Effect of precursor concentration on physical

Journal of Asian Ceramic Societies 4 (2016) 357–366

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Effect of precursor concentration on physical properties of nebulized spray deposited In2 S3 thin films J. Raj Mohamed a,b , L. Amalraj a,∗ a b

PG & Research Department of Physics, V.H.N.S.N. College, Virudhunagar 626001, Tamilnadu, India PG & Research Department of Physics, H.H. The Rajah’s College, Pudukkottai 622001, Tamilnadu, India

a r t i c l e

i n f o

Article history: Received 30 March 2016 Received in revised form 26 June 2016 Accepted 4 July 2016 Available online 18 July 2016 Keywords: In2 S3 Resistivity Band gap Urbach Crystallite size

a b s t r a c t The present work investigates the effect of precursor concentration (mc ) on the structural, optical, morphological and electrical conductivity properties of In2 S3 thin films grown on amorphous glass substrates by nebulized spray pyrolysis (NSP) technique. The mixed phase of cubic and tetragonal structure of In2 S3 thin films at higher concentration has been observed by X-ray diffraction pattern. The reduced strain by increasing the precursor concentration increased the average crystallite from 17.8 to 28.9 nm. The energy dispersive analysis by X-ray (EDAX) studies confirmed the presence of In and S. The transmittance, optical direct band gap energy, Urbach energy and skin depth of In2 S3 films have been analyzed by optical absorption spectra. The better conductivity and mobility noticed at mc = 0.15 M are explained by carrier concentration and crystallite. Better optical and electrical conductivity behaviour of In2 S3 thin film sample proposes for effective solar cell fabrication. © 2016 The Ceramic Society of Japan and the Korean Ceramic Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

1. Introduction Despite the fact that the highest efficiency of chalcopyrite (CuFeS2 ) based solar cells is accomplished with CdS absorbing material [1,2], there are various reasons to replace the deposition method as well as the materials. The high absorption coefficient (105 cm−1 ) and comparatively low energy band (2.4 eV) of cadmium sulphide (CdS) bound the spectral response of the device in the wavelength in the low region (99% purity) such as indium chloride (In2 Cl3 ) (Sigma–Aldrich) and thiourea (CS (NH2 )2 ) (GR E Merck) were used as precursors without further purification. The precursors InCl3 and CS (NH2 )2 were used as source materials of In2+ and S2− ions respectively. Micro glass slides have been used as substrates to deposit In2 S3 thin films. Substrate cleaning leads to a major role in the thin film deposition. The contamination on the surface of the substrate may create nucleation sites alleviating the growth, which results in non-uniform film growth. Hence, the micro glass substrate of dimension 7.5 cm × 2.5 cm × 0.25 cm was first water washed well with soap detergent. The washed glass slides were kept in hot chromic acid for an hour to remove grease or oil presented

Fig. 1. Schematic diagram of the simple nebulizer.

during the manufacturing process of glass plates. After that, they were rinsed with acetone and double distilled water before the deposition of the films. In this work, the In2 S3 thin films were deposited with different precursor concentrations from 0.05 M to 0.15 M. The substrate temperature was constrained by an ironconstantan type thermocouple and kept constant as its optimized value of 300 ◦ C. The oxygen carrier gas flow rate was maintained at 1 kg/cm2 corresponding to an average pressure solution rate of 5 ml per 20 min. The schematic diagram of an experimental set-up of NSP technique is shown in Fig. 2. The precursor solution was held in the nebulizer unit, which is connected to an air compressor. The compressed air is transported by tubing and stimulates the precursor solution through an “L” glass tube. The mist-like tiny droplets of particles were carried from the glass tube to deposit onto the glass substrate kept in the uniform hot zone of the furnace. After deposition, the films were allowed to cool at room temperature and then preserved them in desiccators.

Fig. 2. Experimental set-up of nebulized spray pyrolysis technique.

J. Raj Mohamed, L. Amalraj / Journal of Asian Ceramic Societies 4 (2016) 357–366

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Fig. 3. X-ray diffraction pattern of nebulized spray deposited In2 S3 thin films at (a) 0.05 M, (b) 0.075 M, (c) 0.1 M, (d) 0.125 M and (e) 0.15 M.

2.3. Characterization technique

Fig. 4. Variation of thickness of In2 S3 thin films at different precursor concentrations.

