thin films by nebulizer spray pyrolysis (NSP) for solar

Journal of Molecular Structure 1152 (2018) 137e144

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Development of SnS (FTO/CdS/SnS) thin films by nebulizer spray pyrolysis (NSP) for solar cell applications A.M.S. Arulanantham a, S. Valanarasu a, *, K. Jeyadheepan b, V. Ganesh c, d, Mohd Shkir c, d, ** a

PG & Research Department of Physics Arul Anandar College, Karumathur 625 514, India Multifunctional Materials & Devices Lab, Anusandhan Kendra e II, School of Electrical and Electronics Engineering, SASTRA University, Tirumalaisamudram, Thanjavur 613 401, India c Advanced Functional Materials and Optoelectronic Laboratory (AFMOL), Department of Physics, Faculty of Science, King Khalid University, P.O. Box. 9004, Abha 61413, Saudi Arabia d Research Center for Advanced Materials Science (RCAMS), King Khalid University, Abha 61413, P.O. Box 9004, Saudi Arabia b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 8 July 2017 Received in revised form 13 September 2017 Accepted 20 September 2017 Available online 21 September 2017

Herein we report a well-organized analysis on various key-properties of SnS thin films for solar cell fabricated by nebulizer spray pyrolysis technique. X-ray diffraction study reveals the polycrystalline nature of deposited films with orthorhombic crystal structure. The crystallite size was calculated and observed to be in the range of 8e28 nm with increasing molarity of precursor solution. The stoichiometry composition of SnS was confirmed by EDX study. SEM/AFM studies divulge the well-covered deposited surface with spherical grains and the size of grains is increasing with concentration and so the roughness. A remarkable decrease in band gap from 2.6 eV to 1.6 eV was noticed by raising the molar concentration from 0.025 M up to 0.075 M. A single strong emission peak at about 825 nm is observed in PL spectra with enhanced intensity which may be attributed to near band edge emission. From the Hall effect measurement, it was found that the SnS thin film exhibits p-type conductivity. The calculated values of resistivity and carrier concentration are 0.729 U cm and 3.67 1018/cm3 respectively. Furthermore, to study the photovoltaic properties of SnS thin films a heterojunction solar cell, FTO/n-CdS/p-SnS was produced and the conversion efficiency was recorded about 0.01%. © 2017 Elsevier B.V. All rights reserved.

Keywords: Thin films X-ray diffraction SEM/AFM/EDX Hall Effect measurement Heterojunction Resistivity

1. Introduction In recent times semiconducting metal chalogenides thin films have attracted a huge attention for their potential application in solid-state devices like photovoltaic, photo-electrochemical (PEC), photoconductive cells, solar cells, polarizers, sensors etc. [1]. Owing to their wide-range of functions, it appears to be indispensable to spotlight the delve intonew photovoltaic materials that construct low-cost solar cell with more efficiency and applied in producing appreciable more energy [2]. Among various solar cell materials, Tin sulfide (SnS) is in the spot for research and development due to its narrow direct and indirect band gap 1.1e2.33 eV, thriftily nature,

* Corresponding author. ** Corresponding author. Department of Physics, Faculty of Science, King Khalid University, Abha, Saudi Arabia. E-mail addresses: [email protected] (S. Valanarasu), shkirphysics@gmail. com, [email protected] (M. Shkir). https://doi.org/10.1016/j.molstruc.2017.09.077 0022-2860/© 2017 Elsevier B.V. All rights reserved.

and resource abundant from IV-VI semiconductor family and found to be a highly absorbing materials used in solar cells [3e5]. About 33% efficiency is achieveable for the materials who possess band gap around 1.3 eV as suggested in ShockleyeQueisser criteria [6]. The various reasons have been reported for low efficiency SnS based solar cell in the literature [7]. As per past-literature on SnS, different techniques are used to fabricate its thin films like: CBD [8e10], thermal evaporation [11],ultrasonic spray [12], electrodeposition [13,14], D.C. magnetron sputtering [15], electron beam evaporation [16], atomic layer deposition (ALD) [17], SILAR [1,18], spray pyrolysis [5,19] and APCVD [20] and enhanced efficiency has been achieved. However, no report on the fabrication of SnS thin films/thin films based solar cell by nebulizer spray pyrolysis (NSP) method is available so far. Due to wide-range of exceptional applications, we feels that it is justified to fabricate the thin films of SnS using NSP technique (using just atmospheric air as carrier gas and water as solvent) and study their structural, vibrational and optoelectronic properties. Hence, herein we report a orderly

