International Journal On Engineering Technology and Sciences – IJETS™
ISSN(P): 2349-3968, ISSN (O): 2349-3976
Volume I, Issue II, June - 2014
INVESTIGATION OF N TYPE CU2O AND SE2 LAYER
PREPARATION BY LOW COST CHEMICAL METHOD
Stephen Raja John Britto
Email ID: steprj76@gmail.com
ABSTRACT: - Solar energy is considered as the most promising alternative energy source to replace
environmentally distractive fossil fuel. Solar energy is radiant light and heat from the sun harnessed using a
range of ever-evolving technologies such as solar heating, solar photovoltaics, solar thermal energy, solar
architecture and artificial photosynthesis. A solar cell, or photovoltaic cell, is an electrical device that converts
the energy of light directly into electricity by the photovoltaic effect. Solar cell based on thin-film technology.
Clearly, The thinness of the cell is the defining characteristic of the technology. Thin-film solar cell
manufacturers building their solar cells by depositing several layers of a light-absorbing material, a
semiconductors on to a substrate -- coated glass, metal or plastic. The materials used as semiconductors don't
have to be thick because they absorb energy from the sun very efficiently. As a result, thin-film solar cells are
lightweight, durable and easy to use. There are three main types of thin-film solar cells, depending on the type
of semiconductor used: amorphous silicon (a-Si), cadmium telluride (CdTe) and copper indium gallium
deselenide (CIGS). Amorphous silicon is basically a trimmed-down version of the traditional silicon-wafer cell.
As such, a-Si is well understood and is commonly used in solar-powered electronics. However, it is a
challenging task to develop solar energy converting devices using low cost techniques and environmentally
friendly materials. This paper investigates the low cost method for the production of the CIGS layer in the thin
film production process.
Key words: Solar cell, CIGS, CdTe, Electro deposition.
multi
source
evaporation,
physical
and
I.INTRODUCTION
chemical vapour deposition to electrochemical,
Photovoltaic, or PV, refers to the conversion of
plasma based and hybrid techniques.
light energy into electricity using electronic
II.OBJECTIVE:
devices called solar cells. Solar cell is Unlike
Copper indium diselenide (CuInSe2 or "CIS")
silicon-wafer cells, which have light-absorbing
has an extremely high absorptivity, which
layers that are traditionally 350 microns thick,
means that 99% of the light shining on CIS will
thin-film solar cells have light-absorbing layers
be absorbed in the first micrometer of the
that are just one micron thick. A micron, for
material. Cells made from CIS are usually
reference,
meter
heterojunction structures – structures in which
(1/1,000,000 m or 1 µm). . A number of
the junction is formed between semiconductors
methods exist for thin film deposition, that
having different bandgaps. The most common
range from simple thermal evaporation over
material for the top or window layer in CIS
is
one-millionth
of
a
43
International Journal On Engineering Technology and Sciences – IJETS™
ISSN(P): 2349-3968, ISSN (O): 2349-3976
Volume I, Issue II, June - 2014
devices is cadmium sulfide (CdS), although
a-Si is deposited followed by P2 laser scribing.
zinc
Then a metal conductive layer is placed as back
is
sometimes
added
to
improve
transparency. Adding small amounts of gallium
contact with the relative P3 laser scribing.
to the lower absorbing CIS layer boosts its
bandgap from its normal 1.0 electron-volts
(eV), which improves the voltage and therefore
the efficiency of the device. This particular
variation is commonly called a copper indium
gallium diselenide or "CIGS" PV cell. Solar
Figure 3.1Amorphous silicon (a-Si)
cells based on these materials are also very
3.2 CIGS/ CIS: it is the semiconductor material
stable, thus allowing long operational lifetimes.
composed of copper, indium, selenium, and/or
The preparation of a thin film solar cell is a
gallium. In thin film technology, CIGS has the
multistage process where every step affects the
highest PV conversion efficiency. CIGS/CIS
resulting cell performance and the production
has similar manufacturing process as a-Si thin
cost. CuInSe2 and other Cu chalcopyrites can
films. However, as opposed to a-Si thin film,
be prepared by a variety of methods, ranging
the glass substrate on CIGS/CIS is at the rear
from physical vapor deposition methods such
instead of the front. In addition, Cds is applied
as
as a buffer layer.
evaporation
and
sputtering
to
low-
temperature liquid phase methods such as
electro deposition.
III. Different types materials used in thin films
are amorphous silicon (a-Si), CIGS/CIS and
CdTe.
3.1 Amorphous silicon (a-Si): most common
and developed. It is the non-crystalline form of
silicon. The cell structure has a single sequence
of p-i-n layers. When exposed to sun, their
power output is significantly decreased. A-Si
type thin film solar cells are commonly found
in
calculators.
A-Si
type
thin
film
Figure 3.2 CIGS (Copper indium gallium (di)
is
selenide)
manufactured in 6 steps. First the glass
3.3 CdTe: it is formed from cadmium and
substrate is coated with a TCO (transparent
tellurium. It is usually combined together with
conductive oxide) layer as front contact,
cadmium sulfide to form a p-n junction PV
followed by P1 laser scribing. Then a layer of
cell. the composition is similar to a-Si solar cell
44
International Journal On Engineering Technology and Sciences – IJETS™
ISSN(P): 2349-3968, ISSN (O): 2349-3976
Volume I, Issue II, June - 2014
with an additional Cds layer for buffer. First
Solar is the largest manufacturer.
IV.CIGS
(Copper
indium
gallium
(di)
selenide)has an extremely high absorptivity,
which means that 99% of the light shining on
CIGS will be absorbed in the first micrometer
of the material.
Figure 4.1 CIGS unit cell Red = Cu, yellow =
CIGS (Copper indium gallium (di) selenide)
CIGS is a I-III-VI2 semiconductor material
Se, blue = In/Ga
composed of copper, indium, gallium, and
CIGS is a tetrahedrally bonded semiconductor,
selenium. The material is a solid solution of
with the chalcopyrite crystal structure. Upon
copper indium selenide (often abbreviated
heating it transforms to the zinc blende form
"CIS") and copper gallium selenide. It has a
and the transition temperature decreases from
chemical formula of CuInx Ga(1-x)Se2 CIGS
1045 °C for x=0 to 805 °C for x=1. They are
is a tetrahedrally bonded semiconductor, with
manufactured by depositing a thin layer of
the chalcopyrite crystal structure, and a
copper, indium, gallium and
abandgap varying continuously with x from
selenide on glass or plastic backing, along with
about 1.0eV (for copper indium selenide) to
electrodes on the front and back to collect
current. Because the material has a high
CAS number
12018-95-0(CuInSe2)
Molecular
CuInxGa(1-x)Se2
absorption coefficient and strongly absorbs
sunlight, a much thinner film is required than
formula
of other semiconductor materials.
Density
~5.7 g/cm3
Melting point
1070-990 °C(x=0–1)
coefficient of more than 105/cm for 1.5eV and
Band gap
1.7–1.0 eV (x=0–1)
higher energy photons. CIGS solar cells with
Crystal
tetragonal
efficiencies around 20% have been claimed by
CIGS has an exceptionally high absorption
structure
both
Space group
I42d
Lattice
a = 0.56–0.58
constant
1),c = 1.10–1.15 nm (x=0–1)
the
National
Renewable
Energy
Laboratory (NREL) and the Zentrum für
nm
(x=0–
Sonnenenergie und Wasserstoff Forschung
(ZSW), which is the record to date for any thin
about 1.7eV (for copper gallium selenide).
film solar cell.
4.2 STRUCTURE
Table 4.2 Properties of CIGS
45
International Journal On Engineering Technology and Sciences – IJETS™
ISSN(P): 2349-3968, ISSN (O): 2349-3976
Volume I, Issue II, June - 2014
IV.THIN FILM DEPOSITION METHODS
which improves the voltage and therefore the
Evaporation
efficiency of the device. This particular