The structural and chemical phases of the In2 S3 films were ascer˚ tained by X-Pert Pro X-ray diffractometer (Cu K␣, = 1.5418 A) over a 2 range of 10–65◦ . The optical properties using optical absorption spectrum were observed using UV–vis–NIR double beam spectrophotometer (Hitachi U3410 model) over the wavelength range 300–1100 nm. Scanning electron microscope (SEM) was used to find the dispersion of particles, rough morphology and the particle size on the surface of the film. The surface morphology of the as-deposited In2 S3 films was analyzed by scanning electron microscope (SEM, Genesis model). The chemical composition of In and S was determined by energy dispersive analysis by X-rays (EDAX) on K and L lines. The electrical conductivity of the as-deposited films was found by Hall Effect measurement system by ECOPIA-HMS 5000 model. The thickness of the In2 S3 layers was determined with a stylus profile meter (Mitutoyo, SJ-301).

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Fig. 5. The Williamson–Hall analysis of In2 S3 thin films at different precursor concentrations assuming UDM. Fit to the data, the strain is extracted from the slope and the crystallite size is extracted from the y-intercept of the fit.

3. Results and discussion 3.1. Structural analysis The X-ray diffraction pattern of In2 S3 films of different precursor concentrations deposited at an optimized substrate temperature of 300 ◦ C is shown in Fig. 3. The XRD measurement exposed that all the as-grown film layers were polycrystalline in nature. The four leading diffraction peaks in the XRD pattern of In2 S3 thin films at mc = 0.05 M clearly show the peaks at 14.22◦ , 28.62◦ , 42.62◦ and 57.42◦ corresponding to (111), (222), (511) and (444) planes of cubic phase. The appearance of a peak around 2 = 14.22◦ points a preferred orientation along the (111) plane. The designation of diffraction lines is caused by comparing with JCPDS files of In2 S3 (Cubic, JCPDS 65-0459) with the reflectance (111), (222), (511) and

(444). The intensity of the diffraction peaks with cubic phase turned more intense and sharp with the increase of precursor concentration up to 0.1 M, which notices an improvement of the crystallinity of the grain layers. Zhang et al. and Kraini et al. [28,29] showed similar observation for the In2 S3 thin films deposited using facile hydrothermal and spray pyrolysis techniques respectively. Further, the films prepared at precursor concentration 0.125 M depicted mixed phases of both cubic and tetragonal structures and the crystallinity increased with the increase in precursor concentration. With the increase of precursor concentration to 0.125 M the layer showed (103) as the preferred orientation that corresponds to the tetragonal In2 S3 at 2 = 14.24◦ along with (222), (444) orientations corresponding to cubic structure. At mc = 0.15 M, the diffraction peaks at 14.24◦ , 28.68◦ and 43.60◦ corresponding to In2 S3 film with tetragonal phase along with the peaks of cubic phase at (444)


