Tin(II) sulfide explained

Tin(II) sulfide is a chemical compound of tin and sulfur. The chemical formula is SnS. Its natural occurrence concerns herzenbergite (α-SnS), a rare mineral. At elevated temperatures above 905 K, SnS undergoes a second order phase transition to β-SnS (space group: Cmcm, No. 63).[1] In recent years, it has become evident that a new polymorph of SnS exists based upon the cubic crystal system, known as π-SnS (space group: P213, No. 198).[2] [3]

Synthesis

In principle, tin(II) sulfide can be prepared directly from the elements:

Sn + S → SnSHowever, the high-temperature reaction vaporizes sulfur. Consequently effecting the proper stoichiometry is difficult.[4] At near-room temperature in liquid ammonia solution, the same reaction still gives a mixture of 60% stannous and 35% stannic sulfide.[5] Likewise metallic tin contaminates triaryltin sulfide pyrolysates.[5]

At cryogenic temperatures, stannous chloride dissolves in liquid hydrogen sulfide. It then decomposes to the sulfide, but only slowly.[6]

Instead, molten, pure, anhydrous potassium thiocyanate reliably reduces stannic oxide to SnS at 450 °C. An aqueous rinse then removes the potassium sulfide coproduct:[4]

SnO2 + 2 KSCN → SnS + K2S + 2CO + N2

Properties

Tin(II) sulfide is a dark brown or black solid, insoluble in water, but soluble in concentrated hydrochloric acid. Tin(II) sulfide is insoluble in (NH4)2S. It has a layer structure similar to that of black phosphorus. As per black phosphorus, tin(II) sulfide can be ultrasonically exfoliated in liquids to produce atomically thin semiconducting SnS sheets that have a wider optical band gap (>1.5 eV) compared to the bulk crystal.[7]

Photovoltaic applications

Tin(II) sulfide is an interesting potential candidate for next generation thin-film solar cells. Currently, both cadmium telluride and CIGS (copper indium gallium selenide) are used as p-type absorber layers, but they are formulated from toxic, scarce constituents.[8] Tin(II) 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.[9] Based on the a detailed balance calculation using the material bandgap, the power conversion efficiency of a solar cell utilizing a tin(II) sulfide absorber layer could be as high as 32%, which is comparable to crystalline silicon.[10] Finally, Tin(II) sulfide is stable in both alkaline and acidic conditions.[11] All aforementioned characteristics suggest tin(II) sulfide as an interesting material to be used as a solar cell absorber layer.

At present, tin(II) sulfide thin films for use in photovoltaic cells are still in the research phase of development with power conversion efficiencies currently less than 5%.[12] 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(II) sulfide still remains a promising material if these technical challenges are overcome.

References

  1. Refinement of the structures of GeS, GeSe, SnS and SnSe : Zeitschrift für Kristallographie. Zeitschrift für Kristallographie. 148. 3–4. 295–303. 1978-01-01. en. 10.1524/zkri.1978.148.3-4.295. Wiedemeier. Heribert. von Schnering. Hans Georg. 53314748 .
  2. Rabkin. Alexander. Samuha. Shmuel. Abutbul. Ran E.. Ezersky. Vladimir. Meshi. Louisa. Golan. Yuval. 2015-03-11. New Nanocrystalline Materials: A Previously Unknown Simple Cubic Phase in the SnS Binary System. Nano Letters. 15. 3. 2174–2179. 10.1021/acs.nanolett.5b00209. 25710674. 2015NanoL..15.2174R. 1530-6984.
  3. Abutbul. R. E.. Segev. E.. Zeiri. L.. Ezersky. V.. Makov. G.. Golan. Y.. 2016-01-12. Synthesis and properties of nanocrystalline π-SnS – a new cubic phase of tin sulphide. RSC Advances. en. 6. 7. 5848–5855. 10.1039/c5ra23092f. 2016RSCAd...6.5848A. 2046-2069.
  4. Book: Baudler, M.. Handbook of Preparative Inorganic Chemistry. 1. Georg. Brauer. Reed F.. Riley. 1963. Academic. New York. 63-14307. 1960. 2nd. Tin and lead. 739–740.
  5. Journal of Materials Chemistry. Atmospheric pressure chemical vapour deposition of tin(II) sulfide films on glass substrates from BuSnO2CCF3 with hydrogen sulfide. Louise S.. Price. Ivan P.. Parkin. Mark N.. Field. Amanda M. E.. Hardy. Robin J. H.. Clark. Thomas G.. Hibbert. Kieran C.. Molloy. 4 Oct 1999. 27 Jan 2000. 10. 2 . 527. 10.1039/a907939d . CiteSeerX.
  6. 8 Jan 1925. A study of reactions in liquid hydrogen sulfide. G. N.. Quam. 5 Sept 1924. 47. 105–106. 10.1021/ja01678a014. Journal of the American Chemical Society. (Excerpted from a PhD thesis at Iowa State College.) "The chlorides of tin and phosphorus were all soluble, and slow decomposition resulted in the formation of the respective sulfides." See also Table 1, wherein "Stannous chloride" and "Stannic chloride" are both listed as "Soluble and reactive".
  7. Brent . etal . 2015 . Tin(II) Sulfide (SnS) Nanosheets by Liquid-Phase Exfoliation of Herzenbergite: IV–VI Main Group Two-Dimensional Atomic Crystals. J. Am. Chem. Soc. . 137 . 39. 12689–12696 . 10.1021/jacs.5b08236 . 26352047. free .
  8. Ginley. D.. Green. M.A.. 2008. Solar energy conversion towards 1 terawatt. MRS Bulletin. 33. 4. 355–364. 10.1557/mrs2008.71. free.
  9. Andrade-Arvizu. Jacob A.. Courel-Piedrahita. Maykel. Vigil-Galán. Osvaldo. 2015-04-14. SnS-based thin film solar cells: perspectives over the last 25 years. Journal of Materials Science: Materials in Electronics. en. 26. 7. 4541–4556. 10.1007/s10854-015-3050-z. 137524157. 0957-4522.
  10. Nair. P. K.. Garcia-Angelmo. A. R.. Nair. M. T. S.. 2016-01-01. Cubic and orthorhombic SnS thin-film absorbers for tin sulfide solar cells. Physica Status Solidi A. en. 213. 1. 170–177. 10.1002/pssa.201532426. 2016PSSAR.213..170N. 124780995 . 1862-6319.
  11. Sato. N.. Ichimura. E.. 2003. Characterization of electrical properties of SnS thin films prepared by the electrochemical deposition method. Proceedings of 3rd World Conference on Photovoltaic Energy Conversion. A.
  12. Jaramillo. R.. Steinmann. V.. Yang. C.. Chakraborty. R.. Poindexter. J. R.. 2015. Making Record-efficiency SnS Solar Cells by Thermal Evaporation and Atomic Layer Deposition. J. Vis. Exp.. 99. e52705. 10.3791/52705. 26067454. 4542955.

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