NANO VISION
An International Open Free Access, Peer Reviewed Research Journal
www.nano-journal.org
ISSN 2231-2579 (Print)
ISSN 2319-7633 (Online)
Abbr: Nano Vision.
2013, Vol.3(3): Pg.175-178
Compound Preparation and Fabrication of Electron Beam
Evoparated Cadmium Selenide (CdSe) Thin Film
Solar Cells
S. Sakthivel and V. Baskaran
Thin Film Physics and Nano Science Laboratory,
PG and Research Department of Physics,
Rajah Serfoji Govt., College (Autonomous), Thanjavur, Tamilnadu, INDIA.
email: sakthivel.sunmugam@yahoo,com; bass.physikz@yahoo.com
Presented in First National Conference on Thin Film Science and Nano Technology
(FIRST-NCTFSANT-2013) September 2-3, 2013, Rajah Serfoji Govt. College, Thanjavur, T.N.(India).
ABSTRACT
Highly oriented Cadmium Selenide (CdSe) thin film solar cells
were fabricated on glass substrates by Electron beam evaporation
technique in the vacuum about 10-6 torr. Cadmium Selenide
(CdSe) is an important semiconductor is well suited for optoelectronic applications. The device is composed of two electrodes,
Al-ZnO film as the n-type and Cu2O films as the P-type. A thin
layer of CdSe absorber was deposited by Electron beam
evaporation, coating the ZnO nano structures and the entire
assembly formed p-i-n junction. The deposited films were
subjected to X-ray diffraction (XRD), Scanning electron
microscopy (SEM) and UV-Vis measurements to study their
characterizations. The interplanar distance and structural
parameters were taken from X-ray diffraction (XRD) studies. The
surface morphology and defect studies were done by scanning
electron microscopy (SEM).The values of band gap energy and
absorption coefficient were calculated by UV-Vis absorption
studies. The photovoltaic characteristics were confirmed with cell
structure of < Glass/Al-ZnO/nanostructured Al- ZnO/CdSe/Cu2O
>; Cadmium Selenide (CdSe) is a suitable potential candidate for
developing newer photovoltaic devices.
Keywords: Cadmium Selenide, Nano structured Al-ZnO, Vacuum
Evaporation, Solar cell.
Nano Vision Vol. 3, Issue 3, 31 October, 2013 Pages (93-239)
176
S. Sakthivel, et al., Nano Vision, Vol.3 (3), 175-178 (2013)
1. INTRODUCTION
Cadmium Selenide (CdSe) is one of
the promising semiconductor materials for
high efficiency thin film photovoltaic cells
as absorbing layer in manufacturing low
cost thin film photovoltaic solar cell1. The
CdSe thin films possess n-type as well as ptype semi conductivity depending upon the
type of vacancies created during deposition
of thin films. CdSe with a narrow direct
band gap of 1.74 eV with hexagonal
structure2 and high absorption coefficient
(104 cm1) is one of the promising
candidates for quantum dot LED,
photovoltaic, optoelectronic applications3-5.
In addition, CdSe is low cost and most
stable absorber material for processing of
solar cell with good efficiency. Several
deposition methods such as were vacuum or
non-vacuum6,7, laser ablation8, electro
chemical deposition9, chemical deposition10,
hot wall deposition11 and spray pyrolysis12
employed for the deposition of CdTe thin
films. The electron beam evaporation
technique is suitable for the deposition of nCdSe thin films due to high power density,
wide range of controlled evaporation as well
as directly evaporent material converted into
vapour13.
In the present work, we first utilized
electron beam evaporation technique to
fabricate p-CdSe/n-Cu2O thin film solar
cell. Electron beam evaporation is more
advantage because of avoiding impurities
during film growth, the tendency to form
oxides can be considerably reduced and
very slow rate of deposition is possible.
2. EXPERIMENTAL DETAILS
A thin film solar cell with the
structure Glass/Al-ZnO/p-CdSe/ n-Cu2O
/ZnO has been fabricated in which CdSe
layer was deposited on top of the Al-ZnO
chemical bath coated glass substrate by
electron beam evaporation technique. The
thickness of CdSe layer was controlled by a
quartz thickness monitor (QTM) on the
evaporation equipment. Then, a layer of
Cu2O was deposited on the top of the CdSe
layer by the thermal evaporation method at
a pressure of 10-6 mbar. Finally a layer of
ZnO was deposited on the top as a back
contact by the thermal evaporation method.
