Influence of Field Assisted Chemical Spray Pyrolysis Deposition Technique on the Structural and Optical Properties of CdS Thin Films Original Research Article Journal of Chemistry and Materials Research Vol. 1 (2), 2014, 23–27 U.U. Iwok*, J.A. Bwamba, N.O. Alu, K.K. Adama, Z. Abdullahi, A.C. Egba, A.A. Oberafo, B.O. Akogwu

1. Online available since 2014/ August /14 at www.oricpub.com
© (2014) Copyright ORIC Publications
Journal of Chemistry and Materials Research
Vol. 1 (2), 2014, 23–27
JCMR
Journal of Chemistry and
Materials Research
ORICPublications
www.oricpub.com
www.oricpub.com/jcmr
Original Research
Influence of Field Assisted Chemical Spray Pyrolysis Deposition
Technique on the Structural and Optical Properties of CdS Thin Films
U.U. Iwok*, J.A. Bwamba, N.O. Alu, K.K. Adama, Z. Abdullahi, A.C. Egba, A.A. Oberafo, B.O. Akogwu
Physics Advanced Laboratory, Sheda Science & Technology Complex, P. M. B. 181, Garki – Abuja-Nigeria.
Received 19 May 2014; received in revised form 24 July 2014; accepted 04 August 2014
Abstract
In this paper, we report the preparation and characterization of CdS films prepared by field assisted chemical spray pyrolysis deposition
technique. The effect of the deposition process parameters was investigated with respect to its influence on the structural and optical properties
of CdS thin films. The films were prepared by depositing aqueous solutions of cadmium acetate and thiourea on to a soda-lime glass substrate
at a substrate temperature of 300 °C. The as-deposited films were characterized using X-ray diffraction (XRD) technique to investigate the
crystallographic structure and grain size of the films while the optical properties of the thin films were determined using Avantes single beam
UV-VIS-NIR unpolarized direct incidence spectrophotometer giving a transmittance and absorbance spectrum plot in the wavelength range of
200 – 800 nm. The result of the structural study revealed that the films obtained had polycrystalline hexagonal structure which was consistent
with that obtained for other deposition techniques. It also showed a peak at the 2θ position of 26.4148° with a FWHM of 0.9216° and d-
spacing of 3.37101A° while estimation of the optical band gap showed a cutoff on the absorption versus wavelength spectra at the 533.3nm
position which gave an energy bandgap of 2.33eV.
Keywords: Field assisted chemical Spray Pyrolysis; Structural properties; Optical properties; CdS thin films.
1. Introduction
The properties of semiconductor materials are very
important for determining their applicability in various fields
of science and engineering [1]. The efficiency of a material for
PV applications can be greatly influenced by the method
chosen to fabricate the semiconductor material. Since thin film
polycrystalline semiconductors have shown to be a more
suitable and less expensive alternative to the widely used
silicon devices, deposition methods employed for their
fabrication should be such that can maintain the desired
properties of the materials being fabricated [2]. In the case of
optical properties of materials, the bandgap is one of the most
important properties of modern semiconductors [3]. With
applications in photovoltaics, microprocessing, visual display,
* Corresponding author.
E-mail address: maribanga@yahoo.com (U.U. Iwok).
All rights reserved. No part of contents of this paper may be reproduced or
transmitted in any form or by any means without the written permission of
ORIC Publications, www.oricpub.com.
and lighting sources, the bandgap of a semiconductor is an
important property for designing and discovering new
applications for semiconductors.
