A process has been devised for making ternary (specifically, CuInS2) nanocrystals for use as quantum dots (QDs) in a contemplated next generation of high-efficiency solar photovoltaic cells. The process parameters can be chosen to tailor the sizes (and, thus, the absorption and emission spectra) of the QDs.

CuInS2 Nanocrystals and Agglomerates on a polished silicon surface are shown in this scanning electron micrograph. The average diameter of the nanocrystals in this batch is 13.4 nm.

The process used heretofore to synthesize quantum dots in general involves in situ pyrolysis of reagents in the presence of a passivating solvent/ligand that not only serves as a medium for the formation of the QDs via pyrolysis, but also readily coordinates to the surfaces of the QDs, thereby preventing further nucleation. The prevention of further nucleation, also known as capping, serves to regulate the size of the QDs.

The present process is simpler and involves less handling of toxic reagents. Instead of the reagents of the prior process, one uses a compound of the type described in the first of the two immediately preceding articles, "Improved Single- Source Precursors for Solar-Cell Absorbers." The single-source precursor is dissolved in trioctylphosphine under an inert atmosphere. The resulting solution is subsequently injected into a hot stirred solution of trioctylphosphine oxide (TOPO) in order to facilitate controlled decomposition of the precursor to obtain the desired capped ternary quantum dots.

Aliquots of the solution are removed during the formation of the nanocrystals and are monitored via ultraviolet/visible-light spectroscopy to obtain information on the sizes of the nanocrystals. When the desired size range is reached, the reaction solution is cooled and methanol is added to remove excess precursor, leaving the TOPO-capped ternary nanocrystals to be harvested. The figure shows the product of one of several experiments performed to test this process.

This work was done by Sheila Bailey, Kulbinder Banger, Stephanie Castro, and Aloysius Hepp of Glenn Research Center. 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-17446-1.


NASA Tech Briefs Magazine

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

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