Ammonium sulfide aqueous-based ink for Cu2ZnSnS4 thin film preparation

•Ammonium sulfide aqueous-based ink for CZTS thin film deposition is proposed.•The pyrolysis evolutions of the components and intermediate were investigated.•High crystallinity single-phase CZTS thin film was prepared by using the ink.•The ink is hydrazine-free and thus non-toxic.•The ink can facilitate green and low-cost CZTS photovoltaic cells fabrication. In this work, a novel ink for Cu2ZnSnS4 (CZTS) thin film deposition is proposed. (NH4)2S aqueous solution was used as single solvent; NH4CuS4, ZnS nanocrystals with polysulfide ligand and SnS2 as the metal-based components. The pyrolysis evolutions of the components were investigated by thermogravimetric analysis (TGA) and X-ray diffraction (XRD). It is found that NH4CuS4, ZnS nanocrystals with polysulfide ligand and the intermediate (NH4)6Sn3S9·1.3H2O can readily decompose into binary metal chalcogenides at low temperature. The rapid decomposition of ink components during spray pyrolysis deposition makes the ink favorably to form amorphous CZTS film. After deposition, the film was annealed and a high crystalline single-phase CZTS thin film was achieved.