This study focuses on the preparation and characterization of single phase CuInS2 nanoparticles with a copper complex as precursor via microwave technique. The effect of sulfur sources on product size and morphology was investigated. The products were characterized by X-ray diffraction, scanning electron microscopy, ultraviolet–visible spectroscopy, and photoluminescence spectroscopy. Thin films CuInS2 were prepared by doctor’s blade method and then studied via I-V characterization

Sabet, M.

Salavati-Niasari, M.

English

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 3 No 2, 02NEA01(3pp) (2014) 
 
 
2304-1862/2014/3(2)02NEA01(3) 02NEA01-1  2014 Sumy State University 
Using Simple Microwave Approach for Synthesize of CuInS2 Nanostructures and  
Investigation of their Performance in Solar Cells  
 
M. Sabet, M. Salavati-Niasari* 
 
Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box. 87317–51167, I.R. Iran 
 
(Received 05 January 2014; published online 29 August 2014) 
 
This study focuses on the preparation and characterization of single phase CuInS2 nanoparticles with a 
copper complex as precursor via microwave technique. The effect of sulfur sources on product size and 
morphology was investigated. The products were characterized by X-ray diffraction, scanning electron mi-
croscopy, ultraviolet-visible spectroscopy, and photoluminescence spectroscopy. Thin films CuInS2 were 
prepared by doctor’s blade method and then studied via I-V characterization. 
 
Keywords: CuInS2, Microwave, Nanoparticles, Solar cell. 
 
 PACS numbers: 68.37.Hk, 88.40.H –, 84.40. – x 
 
 
                                                          
* salavati@kashanu.ac.ir 
1. INTRODUCTION 
 
Semiconductor nanocrystals (NCs), and luminescent 
NCs have attracted considerable interest during the 
past decades because of their numerous applications in 
photoelectronic devices and biotechnology [1]. Among 
ternary semiconductor compounds belonging to the I-
IIIVI2 series, CuInX2 (X  Se, Te, S) are promising ma-
terials for photovoltaic applications because of the suit-
ability of their electrical and optical properties [2]. Qi-
an’s group reported the preparation of CIS nanocrys-
tals (NCs) via solvo / hydrothermal routes from dual 
multiple sources [3]. Castro et al. synthesized ultrafine 
CIS NCs by thermal decomposition of the single-source 
precursor, [(PPh3)2CuIn(SEt)4] [4]. several deposition 
methods have been developed for preparing CuInS2 
thin films, such as single source evaporation [5], co-
evaporation [6], sulfurization of metallic precursors [7], 
chemical vapor deposition [8], electro-deposition [9], 
spray pyrolysis [10], sputtering [11] and rapid thermal 
process [12] etc. Up to now, different morphologies of 
CuInS2 thin film and powders have been obtained, such 
as nanoparticles [13], nanorods [14], nanotubes [15], 
nanowires [16], foamlike CuInS2 nanocrystallites [17], 
and porous microspheres [18]. Microwave irradiation 
plays an important role in chemical reactions in aque-
ous media [19], reducing the time [20] and the cost, 
decreasing particle size with narrow size distribution, 
increasing the product yield rate, and producing high 
purity products in comparison with conventional meth-
ods [21]. Microwave irradiation suggests great ad-
vantages as the simplest and fastest technique since 
selective dielectric heating, due to the difference in the 
solvent and reactant dielectric constants, can provide 
significant improvement in reaction rates [22]. In this 
experiment CuInS2 nanoparticles were synthesized and 
characterized with different physical measurement. 
The effects of sulfur sources, solvents, microwave heat-
ing time and irradiation power were investigated. Thin 
film of CuInS2 was fabricated by doctor’s blade and I-V 
characterization was used for calculating solar cell 
characteristic. 
2. SYNTHESIS AND CHARACTERIZATION 
 
2.1 Method of Sample Manufacturing and 
Anaysis 
 
To synthesize CuInS2 nanoparticles, 0.02 mol of 
[Cu(Hsal)2] and 0.02 mole of indium chloride (InCl3) 
were solublized in 30 ml propylene glycol separately and 
stirred for 10 min. Subsequently two solutions mixed 
together. This mixture was then combined with sulfur 
(0.04 mole in 50 ml propylene glycol) sources. Final com-
pound was stirred for 10 min and left for the reaction to 
proceed by cyclic microwave radiation at 750 powers in 
propylene glycol as solvent for 6 min. Each cycle was 
90 s long, and composed of 30 and 60 s for the on and off 
periods, respectively. The precipitates were washed with 
water and ethanol, dried at 80 C for 24 h and were 
characterized by SEM, PL, UV-Vis, and XRD analyses. 
CuInS2 films were prepared by Doctor’s blade coating 
using slurry of 0.05 g CuInS2 powders dispersed in 5 ml 
ethanol, 0.05 g ethyl cellulose and 0.05 ml Triton X-100 
mixture on Indium Tin Oxide (ITO)-coated glass sub-
strate. Then, the glass substrate was maintained at 
300 C for 30 min to remove the organic compounds. 
With a chemical bath deposition (CBD), CdS thin film 
have coated on CuInS2 electrode. CBD was performed 
with a solution consisting of 0.01M Cd(NO3)2, and 0.08M 
thiourea. The bath was heated to 80 °C then the sample 
was immersed. The counter-electrode was prepared by 
chemical deposition of a platinum solution above an ITO 
electrode. This electrode was placed over the 
CdS / CuInS2 electrode. The redox electrolyte consisted 
of 0.05 M LiI, 0.05 M I2 and 0.5 M 4-tert-butylpyridine at 
acetonitrile as a solvent. The photocurrent–voltage (I-V) 
curves were used to calculate short-circuit current (Isc), 
open-circuit voltage (Voc) and fillfactor (FF) of the 
DSSCs. I-V mesurement was made under simulated Air 
Mass 1.5 global illumination. 
 
