Copper Zinc Tin Sulphide compound was synthesized from its elemetal precursurs using simple solid state method. Being quarternary material, there is a large probability of formation of secondary phases like SnS, ZnS, CuS during the material growth process and it requires a detail investigation on the effects of synthesis parameters on the composition and structural properties of the CZTS compound. Here we report the study of effects of annealing on the synthesized compound. The annealing was performed at two different temperatures in the presence of Sulphur. The structural and compositional properties of the as-grown and annealed samples were examined by X-ray diffraction (XRD) and Energy Dispersive Analysis of X-Ray (EDAX). The formation of Kesterite CZTS phase was confirmed by Raman Spectroscopy.
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Kheraj, Vipul

Patel, K.K.

Shah, D.V.

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 5 No 2, 02031(3pp) (2013) Том 5 № 2, 02031(3cc) (2013) 
 
 
2077-6772/2013/5(2)02031(3) 02031-1  2013 Sumy State University 
Effects of Annealing on Structural Properties of Copper Zinc Tin Sulphide (CZTS) Material 
 
K.K. Patel, D.V. Shah, Vipul Kheraj* 
 
Department of Applied Physics, Sardar Vallabhbhai National Institute of Technology, 395007 Surat, India 
 
(Received 15 February 2013; revised manuscript received 01 May 2013; published online 04 May 2013) 
 
Copper Zinc Tin Sulphide compound was synthesized from its elemetal precursurs using simple solid 
state method. Being quarternary material, there is a large probability of formation of secondary phases 
like SnS, ZnS, CuS during the material growth process and it requires a detail investigation on the effects 
of synthesis parameters on the composition and structural properties of the CZTS compound. Here we 
report the study of effects of annealing on the synthesized compound. The annealing was performed at two 
different temperatures in the presence of Sulphur. The structural and compositional properties of the as-
grown and annealed samples were examined by X-ray diffraction (XRD) and Energy Dispersive Analysis of 
X-Ray (EDAX). The formation of Kesterite CZTS phase was confirmed by Raman Spectroscopy. 
 
Keywords: Synthesis, Structural properties, Stoichiometry. 
 
 PACS numbers: 81.16.Be, 61.66.Fn, 61.50.Nw 
 
 
                                                                
* vipulkheraj@gmail.com 
1. INTRODUCTION 
 
Low cost, high efficiency and less environmental pol-
lution have been regarded as the requirements of the 
next generation thin film solar Photovoltaics (PV). 
Chalcopyrite semiconductors such as CdTe and Cu-
InGaSe2 (CIGSe) have already been commercialized 
materials as absorbers in thin film solar cells. The per-
formance of CIGSe based solar cells have also improved 
remarkably over the past decade with the power con-
version efficiency as high as 20.3 % [1]. However, the 
toxicity of Cadmium as well as steep hikes and fluctua-
tions in the prices of Indium and Gallium have motivat-
ed research community to search for an alternative ma-
terial with low toxicity, low cost and sufficient availabil-
ity of resources. Copper Zinc Tin Sulphide (CZTS) is one 
of such promising materials which is formed by replac-
ing Indium and Gallium with Zinc and Tin. CZTS has 
sparkled tremendous research due to its less toxicity 
and earth-abundant constituents. It is a p-type quater-
nary compound semiconductor with kesterite crystal 
structure, high absorption coefficient of the order of 
104 cm – 1 and direct band gap of about 1.5 eV which 
makes it one of the most suitable material for low cost 
thin-film solar PV [2-3]. 
In 1966, R. Nistche et al. [4] reported synthesis of 
CZTS matrial by Iodine vapour transport method. Near-
ly 2 decades later, in 1988, K. Ito and T. Nakazawa re-
ported the photovoltaic effect in CZTS based hetero di-
ode for the first time [5]. Since then various groups have 
studied CZTS material with different techniques. These 
include solvothermal [6], hot injection method [7] and 
solid state methods [8]. The CZTS has also been inves-
tigated extensively as a thin-film absorber material in 
solar cells using variety of deposition methods based on 
vacuum and non vacuum techniques such as co-
evaporation [9], e-beam evaporation [10], pulsed laser 
deposition [11], sputtering [12], spray pyrolysis [13], and 
electrodeposition [14]. However, being quaternary com-
pound, the control over the composition, stoichiometry 
and consequently the structural and optical properties 
of the material is very challenging. This is clearly evi-
dent from the vast gap, that exists between the values 
of Schockley-Queisser efficiency limit for a single junc-
tion cell based on CZTS (~ 30 %) and the highest effi-
ciency of CZTS based solar cell achieved so far (10.1 %) 
[15]. Thus it requires a detail systematic study of the 
fundamental structural and compositional properties of 
the material and its dependence on the synthesis pa-
rameters in order to narrow-down the gap. Here we 
report the effects of annealing on the structural and 
compositional properties of CZTS material synthesized 
by a simple solid state method. 
 
