Copper Indium Gallium Diselenide (CIGS) is a compound semiconductor material from the group of I-III-VI. The material is a solid solution of copper, indium and selenium (CIS) and copper, gallium and selenium with an empirical formula of CuIn(1 – x)GaxSe2, where 0  x  1. CIGS has an exceptionally high absorption coefficient of more than 105 cm – 1 for 1.5 eV. Solar cells prepared from absorber layers of CIGS materials have shown an efficiency higher than 20 %. CuIn(1 – x)GaxSe2 (x  0.3) nanocrystalline compound was mechanochemically synthesized by high-energy milling in a planetary ball mill. The phase identification and crystallite size of milled powders at different time intervals were carried out by X-ray diffraction (XRD). The XRD analysis indicates chalcopyrite structure and the crystallite size of about 10 nm of high-energy milled CIGS powder after two and half hours of milling. An attempt for preparing the thin film from CIGS nanocrystalline powder was carried out using the flash evaporation technique. Scanning electron microscopy (SEM) reveals uniform distribution of CIGS particles in thin film.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3100

Desai, R.R.

Master, Hamza

Panchal, C.J.

Patel, P.B.

Ray, J.R.

Rehani, Bharati

English

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 5 No 2, 02007(4pp) (2013) Том 5 № 2, 02007(4cc) (2013) 
 
 
2077-6772/2013/5(2)02007(4) 02007-1  2013 Sumy State University  
Mechanochemically Synthesized CIGS Nanocrystalline Powder for Solar Cell Application 
 
Bharati Rehani1,*, J.R. Ray 2, C.J. Panchal2, Hamza Master1, R.R. Desai3, P.B. Patel4 
 
1 Metallurgical and Materials Engineering Department, Faculty of Technology and Engineering,  
The M.S. University of Baroda, Vadodara-390001, Gujarat, India 
2 Applied Physics Department, Faculty of Technology and Engineering,  
The M.S. University of Baroda, Vadodara-390001, Gujarat, India 
3 Department of Chemistry, Sardar Patel University, Vallabh Vidhyanagar-380120, India 
4 Department of Electronics, Sardar Patel University, Vallabh Vidhyanagar-380120, India 
 
(Received 15 February 2013; revised manuscript received 26 April 2013; published online 04 May 2013) 
 
Copper Indium Gallium Diselenide (CIGS) is a compound semiconductor material from the group of I-
III-VI. The material is a solid solution of copper, indium and selenium (CIS) and copper, gallium and sele-
nium with an empirical formula of CuIn(1 – x)GaxSe2, where 0  x  1. CIGS has an exceptionally high ab-
sorption coefficient of more than 105 cm – 1 for 1.5 eV. Solar cells prepared from absorber layers of CIGS 
materials have shown an efficiency higher than 20 %. CuIn(1 – x)GaxSe2 (x  0.3) nanocrystalline compound 
was mechanochemically synthesized by high-energy milling in a planetary ball mill. The phase identifica-
tion and crystallite size of milled powders at different time intervals were carried out by X-ray diffraction 
(XRD). The XRD analysis indicates chalcopyrite structure and the crystallite size of about 10 nm of high-
energy milled CIGS powder after two and half hours of milling. An attempt for preparing the thin film 
from CIGS nanocrystalline powder was carried out using the flash evaporation technique. Scanning elec-
tron microscopy (SEM) reveals uniform distribution of CIGS particles in thin film. 
 
Keywords: Mechanochemical synthesis, Nanocystalline powder, XRD, SEM, Flash evaporation. 
 
 PACS numbers: 81.20.Ev, 81.07.Bc, 61.05.cp 
 
 
                                                 
