Chemistry Reference
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origin in the decomposition products of TOPO described later. Tang
et al.
extended this method, using metal acetates and selenium in oleylamine
(OAm) at 250
C to produce a range of ternary compounds such as CuInSe
2
(a mix of triangular, spherical and hexagonal,
ca.
16 nm in size), CuGaSe
2
(11 nm plates) and Cu(InGa)Se
2
(15 nm triangular particles). The particles
displayed di
raction patterns consistent with the target phase, and the
stoichiometry of Cu(InGa)Se
2
could be changed by altering the amount of
reagents. The reaction solvent/capping agent was a key factor in the
synthesis; reactions that contained TOP, TOPO, dodecanethiol or stearic acid
all failed.
6
Very similar chemistry was used to again prepare QDs of CuInSe
2
,
using the metal chloride salts as precursors, although in contrast to the
earlier report, TOP could be used as a precursor.
1
In this case, the addition of
the selenium precursor dictated the crystalline phase; with the metal
precursors dissolved in OAm, rapid injection of OAm/Se resulted in the
formation of sphalerite particles, whereas addition of OAm/Se with the metal
precursors followed by gradual heating resulted in chalcopyrite-structured
particles. Unusually, hexagonal rings of CuInSe
2
were obtained by using TOP/
InCl
3,
TOP/CuCl and TOPSe as precursors (Figure 4.1). This chemistry was
extended to the synthesis of Cu(In
1
x
Ga
x
)(S
1
y
Se
y
)
2
nanocrystal inks for
photovoltaic applications.
7
Using a di
d
n
1
y
4
n
g
|
2
erent selenium precursor, Ph
2
Se
2
, in the OAm system gave
another crystalline metastable phase of CuInSe
2
with an onset of absorption
at
ca.
1000 nm.
8
Injection of a Ph
2
Se
2
solution into a solution of CuCl and
In(CH
3
C(O)CH
2
C(O)CH
3
)
3
in OAm at 180
C followed by 3 hours growth
resulted in the wurtzite-structured particles of CuInSe
2
, approximately
.
Figure 4.1
Electron microscope images of CuInSe
2
rings. Reprinted with permission
from Q. Guo, S. J. Kim, M. Kar, W. N. Shafarman, R. W. Birkmire, E. A.
Stach, R. Agrawal and H. W. Hillhouse,
Nano Lett.
, 2008, 8, 2982.
Copyright 2008 American Chemical Society.
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