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analysis on the effect of precursor molar concentration on above mentioned properties. 2. Experimental procedure Fabrication of SnS films was done on well-cleaned glass substrates using nebulizer spray pyrolysis (NSP) technique. Precursor solution consists of tin chloride dehydrate (SnCl2.2H2O) and thiourea [CS (NH2)2]. The 1:1 M ratio of tin and thiourea both of them were dissolved in 10 ml of de-ionized water. A few drop of HCl was added for complete dissolution. The substrate temperature maintained at 325 C (±5 C) for all thin films fabrication. The compressed air is used as gas carrier of nebulizer spray technique to produce aerosol particles and the carrier gas flow rate was maintained at 1.5 kg/cm2. Distance between spray nozzle and substrate was fixed at 50 mm and all of them were kept constant. However, the precursor molarities varied from 0.025 M to 0.075 M. To achieve the uniformly deposited films the nebulizer spray gun is connected to microprocessor controlled stepper motor system to regulate it in XeY plane. After deposition, the films were cooled down slowly to 30 C and then the films were taken from the heater. After having developed film layers, we have characterized them by structural, morphological, optical and electrical properties. The structural study was done using the X-ray diffractometer having a CuKa radiation source with a wavelength l ¼ 1.5418 Å in the range 10e80 . The morphology of film layers was observed using a scanning electron microscope and EDAX spectra conforms the elements present in the film. The surface roughness of the films was analyzed using an atomic force microscopy (AFM). A double-beam UVeViseNIR spectrophotometer is used to measure the transmittance, reflectance and absorption in wavelength range of 300e2500 nm. The photoluminescence (PL) studies were carried out on Jobin Yvon Fluorolog-FL3-11 using an excitation source (lexc ¼ 325 nm). The room temperature electrical conductivity, Hall mobility and carrier concentration were measured using fourterminal sensing technique by Hall Effect measurements. Keithley Source Meter (Model 2450) is used for the IeV measurement and FTO/CdS/SnS heterojunction cell was fabricated by same technique as applied above and contacts were made uing silver adhesive. 3. Result and discussion 3.1. Structural studies X-ray diffraction (XRD) patterns of SnS films deposited with different molar concentrations such as 0.025, 0.05 and 0.075 M are shown in Fig. 1. XRD pattern shows that the fabricated films possess orthorhombic structure with polycrystalline nature and strongly oriented along the (210) and (111) direction as the intensity of these planes is higher compare to others. The other diffraction peaks are correspond to (301), (211), (311), (202), (610) and (222) orientations. The XRD pattern of the prepared films were also agreement with the literature of SnS films prepared by spray pyrolysis technique [21]. The structural data of deposited SnS films is indexed with JCPDS#65e2610. A homogeneous increase in the intensity of the same diffraction peak, corresponding to improved layer orientation and enhanced crystal quality was inferred. The orthorhombic phase grows proportional to the rock-salt [9]. The thickness of the film increases from 760 nm to 1.22 mm nm for increase the precursor molar concentration from 0.025 M to 0.075 M. The lattice constants were estimated using the observed values of 2q ¼ 27.01, 30.81, 31.64 , 33.87, 38.21, 51.59 for (2 1 0), (3 0 1), (1 1 1), (2 1 1), (3 1 1) and (6 0 1) planes and d values by the below equation for orthorhombic structure [10]:

Fig. 1. XRD pattern of SnS thin films prepared at different molar concentration.

1 h2 k2 l2 ¼ þ þ d2hkl a2 b2 c2

(1)

where the notations are having their usual sense. The calculated lattice parameters have been shown in Table 1 which are in accordance with earlier reported JCPDS # 65e2610 data. It can be noticed from the tabulated data that the unit cell volume is increased with increasing molar concentration of precursor that may be judged as development of stress due to non-hydrostatic pressure [22]. The crystallite size (D) of SnS films were investigated using XRD kl , data by employing the Debye Scherer's relation [23e26]: D ¼ b cos q

where the symbols are of usual sense. Crystallite size obtained from above equation corresponds to the mean minimum dimension of a coherent-diffraction-domain. Table 2 presents the crystallite size values calculated from Scherer's equation for (2 1 0) diffraction peak. The dislocation density (d) was estimated using the Williamson and Smallman's formula [27]: d ¼ D12 . The value of microq strain (ε) is evaluated using [12,28,29] ε ¼ b cos 4 . The values of d and ε are tabulated in Table 2. From the tabulated data, it can be noticed that the values of d and ε are decreasing and grain size is increasing with increasing molar concentration. The reduced values of ε and d with molarities designate the creation of high quality films at higher molar concentration. This may be due to the fact that when the molar concentration of precursor is kept higher, the dislocations entertain more energy and possess higher mobility and these activated dislocations could be moved to grain boundaries from inside the crystallites and neutralized [30].