* rehanirr@yahoo.com 
1. INTRODUCTION 
 
The application of nanotechnology is regarded as an 
important factor for photovoltaic application. It will 
achieve broad economic acceptance through considera-
ble cost savings and increase in efficiency. This devel-
opment is based on new materials and solar cell types 
with simpler production processes [1]. However, the 
conventional vacuum based evaporation methods have 
drawbacks such as the process complexity, high produc-
tion costs and issues regarding the scaling up. Before 
the commercialization of the solar cells, these factors 
need to be considered. 
In this regard, a nanoparticle based preparation of 
the CIGS material and the absorber layer is believed to 
be a promising process due to a relatively low cost sim-
ple preparation method and flexibility for scaling up 
supports the recent advances in nanoparticle synthesis 
technologies. The various processes for the synthesis of 
CIGS nanoparticles/nanocrystalline powder are colloidal 
process [2], precipitation [3], thermolysis [4] and mech-
nical alloying [5]. The advantage of the nano size effect 
of particles is that it lowers the melting temperature of 
the material [6] and therefore an exothermal reactive 
sintering occurs. 
Pure metal powders in desired stoichiometry are 
generally milled in planetary ball mill. The particles are 
repeatedly flattened, fractured and rewelded during the 
process of milling. The kinetic energy of alloying with 
phase transformation during milling depends upon en-
ergy transferred by balls to the powder [8]. Copper In-
dium diselenide (CIS) nanocrystalline powder is very 
easy to prepare without mechanical milling. Addition of 
Gallium (Ga) in the CIS could make this process diffi-
cult, due to the low melting temperature of Ga. Thus, 
mechanochemical synthesis is considered as a suitable 
method. The major advantage of Ga addition is that 
band gap is increasing from 1.02 to 1.66 eV, as the con-
tent of Ga increases from 0 to 1. In CIGS based thin 
film solar cell highest efficiency reported was 20.3 % [7] 
for addition of 0.3 of Ga.  
In this work the CIGS nanocystalline powder was 
synthesized by mechanochemical process, i.e. ball mill-
ing process. Effect of milling time on the material phase 
formation, and crystallite size has been discussed. The 
phase identification and crystallite size measurement 
were carried out using the X-ray Diffraction (XRD) 
method. In addition to this an attempt was made to 
prepare CIGS thin film on glass substrate using flash 
evaporation technique. The surface morphology of the 
CIGS thin film was studied using Scanning Electron 
Microscopy (SEM).  
 
2. EXPERIMENTAL 
 
Copper (Cu), Indium (In), Selenium (Se) and Galli-
um (Ga) are taken in stoichiometric quantities accord-
ing to Cu1In(1 – x)GaxSe2 where x  0.3. The mixed pow-
der was blended in a rolling milling for 30 min prior to 
high-energy milling. High-energy milling was carried 
out in a 250 ml capacity twin-bowl type planetary ball 
mill of M/s. Insmart Systems, Hyderabad. The milling 
was carried out in tungsten carbide lined stainless 
steel vial using tungsten carbide balls of 10 mm and 
6 mm diameters as grinding bodies. The photograph of 
twin-bowl type planetary ball mill system is shown in 
Fig. 1. 
 
 BHARATI REHANI, J.R. RAY, C.J. PANCHAL, ET AL. J. NANO- ELECTRON. PHYS. 5, 02007 (2013) 
 
 
02007-2 
 
 
Fig. 1 – Twin-bowl type planetary ball mill system. Inset fi-
gure shows the tungsten carbide (WC) lined stainless steel 
vial and WC balls 
 
The mill was operated at a speed of 400 rpm and ball to 
charge ratio of 10 : 1. Argon gas was purged inside the 
jars before milling to avoid any oxidation during high-
energy milling. During the course of milling, powder 
samples were drawn at an interval of 30 minute for 
characterization by X-ray diffraction (XRD). The pow-
der diffraction profiles were obtained using Brucker 
AXS, D8 advance diffractometer, within the 2θ range of 
20°-80° at a scan speed of 3° per min using Cu target 
and Cu-Kα radiation of 0.154056 nm wavelength at a 
power rating of 40 kV and 40 mA. 
The thin film of CIGS was prepared on glass sub-
strate by flash evaporation technique from CIGS nano-
crystalline powder in vacuum coating unit of HIND 
HIVAC, Banglore (model no. 15F6). The surface mor-
phology of thin film was studied using Scanning Elec-
tron Microscope model JEOL JSM-5610 LV at different 
magnifications [9]. 
 
