Spray chemical vapor deposition (spray CVD) processes of a special type have been investigated for use in making CuInS2 absorber layers of thin-film solar photovoltaic cells from either of two subclasses of precursor compounds: [(PBu3) 2Cu(SEt)2In(SEt)2] or [(PPh3)2Cu(SEt)2 In(SEt)2]. The CuInS2 films produced in the experiments have been characterized by x-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and four-point-probe electrical tests

Banger, Kulbinder K.

Harris, Jerry

Hepp, Aloysius

Jin, Michael H.

NASA Technical Reports Server

20 NASA Tech Briefs, June 2007
Spray chemical vapor deposition (spray
CVD) processes of a special type have
been investigated for use in making
CuInS2 absorber layers of thin-film solar
photovoltaic cells from either of two sub-
classes of precursor compounds: [(PBu3)
2Cu(SEt)2In(SEt)2] or [(PPh3)2Cu(SEt)2
In(SEt)2] {where Bu, Et, and Ph signify
butyl, ethyl, and phenyl groups, respec-
tively}. CuInS2 is a member of the class of
chalcopyrite semiconductors described in
the immediately preceding article.
[(PBu3)2Cu(SEt)2In(SEt)2] and [(PPh3)2
Cu(SEt)2In(SEt)2] are members of the
class of single-source precursors also de-
scribed in the preceding article.
In a spray CVD process of this type, a
room-temperature solution containing
the precursor compound is first ultra-
sonically nebulized. The resulting
aerosol is swept into a two-zone reactor
by a flow of argon, which serves as a
nonreactive carrier gas. In the reactor,
the aerosol first encounters the evapo-
ration zone, which is a warm zone
wherein the solvent and precursor
evaporate. The resulting mixture of
gases then enters the deposition zone,
which is a hot zone wherein the precur-
sor decomposes and the semiconduc-
tor film grows on a substrate as in con-
ventional CVD. 
Spray CVD affords a combination of
the most desirable features (but without
the major difficulties)
of metalorganic CVD
and spray pyrolysis.
These desirable fea-
tures include growth
of the film in an inert
atmosphere, capability
for deposition on a
large area, laminar
flow over the substrate,
and storage and deliv-
ery of the precursor
from a cool solution
reservoir. The last-
mentioned feature is
especially advanta-
geous in that it can
prevent premature de-
composition of a ther-
mally labile precursor. 
Two different spray
CVD processes of this
type have been tested
in experiments thus far.
In one process, a hori-
zontal hot-wall reactor
was used; in the other
process, a vertical cold-
wall reactor was used
(see figure). In each
process, the flow rate of
argon was typically
about 4 L/min. For the
horizontal hot-wall re-
value between 1.0 and 2.4 eV, thus
making it possible to fabricate cells
containing high and/or graded
bandgaps. 
A “single-source precursor com-
pound” is  a single molecular compound
that contains all the required elements,
which when used under the spray CVD
conditions, thermally decomposes to
form CuInxGa1–xSySe2–y. Relative to the
use of multiple precursor reagents, the
use of  single-source precursors offers
the advantage of better regulation of the
chemical composition of the deposit,
less susceptibility to contamination, and,
most importantly, a simplified fabrica-
tion process.
The improved single-source precur-
sor compounds of the invention are
denoted by the general formula
[(LR3)2Cu(ER′)2M(ER′)2], where L
signifies P, As, or Sb; R or R′ signifies
an alkyl or aryl group; and E signifies S
or Se. The general formula and molec-
ular structure afford flexibility for tai-
loring the precursor to suit a specific
CVD spray process and to tailor the
chemical composition (more specifi-
cally, the proportions x and y) of
CuInxGa1–xSySe2–y formed in the
process. In addition, by choosing L, R,
R′, and E according to their steric and
electronic properties, one can tailor
decomposition temperatures and the
phases in the deposit. 
A single-source precursor of the inven-
tion can by synthesized by the reaction
of a stabilized Cu(I) cation with an
In(III) or Ga(III) chalcogenide anion
prepared in situ by reaction of the conju-
gate acid of the thiol or senenol with
NaOEt (where Et signifies an ethyl
group) in CH3OH, as in the example of
the figure. Alternatively, one could syn-
thesize a single-source precursor by use
of commercially available reagents in a
new facile one-pot process: For example
one could react NaSCH3 with InCl3 and
add CuCl and PR3. 
This work was done by Kulbinder K. Banger,
Jerry Harris, and Aloysius Hepp of Glenn Re-
search Center. Further information is con-
tained in a TSP (see page 1).
Inquiries concerning rights for the com-
mercial use of this invention should be ad-
dressed to NASA Glenn Research Center, In-
novative Partnerships Office, Attn: Steve
Fedor, Mail Stop 4–8, 21000 Brookpark
Road, Cleveland, Ohio 44135. Refer 
to LEW-17445-1.