The fabrication of CdS thin films has over the years been
greatly explored for its versatility in sensors, opto-electronics,
energy, materials for hetero-junction solar cell applications
and as a promising material for window layers in low cost high
efficiency thin film solar cells because of its suitable band gap,
high optical transparency and absorption coefficient in the
visible range of the solar spectrum [1,4, 5–7]. Research has
shown that chemically deposited methods ensure better
efficiency of CdS buffer layers for solar cells and is most
convenient [8]. Several techniques have been reported for the
preparation of thin films such as electro-deposition [9]; Pulse
laser deposition [10], Physical Vapor deposition [11], Vacuum
evaporation [12], and solid state reaction [13] .All of these
have sophisticated requirements of temperature and pressure
controls. One of the promising techniques for producing large
areas of CdS thin films for terrestrial photovoltaic applications
is the spray pyrolysis technique which presents a more
convenient, simple and cheap technology for thin film
preparation. During the spray pyrolysis deposition process, a
precursor aerosol is sprayed on to a heated substrate by means

2. 24 U.U. Iwok et al. / Journal of Chemistry and Materials Research 1 (2014) 23–27
of a carrier gas or some electrostatic charge. The components
in the precursor aerosol react to form a new chemical
compound on the substrate surface and usually some
byproducts that should vapourise in the open atmosphere. The
properties of the deposited films depend on the precursors’
solution, qualitative composition, spraying rate, substrate
temperature, ambient atmosphere, carrier gas, droplet size and
the cooling rate after deposition. The thickness of the prepared
film is influenced by the spray nozzle distance, the substrate
temperature, the concentration of the precursor and the amount
of the sprayed precursor solution. The thin film formation
depends on the reactant/solvent evaporation and on the process
of droplet landing. The ideal deposition condition is
considered when the solvent is completely removed at the
moment the droplet approaches the substrate where the
chemical reaction occurs [14]. The reactant molecules undergo
the process of absorption, surface diffusion and chemical
reaction, leading to nucleation and layer growth while volatile
byproducts evaporate and diffuse away from the surface. In the
preparation of cadmium sulphide thin films, previous research
works have reported various cadmium precursors for the
fabrication of CdS thin films such as Cadmium chloride [3,15],
cadmium sulphate [16], cadmium iodide [17], and cadmium
nitrate [18]. The preparation of cadmium sulphide thin films
by field assisted chemical spray pyrolysis technique, being
reported in this paper, was obtained by using cadmium acetate
as a precursor for cadmium and thiourea for sulfur. As an
integral part of the industrial process for cell preparation on a
large scale it has found great success in recent years. The
structural and optical properties of the prepared thin films
were analyzed by A PANalytical XPERT PRO MPD X-ray
diffraction PW 3040/60 system and Avantes single beam UV-
VIS-NIR unpolarized direct incidence spectrophotometer
respectively.
2. Materials and Methods
Analytical grade cadmium acetate and thiourea were used as
precursors as sources of Cadmium and Sulphur. Appropriate
weight quantities of cadmium acetate Cd(COOCH3)2 and
thiourea (NH2CSNH2) salts were weighed out using a digital
weighing balance and used to prepare 100 and 200 ml aqueous
solutions of cadmium acetate and thiourea respectively with
absolute ethanol in the ratio of 1:1:1 respectively. The
resulting 0.1M of cadmium acetate and 0.2M of thiourea
obtained was used to deposit CdS thin films on soda-lime glass
substrate by the method of field assisted chemical spray
pyrolysis. The field assisted chemical spray pyrolysis setup
used for the solution delivery and subsequent film deposition
consisted of a high voltage source –14 kV, delivery pump,
atomizing nozzle –24 hypodermic needle, temperature
controller and a substrate heater. Since substrate temperature is
a very important parameter in spray pyrolysis deposition and
in order to optimize CdS film preparation, initial depositions
were done at different temperatures of 200, 250 and 300 °C.
The optimized uniform films were obtained at 300 °C which
was also the temperature of choice for preparing the rest of the
thin films. In the same way, the deposition time was varied
from 5, 8, 10 and 12 mins respectively and it was observed
that uniformly deposited films was obtained at 10 minutes
deposition time. In this process of preparation, the atomization
of the chemical solutions of cadmium acetate and thiourea
loaded in the delivery chamber of the spray pyrolysis
equipment into fine droplets was done by an electro-statically
charged spray nozzle at a voltage of 14 kV and the solution
was sprayed on to the heated substrate. The optimized
deposition parameters used for producing uniformly
homogenous thin films were: flow rate of 15 cm3
/min,
substrate temperature of 300 °C, nozzle distance of 10 cm and
deposition time of 10 mins. The chemicals vaporized and
reacted on the surface of the substrate to produce thin films of
uniform thickness. They were thereafter allowed to cool to
room temperature and thoroughly rinsed with acetone to
remove any impurities. The chemical reaction involved in the
production of the CdS thin films is represented as follows:
Cd (CH3COO )2, 2H2O + NH2CSNH2 + H2O CdS +
CO2 + CH4 + Steam + NO2 (1)
The films prepared were golden yellow in appearance.
Thereafter, the CdS thin films prepared were characterized
structurally and optically to obtain their properties. A
PANalytical XPERT PRO MPD X–ray diffraction PW
3040/60 system with CuKα monochromatic radiations was
used for the structural characterization of the CdS thin films.