3.2. Raman analysis The Raman spectroscopic analysis has been carried out to further understand the structural phases of as-deposited thin films in the range of 50e500 cm1 at room temperature. The predominant LO and TO modes are in the range of 50e500 cm1. Fig. 2 shows Raman modes present at 94 cm1, 164 cm1, 191 cm1, and 220 cm1 are related to various optical phonons modes of SnS phase, which is in close agreement with reported databy Reddy et al. [31]. The peak presented at 191 cm1 and 220 cm1are assigned to the longitudinal optical Ag (LO) mode, where as the other peak 94 cm1 belongs to the transverse optical Ag (TO) mode. These Ag (TO) and Ag (LO) modes are also very close to the reported


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Table 1 Lattice parameter calculation. Molar concentration (M)

Lattice parameter values (Å)

Unit cell volume (Å)

Observed values

0.025 0.050 0.075

Standard values

a

b

c

a

b

c

11.81 11.82 11.83

4.10 4.00 4.01

4.19 4.29 4.28

11.82

3.988

4.340

202.8 203.3 203.7

Table 2 Structural parameters of SnS films deposited at various molar concentration. Molar concentration (M)

Crystallite size (nm)

Dislocation density (d 1015 lines. m2)

Strain ε 103

0.025 0.050 0.075

8.3 13.8 27.7

14 5.1 1.3

17 10 5.3

Fig. 3. EDAX spectrum and composition table of SnS thin films deposited at (a) 0.025 M, (b) 0.050 M and (c) 0.075 M concentrations.

Fig. 2. Raman spectra of SnS thin films fabricated at different molar concentration.

value [32]. It is observed that the intensity of Raman mode at 94 cm1, 164 cm1, 191 cm1 and 220 cm1increases with the increase of molar concentration. There are no bands corresponding to the secondary phases of Sn and S observed in the spectrum. This result confirms that the films grown at different molarities are pure SnS without any impurity phases like SnS2, SnO2and Sn2S3, which have their strongest Raman peaks at around 312 cm1 and 308 cm1, respectively. Thus Raman studies along with XRD confirm single phase SnS thin films fabrication by NSP technique.

XRD and Raman analyses. FESEM micrographs for SnS thin films are shown in Fig. 4(aec). It shows that the films are uniform without any cracks and pinholes. The surface morphology was found to be affected by molar concentrations. The films are densely packed with crystallites and grown with different sizes in same directions. From Fig. 4(aeb) shows that the photograph it is clearly seen that the film consists fine-grains with nanometer sized particles. As shown in Fig. 4(aeb), FESEM characterization of film deposited with below 0.075 M concentrations of precursor revealed that the films are having spherical shaped particles containing no pores and void [33] and the films deposited with 0.075 M molar concentration (Fig. 4(c)) have fine spherical shaped grain with smooth surface with larger agglomeration of grains as compared to the films deposited with 0.025 M and 0.050 M molar concentration. The grain size increased as the molar concentration of precursor increased. The increase in molar concentration promotes the grain growth and sintering. This scenery of SnS electrode leads to high surface area that can be used in hybrid inorganiceorganic solar cells [34]. The films deposited with 0.075 M concentration possess more homogeneous and compact structure and the size of separately standing grains is ~31 nm.

3.3. Composition and FESEM analyses 3.4. AFM analysis Fig. 3 along with table shows the elemental compositions (EDX spectra) of the SnS thin films deposited with various molar concentration. However, the Sn/Sratio was found to be independent of the substrate temperature. EDX studies were carried out at different molar concentration of thin films and the composition of Sn to S ratios was almost same which shows that there no compositional variation across the surface of deposited films [see Table 2]. The ‘O’ line in EDX spectra is significally for the substrate. These results indicate that the atomic ratio increases with increase in molar concentration of precursor. The process takes place without any secondary phase formation which is also supported by

Atomic force microscopy (AFM) is an excellent tool to study the various parameter of thin films [35]. Fig. 5(aec) shows that the 2D and 3D micrographs of SnS thin films, recorded with a scan area of 1 mm 1 mm. The AFM image indicates that these coatings cover the surface of the substrate completely. Fig. 5(aeb) illustrates 2D and 3D AFM topography of SnS films deposited by 0.025 M and 0.050 M. The surface shows clusters having spherical shape over an area of 1 mm2. Fig. 5(c) shows the AFM image of 2D and 3D-visualisations of the tin sulfide films deposited by 0.075 M molar concentration. The AFM results propose island-type SnS film growth.