3. RESULTS AND DISCUSSIONS 
 
3.1 XRD Analysis 
 
XRD profile of milled powder samples at different 
milling time is shown in Fig. 2. Main peaks appear at 
(112), (220)/(204), (116), and (400) planes indicating 
tetragonal chalcopyrite structure of Cu(In, Ga)Se2 
(CIGS) compound. Peaks appear to be sharp indicating 
crystalline phase of compound. With the CIGS phase 
and additional CuSe phase is also observed as milling 
time increases, particularly after 2 h milling time. The 
d-values of CuSe phase match with the PDF-ICDD 
no. 26-0556, which shows its hexagonal structure. At 
room temperature, CuSe exists as hexagonal phase but 
at 48 °C, it is converted to orthorhombic form and re-
verts back to hexagonal form at 120 °C [10]. The pres-
ence of CuSe in this case after 2 h milling may be  
due to increase in temperature during high- energy ball 
milling. During milling the frictional forces between jar 
and grinding media leads to moderate increase in tem- 
 
 
Fig. 2 – XRD spectra of CIGS powder prepared by ball milling 
having a different milling time 1 h (a), 1.5 h (b), 2.0 h (c), and 
2.5 h (b) 
 
perature during milling. In Fig. 2 the crystalline planes 
for CuSe are (100), (001), (110), and (210) as indicated.  
The broadening of major peak i.e. (112) is clearly ob-
served from the XRD spectra. This indicates that the 
crystallite size reduces with increase in milling time 
from 1 h to 2.5 h. Relatively broad X-ray peaks were ob-
tained for 2.5 h ball milling time, which are indicative of 
crystallite size in nano size regime. Crystallite size was 
calculated using Scherrer’s equation for different milling 
time as given in Table 1. The Table 1 also give the inter-
planar distance (d), corresponding 2θ values and Full-
width half maximum (FWHM) of CIGS nanocrystalline 
powder at different milling time. 
 
Table 1 – Crystallite size and interplanar distance of CIGS 
nanocystalline powder at different milling time 
 
Milling 
time (h) 
2θ (o) 
FWHM 
(radians) 
Crystallite 
Size, 
D (nm) 
d –
spacing 
(nm) 
1 27.05 0.01047 13.62 0.3295 
1.5 27.05 0.01134 13.62 0.3295 
2 27.05 0.01134 12.58 0.3295 
2.5 27.1 0.01309 10.9 0.3289 
 
The XRD spectra shown in Fig. 2 have been com-
pared to standard data, PDF-ICDD no. 35-1102, it shows 
a slight shift of the peaks towards higher 2θ angles. 
Shifting to the higher diffraction angles may due to lat-
tice distortion and internal stresses induced during the 
course of milling [5]. The internal stresses modify the 
lattice parameters and consequently produce an angular 
shift of XRD peak. The XRD profiles when compared for 
different milling times reveal minor shift of peaks to-
wards higher 2θ angles, especially for 2.5 h of milling. 
This shift is possibly due to integration of gallium atom 
in place of indium and thus changes in lattice parame-
ters. When relatively smaller gallium atoms substitute 
for indium atoms in the lattice, it results in gradual 
change in lattice parameters (d – spacing) [11]. The Lat-
tice parameters ‘a’ and ‘c’ were calculated using Equa-
tion 1. 
 MECHANOCHEMICALLY SYNTHESIZED CIGS NANOCRYSTALLINE … J. NANO- ELECTRON. PHYS. 5, 02007 (2013) 
 
 
02007-3 
 
2 2 2
2 2 2
1 ( )h k l
d a c
 (1) 
 
The ‘a’ and ‘c’ values obtained match closely with 
the standard data i.e. PDF-ICDD no. 35-1102. Vegard’s 
law states that there is a linear relationship between 
the lattice parameter ‘c’ and the composition x of  
gallium. The value of lattice parameter ‘c’ decreases 
linearly with gradual decrease in indium content [4]. 
As milling duration increases values of lattice parame-
ter ‘c’ decreases as shown in Table 2. This result sup-
ports the fact that milling does improve the composi-
tion of CIGS compounds by increasing gallium rich 
phases. Also, it reduces the probability of generation of 
the secondary crystalline phases. 
CIGS compound possess tetragonal chalcopyrite 
structure with Bravais lattice values given as {x, y, 
z}  {1, 1, 2}. Each group I element (Cu) and group III 
element (In/Ga) atoms has four bonds to group VI ele-
ment (Se). In turn each Se atom has two bonds to Cu 
and two bonds to In/Ga. As the strength of the group I-
VI and group III-VI bonds are in general different, the 
ratio of the lattice constants c/a is not exactly ‘2’ [11]. 
The c / a ratios for CIGS nano-crystalline powder is in 
good agreement with the literature as shown in Table 2. 
Quantity ‘U’ equals to (2 – c / a) is a measure of the te-
tragonal distortion in chalcopyrite materials. 
 