direction. This is in good agreement with standard JCPDS file (250390) of In2 S3 crystallites with tetragonal structure. There were reports in the literature concerning the presence of both the cubic and tetragonal phases of In2 S3 crystallites [30,31]. In literature indium sulphide films are described to exist contingent on the technique and the conditions used in their growth either in cubic or tetragonal phase or in a mixed phase incorporating both cubic and tetragonal polymorphs. Nevertheless, a precise statement of a particular phase or an allocation of cubic and tetragonal phases is difficult as the diffraction patterns are in general different from the bulk counterparts owing to factors including as stress, preferred orientations, etc. Currently, the existence of tetragonal phase in the film is assumed on the basis of the concurrence that (a) the recorded reflections are sharp, (b) there is no perceptible reflection from the (111) phase of the cubic phase at 2 = 14◦ and (c) the tetragonal ␤ phase is the steady phase at room temperature. In reference to observation, it is precise to refer that the angles of all major reflections of cubic and tetragonal phases of indium sulphide differ only a bit, and hence reflections from films having mixed phases would be broad. As far as observation is concerned, a critical appraisal of reflections in the vicinity of 2 = 14◦ in relation to other reflections provides the best possibility, though not unequivocally, to differentiate between cubic and tetragonal phases. It is observed that except the (103), (206) and (1 0 15) planes, the reflections from the plane in cubic phase take place at a higher angle (444) in comparison to the applicable planes in tetragonal phase. Fig. 4 shows the variation of thickness as a function of precursor concentrations from 0.05 M to 0.15 M. When precursor concentration is increased from 0.05 M to 0.15 M the film thickness increases from 415 to 513 nm. The preparative parameters including substrate temperature, deposition time, mol ratio, compressed air, etc. decide the growth and quality of the film. According to Bauer [32], there are two attainable mechanisms of the orientation owing to nucleation and final growth, both of which effect from the nucleation at the film/substrate with the inclination of nuclei to work out a minimum free energy configuration. The final growth orientation results from the endurance of nuclei having an energetically unstable plane parallel to the substrate surface amidst randomly oriented nuclei due to their different growth rates. This means that the growth orientation is formulated into one crystallographic direction of the lowest surface energy. Then, the grains became larger as the film grows with lower surface energy density. Thenceforth, with increasing molarity, the solution comprises more sulphur ions. As thickness calculated for the film deposited at higher molar concentrations are thicker as compared to films deposited at lower molar concentration. Since in thin films, the average crystallite size is proportional to thickness of films, the decrease in band gap with the increase in film thickness in this study indicates that there is no charge accumulation at grain boundaries in In2 S3 thin films. The average crystallite size and strain for the as-grown In2 S3 thin films for the different precursor concentrations can be determined by Williamson–Hall plot as shown in Fig. 5. In general, crystallite size and lattice strain regulate the Bragg peaks in different ways such as instrumental factors, the existence of defects to the ideal lattice, differences in strain in different grains and the crystallite size. Both these two effects elevate the peak width and intensity and shift the Bragg peak (2) position consequently. It is much executable to divide the effects of size and strain. The size broadening is independent of the length of the reciprocal lattice vector (q) and strain broadening increases with increasing q values. There will be both size and strain broadening that occurs in most of the cases. Williamson–Hall analysis is mainly used to divide these size and strain by combining the two equations [33]. ˇhkl = ˇs + ˇD

(1)

ˇhkl =

k D cos

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+ (4ε tan )

(2)

Rearranging the equation gives: ˇhkl cos =

k D

+ (4ε sin )

(3)

Eq. (3) stands for the uniform deformation model (UDM), where the strain was assumed uniform in all crystallographic directions. The term (ˇ cos ) was plotted with respect to (4 sin ) for the peaks of In2 S3 with cubic and mixed phase. Therefore, the slope and yintercept of the fitted time represent strain and crystallite size respectively. The results of the UDM analysis for the In2 S3 thin films are shown in Fig. 5. The texture coefficient Tc(hkl) of the In2 S3 thin films [25] have been calculated from the XRD data using the relation Tc(hkl)

I0 (hkl) = Is (hkl)

1 I0 (hkl) N Is (hkl) n

−1 (4)

i=1

where I0 (hkl) is the observed intensity, Is (hkl) is the standard intensity, Tc is the texture coefficient and N is a number of diffraction

Fig. 6. The variation of structural parameters with different precursor concentrations of In2 S3 thin films.

Fig. 7. Transmittance spectra of nebulized spray deposited In2 S3 thin films at different precursor concentrations.

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Fig. 8. Plot of (˛hϑ)2 versus h for nebulized spray deposited In2 S3 thin films for precursor concentrations: (a) 0.05 M, (b) 0.075 M, (c) 0.1 M, (d) 0.125 M and (e) 0.15 M.

peaks. The preferred orientation of the films can be confirmed by the higher value of texture coefficient. The increased number of grains along the plane associates the increase in preferred orientations [34]. The dislocation density (ı) defined as length of dislocation lines per unit volume of the crystal using crystallite size values (D) has been calculated using the Williamson and Smallman’s formula [35] ı=

1 (lines/m2 ) D2

(5)

The number of crystallites per unit area (N) of the samples was found using the relation [36] N=

t D3

where D is the crystallite size and t is the thickness of the film.