Thermal evaporation
variation is commonly called a copper indium

E-beam evaporation
gallium diselenide or "CIGS" solar cell.
Sputtering
So far the promise of CIGS solar cell

DC Sputtering
technology has been greater than the reality,

DC Magnetron sputtering
but certain advantages of this technology are

RF sputtering
beginning to emerge, namely:
Chemical vapour deposition
•The active layer (CIGS) can be deposited in a

Low-pressure CVD
polycrystalline form directly onto molybdenum

Plasma-Enhanced CVD
coated glass sheets or steel bands. This uses

Metal-organic CVD
less energy than growing large crystals, which
is a necessary step in the manufacture of
crystalline silicon solar cells. Also unlike
4.1 Advantages of CIGS in the photo voltaic
crystalline silicon, these substrates can be
cells:
flexible.
In thin film technology, CIGS has the highest
•One environmental advantage of CIGS solar
PV conversion efficiency. CIGS/CIS has
cell technologies have over Cadmium Telluride
similar manufacturing process as a-Si thin
solar cell panels is that it uses a much lower
films. However, as opposed to a-Si thin film,
level of cadmium, in the form of cadmium
the glass substrate on CIGS/CIS is at the rear
sulfide. In some designs, sometimes zinc is
instead of the front. In addition, Cds is applied
used instead of cadmium sulfide all together.
as a buffer layer. 99% of the light shining on a
•Like Cadmium Telluride panels, CIGS solar
CIGS solar cell will be absorbed in the first
cell panels show a better resistance to heat than
micrometer of the material. Cells made from
silicon based solar panels.
CIGS are usually hetero-junction structures—
4.2 Electro deposition of CIGS layer
structures in which the junction is formed
between
semiconductors
having
Efficient CIGS solar cells prepared directly
different
from
bandgaps. The most common material for the
electrodeposited
near
stoichiometric
precursor films without the post PVD process
top or window layer in CIS devices is cadmium
were reported by several research groups.
sulfide (CdS), although zinc is sometimes
Lincot et al. reported an efficiency of 11.3%
added to improve transparency.Adding small
(Jsc= 23.2mA/cm2, Voc= 0.77 V, FF = 63.4%)
amounts of gallium to the lower absorbing CIS
for an electrodeposited CIGS absorber with a
layer boosts its bandgap from its normal 1.0eV,
band gap of 1.47 eV. Guimard et al. recorded a
46
International Journal On Engineering Technology and Sciences – IJETS™
ISSN(P): 2349-3968, ISSN (O): 2349-3976
Volume I, Issue II, June - 2014
cell efficiency of 10.2% without the PVD step.
period,
The cell parameters were Jsc= 23.2mA/cm2,
demonstrated the capability of its electro
Voc=
deposition
0.74V
and
FF
=
59.6%.
the
company
process
to
developed
yield
and
Cu-In-Ga-Se
Electrodeposition of an elemental layer stack
precursor layers with controlled and repeatable
followed by the selenization treatment led to 7-
Cu/(In+Ga) and Ga/(In+Ga) molar ratios. After
10% efficient devices. Ganchev et al. deposited
roll-to-roll plating hardware to process a 13.5-
the absorber film from a thiocynate assisted
in.-wide web was installed, the capability of the
bath, followed by selenization in a quartz tube
tool to deposit films with uniform thickness
furnace at 560oC under the Se pressure of
was first demonstrated. Then the compositional
10mbar. However, the efficiency of the best
control was shown through measurement of
cell (Mo/CIGS/CdS/i-ZnO/Al : ZnO) was of
electrodeposited Cu-In-Ga-Se precursor layers.
only 4.35%, with Jsc= 31.7mA/cm2, Voc = 300
mV and FF = 45.6%. Dale et al. reported a cell
efficiency of 4.5%.
These reported works showed that the cell
efficiency increased considerably as a result of
the post vacuum deposition. This increase was
Figure 4.2.1 R2R PECVD Process
attributed to the near film stoichiometry and the
resulting band gap. However stoichiometric
One of the most important requirements for
films prepared without the post vacuum
successful application of an electro deposition
deposition always showed lower efficiency. It
technique to CIGS absorber formation is the
can be noticed that the cells constructed with
demonstration of the ability of the technique to
the post vacuum deposited CIGS layer always
control the composition of the deposited films
showed higher FF values.
in a reliable and repeatable manner. Figure
This may be another reason for the obtained