140


Fig. 4. FE-SEM images of SnS thin films prepared at (a) 0.025 M, (b) 0.050 M and (c) 0.075 M concentrations.

The VolmereWeber mode provides equilibrium conditions of a newly formed crystal of the SnS film staying in contact with the glass or ceramic substrate [36]. At the same time, there is no condensed SnS in some other areas of the substrate surface. From 3D micrographs,it is observed that the average grain size and

surface roughness increases with increase of the molar concentration. The value of grain size and the root-mean-square roughness are tabulated in Table 3. It is apparent from the AFM studies that the grain sizes as well as the surface roughness vary with the molar concentration. 3.5. Optical studies Fig. 6(a) shows the measured transmittance spectra of SnS films. The fringes obtained for all the samples confirm the uniformity of the films prepared. It can be noticed from the figure that the transmittance decreases with the increasing molar concentration. The optical transmittance of deposited films is in the range ~60e80%. Fig. 6(b) shows the reflectance spectra obtained for SnS with different films molar concentration of precursor. Occurrence of interference fringes in spectra [Fig. 6(b)] verify its high homogeneity and uniformity. A quick fall in reflectance near primary absorption edge denotes the direct optical transition and also in NIR region increase and decrease in R and T shows light attenuation due to carrier scattering [37,38]. Fig. 6(c) shows the noticeable increase in absorbance value of fabricated films with increasing the molar concentration. Optical band-gap (Eg) was evaluated by Tauc's plot. The plot is derived from expression [6, 39e41]:

Table 3 Roughness and grains size of SnS films deposited at various molar concentration.

Fig. 5. AFM images of SnS films deposited at (a) 0.025 M, (b) 0.050 M and (c) 0.075 M concentrations.

Molar concentration (M)

Roughness (nm)

Grain size (nm)

0.025 0.050 0.075

16 24 29

11 21 32


k¼

R¼

Fig. 6. (a) Transmittance, (b) reflectance and (c) absorbance spectra for SnS thin films prepared at a different molar concentration.

hna1=n ¼ A hn Eg

(2)

where h is Planck's constant, n is photon frequency and A is proportionality constant. The value of exponent m denotes the type of radiative transition. In the present case n ¼ 1/2 is found to have a linearfit of the Tauc's plot and confirm direct optical transition, and optical band-gap was gauged. As shown in Fig. 7(a), a remarkable decrease in energy gap energy from 2.6 eVe1.6 eV was noticed by raising the molar concentration from 0.025 M to 0.075 M, such a decrease may be due to the enhanced crystallinity with molar concentration that resulted in the optical band gap varies with tinto-sulfur ratio in the structure leading to the change in energy band structure and also density of states (DOS) of valence band and conduction band [1,42]. Determining the refractive index of semiconductor is important for optical wave guiding in optoelectronic structures such as heterojunction laser diodes, optical amplifiers or optical fibers. Hence, many attempts have been made to correlate the energy bandgap to the optical refractive index of semiconductors. The reflectance (R), extinction coefficient (k) and the refractive index (n) of a solid at a certain constant wavelength (l) are related through the following equations [42e44].

Fig. 7. Plots of (a) (ahn)2 vs (hn), (b) Extinction coefficient and (c) Refractive index (n) of SnS thin films.

al 4p ðn 1Þ2 þ k2 ðn þ 1Þ2 þ k2

141

(3)

(4)

Fig. 7(b) and (c) depicts spectral variation of ‘k’ and ‘n’ as a function of wavelength. It is can be seen in figure (b) that k is slightly increased and then suddenly reduced, this may be due to light fraction because of scattering and decrease and increase in absorbance, it means k tends to zero at Eg. Similar type of behavior was also reported for SnS films by Subramanian et al., [45]. Fig. 7(c) indicates that the value of ‘n’ achieve a peak in the absorption region (below 1000 nm), which was found to be minutely shifted towards higher wavelengths as molar concentration increases up to the optimum value 0.075 M [42]. Similar nature of ‘n’ value was observed for SnS2 films by Kotte Tulasi Ramakrishna Reddy et al. [46]. Refractive index plays an important role in solar cell [42]. 3.6. Photoluminescence (PL) studies Fig. 8 displays the PL spectra of SnS films recorded in the wavelength range from 700 to 900 nm, with photon excitation at 550 nm. For excitation at 550 nm, a sharp emission peak was observed at about 825 nm, corresponds to energy ~1.50 eV which may be attributed to near band edge emission, and is slightly higher than bandgap estimated from UVeVis data. The origin of sharp emission peak around 825 nm was apparent due to emission from vacancies or defects that are intrinsic to the growth process, i.e. interstitial and stacking faults. All defect related bands emerge at lower values than band gap. Ghosh et al. [47,48]. also reports the PL in SnS (at 550 nm) with larger energy than band gap. The intensity of the band edge emission peak enlarged with increase of molar concentration of precursor. This observation agrees with the XRD pattern in which the intensity of peak increased with increase of precursor concentration. 4. Electrical studies 4.1. Hall Effect measurement The electric properties of the materials are of great importance in determining the use of the films in photovoltaic field. The electric

Fig. 8. PL spectra of SnS thin films deposited at different molar concentration.