2. EXPERIMENTAL 
 
The elemental precursors, Cu:Zn:Sn:S, were 
weighted in atomic stoichiometric proportion of 2:1:1:4 
and sealed in a evacuated quartz ampoule at a base 
pressure of 10 – 5 mbar. The ampoules were heated in 
electrical arc furnace from room temperature to 670 K 
at the rate of 4 K/min and then up to 1030 K at the rate 
of 2 K/min, where it was kept for 24 hours to ensure 
homogenous crystallization. It was cooled down up to 
670 K at the rate of 4 K/min and then up to room tem-
perature naturally. The solid ingot was then powdered 
by mechanical grinding. To study the effects of anneal-
ing, the synthesized as-grown sample (S1) was then 
sealed in two different evacuated quartz ampoules with 
25 % excess sulphur and sealed with the base pressure 
of 10 – 5 mbar. One ampoule was then heated to anneal 
the compound at 1073 K, whereas the other ampoule 
was heated at 773 K. The annealing was done for one 
hour at constant temperatures. The heating and cool-
ing was done with the same ramp-up and ramp-down 
rate as mentioned above. The other two samples, “S2” 
and “S3”, were prepared by mechanical grinding of sol-
id ingots taken out from the ampoules heated at 
1073 K and 773 K, respectively. 
 
3. RESULTS AND DISCUSSION 
 
The structure of the synthesized powder was stud-
ied using X-ray Diffraction (XRD) made by PANalytical  
 K.K. PATEL, D.V. SHAH, VIPUL KHERAJ J. NANO- ELECTRON. PHYS. 5, 02031 (2013) 
 
 
02031-2 
 
 
Fig. 1 – XRD profiles (a) S1 (b) S2 ( sample S1 annealed at 
1073 K) (c) S3 (sample S1 annealed at 773 K) 
 
X’pert Pro (Cu Kα). The XRD profiles of CZTS powder samples 
S1, S2 and S3 are shown in Fig. 1. 
Diffractogram of the sample S1 shows sharp peaks 
at 2θ values of 18.3 , 28.5 , 32.9 , 47.4  and 56.1 , 
which are identified as the diffractions from (101), 
(112), (200), (220) and (312) planes of the CZTS crystal 
respectively. The diffractions from (112), (220) and 
(303) planes were observed clearly in all the samples 
indicating the formation of Kesterite CZTS phase. The 
lattice parameters calculated for the CZTS samples 
from XRD analysis come out to be a  5.427 Å and 
c  10.854 Å, which are in good agreement with the 
reported values [16]. However, as discussed earlier, the 
CZTS is quaternary compound; the presence of second-
ary phases is always expected in the compound synthe-
sized by solid state method. Here, as seen from Fig. 1, 
the peaks at 15  and 26.4  indicate the diffraction from 
from (001) plane of SnS2 [17] and (120) plane of SnS 
[18], clearly revealing the presence of these secondary 
phases in the as-grown compound. For sample S2 and 
S3 diffraction patterns also show peaks at 43.3 , which 
corresponds to (105) plane of CZTS [16]. The peak from 
(120) plane of SnS enhances in both the annealed sam-
ples, S2 and S3. However, the peaks from CZTS are 
prominent in both these samples. This indicates that in 
both annealed samples, the SnS phase co-exists with 
the dominant CZTS phase. 
Apart from SnS, another probable phase which 
could be present in the samples is -ZnS. However, the 
XRD profile of CZTS and that of -ZnS are identical 
and the angle differences in the major peaks are within 
the instrument accuracy. Hence, for the investigation 
of presence of -ZnS phase in the sample, Raman Scat-
tering Spectroscopy was performed on samples using 
JOBIN YVON HR800 with an excitation wavelength of 
514.5 nm. Fig. 2 shows the Raman spectra of the sam-
ples. 
 
 
Fig. 2 – Raman spectra of (a) S1 (b) S2 ( sample S1 annealed 
at 1073 K) (c) S3 (sample S1 annealed at 773 K). 
 
