Tin sulfide is a chemical compound of tin and sulfur. The chemical formula is SnS. Its natural occurrence concerns herzenbergite, a rare mineral. At elevated temperatures above 905K, SnS undergoes a second order phase transition to β-SnS. in recent years, it has become evident that a new polymorph of SnS exist based upon the cubic crystal system, π-SnS.
Synthesis
Tin sulfide can be prepared by reacting tin with sulfur, or tin chloride with hydrogen sulfide.
Properties
Tin sulfide is a dark brown or black solid, insoluble in water, but soluble in concentrated hydrochloric acid. Tin sulfide is soluble in 2S. It has a layer structure similar to that of black phosphorus. As per black phosphorus, tin sulfide can be ultrasonically exfoliated in liquids to produce atomically thin semiconducting SnS sheets that have a wider optical band gap compared to the bulk crystal.
Photovoltaic applications
Tin sulfide is an interesting potential candidate for next generation thin film solar cells. Currently, both Cadmium Telluride and CIGS are used as p-type absorber layers, but they are formulated from toxic, scarce constituents. Tin sulfide, by contrast, is formed from cheap, earth abundant elements, and is nontoxic. This material also has a high optical absorption coefficient, p-type conductivity, and a mid range direct band gap of 1.3-1.4 eV, required electronic properties for this type of absorber layer. Based on the a detailed balance calculation using the material bandgap, the power conversion efficiency of a solar cell utilizing a tin sulfide absorber layer could be as high as 32%, which is comparable to crystalline silicon. Finally, Tin sulfide is stable in both alkaline and acidic conditions. All aforementioned characteristics suggest tin sulfide as an interesting material to be used as a solar cell absorber layer. At present, tin sulfide thin films for use in photovoltaic cells are still in the research phase of development with power conversion efficiencies currently less than 5%. Barriers for use include a low open circuit voltage and an inability to realize many of the above properties due to challenges in fabrication, but tin sulfide still remains a promising material if these technical challenges are overcome.