Table 2 – FWHM, lattice constants ‘a’ and ‘c’, with the tetrag-
onal distortion factor (U) of CIGS nanocystalline powder at 
different milling time. 
 
Milling 
Time (h) 
FWHM 
(radians) 
a (Å) c (Å) 
c / a  
(Å) 
U  2 –
c / a 
1 0.01047 5.698 11.47 2.012 – 0.0129 
1.5 0.01134 5.715 11.39 1.993 0.0070 
2 0.01134 5.698 11.46 2.011 – 0.0112 
2.5 0.01309 5.698 11.40 2.007 – 0.0007 
 
As seen from the Table 2 the tetragonal distortion 
factor is near to zero at 2.5 h milling time i.e. – 0.0007. 
This indicates the minimum stress is present in the 
CIGS powder prepared at higher milling time. 
 
3.2 SEM Analysis of CIGS Thin Film 
 
SEM micrographs of flash evaporated CIGS thin film 
prepared from nanocrystalline powder at different mag-
nifications are shown in Fig. 3a and 3b. The thin films 
are deposited on glass slide of 7.5 cm  2.5 cm at a pre-
disposition temperature of 523 K. The thickness of the 
film was kept near to 250 nm. The film thickness was 
measured using the quartz crystal thickness monitor. 
The film is quiet dense with average distance between 
grains is 0.5 to 1 m as seen in Fig. 3. Grains shown in 
SEM images are worm shaped with approximately 
0.5 m in length and 0.08-0.1 m in width. These worms 
like grains possess a white shinning appearance. In the 
early stages of deposition, adsorption occurs at discrete 
nucleation sites. As atoms approach the surface, islands 
are formed which grows in size until they merge with 
neighboring islands to form a continuous film. The pro-
bability of migration for adsorbed atom on the surface is 
relatively less at lower substrate temperature. 
Deposition at lower substrate temperature leads to 
formation of small isolated grains with large number of 
voids. Surface migration increases at higher substrate 
temperature resulting in enhanced interaction of ad-
sorbed atoms to form large grains [13]. This will have a 
major effect on the size and number of voids present in 
the film. At higher substrate temperatures, i.e. 573 K, 
grain distribution becomes uniform and dense as shown 
in Fig. 3. The surface morphology shows nearly uniform 
distribution of grains. 
 
 
a 
 
 
b 
 
Fig. 3 – SEM microphotograph of CIGS thin film (thickness 
250 nm) deposited at 523 K substrate temperature prepared 
from nanocrystalline powder at 500X (a) and 2000X (b). 
 
4. CONCLUSIONS 
 
High-energy ball milling of elemental of Copper, In-
dium, Gallium and Selenium appears a suitable pro-
cess for the production of Cu(In, Ga)Se2 (CIGS) nano-
crystalline powder having tetragonal chalcopyrite 
structure. Minor secondary CuSe phase appears after 
2 h milling. The milled CIGS powder has crystallite 
size less than 10 nm after two and half hours (2.5 h) of 
milling. Scanning Electron Microscopy (SEM) of as-
deposited CIGS thin film by flash evaporation tech-
nique at a substrate temperature of 523 K shows shin-
ing white worm like grains uniformly distributed on 
the surface.  
 BHARATI REHANI, J.R. RAY, C.J. PANCHAL, ET AL. J. NANO- ELECTRON. PHYS. 5, 02007 (2013) 
 
 
02007-4 
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Mechanochemically Synthesized CIGS Nanocrystalline Powder for Solar Cell Application