With a wavelength of 1.54060Å, accelerating voltage of 45KV
and current of 40mA respectively, the data was collected over
a scanning range of angle 2θ = 10° to 100˚C using a step size
of 0.0840˚ and an acquisition scan step time of 421.0050 s.
The systems software was used to determine sample
crystallinity and other parameters. The optical properties of the
CdS thin films were obtained using Avantes single beam UV-
VIS-NIR unpolarized direct incidence spectrophotometer in
the wavelength range of 200 – 800 nm. The transmittance data
from the spectrophotometer was used to determine the
absorbance data and spectra.
Table1 Solutions used for the production of CdS thin films.
Cd Acetate (0.1M) (ml) Thiourea (0.2M)(ml)
1 1
0.95 0.95
0.9 0.9
0.6 0.6

3. U.U. Iwok et al. / Journal of Chemistry and Materials Research 1 (2014) 23–27 25
3. Results and discussion
3.1.Structural Properties
The XRD pattern showed the as-deposited thin films to be
amorphous (or consisted of small grains), single phase
polycrystalline hexagonal structure which is consistent with the
structure of CdS thin films produced by Chemical bath
deposition and SILAR techniques [18]. XRD profile for the as-
deposited thin film is shown in Fig. 1. The spectra showed the
presence of a peak at 2θ position of 26.4184°. This is
indicative of a highly preferential growth which is oriented
towards the (003) direction/plane with reference to the peak
thereby exhibiting a polycrystalline hexagonal structure which
is in tandem with the report of other authors who have reported
hexagonal structures for CdS films deposited by other
techniques [17,19]. Other structural parameters such as lattice
constant were determined from the XRD software and grain
size by the use of appropriate equations. The structural
parameter of CdS films formed at the pronounced peak gave a
peak position 2θ of 26.4184°, Full Width at Half Maximum
(FWHM) of 0.9216, d-spacing of 3.37101A°, and orientation
plane/direction of (003).The identification and assignments of
the observed diffraction patterns were found to be in
agreement with International Center for Diffraction Data
(ICDD) reference values. Invariably hexagonal structures were
obtained by the field assisted- electrostatic spray pyrolysis
deposition technique employed which agrees with reports of
several authors as [18]. However, the structural parameters
were obtained with reference to the pronounced [003] peak
position while Scherrer’s formula Eq. (2) was used to
determine the average crystallite size and this was found to be
1.54 nm [18,19]:
D = 0.9λ / (β cos θ) (2)
where λ is the wavelength of the wave used; β is the Full
Width Half Maximum (FWHM); θ is the diffraction angle.
Fig. 1. X-Ray diffraction profile of CdS thin film.
3.2.Optical Properties
The influence of field assisted chemical spray pyrolysis
technique on the optical properties of the CdS thin films was
evaluated using the Avantes single beam unpolarized
spectrophotometer. Transmittance versus wavelength as well
as absorbance versus wavelength were obtained for the thin
films in the wavelength range 200 – 80 nm and are shown in
Figs. 2 and 3, respectively.
From these Figs., it was observed that the transmittance of the
deposited thinfilms increased with wavelength between 350 to
800 nm which indicated that the region of absorbance lies
below this wavelength. The relative optical transmittance in
the optical spectrum was observed to be about 70 % indicative
of a good material for optoelectronic and sensor devices. The
absorbance spectra in Fig. 3 shows an overall absorption of the
CdS thin films at wave lengths ranging from 300 – 590nm, the
maximum absorption was at 300 nm. This is indicative of
better aborption at the visible region of the absorption
spectrum thus making it very useful for solar applications.
The transmittance spectra of CdS thin films prepared by field
assisted chemical spray pyrolysis technique were obtained as
seen in Fig. 2 below.
The absorption spectra of CdS thin films prepared by field
assisted chemical spray pyrolysis technique were obtained as
seen in Fig. 3.
Fig. 2. Optical transmittance spectra of the CdS thin film.
Fig. 3. Optical absorbance spectra of the CdS thin film.

4. 26 U.U. Iwok et al. / Journal of Chemistry and Materials Research 1 (2014) 23–27
The CdS thin films had excellent absorption at relatively
shorter wavelength regions thus increasing the wavelength
resulted in decreased absorption. The band gap of the prepared
films was obtained from the plot of the absorption coefficient
against photon energy using the Tauc expression below.