4.2.1.a shows the Ga/(Ga+In) molar ratio data
higher efficiency. The post-deposition may also
collected from the electrodeposited layers by
be beneficial in avoiding micro cracks and
ICP measurements during a period of 95 days.
defects in the film. However, it should be noted
The target in this experiment was a molar ratio
that the post PVD step is not acceptable in
of 0.3 in the deposited film. The electrolyte and
terms of cost factor.
the process conditions were kept unchanged
4.2.1ROLL-TO-ROLL
during the whole test period.
ELECTRODEPOSITION
The data of Figure 4.2.1.a demonstrate that the
The electro deposition step is the heart of the
electro deposition process of this work has the
SoloPower technology. During this project
47
International Journal On Engineering Technology and Sciences – IJETS™
ISSN(P): 2349-3968, ISSN (O): 2349-3976
Volume I, Issue II, June - 2014
capability to include Ga in the deposited films
in a reliable and repeatable manner. Figure
4.2.1.b shows the Cu/(Ga+In) molar ratio data
collected from the same plated samples during
the same 95-day period. The target ratio in this
case was 0.8, and as can be seen from the data,
this ratio was controlled between the values of
Figure 4.2.1.b. The Cu/(Ga+In) molar ratio
0.76 and 0.84 as measured by ICP. This is
data collected from samples electroplated
within the accuracy band of the measurement
during a period of 95 days.
method, and therefore the results demonstrate a
In addition to the repeatability and robustness
good ability for the technique to control
of the electro deposition process in terms of its
composition. It should be noted that for the two
compositional control, experiments were also
excursion points in the data of Figure 4.2.1.b,
carried out with the roll-to-roll electroplating
the measurement instrument was found to be
tool to demonstrate that the film thickness and
faulty. The data of Figures 4.2.1.a and 4.2.1.b
the stoichiometry were uniform throughout a
were collected from the batch process line to
large-area substrate. In one early experiment
evaluate the behavior and stability of the
during the Phase I program, a 13.5-in.-wide and
plating
results
400-ft-long foil substrate was continuously
demonstrated, even for baths with limited
processed through the roll-to-roll electroplating
volume, the chemistry did not show any time-
system and then the deposited film thickness,
dependent instabilities.
the Cu/(Ga+In) ratio, and the Ga/(Ga+In) molar
baths.
As
the
above
ratio were measured across the 12.5-in.-wide
section of the web as well as along the web, at
100-ft intervals. The thickness of the deposit
was found to be within 10% of the target value.
Figure 4.2.1.a. The Ga/(Ga+In) molar ratio
data collected from samples electroplated
during a period of 95 days. Experiment was
Figure 4.2.1 c Back-contact resistivity
carried out in the batch plater.
for different types of contacts and the stability
of the contact resistance at elevated
temperature for up to 728 h.
48
International Journal On Engineering Technology and Sciences – IJETS™
ISSN(P): 2349-3968, ISSN (O): 2349-3976
Volume I, Issue II, June - 2014
ADVANTAGES:
of Cu2O and application for solar cells. Sol. Energy,
The system generates plasma between a pair of
Vol. 80, 715-722
2.Anandan, S., Wen, X. & Yang, S. (2005). Room
rollers connected to power supply. Since the
temperature growth of CuO nanorod arrays on copper
surface of the rollers is covered with the film
and their application as a cathode in dye-sensitized solar
substrate to be coated, the system does not have
cells. Mater. Chem. Phys., Vol. 93, 35-40
powered electrodes to be contaminated with the
3. V. S. Arunachalam (Center for Study of Science,
coating, and this results in stable process during
India) and E. L. Fleischer
(MRS) MRS Bulletin (2008).
a long deposition process for a web.By using
4. M.A. Contreras, K. Ramanathan, J. AbuShama, F.
HMDSO/O2 mixture as process gases, the
Hasoon, D.L. Young, B. Egaas and R. Noufi, Prog.
system is able to deposit SiOx coating as a
Photovolt: Res. Appl. 2005; 13:209–216.
deposition rate up to 900nm·m/min.
5.M. Contreras, M. Romero, B. To, F. Hasoon, R. Noufi,
This
mechanism
gives
the
S. Ward and K. Ramanathan, “Optimization of CBD
following
CdS Process in High-Efficiency Cu(In,Ga)Se2-Based
advantages
Solar Cells,” Thin Solid Films, Vol. 403-404, No. 579,