Electronic Sumy State University Institutional Repository

JOURNAL OF NANO- AND ELECTRONIC PHYSICS  ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 5 No 2, 02007(4pp) (2013)  Том 5 № 2, 02007(4cc) (2013)   2077-6772/2013/5(2)02007(4)  02007-1   2013 Sumy State University   Mechanochemically Synthesized CIGS Nanocrystalline Powder for Solar Cell Application  Bharati Rehani1,*, J.R. Ray 2, C.J. Panchal2, Hamza Master1, R.R. Desai3, P.B. Patel4  1  Metallurgical and Materials Engineering Department, Faculty of Technology and Engineering,  The M.S. University of Baroda, Vadodara-390001, Gujarat, India 2  Applied Physics Department, Faculty of Technology and Engineering,  The M.S. University of Baroda, Vadodara-390001, Gujarat, India 3  Department of Chemistry, Sardar Patel University, Vallabh Vidhyanagar-380120, India 4  Department of Electronics, Sardar Patel University, Vallabh Vidhyanagar-380120, India  (Received 15 February 2013; revised manuscript received 26 April 2013; published online 04 May 2013)  Copper Indium Gallium Diselenide (CIGS) is a compound semiconductor material from the group of I-III-VI. The material is a solid solution of copper, indium and selenium (CIS) and copper, gallium and sele-nium with an empirical formula of CuIn(1 – x)GaxSe2, where 0   x   1. CIGS has an exceptionally high ab-sorption coefficient of more than 105 cm – 1 for 1.5 eV. Solar cells prepared from absorber layers of CIGS materials have shown an efficiency higher than 20 %. CuIn(1 – x)GaxSe2 (x   0.3) nanocrystalline compound was mechanochemically synthesized by high-energy milling in a planetary ball mill. The phase identifica-tion and crystallite size of milled powders at different time intervals were carried out by X-ray diffraction (XRD). The XRD analysis indicates chalcopyrite structure and the crystallite size of about 10 nm of high-energy milled CIGS powder after two and half hours of milling. An attempt for preparing the thin film from CIGS nanocrystalline powder was carried out using the flash evaporation technique. Scanning elec-tron microscopy (SEM) reveals uniform distribution of CIGS particles in thin film.  Keywords: Mechanochemical synthesis, Nanocystalline powder, XRD, SEM, Flash evaporation.    PACS numbers: 81.20.Ev, 81.07.Bc, 61.05.cp                                                    * rehanirr@yahoo.com 1.  INTRODUCTION  The application of nanotechnology is regarded as an important  factor  for  photovoltaic  application.  It  will achieve broad economic acceptance through considera-ble cost savings and increase in efficiency. This devel-opment is based on new materials and solar cell types with  simpler  production  processes  [1].  However,  the conventional vacuum based evaporation methods have drawbacks such as the process complexity, high produc-tion costs and issues regarding the scaling up. Before the commercialization of  the  solar  cells,  these  factors need to be considered. In this regard, a nanoparticle based preparation of the CIGS material and the absorber layer is believed to be a promising process due to a relatively low cost sim-ple  preparation  method  and  flexibility  for  scaling  up supports the recent advances in nanoparticle synthesis technologies. The various processes for the synthesis of CIGS nanoparticles/nanocrystalline powder are colloidal process [2], precipitation [3], thermolysis [4] and mech-nical alloying [5]. The advantage of the nano size effect of particles is that it lowers the melting temperature of the material [6] and therefore an exothermal reactive sintering occurs. Pure  metal  powders  in  desired  stoichiometry  are generally milled in planetary ball mill. The particles are repeatedly flattened, fractured and rewelded during the process of milling. The kinetic energy of alloying with phase transformation during milling depends upon en-ergy transferred by balls to the powder [8]. Copper In-dium  diselenide  (CIS)  nanocrystalline  powder  is  very easy to prepare without mechanical milling. Addition of Gallium (Ga) in the CIS could make this process diffi-cult, due to the low melting temperature of Ga. Thus, mechanochemical synthesis is considered as a suitable method.  