142


parameters can be determined by studying the Hall effect on the sample. The Hall Effect measurement was carried out at room temperature using Hall Effect measurement system. The measurement includes resistivity, conductivity, carrier concentration, Hall coefficient and Hall mobility. Electrical measurements were carried out with silver electrodes deposited on the films. The electrical resistivity (r) of the films formed at different molar concentration are shown in Table 4. According to this table, resistivity decreased slightly from 2.415 104 to 0.729 U cm with increasing molar concentration from 0.025 M to 0.075 M. The lowest resistivity (0.729 Ucm) obtained for the concentration equals 0.075 M, which is due to superior crystallinity of films deposited at this concentration. These results are firmly supported by XRD analysis (Fig. 1), which indicates that film deposited at 0.075 M contain larger grain size than the other films. It is wellknown that the grain boundary scattering reduced with increase in grain size of this film that results lesser electrical resistivity [28]. Guneri et al. [49] also reported the nearer value for SnS film by CBD. A spiky change in conductivity of films at higher molar concentration is due to formation of high crystalline SnS phase. The films deposited at 0.075 M have showed an average conductivity value about 13.7 (U1cm1) which is higher than previous report Devika et al. [50] deposited by thermal evaporation technique. The Hall measurements conformed that all the films showed p-type conductivity and with increased molar concentration there has been a substantial increase in the carrier concentration (p) from the order of 1017 to 1018 cm3 owing to the increased metallic component (tin) [51]. The increasing molar concentration from 0.025 to 0.075 M induced a significant increase in Hall mobility from 0.73 to 2.36 cm2/vs. The high carrier concentration and mobility are fully based on the thickness as well as crystalline feature.

Fig. 9. IeV characteristics of FTO/CdS/SnS heterostructures (SnS - 0.075 M). Inset (a) shows FTO/CdS/SnS heterostructures sample and inset (b) shows semi-log I-V for a FTO/CdS/SnS heterostructures.

4.2. IeV characteristics of FTO/CdS/SnS heterostructure The SnS based PV cells was fabricated with nebulizer spray deposited CdS/SnS on FTO coated glass substrate, as shown in inset of Fig. 9. The IeV characteristics of FTO/CdS/SnS heterostructure are shown in Fig. 9. The IeV characteristics in semi-log plot is shown in inset of Fig. 9(b). Due to minority carriers the value of current is minimum in dark, however, after illumination the current value increased due to charge carriers created by incident photon. Thin film heterojunction solar cells with the configuration FTO/ n-CdS/p-SnS was developed by nebulizer spray deposited CdS and SnS with active area about 0.5 cm2. Fig. 10 depicts the illuminated IV characteristic curve of n-CdS/p-SnS heterojunction solar cell. The fabricated solar cell device possess a short circuit current density (Jsc) of about 20.1 mA/cm2, an open circuit voltage (Voc) of 194 mV, a fill factor of 0.26 with a conversion efficiency of about 0.01% when illuminated by a source of light of about 100 mW/cm2. The photovoltaic effects of the FTO/CdS/SnS cells are observed to be higher than CdS/SnS cells [52]. Moreover, a thorough study on various key properties and cell characteristics of n-CdS/p-SnS devices are in evolution. 5. Conclusion A successful optimization of SnS thin films by NSP technique

Fig. 10. Illuminated I-V characteristics of FTO/CdS/SnS heterostructure.

was obtained and further it is used in the development of solar cell device. The grown SnS thin films are in single phase and polycrystalline, having the orthorhombic structure with high intense peaks at (210) and (111) orientation. The crystallite size was found to be increase on increasing the molar concentration and was about 27.7 nm for the 0.075 M concentration, which was the optimized condition for SnS. Raman analysis showed a high intense peaks at 94 cm1, 164 cm1, 191 cm1, and 220 cm1, confirm the formation of SnS thin films. From EDAX, the atomic composition was found to be increasing with increasing molar concentration from 0.025 to 0.075 M. Nano sized spherical shape grains covered the entire films, were confirmed from FESEM analyses. AFM images conclude that regular, homogeneous and rough SnS thin film can be obtained

