controlling the chemical composition and phase profile in the thin films and normally have good reproducibility. However, the real low-cost potential of kesterites could be more efficiently exploited if combined with a scalable, non-vacuum deposition method. Starting from a sol-gel recipe proposed by Tanaka et al. [1] this work aims at fabricating CZTS using less expensive metallic precursors spin-coated on a rigid substrate. The annealing step was conducted using elemental sulphur rather than hydrogen sulphide, in order to develop a safer sulphurization method.