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

Bailey, Sheila

Banger, Kulbinder

Castro, Stephanie

Hepp, Aloysius

NASA Technical Reports Server

NASA Tech Briefs, June 2007 19
Materials
A process has been devised for making
ternary (specifically, CuInS2) nanocrystals
for use as quantum dots (QDs) in a con-
templated next generation of high-effi-
ciency solar photovoltaic cells. The
process parameters can be chosen to tai-
lor the sizes (and, thus, the absorption
and emission spectra) of the QDs.
The process used heretofore to synthesize
quantum dots in general involves in situ py-
rolysis of reagents in the presence of a passi-
vating 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 fur-
ther nucleation. The prevention of further
nucleation, also known as capping, serves to
regulate the size of the QDs.
The present process is simpler and in-
volves less handling of toxic reagents. In-
stead of the reagents of the prior process,
one uses a compound of the type de-
scribed in the first of the two immediately
preceding articles, “Improved Single-
Source Precursors for Solar-Cell Ab-
sorbers.” The single-source precursor is
dissolved in trioctylphosphine under an
inert atmosphere. The resulting solution is
subsequently injected into a hot stirred so-
lution of trioctylphosphine oxide (TOPO)
in order to facilitate controlled decompo-
sition of the precursor to obtain the de-
sired capped ternary quantum dots.
Aliquots of the solution are removed dur-
ing 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. Further information is
contained in a TSP (see page 1).
Inquiries concerning rights for the commer-
cial 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.
Making Ternary Quantum Dots From Single-Source Precursors 
Relative to a prior process, this process is simpler and safer. 
John H. Glenn Research Center, Cleveland, Ohio
CuInS2 Nanocrystals and Agglomerates on a pol-
ished silicon surface are shown in this scanning
electron micrograph. The average diameter of
the nanocrystals in this batch is 13.4 nm. 
Improved Single-Source Precursors for Solar-Cell Absorbers 
Deposition properties and final compositions can be tailored. 
John H. Glenn Research Center, Cleveland, Ohio
Improved single-source precursor
compounds have been invented for use
in spray chemical vapor deposition
(spray CVD) of chalcopyrite semicon-
ductor absorber layers of thin-film
solar photovoltaic cells. The semicon-
ductors in question are denoted by the
general formula CuInxGa1–xSySe2–y,
where x≤1 and y≤2. These semicon-
ductors have been investigated inten-
sively for use in solar cells because they
exhibit long-term stability and a high
degree of tolerance of radiation, and
their bandgaps correlate well with the
maximum photon power density in the
solar spectrum. In addition, through
selection of the proportions of Ga ver-
sus In and S versus Se, the bandgap of
CuInxGa1–xSySe2–y can be tailored to a
+ 
CU2O   +   HPF6       
MeCN              [Cu{MeCN}4]
+PF6
- 
[Cu{MeCN}4]
+PF6
-   +   2LR3     
CH2Cl2/Ar 
-2MeCN 
[{LR3}2Cu{MeCN}2]
+PF6
- 
NaOEt  +   HER'    MeOH/Ar    NaER'  +  MeOH 
4 NaER'  +  InCl3  
MeOH/Ar 
-3NaCl 
Na+[In(ER')4] 
(LR3)2Cu(ER')2In(ER')2 CuInE2 
 
 Key to  
Nonstandard  
Abbreviations 
L = P, As, or Sb 
E = S or Se 
R = Alkyl or Aryl 
R' = Alkyl or Aryl 
Me = CH3 
Et = CH2CH3 
These Sequences of Chemical Reactions are representative of the synthesis of a single-source precursor,
in this case, [(LR3)2Cu(ER′)2M(ER′)2] followed by formation of the chalcopyrite semiconductor (in this
case, CuInE2) from the precursor.
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Making Ternary Quantum Dots From Single-Source Precursors

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