Table 4 Electrical Properties of SnS films deposited at different molar concentration. Molar concentration (M) 0.025 0.050 0.075

Resistivity (U cm) 24.15 11.58 0.7298

Conductivity (U1cm1) 1

4.07 10 8.62 101 1.37 101

Carrier concentration (p) (/cm3) 17

3.54 10 2.48 1018 3.67 1018

Mobility (cm2/vs)

Type of conductivity

0.728 1.60 2.36

P P P


under these conditions. Optical characterization showed a band gap variation from 2.6 to 1.6 eV for precursor concentration from 0.025 M to 0.075 M, respectively and had high optical absorption. From electrical studies, the observed low resistivity value is 0.729 Ucm for the films deposited at 0.075 M concentration. The SnS film prepared at 0.075 M concentration shows good crystallinity, dense morphology, and high photosensitivity. Hence, results of the SnS film in the present study conclude that the SnS thin films deposited at 0.075 M can be used for photovoltaic device. Fabrication of a solar cell having the structure of FTO/n-CdS/p-SnS type was achieved from the above optimized condition, which verified the use of SnS films as an absorber layer for PV device applications. Acknowledgements The authors wish to express their sincere thanks to the Department of Science and Technology, New Delhi, India for their financial assistance for the worksupport by the project number (DST-SERB) (SB/FTP/PS-131/2013). References [1] A. Mukherjee, P. Mitra, Structural and optical characteristics of SnS thin film prepared by SILAR, Mater. Sci. Pol. 33 (2015) 847e851. [2] B.A. Hasan, I.H. Shallal, Structural and Optical Properties of SnS Thin Films, 2012. [3] G.G. Ninan, C.S. Kartha, K. Vijayakumar, Spray pyrolysed SnS thin films in n and p type: optimization of deposition process and characterization of samples, J. Anal. Appl. Pyrolysis 120 (2016) 121e125. [4] T. Sajeesh, K. Jinesh, M. Rao, C.S. Kartha, K. Vijayakumar, Defect levels in SnS thin films prepared using chemical spray pyrolysis, Phys. Status Solidi (a) 209 (2012) 1274e1278. [5] J.A. Andrade-Arvizu, M. García-S anchez, M. Courel-Piedrahita, F. PulgarínAgudelo, E. Santiago-Jaimes, E. Valencia-Resendiz, A. Arce-Plaza, O. Vigiln, Suited growth parameters inducing type of conductivity conversions Gala on chemical spray pyrolysis synthesized SnS thin films, J. Anal. Appl. Pyrolysis 121 (2016) 347e359. [6] M. Patel, I. Mukhopadhyay, A. Ray, Annealing influence over structural and optical properties of sprayed SnS thin films, Opt. Mater. 35 (2013) 1693e1699. [7] J. Vidal, S. Lany, M. d'Avezac, A. Zunger, A. Zakutayev, J. Francis, J. Tate, Bandstructure, optical properties, and defect physics of the photovoltaic semiconductor SnS, Appl. Phys. Lett. 100 (2012) 032104. [8] U. Chalapathi, B. Poornaprakash, S.-H. Park, Chemically deposited cubic SnS thin films for solar cell applications, Sol. Energy 139 (2016) 238e248. [9] M. Reghima, A. Akkari, C. Guasch, N. Turki-Kamoun, Structure, surface morphology, and optical and electronic properties of annealed SnS thin films obtained by CBD, J. Electron. Mater. 43 (2014) 3138. [10] E. Turan, M. Kul, A.S. Aybek, M. Zor, Structural and optical properties of SnS semiconductor films produced by chemical bath deposition, J. Phys. D. Appl. Phys. 42 (2009) 245408. [11] R.W. Miles, O.E. Ogah, G. Zoppi, I. Forbes, Thermally evaporated thin films of SnS for application in solar cell devices, Thin Solid Films 517 (2009) 4702e4705. [12] I.B. Kherchachi, H. Saidi, A. Attaf, N. Attaf, R. Azizi, M. Jlassi, Influence of solution flow rate on the properties of SnS 2 films prepared by ultrasonic spray, Optik-Int. J. Light Electron Opt. 127 (2016) 4043e4046. [13] A. Ghazali, Z. Zainal, M.Z. Hussein, A. Kassim, Cathodic electrodeposition of SnS in the presence of EDTA in aqueous media, Sol. energy Mater. Sol. cells 55 (1998) 237e249. [14] B. Ghosh, M. Das, P. Banerjee, S. Das, Fabrication of the SnS/ZnO heterojunction for PV applications using electrodeposited ZnO films, Semicond. Sci. Technol. 24 (2009) 025024. [15] K.R. Reddy, P.P. Reddy, P. Datta, R. Miles, Formation of polycrystalline SnS layers by a two-step process, Thin Solid Films 403 (2002) 116e119. [16] J. Henry, K. Mohanraj, S. Kannan, S. Barathan, G. Sivakumar, Effect of selenium doping on structural and optical properties of SnS: Se thin films by electron beam evaporation method, Eur. Phys. J. Appl. Phys. 61 (2013) 10301. [17] P. Sinsermsuksakul, J. Heo, W. Noh, A.S. Hock, R.G. Gordon, Atomic layer deposition of tin monosulfide thin films, Adv. Energy Mater. 1 (2011) 1116e1125. [18] A. Abdelrahman, W. Yunus, A. Arof, Optical properties of tin sulphide (SnS) thin film estimated from transmission spectra, J. Non-Cryst. Solids 358 (2012) 1447e1451. [19] K.R. Reddy, P.P. Reddy, R. Miles, P. Datta, Investigations on SnS films deposited by spray pyrolysis, Opt. Mater. 17 (2001) 295e298. [20] L.S. Price, I.P. Parkin, A.M. Hardy, R.J. Clark, T.G. Hibbert, K.C. Molloy, Atmospheric pressure chemical vapor deposition of tin sulfides (SnS, Sn2S3, and SnS2) on glass, Chem. Mater. 11 (1999) 1792e1799.