Presaturation
Bubbler
Solution in
Reservoir
Ar
Hot Zone Warm Zone
Atomization
Chamber
Reactor
To Cold
Trap and
Scrubbers
Ultrasonic Plate
Nebulizer
Syringe Pump
Solution
Ultrasonic
Nozzle
Ar
Substrate
Heater
To Cold Trap
HORIZONTAL HOT-WALL REACTOR
VERTICAL COLD-WALL REACTOR
A Horizontal Hot-Wall and a Vertical Cold-Wall Reactor have been
used in experiments on spray CVD for deposition of thin CuInS2 films.
Spray CVD for Making Solar-Cell Absorber Layers 
Spray CVD combines the advantages of metalorganic CVD and spray pyrolysis. 
John H. Glenn Research Center, Cleveland, Ohio 
https://ntrs.nasa.gov/search.jsp?R=20100002254 2019-08-30T08:33:15+00:00Z
NASA Tech Briefs, June 2007 21
actor, the aerosol was generated by use
of an ultrasonic plate nebulizer excited
at a frequency of 2.5 MHz; for the verti-
cal-cold-wall reactor, a syringe pump de-
livered the solution at a rate of 1.5
mL/min to the nebulizer, wherein the
aerosol was generated by use of an atom-
izing ultrasonic nozzle excited at a fre-
quency of 120 kHz. In the horizontal
hot-wall reactor, the portion of the wall
in the evaporation zone was heated to a
temperature of 130 °C, while the portion
of the wall in the deposition zone was
heated to about 400 °C. In the vertical
cold-wall reactor, as its name suggests,
the wall was not heated; instead, the sub-
strate was heated to 400 °C.
The CuInS2 films produced in the ex-
periments have been characterized by x-
ray diffraction, scanning electron mi-
croscopy, energy-dispersive spectroscopy,
and four-point-probe electrical tests. The
results of these tests have provided some
guidance for refinement of the spray
CVD processes and for annealing and
possibly other post-process steps to im-
prove the quality of the deposited
CuInS2 films. 
This work was done by Kulbinder K.
Banger, Jerry Harris, Michael H. Jin, 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, Cleve-
land, Ohio 44135. Refer to LEW-17447-1.
A material consisting of a barium cal-
cium aluminosilicate glass reinforced
with 4 weight percent of boron nitride
nanotubes (BNNTs) has shown promise
for use as a sealant in planar solid oxide
fuel cells (SOFCs). The composition of
the glass in question in mole percent-
ages is 35BaO + 15CaO + 5Al2O3 +
10B2O3 + 35SiO2. The glass was formu-
lated to have physical and chemical
properties suitable for use as a planar-
SOFC sealant, but has been found to be
deficient in one aspect: it is susceptible
to cracking during thermal cycling of
the fuel cells. The goal in formulating
the glass/BNNT composite material was
to (1) retain the physical and chemical
advantages that led to the prior selec-
tion of the barium calcium aluminosili-
cate glass as the sealant while (2) in-
creasing strength and fracture
toughness so as to reduce the tendency
toward cracking.
In preparation for tests, panels of the
glass/BNNT composite were hot pressed
and machined into test bars. Properties
of the test bars, including four-point flex-
ure strength, modulus of elasticity, mi-
crohardness, and density were deter-
mined. In addition, fracture toughness
was measured by the single-edge V-
notch-beam method. Among the conclu-
sions drawn from the results of the tests
were that the flexure strength and frac-
ture toughness of the glass/BNNT com-
posite specimens were greater than
those of neat glass specimens by
amounts of about 90 percent and about
35 percent, respectively (see figure). It
was further concluded that these in-
creases would greatly prolong the life-
times of SOFC seals, yet there would be
little adverse effect on sealing behavior
of the glass because the relatively small
concentration of BNNTs needed to ob-
tain these increases would not cause
much change in the viscosity of the com-
posite sealant material. 
This work was done by Narottam P. Bansal
and Janet B. Hurst of Glenn Research Center
and Sung R. Choi of the University of Toledo.
Further information is contained in a TSP
(see page 1).
Inquiries concerning rights for the com-
mercial use of this invention should be ad-
dressed to NASA Glenn Research Center, In-
novative Partnerships Office, Attn: Steve
Fedor, Mail Stop 4–8, 21000 Brookpark
Road, Cleveland, Ohio 44135. Refer to
LEW-18094-1 
Glass/BNNT Composite for Sealing Solid Oxide Fuel Cells 
Boron nitride nanotubes contribute to strength and fracture toughness. 
John H. Glenn Research Center, Cleveland, Ohio
1.0 
0.5 
0 
140 
120 
100 
80 
60 
40 
20 
0 
Glass Glass/BNNT 
Composite 
Glass Glass/BNNT 
Composite 
Fl
ex
u
re
 S
tr
en
g
th
, M
Pa
 
Fr
ac
tu
re
 T
o
u
g
h
n
es
s,
 M
Pa
·m
1/
2 
Flexure Strength and Fracture Toughness of the
glass and the glass/BNNT composite are com-
pared here, with error bars signifying one stan-
dard deviation.


Spray CVD for Making Solar-Cell Absorber Layers

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server