According to Tauc, the dependence of the absorption
coefficient, α, on the photon energy, hν, for near-edge optical
absorption in semiconductors is represented in the form
[20,21]:
αhν = A(hν – Eg)m
(3)
and
e = hν (4)
where A is a constant, Eg is the band gap corresponding to a
particular transition occurring in the film, ν is the transition
frequency, h is Planks constant given by 6.63 x 10–34
m2
Kg/s,
m is the characterizes the nature of the band transition. For m =
½ for an allowed direct energy gap and m = 3/2 for a forbidden
direct energy gap [22,23].
Also, the absorption coefficient α and absorption index
(extinction coefficient) Kf were obtained from the
transmittance, T, as follows [24].
Kf = [2.303 *log (1/T) λ]/4πt (5)
where t is the thin film thickness. Generally, absorption
coefficient α and absorption index Kf, are related by [25]:
α = 4πKf /λ (6)
Also, using equation (7) below, for the band gap energy [26]
E = h*C/λ (7)
where h is the Planks constant = 6.63 x 10–34
Joules sec, C is
the Speed of light = 3.0 x 108
meter/sec and λ = Cut off
wavelength = 533.5 nm (obtained from absorbance versus
wavelength plot in Fig. 3).
Estimation of the optical energy gap of the CdS thin films was
done from the above equations and uv-spectroscopy data and
was found to be 2.33 eV. The optical study of the CdS thin
films prepared by field assisted chemical spray pyrolysis
technique at a substrate temperature of 300 °C had the
following parameters: Film thickness 100 nm, absorption
coefficient (106
m–1
) – 4.39, absorption index – 0.10672 and
estimated energy gap of 2.33 eV.
The optical bandgap energy was also obtained from the plot of
the absorption coefficient versus photon energy by using
equation 3 and taking m = ½. From the expression obtained,
extrapolating the curve of (αhυ)2
plotted against photon energy
(hυ) to the the zero of the ordinate as shown in Fig. 4, the
value of the energy gap obtained from the plot in figure 4 was
≈ 2.3eV for a film thickness of 100 nm.
Fig. 4. Optical absorption coefficient spectra of CdS thin film against
photon energy.
4. CONCLUSION
We have successfully prepared CdS thin films by field
assisted chemical spray pyrolysis technique using cadmium
acetate and thiourea as precursors. The as-deposited CdS thin
films were characterized by X-ray diffraction and avantes UV–
VIS–NIR single beam unpolarised spectrophotometer. The
XRD spectra revealed the films to be amorphous with
polycrystalline hexagonal structure of small grains. The optical
study results showed the CdS thin film to be a direct band gap
material as reported in other studies and its high transmittance
makes it suitable as a window material for solar cell
applications. Similarly, its absorbance properties also make it
suitable for sensor applications. The results obtained revealed
that the chemical spray pyrolysis technique used for the
production of the thin films gives very good thin films for use
in the fabrication of high efficiency solar cells which would go
a long way to minimize resources as a result of its cheap and
inexpensive technology.
Acknowledgement
The authors of this research work wish to acknowledge the
management of Sheda Science and Technology Complex
(SHESTCO), Abuja for making available the equipment used
in this research work.
References
[1] Sanjeeviraja, P.R.C., Ramachandran, K. (2005). Thermal and structural
properties of spray pyrolysis CdS thin films. Bulletin of Materials
Science, 28, 233–238.
[2] Ottih, I. E., Ekpunobi, A.J. (2011). Fabrication and characterisation of
high efficiency solar cell thin films (CdNiS). The Pacific Journal of
Science and Technology, 12, 351–355.
[3] Adnan, M.A. (2009). The effect of doping on the optical properties of
CdS thin films prepared by spray pyrolysis. Journal of Kerbala
University, 7, 40–49.

5. U.U. Iwok et al. / Journal of Chemistry and Materials Research 1 (2014) 23–27 27
[4] Saikia, D., Saikia, P. K., Gogoi, P. K., Saikia, P. (2011). Synthesis,
characterisation and photovoltaic application of silver doped CdS/PVA
nanocomposite thin films. Digest Journal of Nanomaterials and
Biostructures, 6, 589–597.
[5] Burton, L. C., Hench T. L. (1976). ZnxCd1−xS films for use in
heterojunction solar cells. Applied Physics Letters, 29, 612–615.
[6] Romes, N., Sbervegluri, G. Tarricone, L. (1976). Effect of film
thickness on the transmittance of chemical bath fabricated CdS thin
films. Applied Physics Lett. 32, 8.
[7] Oliva, A.I., Solis-Canto, O., Castro-Rodriguez, R., Quintana, P. (2001).