143

[21] N.K. Reddy, K.R. Reddy, Growth of polycrystalline SnS films by spray pyrolysis, Thin Solid Films 325 (1998) 4e6. [22] M. Patel, I. Mukhopadhyay, A. Ray, Molar optimization of spray pyrolyzed SnS thin films for photoelectrochemical applications, J. Alloys Compd. 619 (2015) 458e463. [23] E. Guneri, F. Gode, C. Ulutas, F. Kirmizigul, G. Altindemir, C. Gumus, Properties of p-type SnS thin films prepared by chemical bath deposition, Chalcogenide Lett. 7 (2010) 685. [24] S. Panda, A. Antonakos, E. Liarokapis, S. Bhattacharya, S. Chaudhuri, Optical properties of nanocrystalline SnS 2 thin films, Mater. Res. Bull. 42 (2007) 576e583. [25] M. Shkir, H. Abbas, Z.R. Khan, Effect of thickness on the structural, optical and electrical properties of thermally evaporated PbI< sub> 2 thin films, J. Phys. Chem. Solids 73 (2012) 1309e1313. [26] M. Shkir, I.S. Yahia, S. AlFaify, M.M. Abutalib, S. Muhammad, Facile synthesis of lead iodide nanostructures by microwave irradiation technique and their structural, morphological, photoluminescence and dielectric studies, J. Mol. Struct. 1110 (2016) 83e90. [27] I.S. Yahia, M. Shkir, S. AlFaify, V. Ganesh, H.Y. Zahran, M. Kilany, Facile microwave-assisted synthesis of Te-doped hydroxyapatite nanorods and nanosheets and their characterizations for bone cement applications, Mater. Sci. Eng. C 72 (2017) 472e480. [28] I. Kherchachi, A. Attaf, H. Saidi, A. Bouhdjer, H. Bendjedidi, Y. Benkhetta, R. Azizi, Structural, optical and electrical properties of Sn x S y thin films grown by spray ultrasonic, J. Semicond. 37 (2016) 032001. [29] M. Shkir, S. AlFaify, I.S. Yahia, V. Ganesh, H. Shoukry, Microwave-assisted synthesis of Gd3þ doped PbI2 hierarchical nanostructures for optoelectronic and radiation detection applications, Phys. B Condens. Matter 508 (2017) 41e46. [30] N. Koteeswara Reddy, K. Ramesh, R. Ganesan, K. Ramakrishna Reddy, K. Gunasekhar, E. Gopal, Synthesis and characterisation of co-evaporated tin sulphide thin films, Appl. Phys. A Mater. Sci. Process. 83 (2006) 133e138. [31] T.S. Reddy, M.S. Kumar, Co-evaporated SnS thin films for visible light photodetector applications, RSC Adv. 6 (2016) 95680e95692. [32] K. Reddy, M. Devika, K. Gunasekhar, Stable and low resistive zinc contacts for SnS based optoelectronic devices, Thin Solid Films 558 (2014) 326e329. [33] S. Polivtseva, I.O. Acik, A. Katerski, A. Mere, V. Mikli, M. Krunks, Spray pyrolysis deposition of SnxSy thin films, Energy Procedia 60 (2014) 156e165. [34] T. Rath, L. Gury, I. Sanchez-Molina, L. Martinez, S. Haque, Formation of porous SnS nanoplate networks from solution and their application in hybrid solar cells, Chem. Commun. 51 (2015) 10198e10201. [35] A.A. Shehab, N.A. AL-Hamadni, D.M. Latif, Effect of annealing temperature on structure properties of SnS thin films, Phys. Chem. An Indian J. 9 (2014) 255e259. [36] V. An, M. Dronova, A. Zakharov, Optical and AFM studies on p-SnS thin films deposited by magnetron sputtering, Chalcogenide Lett. 12 (2015) 483e487. [37] P. Nwofe, K.R. Reddy, J. Tan, I. Forbes, R. Miles, Thickness dependent optical properties of thermally evaporated SnS thin