The  major  advantage  of  Ga  addition  is  that band gap is increasing from 1.02 to 1.66 eV, as the con-tent of Ga increases from 0 to 1. In CIGS based thin film solar cell highest efficiency reported was 20.3 % [7] for addition of 0.3 of Ga.  In  this  work  the  CIGS nanocystalline  powder  was synthesized by mechanochemical process, i.e. ball mill-ing process. Effect of milling time on the material phase formation, and crystallite size has been discussed. The phase  identification  and  crystallite  size  measurement were  carried  out  using  the  X-ray  Diffraction  (XRD) method.  In  addition  to  this  an  attempt  was  made  to prepare CIGS thin film on glass substrate using flash evaporation  technique. The surface morphology of  the CIGS  thin  film  was  studied  using  Scanning  Electron Microscopy (SEM).   2.  EXPERIMENTAL  Copper (Cu), Indium (In), Selenium (Se) and Galli-um (Ga) are taken in stoichiometric quantities accord-ing to Cu1In(1 – x)GaxSe2 where x   0.3. The mixed pow-der was blended in a rolling milling for 30 min prior to high-energy  milling.  High-energy  milling  was  carried out in a 250 ml capacity twin-bowl type planetary ball mill of M/s. Insmart Systems, Hyderabad. The milling was  carried  out  in  tungsten  carbide  lined  stainless steel  vial  using  tungsten  carbide  balls  of  10 mm  and 6 mm diameters as grinding bodies. The photograph of twin-bowl type planetary ball mill system is shown in Fig. 1.   BHARATI REHANI, J.R. RAY, C.J. PANCHAL, ET AL.  J. NANO- ELECTRON. PHYS. 5, 02007 (2013)   02007-2   Fig. 1 – Twin-bowl type planetary ball mill system. Inset fi-gure  shows  the  tungsten  carbide  (WC)  lined  stainless  steel vial and WC balls  The mill was operated at a speed of 400 rpm and ball to charge ratio of 10 : 1. Argon gas was purged inside the jars before milling to avoid any oxidation during high-energy  milling.  During  the  course  of  milling,  powder samples  were  drawn  at  an  interval  of  30 minute  for characterization by X-ray diffraction (XRD). The pow-der  diffraction  profiles  were  obtained  using  Brucker AXS, D8 advance diffractometer, within the 2θ range of 20°-80° at a scan speed of 3° per min using Cu target and Cu-Kα radiation of 0.154056 nm wavelength at a power rating of 40 kV and 40 mA. The thin film of CIGS was prepared on glass sub-strate by flash evaporation technique from CIGS nano-crystalline  powder  in  vacuum  coating  unit  of  HIND HIVAC,  Banglore  (model  no. 15F6).  The  surface  mor-phology of thin film was studied using Scanning Elec-tron Microscope model JEOL JSM-5610 LV at different magnifications [9].  3.  RESULTS AND DISCUSSIONS  3.1  XRD Analysis  XRD profile of milled powder samples at different milling time is shown in Fig. 2. Main peaks appear at (112),  (220)/(204),  (116),  and  (400)  planes  indicating tetragonal  chalcopyrite  structure  of  Cu(In,  Ga)Se2 (CIGS) compound. Peaks appear to be sharp indicating crystalline  phase of  compound.  With  the  CIGS  phase and additional CuSe phase is also observed as milling time increases, particularly after 2 h milling time. The d-values  of  CuSe  phase  match  with  the  PDF-ICDD no. 26-0556,  which  shows  its  hexagonal  structure.  At room temperature, CuSe exists as hexagonal phase but at 48 °C, it is converted to orthorhombic form and re-verts back to hexagonal form at 120 °C [10]. The pres-ence  of  CuSe  in  this  case  after  2 h  milling  may  be  due to increase in temperature during high- energy ball milling. During milling the frictional forces between jar and grinding media leads to moderate increase in tem-   Fig. 2 – XRD spectra of CIGS powder prepared by ball milling having a different milling time 1 h (a), 1.5 h (b), 2.0 h (c), and 2.5 h (b)  perature during milling. In Fig. 2 the crystalline planes for CuSe are (100), (001), (110), and (210) as indicated.  The broadening of major peak i.e. (112) is clearly ob-served  from  the  XRD  spectra.  