Formation of the band gap energy on CdS thin films growth by two
different techniques. Thin Solid Films, 391, 28–35.
[8] Devi, R., Purkayashtha, P., Kalita, P. K., Sarma, R., Das, H. L., Sarma,
B. K. (2007). Photoelectric properties of CdS thin film prepared by
chemical bath deposition. Indian Journal of Pure and Applied Physics,
Volume 45, pp. 624–627.
[9] Choy, K. L., Su, B. (2001). Growth behavior and microstructure of CdS
thin films deposited by an electrostatic spray assisted vapor deposition
(ESAVD) process. Thin Solid Films, 388, 13–22.
[10] Hoffmann, Ph., Horn K., Bradshaw A.M., Johnson R.L., Fuchs D.
Cardona M. (1993). Dielectric function of cubic and hexagonal CdS in
the vacuum ultraviolet region. Phys. Rev., B47, 1639–1642.
[11] McCandless, B.E., Birkmire, R.W. (1992). Analysis of post deposition
processing for CdTe/CdS thin film solar cells. Solar Energy, 31, 527–
535.
[12] Ugwn, E. I., Ugwn, and Onan D. U. (2007). Optical Characteristics of
Chemical Bath Deposited CdS Thin Film Characteristics within UV,
Visible, and NIR Radiation. Pacific Journal of Science and Technology,
8, 155–165.
[13] Wang, W., Liu, Z., Xu, C., Liu, Y., Wang, G. (2008). Catalyst and
temperature dependent growth of silicon nitride micro/ nanoribbons.
Journal of Nanoscience and Nanotech, 8, 3926–3929.
[14] Patil, P.S., (1999). Versatility of chemical spray pyrolysis technique.
Materials Chemistry and Physics, 59, 185–198.
[15] Baykul, M. C., Orhan, N. (2010). Band alignment of Cd(1-x)ZnxS
produced by spray pyrolysis method, Thin Solid films, 518, 1925–1928.
[16] Nagao, M., Watanabe, S. (1968). Chemically deposited thick CdS and
their properties, Japan Journal of Applied Physics, 7, 684–685.
[17] Anbarasi, M.L., Sivaraman, T.L., Nagarethinam, V. S., Balu, A.R.
(2014). CdS thin films fabricated by a simplified spray technique using
cadmium acetate as cationic precursor. International Journal of
Chemical and Physical Sciences, 3, 1–9.
[18] Desale D.J., Shaikh S., Siddiqui, F., Ghosh, A., Ravikiran B., Ghule, A.,
Ramphal S. (2011). Effects of annealing on structural and
optoelectronic properties of CdS thin films by SILAR method.
Advances in Applied Science Research, 2, 417–425.
[19] Hasnat, A., Podder, J. (2012). Structural and electrical transport
properties of CdS and Al-doped CdS thin films deposited by spray
pyrolysis. Journal of Scientific Research, 4, 11–19.
[20] Ma. Y.Y., Fahrenbruch, L.A., Bube, R.H. (1977). Photovoltaic
properties of n‐ CdS/p‐ CdTe heterojunctions prepared by spray
pyrolysis. Appl. Phys. Lett. Volume 30, pp. 423–424.
[21] Meshram, R.S., Suryavanshi, B.M., Thombre, R.M. (2012). Structural
and optical properties of CdS thin films obtained by spray pyrolysis.
Advanced in Applied Science Research, 3, 1563–1571.
[22] Ay, F., Aydinlia, A., Agan, S. (2003). Low-loss as grown
germanosilicate layers for optical-wave guides. J. Appl. Phys. 83, 4743–
4745.
[23] Dawar A.I., Shishodia P.K., Chauhan G., Kumar A., Mathur P.C.
(1991). Fabrication of low resistive CdS thin films, Thin Solid Films
201, L1–L5.
[24] Dharma, J. Pisal, A. (2009). Application notes on UV/Vis/NIR
spectrometer. Shelton, CT USA: PerkinElmer, Inc., 2012.
[25] Krunks, M., Bijakina, O., Mikli, V., Rebane, H., Varema, T., Altossar,
M., Mellikov E. (2001). Sprayed CuInS2 thin films for solar cells: The
Effect of solution composition and post-deposition treatments. Solar
Energy Materials and Solar Cells, 69, 93–98.
[26] Ienei, E., Isac L., Duta, A. (2010). Synthesis of alumina thin films by
spray pyrolysis. Revue Roumaine De Chime, 3, 161–165.