(6)

Table 1 exhibits the peak position (2), d-spacing (d), crystallite size (D), dislocation density (ı), lattice strain (εs ), thickness (t) and texture coefficient (Tc ) of In2 S3 thin films with different precursor concentrations from 0.05 M to 0.15 M. Fig. 6 shows the variation in the crystallite size, strain and dislocation density of the films as a function of precursor concentration. The crystallite size is low at lower precursor concentration since the deposited atoms in lieu of incorporating to the neighbouring grains and increasing their size are condensed and stay stuck to the region to constitute small nuclei and clusters. At higher precursor concentration, a large crystallite size is noticed due to the increasing mobility of the surface of atoms and increasing cluster formation. It is observed that the crystallite size increases and obtains a maximum value of 28.96 nm at mc = 0.15 M whereas the decrease in lattice strain was observed by increasing the precursor concentration. Surely, the lattice strain is decreased owing to the prevailing re-crystallization process in the


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Table 1 Structural parameters of In2 S3 thin films at preferred orientation for different precursor concentrations. Precursor concentration

hkl

Peak position 2 (◦ C)

˚ d-Value (A)

Texture coefficient

Crystallite size (nm)

Dislocation density (1015 lines/m)

Lattice strain (10−3 )

No. of crystallites (×1016 m2 )

Thickness (nm)

0.05 M 0.075 M 0.1 M 0.125 M 0.15 M

(111) (111) (111) (103) (103)

14.225 14.227 14.225 14.247 14.245

6.2211 6.2207 6.2211 6.2113 6.2116

1.5611 1.4989 1.4261 2.4430 1.9192

17.89 19.83 24.96 26.32 28.96

3.124 2.527 1.605 1.443 1.192

2.26 1.92 1.49 1.46 1.41

7.24 5.54 3.00 2.69 2.12

415 432 467 491 513

In2 S3 polycrystalline thin films. The observed decrease of full width at half maximum (FWHM) of diffraction peaks with increase of precursor concentration can be attributed to the increase in crystallite size. The dislocation density of as-prepared In2 S3 films decreased as the precursor concentration increased. The minimum values of dislocation density are obtained for the film grown at the precursor concentration 0.15 M. The change in crystallite size with precursor concentration explained this behaviour. Indeed, the larger crystallites have a smaller surface to volume ratio, thus giving up a rise to the dislocation network. The number of crystallites per unit area (N) depends on the parameters like equidimensional crystallites and the degree of the agglomeration of the thin films. It is ascertained that the number of crystallites decreases as the precursor concentration parameter increases. 3.2. Optical analysis Fig. 7 shows the optical transmittance spectra of the asdeposited In2 S3 films of different precursor concentrations. It can be ascertained that the transmittance of the as-deposited layers of precursor concentration 0.05 M is virtually similar as that of the films of mc = 0.075 M (80–85%). While the precursor concentration at 0.1 M showed a significant change in the optical transmittance that decreased from 85% to 75% which may be due to the increase in the thickness of the films. The observed lower transmittance at the precursor concentration 0.1–0.15 M could be due to the stoichiometric deviations and thickness. The optical energy band gap of the as-deposited thin films was measured using the relation ˛hϑ = A(hϑ − Eg )

n

(7)

where A is energy independent constant, n is an integer which is ½ for a direct allowed transition. The optical energy band gap (Eg ) of the as-deposited In2 S3 thin films was found using (˛hϑ)2 versus (h ) plots as shown in Fig. 8. The direct optical band gaps of In2 S3

Fig. 9. Plot of ln(˛) versus h for the Urbach energy determination of nebulized spray deposited In2 S3 thin films, with mc = 0.05–0.15 M.

thin films were found to be 2.83, 2.78, 2.72, 2.63 and 2.60 eV with increase in the precursor concentration from 0.05 M to 0.15 M. The direct band gap values of In2 S3 thin films reported in the literatures extend from 2.3 eV up to 2.8 eV [36–38]. Typically, in polycrystalline semiconductors, the energy band gap can be impacted by the quantum size effect [39], modification in the preferred orientation of the film [40], disorder and dislocation of density at the grain boundaries [41]. The sharp reduction of energy band gap at higher precursor concentration could be owing to the constitution of localized states in the band gap region. These states might be elicited in the band gap on account of the structural disorder owing to the sulphur deficiency. The high concentration of impurity states stimulates the band structure to dislodge, resulting in a prolonged tail extending into the energy band gap. The width of the band tails, generally known as Urbach tails, was determined to measure the structural disorder. The estimated Urbach tail energies increased from 1.49 to 2.03 eV with the increase of precursor concentration and are shown in Fig. 9. Furthermore, the energy band gap could also be influenced by the change of particle size with precursor concentration as it is in the nanometre range even though it is not close to the Bohr radius. Hence, in this study both the improvement in the particle size and the stoichiometric deviations could contribute to the decrease of energy band gap of the films with the increase in the precursor concentration. The skin depth (ı) of the In2 S3 thin films grown by nebulized spray pyrolysis technique can be found by the inverse of the absorption coefficient ı = 2/˛ = c/ωk. The skin depth (ı) is really a measure of the distance of penetration of the optical beam of intensity I = I0 /e−x/ı , into the medium before the beam is scattered. Since ı value is of the order of ␮m, this points that the incidental optical beam on material penetrates only very short distance. It is seen from Fig. 10 that the skin depth changes from 0.48 to 1.04 ␮m with mc .