This  indicates  that  the crystallite  size  reduces  with  increase  in  milling  time from 1 h to 2.5 h. Relatively broad X-ray peaks were ob-tained for 2.5 h ball milling time, which are indicative of crystallite size in nano size regime. Crystallite size was calculated using Scherrer’s equation for different milling time as given in Table 1. The Table 1 also give the inter-planar distance (d), corresponding 2θ values and Full-width half maximum (FWHM) of CIGS nanocrystalline powder at different milling time.  Table 1 – Crystallite  size  and  interplanar  distance  of  CIGS nanocystalline powder at different milling time  Milling time (h)  2θ (o)  FWHM (radians) Crystallite Size, D (nm) d –spacing (nm) 1  27.05  0.01047  13.62  0.3295 1.5  27.05  0.01134  13.62  0.3295 2  27.05  0.01134  12.58  0.3295 2.5  27.1  0.01309  10.9  0.3289  The  XRD  spectra  shown  in Fig. 2  have  been  com-pared to standard data, PDF-ICDD no. 35-1102, it shows a  slight  shift  of  the  peaks  towards  higher  2θ  angles. Shifting to the higher diffraction angles may due to lat-tice distortion and internal stresses induced during the course  of  milling  [5].  The  internal  stresses  modify  the lattice parameters and consequently produce an angular shift of XRD peak. The XRD profiles when compared for different  milling  times  reveal  minor  shift  of  peaks  to-wards higher 2θ angles, especially for 2.5 h of milling. This shift is possibly due to integration of gallium atom in place of indium and thus changes in lattice parame-ters. When relatively smaller gallium atoms substitute for  indium  atoms  in  the  lattice,  it  results  in  gradual change in lattice parameters (d – spacing) [11]. The Lat-tice parameters ‘a’ and ‘c’ were calculated using Equa-tion 1.  MECHANOCHEMICALLY SYNTHESIZED CIGS NANOCRYSTALLINE …  J. NANO- ELECTRON. PHYS. 5, 02007 (2013)   02007-3  2 2 22 2 21 ( ) h k ld a c  (1)  The  ‘a’  and  ‘c’  values obtained match  closely  with the standard data i.e. PDF-ICDD no. 35-1102. Vegard’s law states that there is a linear relationship between the  lattice  parameter  ‘c’  and  the  composition  x  of  gallium.  The  value  of  lattice  parameter  ‘c’  decreases linearly  with  gradual  decrease in indium  content  [4]. As milling duration increases values of lattice parame-ter ‘c’ decreases as shown in Table 2. This result sup-ports the fact that milling does improve the composi-tion  of  CIGS  compounds  by  increasing  gallium  rich phases. Also, it reduces the probability of generation of the secondary crystalline phases. CIGS  compound  possess  tetragonal  chalcopyrite structure  with  Bravais  lattice  values  given  as  {x,  y, z}   {1, 1, 2}. Each group I element (Cu) and group III element (In/Ga) atoms has four bonds to group VI ele-ment (Se). In turn each Se atom has two bonds to Cu and two bonds to In/Ga. As the strength of the group I-VI and group III-VI bonds are in general different, the ratio of the lattice constants c/a is not exactly ‘2’ [11]. The c / a ratios for CIGS nano-crystalline powder is in good agreement with the literature as shown in Table 2. Quantity ‘U’ equals to (2 – c / a) is a measure of the te-tragonal distortion in chalcopyrite materials.  Table 2 – FWHM, lattice constants ‘a’ and ‘c’, with the tetrag-onal  distortion  factor  (U)  of  CIGS  nanocystalline  powder  at different milling time.  Milling Time (h) FWHM (radians)  a (Å)  c (Å) c / a  (Å) U   2 –c / a 1  0.01047  5.698  11.47  2.012  – 0.0129 1.5  0.01134  5.715  11.39  1.993  0.0070 2  0.01134  5.698  11.46  2.011  – 0.0112 2.5  0.01309  5.698  11.40  2.007  – 0.0007  As seen from the Table 2 the tetragonal distortion factor is near to zero at 2.5 h milling time i.e. – 0.0007. This  indicates  the  minimum  stress  is  present  in  the CIGS powder prepared at higher milling time.  3.2  SEM Analysis of CIGS Thin Film  SEM micrographs of flash evaporated CIGS thin film prepared from nanocrystalline powder at different mag-nifications are shown in Fig. 3a and 3b. The thin films are deposited on glass slide of 7.5 cm   2.5 cm at a pre-disposition temperature of 523 K. The thickness of the film was kept near to 250 nm. The film thickness was measured  using  the  quartz  crystal  thickness  monitor. The film is quiet dense with average distance between grains