High material use efficiency
2002, pp. 204-211.

High deposition rate
6. A. Davis, K. Vaccaro, H. Dauplaise, W. Waters and J.

Low contamination
Lorenzo, “Optimization of Chemical Bath-Deposited
Cadmium Sulfide on InP Using a Novel Sulfur Pretreatment,” Journal of The Electrochemical Society, Vol.
7.6 CONCLUSION
146, No. 3, 1999, pp. 1046-1053.
From the investigation of CIGS production, test
7.Fortin, E. & Masson, D. (1981). Photovoltaci effects in
shows that the solar cells efficiency increases
Cu2O-Cu cells growing by anodic oxidation. Solid-St.
with increase in the source temperature, and
Electron., Vol. 25, 4, 281-283
roll to roll electroplating process is the low cost
8.Garuthara,
thin
film
W.
(2006).
type Cu2O films. J. Luminescence, Vol. 121, 173-178
9. Ghijsen, J., Tjeng, L.H., Elp, J. V., H. Eskes,
deposition rate of the material is uniform in this
Westerink, J., & Sawatzky, G.A. (1988). Electronic
process
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the
process.
Siripala,
The
and
production
&
Photoluminescence characterization of polycrystalline n-
method for the production of the CIGS layer in
the
R.
contamination
in
the
11330
production is very low when compared to other
10. Guy, A. C. (1972). Introduction to Material Science
methods. Thus electroplating had given more
(International Student Edition), McGraw-Hill, Tokyo
advantages when compared with the other
Hames,Y. & San,
methods.
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49