3. RESULT AND DISCUSSION 
 
In this work, influence of sulfur sources on morphology 
and particle size of as-prepared CuInS2 nanoparticles was 
 M. SABET, M. SALAVATI-NIASARI PROC. NAP 3, 02NEA01 (2014) 
 
 
02NEA01-2 
studied. As shown in Fig. 1, two different sulfur sources 
were used for preparation of CuInS2 crystals. When thiou-
rea was used as sulfur source, nanoparticles with smallest 
size were obtained (Fig. 1a). When Carbon disulfide was 
used instead of thiourea, aggregated spheres with about 
200 nm diameters were achieved (Fig. 1b).  
 
 
 
Fig. 1 – SEM image of CuInS2 prepared by (a) Thiourea and 
(b) Carbon disulfide as sulfur source 
 
Optical properties of the CuInS2 nanocrystals were in-
vestigated by UV-vis spectroscopy and photoluminescence 
(PL) spectroscopy at room temperature. Fig. 2 (a, b) shows 
UV-Vis spectra and plot of (hν)2 versus photon energy hν. 
The band gap of CuInS2 nanoparticles could be obtained 
by extrapolating the slope of curves to the x-axis in a plot 
of (hν)2 against hν on the basis of the absorbance of UV-
visible measurement. From above information, estimated 
bangap for as-synthesized nanoparticles was 2.2 eV which 
showed about 0.7 eV blue shift in comparison with bulk 
sample with 1.53 eV bandgap. This is due to smaller par-
ticle size of synthesized product compared with the bulk 
one. Fig. 2c illustrates room-temperature photolumines-
cence (PL) spectra of CuInS2 nanoparticles. A broad PL 
band can be observed at 2.07 eV that has 130 meV red 
shift in comparison to UV-vis result. It was found that 
this red shift value is due to presence of defect levels in 
CuInS2 structure [23]. Thus a stokes shift at PL spectrum 
can be seen. 
Fig. 3 shows the diffractograms of CuInS2 nanopar-
ticles. As shown in this Fig, the main diffraction peaks 
were observed at 28.38°, 32.9°, 46.67°, 55.23° in the 
XRD pattern of the CuInS2 which confirm that the 
formed material is CuInS2 with tetragonal structure. 
(JCPDS No. 15-0681, a  5.511 and c  11.05). There is 
no peak from impurity compared with the standard 
diffraction pattern of CuInS2 which indicates the prod-
ucts have high purity. The crystal size of the CuInS2 
nanoparticles was estimated by Debye-Scherrer equa-
tion (d  0.9 k /  cosθ) and it was about 4.7 nm, which 
is in agreement with the other observation results. The 
diffraction peaks are clearly broadened, which can be 
the result of the reduced particle size. 
 
 
Fig. 2 – (a) UV-Vis spectra, (b) plot of (hν)2 versus (hν), and 
PL spectra of CuInS2 nanostructure 
 
 
 
Fig. 3 – XRD pattern of CuInS2 nanostructure 
 
The current-voltage measurement for a CuInS2 so-
lar cell is shown in Fig. 4. The fill factor (FF) and open-
circuit voltage (Voc) were 34 % and 140 mV, respective-
ly. Short-circuit current density, Jsc, was 
0.066 mA/cm2, which is very low value. Because of 
presence of the large number of boundaries grain, the 
high levels of carrier recombination were achieved and 
therefore electron transfer becomes low. These bounda-
ries grain generally have a higher number of deep trap 
states and therefore, act as efficient recombination cen-
ters. Another reason for low short circuit current is 
high bangap of synthesized nanoparticles. A low 
bandgap absorbing material has high absorption, high 
current and low open-circuit voltage and a high band 
gap absorbing material has low absorption, low cur-
rent, and high open-circuit voltage. Also by increasing 
bandgap, trap states that lie within the bandgap has 
increased, so the short circuit current value has de-
creased. 
 
 
 
Fig. 4 – I-V characterization of solar cell 
 а  
 b 
 USING SIMPLE MICROWAVE APPROACH FOR… PROC. NAP 3, 02NEA01 (2014) 
 
 
02NEA01-3 
4. CONCLUSION 
 
In this work CuInS2 nanoparticles were synthesized 
from a new metallic complex as copper precursor. 
CuInS2 nanoparticles were obtained via microwave 
approach at very short time. It was found that the best 
sulfur source for CuInS2 nanoparticles formation was 
thiourea. The bandgap of nanoparticles that were ob-
tained by UV-vis was 2.2 eV. The value of 0.7 eV blue 
shift at bandgap is mainly due to smaller of particle 
size respect to the bulk one. Thin film of CuInS2 was 
prepared by doctor’s blade technique and solar cell was 
made from ITO / CuInS2 / CdS / Pt-ITO layers. I-V 
characterization was obtained from this cell. Calculat-
ed fill factor (FF), open circuit voltage (Voc) and short 
circuit current (Isc) were achieved from I-V curve. The 
small value of Isc is mainly due to very small particles, 
presence of some space between particles in thin film 
and high bandgap of product. 
 
 
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Using Simple Microwave Approach for Synthesize of CuInS2 Nanostructures and  Investigation of their Performance in Solar Cells

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Using Simple Microwave Approach for Synthesize of CuInS2 Nanostructures and Investigation of their Performance in Solar Cells

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