As shown in Fig. 2, the Raman spectrum of sample 
S1 also depicts the presence of other binary phases 
such as SnS and SnS2, which are in aggrement with 
the results of XRD [19]. For sample S2 and S3 two ma-
jor peaks are observed at 287 cm – 1 and 337 cm – 1. The 
strongest peak at 337 cm – 1 along with the presence of 
peak at 287 cm – 1 is attributed to the A1 symmetry of 
Kesterite CZTS [20]. The A1 modes are pure anion 
modes which correspond to the vibration of sulphur 
atoms surrounded by motionless neighbouring atoms. 
A shoulder peak of the main peak at 349 cm – 1 and a 
broad peak at about 368 cm – 1 were also observed, 
which is in agreement with the reported results for 
CZTS [19]. The shoulder peak at 349 cm – 1 and the 
other peak at 368 cm – 1 are attributed to the Trans-
verse optical (TO) modes and Longitudinal Optical (LO) 
mode of Kesterite CZTS phase respectively. Absence of 
peak at 277 cm – 1, which is a characteristic peak of 
Stannite phase in CZTS in sample S2 and S3, indicates 
that the CZTS phase formed in the annealed samples 
exhibit dominant Kesterite phase [20], which is favour-
able for its application as an absorber in the solar PV. 
Thus, the presence of these four peaks i.e. 287 cm – 1, 
337 cm – 1, 349 cm – 1 and 368 cm – 1 in the Raman spec-
tra confirms the formation of Kesterite CZTS phase in 
the compound. Sharp and strong major peak indicates 
the good crystalline quality of the compound. More im-
portantly, the absence of strong peak at 352 cm – 1 and 
271 cm – 1 denies the presence of -ZnS phase [8, 19]. 
The Raman spectra results are in good agreement with 
the XRD findings for samples S1 and S2. But, for sam-
ple S3, no clear peak corresponding to SnS phase is 
detected in the Raman spectrum. This might be either 
due to the very small amount of SnS phase in the sam-
ple or because of a little inhomogeneity in the com-
pound. Overall, the Raman spectrum eliminates the 
possibility of presence of -ZnS phase and confirms the 
formation of dominant CZTS phase in the sample S3, 
annealed at temperature 773 K. 
 EFFECTS OF ANNEALING ON STRUCTURAL PROPERTIES… J. NANO- ELECTRON. PHYS. 5, 02031 (2013) 
 
 
02031-3 
The atomic stoichiometry and compositional analy-
sis of the synthesized compounds were performed by 
Energy Dispersive Analysis of X-Ray (EDAX) using 
Philips make scanning electron microscope ESEM, XL-
30. The atomic stoichiometry of the constituent ele-
ments with the ratio of the Zinc to Tin and S to Metals 
are given in Table 1. 
 
Table 1 – Chemical composition of CZTS samples 
 
Sam-
ple 
Cu 
(%) 
Zn (%) Sn (%) S (%) 
[ ]
[ ]
Zn
Sn
 
 
S1 28.19 24.54 09.78 37.48 2.50 0.59 
S2 26.74 15.83 10.90 46.54 1.45 0.87 
S3 29.23 13.42 11.08 46.28 1.21 0.86 
 
All the samples were found to be Zn-rich and Sn-
poor, which can be due to the poor incorporation effi-
ciency of Sn as well as the loss of Sn in form of its sec-
ondary binary sulphide phase as observed in XRD pro-
files and raman spectra of the samples. Some of this 
secondary phase may evaporate out of CZTS at high 
temperature and get accumulated at cooler surfaces 
near the end of the ampoule making the samples Sn-
poor. 
However, it is also to be considered that the Zn-rich 
material shows better properties as an absorber layer 
in CZTS based solar cells. The results reveal that sam-
ple S1 shows very poor stoichiometry for the CZTS. 
But, after annealing in presence of Sulphur, better 
stoichiometry is achieved for both S2 and S3 samples. 
Moreover, Sulphur is highly volatile in nature and 
melting point of Sulphur is very low. So Sulphur-
content in sample S1 is very less, as expected. The an-
nealing of the sample in presence of Sulphur created 
the Sulphur-environment in the ampoule and enhances 
the Sulphur incorporation, which leads to the improved 
stoichiometry of the material. 
 
4. CONCLUSION 
 
We have investigated the synthesis of CZTS powder 
from its constituent elements viz. Copper, Zinc, Tin and 
Sulphur using simple solid state method. Structural 
properties of material were studied by XRD, Raman 
spectroscopy and EDAX. The XRD profiles in tandem 
with Raman spectra confirms the formation of domi-
nant Kesterite CZTS phase in all the samples. The as-
grown sample S1 was found to have secondary phases 
such as SnS and SnS2 present in the compound. The 
material also shows Tin- and Sulphur-deficient stoichi-
ometry. Sample S2 annealed at 1073 K and S3 an-
nealed at 773 K in presence of Sulphur show better 
stoichiometry as compared to that of as-grown sample. 
Sample S2, annealed at higher temperature than the 
growth temperature, indicates dominant CZTS phase 
along with considerable presence of SnS, whereas sam-
ple S3, annealed at lower temperature than the growth 
temperature, shows significantly strong signature of 
formation of a good quality CZTS phase. 
 
 
 
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[ ]
[ ] [ ] [ ]
S
Cu Zn Sn


Effects of Annealing on Structural Properties of Copper Zinc Tin Sulphide (CZTS) Material

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Effects of Annealing on Structural Properties of Copper Zinc Tin Sulphide (CZTS) Material

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