films, Phys. Procedia 25 (2012) 150e157. [38] M. Selim, M. Gouda, M. El-Shaarawy, A. Salem, W.A. El-Ghany, Effect of thickness on optical properties of thermally evaporated SnS films, Thin Solid Films 527 (2013) 164e169. [39] M. Shkir, S. Aarya, R. Singh, M. Arora, G. Bhagavannarayana, T. Senguttuvan, Synthesis of ZnTe nanoparticles by microwave irradiation technique, and their characterization, Nanosci. Nanotechnol. Lett. 4 (2012) 405e408. [40] M. Shkir, S. Alfaify, S. Muhammad, M. Nasir, N. Vijayan, S. Jat, M. Zulfequar, S. Rubio, E. Dieguez, Structural, elemental, morphological and optical spectroscopic studies on high quality〈 111〉 grown nanocrystalline ZnTe thin films: an effect of thickness, Mater. Focus 4 (2015) 202e207. [41] M. Shkir, V. Ganesh, S. AlFaify, I.S. Yahia, Structural, linear and third order nonlinear optical properties of drop casting deposited high quality nanocrystalline phenol red thin films, J. Mater. Sci. Mater. Electron. 28 (2017) 10573e10581. [42] S. Gedi, V.R.M. Reddy, C. Park, J. Chan-Wook, Comprehensive optical studies on SnS layers synthesized by chemical bath deposition, Opt. Mater. 42 (2015) 468e475. [43] F. Gode, E. Guneri, O. Baglayan, Effect of tri-sodium citrate concentration on structural, optical and electrical properties of chemically deposited tin sulfide films, Appl. Surf. Sci. 318 (2014) 227e233. [44] V. Ganesh, I.S. Yahia, S. AlFaify, M. Shkir, Sn-doped ZnO nanocrystalline thin films with enhanced linear and nonlinear optical properties for optoelectronic applications, J. Phys. Chem. Solids, DOI https://doi.org/10.1016/ j.jpcs.2016.09.022(2016). [45] B. Subramanian, C. Sanjeeviraja, M. Jayachandran, Cathodic electrodeposition and analysis of SnS films for photoelectrochemical cells, Mater. Chem. Phys. 71 (2001) 40e46. [46] K.T.R. Reddy, G. Sreedevi, R.W. Miles, Thickness effect on the structural and optical properties of SnS2 films grown by CBD process, J. Mater. Sci. Eng. A 3 (2013) 182. [47] B. Ghosh, M. Das, P. Banerjee, S. Das, Fabrication and optical properties of SnS thin films by SILAR method, Appl. Surf. Sci. 254 (2008) 6436e6440. [48] B. Ghosh, M. Das, P. Banerjee, S. Das, Fabrication of SnS thin films by the successive ionic layer adsorption and reaction (SILAR) method, Semicond. Sci. Technol. 23 (2008) 125013. [49] E. Guneri, C. Ulutas, F. Kirmizigul, G. Altindemir, F. Gode, C. Gumus, Effect of

144


deposition time on structural, electrical, and optical properties of SnS thin films deposited by chemical bath deposition, Appl. Surf. Sci. 257 (2010) 1189e1195. [50] M. Devika, K. Ramakrishna Reddy, N. Koteeswara Reddy, K. Ramesh, R. Ganesan, E. Gopal, K. Gunasekhar, Microstructure dependent physical properties of evaporated tin sulfide films, J. Appl. Phys. 100 (2006) 023518.

[51] B. Ghosh, R. Bhattacharjee, P. Banerjee, S. Das, Structural and optoelectronic properties of vacuum evaporated SnS thin films annealed in argon ambient, Appl. Surf. Sci. 257 (2011) 3670e3676. [52] H. Li, S. Cheng, J. Zhang, W. Huang, H. Zhou, H. Jia, Fabrication of CdS/SnS heterojunction for photovoltaic application, World J. Condens. Matter Phys. 5 (2015) 10.