Fig. 10. Variation of skin depth with photon energy of In2 S3 thin films at different precursor concentrations.

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Fig. 11. Scanning electron microscope (SEM) images of In2 S3 thin films for precursor concentrations: (a) 0.05 M, (b) 0.075 M, (c) 0.1 M, (d) 0.125 M and (e) 0.15 M.

3.3. Morphological analysis SEM images provide microscopic information of the surface topography. The effect of the precursor concentration on the surface morphology of the film is studied. The films cover the entire substrate surface, and pinholes are not found in the films. Fig. 11a shows SEM image of the film deposited at 0.05 M. At the beginning, the film is composed of round-shaped grains yielding rise to a close-packed and adherent film while the film deposited at the precursor concentration mc = 0.075 M is composed of a porous layer constituted by slightly bigger and irregular agglomerates (Fig. 11b). The surface of the as-deposited In2 S3 thin film at mc = 0.1 M shown in Fig. 11c shows a uniform granular structure with very welldefined grain boundaries and with some larger grains distributed on the film. The irregular round-shaped grains of In2 S3 crystallites have been found. The surface morphology of the film deposited at mc = 0.125 M is quite different. This surface includes larger grains with the dispersion of flower-shaped crystallites, some of them

with an elongated shape as shown in Fig. 11d. The film deposited at the precursor concentration of 0.15 M is composed of big roundshaped grains as shown in Fig. 11e. The different grain shapes in these films can be owing to the different crystallite structures and sizes which are evidenced by the calculated crystallite size values using W–H method. 3.4. Elemental analysis The characteristic EDX spectra of In2 S3 thin films at different precursor concentrations from 0.025 M to 0.15 M are shown in Fig. 12a–e respectively. Fig. 12 depicts the precise chemical composition of In2 S3 thin films. The EDX spectra show well-defined peaks corresponding to In and S. The quantitative weight percentage of the compositional elements such as In and S from mc = 0.025 M to 0.15 M are listed in Table 2. The atomic percentage of sulphur is slightly increased from 56.37 to 58.21 by increasing the precursor concentration. EDX spectrum exhibits that the weight percentage


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Fig. 12. Energy dispersive X-ray (EDX) pictures of In2 S3 thin films for precursor concentrations: (a) 0.05 M, (b) 0.075 M, (c) 0.1 M, (d) 0.125 M and (e) 0.15 M. Table 2 Variation of optical, elemental and electrical properties of In2 S3 thin films at different precursor concentrations. mc (mole)

0.05 0.075 0.1 0.125 0.15

wt%

In

S

43.63 42.59 42.52 41.82 41.79

56.37 57.41 57.48 58.18 58.21

S/In ratio

Eg (eV)

Eu (eV)

Resistivity ( cm)

Conductivity ( cm)−1

Carrier concentration (cm−3 )

Mobility (cm2 /V s)

Hall coefficient (cm3 /C)

