Water-Soluble, Heterometallic Chalcogenide Oligomers As Building Blocks For Functional Films

Monometallic chalcogenide aqueous complexes such as (Sn2S6)(4-) and (Sn4S10)(4-) are widely used as functional ligands with applications in nano-electronics and solar cells. We propose a general process route to the formation of all-inorganic, heterometallic chalcogenide oligomers, thus expanding the range of these functional aqueous ligands. From electrospray ionization mass spectrometry, tetramers were shown to be the most predominant oligomers synthesized in Sn(IV)-Zn(II)-S(II), Sn(IV)-Zn(II)-Se(II) and Sn(IV)-Ga(III)-S(II) systems. While tetramers possessing exclusively one Zn cation were identified in the Sn(IV)-Zn(II)-S(II) system, the full range of solid solutions was achieved for (Sn-a-Ga-b-S-c)(t-) oligomers with 1 <= a <= 4. Using in situ characterization by Sn-119 liquid NMR and Raman spectroscopy, supported by DFT calculations, we demonstrate that the various tetramers adopt a compact adamantane-like structure. The charge of the heterometallic oligomers was shown to be controlled by the doping cation valence and the chalcogenide anion deficiency in the tetramers. These water-soluble heterometallic chalcogenide oligomers can serve as ligands, residue-free dispersants or building blocks for functional film fabrication. Using these oligomers, we report here the fabrication of chalcogenide solar cells employing environmentally friendly, all-aqueous, (Sn-a-Zn-b-S-c) (t-)-capped CZTS nanocrystal inks.