is 0.5 to 1  m as seen in Fig. 3. Grains shown in SEM  images  are  worm  shaped  with  approximately 0.5  m in length and 0.08-0.1  m in width. These worms like grains possess a white shinning appearance. In the early stages of deposition, adsorption occurs at discrete nucleation sites. As atoms approach the surface, islands are formed which grows in size until they merge with neighboring islands to form a continuous film. The pro-bability of migration for adsorbed atom on the surface is relatively less at lower substrate temperature. Deposition at lower substrate temperature leads to formation of small isolated grains with large number of voids.  Surface  migration  increases  at  higher  substrate temperature  resulting  in  enhanced  interaction  of  ad-sorbed atoms to form large grains [13]. This will have a major effect on the size and number of voids present in the film. At higher substrate temperatures, i.e. 573 K, grain distribution becomes uniform and dense as shown in Fig. 3. The surface morphology shows nearly uniform distribution of grains.   a   b  Fig. 3 – SEM  microphotograph of  CIGS  thin  film  (thickness 250 nm) deposited at 523 K substrate temperature prepared from nanocrystalline powder at 500X (a) and 2000X (b).  4.  CONCLUSIONS  High-energy ball milling of elemental of Copper, In-dium,  Gallium  and  Selenium  appears  a  suitable  pro-cess for the production of Cu(In, Ga)Se2 (CIGS) nano-crystalline  powder  having  tetragonal  chalcopyrite structure. Minor secondary CuSe phase appears after 2 h  milling.  The  milled  CIGS  powder  has  crystallite size less than 10 nm after two and half hours (2.5 h) of milling.  Scanning  Electron  Microscopy  (SEM)  of  as-deposited  CIGS  thin  film  by  flash  evaporation  tech-nique at a substrate temperature of 523 K shows shin-ing  white  worm  like  grains  uniformly  distributed  on the surface.   BHARATI REHANI, J.R. RAY, C.J. PANCHAL, ET AL.  J. NANO- ELECTRON. PHYS. 5, 02007 (2013)   02007-4 REFERENCES  1.  W. Luther, Application of Nanotechnologies in the energy sector, 9 (Aktionslinic Hessen: Nanotech: 2008). 2.  Se-Jin Ahn,  Ki-Hyun Kim,  Young Gab Chun,  Kyung-Hoon Yoon, Thin Solid Films 515, 4036 (2007). 3.  M.G. Panthani,  V. Akhavan,  B. Goodfellow, J.P. Schmidtke,  L. Dunn,  A. Dodabalapur,  P.F. Barbara, B.A. Korgel, J. Am. Chem. Soc. 130, 16770 (2008). 4.  Sajid Nawaz Malik,  Preparation  of  CuInSe2  and  Cu-InGaSe2 nanoparticles and thin films for solar cells appli-cations, Thesis (The University of Manchester: UK: 2010). 5.  B. Vidhya, S. Velumani, R. Asomoza, J. Nanopart. Res. 13, 3033 (2011). 6.  J.M. Jacobson,  B.N. Hubert,  B. Ridley,  B. Nivi,  S. Fuller, U.S. Patent No. 6294401 (2001). 7.  G. Cao, Nanostructures & Nanomaterials (London: Impe-rial College Press: 2004). 8.  J.S. Benjamin,  T.E. Volin,  Metall.  Mater.  Trans.  5,  1929 (1974). 9.  J.R. Ray, C.J. Panchal, M.S. Desai, U.B. Trivedi, J. Nano- Electron. Phys. 3 No 1, 747 (2011). 10. A.L.N. Stevels, F. Jellinek, Recueil 111, 273 (1971). 11. Layla Al Juhaiman, Ludmila Scoles, David Kingston, Bus-saraporn Patarachao,  Dashan Wang,  Farid Bensebaa, Green Chem. 12, 1248 (2010). 12. Tom Markvart,  Luis Castaner,  Solar  Cells:  Materials, Manufacture  and  Operation  (Amsterdam,  The  Nether-lands: Elsevier: 2005). 13. E. Ahmed,  R.D. Tomlinson,  R.D. Pilkington,  A.E. Hill, W. Ahmed, Nasar Ali, I.U. Hassan, Thin Solid Films 335, 54 (1998).  

Application of Nanotechnologies in the energy sector, 9 (Aktionslinic Hessen: Nanotech:

Bussaraporn Patarachao, Dashan Wang, Farid Bensebaa,

Ki-Hyun Kim, Young Gab Chun, KyungHoon Yoon, Thin Solid Films 515,

Nanostructures & Nanomaterials (London:

Preparation of CuInSe2 and CuInGaSe2 nanoparticles and thin films for solar cells applications, Thesis (The University of

Solar Cells: Materials, Manufacture and Operation (Amsterdam, The Netherlands: Elsevier:

Thin Solid Films 335,

https://essuir.sumdu.edu.ua/bitstream/123456789/31001/1/Rehani%20B._Mechanochemical%20synthesis.pdf

Mechanochemically Synthesized CIGS Nanocrystalline Powder for Solar Cell Application

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