1.29 1.34 1.35 1.39 1.39

2.83 2.78 2.72 2.63 2.60

1.49 1.57 1.72 1.93 2.03

1.020 0.994 0.947 0.560 0.487

0.98 1.01 1.06 1.79 2.05

1.95 × 1017 4.48 × 1017 1.44 × 1018 1.51 × 1018 3.31 × 1018

4.17 4.25 24.1 33.8 38.8

−4.35 −4.14 −32.0 −13.9 −18.9

is closely equal to their nominal stoichiometry within the experimental error. 3.5. Electrical analysis The electrical conductivity, resistivity, Hall coefficient, mobility and bulk carrier concentration of In2 S3 thin films deposited at different precursor concentrations were determined by Hall Effect measuring instrument and the corresponding values were listed in Table 2. The Hall coefficient values affirm that the films had an n-type characteristic. Fig. 13 shows the variation in the resistivity, carrier concentration and Hall mobility of the films as a function of precursor concentration. The resistivity of the as-deposited films decreases with increase in precursor concentration from 0.05 M to 0.15 M. The lowest resistivity value was 4.87 × 10−1 cm at the precursor concentration of 0.15 M. The decrease of the electrical resistivity of the film layers after increasing the precursor concentration could, therefore, be ascribed to the modification of properties of the grains or their boundaries. Meanwhile, the conductivity of the films is increased with the increase in the precursor concentration. It is ascertained that for the films deposited at five

different precursor concentrations, the conductivity improves as sulphur concentration increases. It is well known that the n-type conductivity in In2 S3 is owing to sulphur vacancy and interstitial indium atoms, both acting as donors. Hence, it gives rise to higher carrier concentration as In and S concentration increases. On the other hand, the enhancement in conductivity with increasing precursor concentration may also be ascribed to the increase in crystallite size. This may be due to the large density of extrinsic traps at the grain boundaries due to the sulphur chemisorptions. These traps deplete the grains and result in a charge barrier at the grain boundary. From these observations, the significant role of the precursor concentration in the formation of In2 S3 thin films with different morphology, crystallite size, electrical and optical properties were explored. The precursor concentration does not affect much for the band gap energy of In2 S3 thin films. Very sparse reports have been involved in the conductivity of In2 S3 thin films whereas Lugo-Loredo et al. [42] had reported the conductivity value such as 2.8 × 10−3 cm−1 after performing the thermal annealing at 400 ◦ C for the In2 S3 thin films deposited by the chemical bath deposition technique. The bulk carrier concentration and mobility of the In2 S3 thin films increase with increasing precursor

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One of the authors, Prof. L. Amalraj, would like to thank CSIR, New Delhi, India for releasing Emeritus Scientist Scheme. References

Fig. 13. Variation of resistivity, carrier concentration and mobility of In2 S3 thin films.

concentration up to 3.31 × 1018 cm−3 and 38.8 cm2 /V s, respectively. The mobility increases as a result of reconstituting and the crystallinity prosperity of the material. The mobility values are closer to the values obtained by Kraini et al. [29] for In2 S3 thin films grown by chemical spray pyrolysis method. The increased bulk carrier concentration caused by increasing precursor concentration shrinks the grain boundary potential barrier. Because of that, the carrier mobility of the films also increases. The results depicted in this work have presented the feasibility of using In2 S3 thin films as window layers in cadmium-free thin film solar cells. 4. Conclusion In2 S3 thin films were prepared at different precursor concentrations from 0.05 M to 0.15 M by nebulized spray pyrolysis technique successfully. The obtained In2 S3 thin films were uniform with good adherence and having the cubic structure up to the precursor concentration 0.1 M and then changed into mixed phase of both cubic and tetragonal structure. The variation in crystallite size and energy gap by increasing precursor concentration made the samples as a favourable candidate for the applications of optoelectronic device such as photoconductors and solar cells. The lower absorption and high transmittance in the visible region observed at lower precursor concentrations represented the good optical quality of the crystals with the low absorption or scattering losses which lead to the applications particularly as a window layer in solar cells. The optical parameters such as direct band gap energy, Urbach energy, and skin depth have been studied in detail. The change in morphology of In2 S3 thin films for different precursor concentrations was studied by scanning electron microscope. Energy dispersive X-ray (EDX) pattern confirmed the presence of In and S with the chemical stoichiometry. The electrical resistivity of the as-deposited In2 S3 thin films is decreased by increasing the precursor concentration. The maximum carrier mobility of 38.8 cm2 /V s was obtained at mc = 0.15 M. The investigation results of the In2 S3 thin films grown by nebulized spray pyrolysis technique assure the stability of the film and their employability in solar cell application. Acknowledgements We are thankful to Dr. N. Gopalakrishnan, Associate Professor, Department of Physics, NIT, Tiruchirappalli, India for analyzing the electrical characterization using Hall measurement instrument.

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