The final cell structure of the device had an
area of 2x2 cm2.
The grain size of the p-CdSe/nCu2O thin films was determined by an X-ray
diffractometer with Cu K radiation ( =
1.5406 A).The optical characteristics of
these films were performed by a
UV/VIS/NIR
spectrometer
in
the
wavelength range from 300 nm to 1400 nm
at room temperature. The surface
morphology was observed by a scanning
electron microscope (SEM).
3. RESULTS AND DISCUSSION
3.1 XRD analysis
Fig.1 XRD pattern spectrum of the CdSe film
Nano Vision Vol. 3, Issue 3, 31 October, 2013 Pages (93-239)
S. Sakthivel, et al., Nano Vision, Vol.3 (3), 175-178 (2013)
A typical X-ray diffraction pattern
of CdSe thin film is shown in fig (1). The
XRD pattern shows several peaks at 2
values of 23.839o, 27.65o, 35.932o, 56.24o
which may be assigned to the diffraction
lines produced by the (100), (101), (102),
and (202) planes of hexagonal structure.
The appearance of the (102) reflection plane
at diffraction angle 2 = 35.932oand 45.36o
is an indication of the hexagonal structure of
CdSe thin film14. The appearance of many
peaks in the XRD pattern is an indication of
polycrystalline nature of the CdSe thin film.
The crystallite size in CdSe thin film is
evaluated from the intensity peaks of
XRD by a Gaussian fit, using
Debye- Scherrer formula,
.
(1)
D =
Where, is the full width at half maximum,
is the wavelength for X-ray used and is
the Braggs angle.
3.2 Morphological analysis
SEM images, of p-CdSe thin film of
thicknesses 25.49 K, are shown in Fig.2. It
has been found from Fig.2 that the films are
fully covered, homogeneous, well adherent
and free from crystal defects such as pin
hole and cracks.
Figure 2: The SEM images of the CdSe thin film (a) 200 m
3.3 Optical Properties
The optical absorption behavior of
p-CdSe thin film is observed that all these
films exhibit good optical absorption in
visible range (400nm-700nm). This
absorption increases with increase of film
thickness due to increase of crystallite size.
The bigger size of crystallite reduces the
reflectivity of incident photon on the film
surface and correspondingly increases
absorption due to multiple reflections. The
177
(b) 50 m
direct energy band gap Eg is obtained by
extrapolating the straight portion of the
curve. The intercept portion of h=0 line
give the value of the direct band gap. The
direct energy band gap of p-CdSe thin film
decreases from 1.60 eV with increase of
film thickness. This decrease in direct band
gap with increase of film thickness is due
to increase in grain size of film thickness,
which can be explained on the basis of
quantum size effect15.
Nano Vision Vol. 3, Issue 3, 31 October, 2013 Pages (93-239)
178
S. Sakthivel, et al., Nano Vision, Vol.3 (3), 175-178 (2013)
4. CHARACTERIZATION OF THE CELL
carry out the present research work.
For the spray deposited CdSe
material, the power conversion efficiency
() of the device was relatively low
(0.97%), since the data of photovoltaic
parameters such as Jsc, Voc, and FF were low.
REFERENCES
5. CONCLUSIONS
The synthesis and characterization
of p-CdSe thin films deposited by Electron
beam evaporation under vacuum preparative
conditions have been investigated. The
results clearly show the role of different
preparative parameters viz purity and
material quantity, substrate temperature
and thickness of the deposited films in
order to get good-quality photosensitive
material. Structural analysis shows that the
films are polycrystalline with a hexagonal
crystal structure. The dislocation density
and strain show a reverse nature to
temperature and thickness. Micrographs
show that the film surface is well covered
by uniformly distributed grains with
varying sizes. The observed direct band
gap for optimized parameters is about 1.60
eV. The photovoltaic efficiency (0.97%)
was studied with cell structure of Glass/AlZnO/nanostructured Al- ZnO/CdSe/Cu2O;
Cadmium Selenide (CdSe) is a suitable
potential candidate for developing newer
photovoltaic devices. Finally, it is
concluded that the CdSe thin films are
potential candidates for solar cell
applications.
ACKNOWLEDGMENTS
The authors would like to express
their thanks to the University Grants
Commission (UGC), New Delhi, India for
sanctioning the financial assistance [F.
No.41-926/2012(SR) Dated 22.07.2012] to
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