&A synthesis route has been developed for the commercial manufacture of single- source precursors of chalcopyrite semiconductor absorber layers of thin-film solar photovoltaic cells. The semiconductors in question are denoted by the general formula CuInxGa1–xSySe2–y, where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1.

A closely related class of single-source precursors of these semiconductors, and their synthesis routes, were reported in "Improved Single-Source Precursors for Solar-Cell Absorbers" (LEW-17445-1), NASA Tech Briefs, Vol. 31, No. 6 (June 2007), page 56. Heretofore, the synthesis of single-source precursors of CuInxGa1–xSySe2–y has involved expensive and/or non-commodity starting reagents and cumbersome, lengthy processes — suitable for laboratory settings but not for commercialization. The present synthesis route is better suited to commercialization because it is simpler and involves the use of commercially available agents, yet offers the flexibility needed for synthesis of a variety of precursors.

A single-source precursor of the type of interest here is denoted by the general formula L2M′(μ-ER)2M(ER)2, where L signifies a Lewis base; M signifies Al, In, or Ga; M′ signifies Ag or Cu; R signifies an alkyl, aryl, silyl, or perfluorocarbon group; E signifies O, S, Se, or Te; and μ signifies a bridging ligand. This compound can be synthesized in a "one-pot" procedure from ingredients that are readily available from almost any chemical supplier. The synthesis of this compound can be summarized in simplified form as MX3 + 4NaER + M′X + 2L →L2M′(μ- ER)2M(ER)2, where X signifies a halogen.

In a demonstration, the following synthesis was performed: Under anaerobic conditions, InCl3 was reacted with sodium ethanethiolate in methanol in a 1:4 molar ratio to afford the ionic stable intermediate compound Na+[In(SEt)4] (where Et signifies ethyl group). After approximately 15 minutes, a heterogeneous solution of CuCl and the Lewis base PPh3 (where Ph signifies phenyl) in a 1:2 ratio in a mixture of CH3CN and CH2Cl2 was added directly to the freshly prepared Na+[In(SEt)4]. After 24 hours, the reaction was essentially complete. The methanolic solution was concentrated, then the product was extracted with CH2Cl2, then the product was washed with dry ether and pentane. The product in its final form was a creamy white solid. Spectroscopic and elemental analysis confirmed that the product was (PPh3)2Cu(μ-SEt)2In(μ-SEt)2, which is known to be a precursor of the ternary semiconductor CuInS2.

This work was done by Aloysius Hepp of Glenn Research Center and Kulbinder K. Banger of the Ohio Aerospace Institute. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Materials category.

&Inquiries concerning rights for the commercial use of this invention should be addressed to

NASA Glenn Research Center
Innovative Partnerships Office
Attn: Steve Fedor
Mail Stop 4–8
21000 Brookpark Road
Cleveland, Ohio 44135.

Refer to LEW-17625.

NASA Tech Briefs Magazine

This article first appeared in the July, 2007 issue of NASA Tech Briefs Magazine.

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