Bismuth dissolving antimony in a Thiol–Amine solvent system

Solution processing of thin-film solar cells, offers a simple route to achieve high processability, low-cost, and scalable processes while allowing deposition on flexible substrates via roll-to-roll or inkjet-printing. In this study, we examine the properties of Thiol–Amine mixture as a solvent system for metal-chalcogenide semiconducting materials. Recently it was found that Thiol–Amine mixture allows for a good film recovery at temperatures <500^oC, while being less hazardous and with lower environmental impacts than contemporary alternatives such as hydrazine. While the dissolution mechanism is still unclear, it is known that chalcogenides (S, Se, and Te) are easily dissolved with mild heating in a Thiol–Amine mixture (e.g., ~40% wt. of Se), and that some post-transition and transition metals such as Cu, In, Zn, Sn, are easily dissolved as well. However, while some metals require the presence of a pre-dissolved chalcogenide in solution, some metals do not.

We have found that Bi can be dissolved using a Thiol-Amine mixture with or without the presence of pre-dissolved chalcogenide, forming a yellow solution with absorbance bands at ~525 nm. In contrast, elemental Sb shows no solubility, unless S or Se are added. Interestingly, Sb is soluble in a pre-dissolved Bi solution. Furthermore, introducing Sb to a Bi solution changes the solution appearance to colorless, with a new absorbance band at 390 nm, indicating an electronic configuration change due to the addition of Sb, and possibly the formation of a metal-to-metal charge-transfer state. While the bi-metallic molecular structure is still investigated, we found preliminary evidence for the formation of a Bi-Sb metal-organic adduct. This is the first report of a non-chalcogenide metal dissolving another non-chalcogenide metal in Thiol–Amine mixture through the formation of a direct metal-metal bond. Such metal-organic adducts are used as precursors for solution deposition of semiconductors for solar cells.