Facile synthesis and photo electrochemical performance of SnSe thin films S. N. Pusawale, P. S. Jadhav, and C. D. Lokhande
Citation: AIP Conference Proceedings 1953, 050055 (2018); doi: 10.1063/1.5032710 View online: https://doi.org/10.1063/1.5032710 View Table of Contents: http://aip.scitation.org/toc/apc/1953/1 Published by the American Institute of Physics
Facile Synthesis And Photo Electrochemical Performance Of SnSe Thin Films S. N. Pusawale1, 2, a)*, P. S. Jadhav 1,2, b) and C. D. Lokhande 2, 3, c) 1. Rajarambapu Institute of Technology, Sakharale, Maharashtra, India. 2. Shivaji Univerisity, Kolhapur, Maharashtra, India. 3. D. Y. Patil University, Kolhapur, Maharashtra, India. a)Corresponding author:
[email protected] b)
[email protected] c)
[email protected] Abstract: Orthorhombic structured SnSe thin films are synthesized via SILAR (successive ionic layer adsorption and reaction) method on glass substrates. The structural properties of thin films are characterized by x-ray diffraction, scanning electron microscopy studies from which nanoparticles with an elongated shape and hydrophilic behavior are observed. UV –VIS absorption spectroscopy study showed the maximum absorption in the visible region with a direct band gap of 1.55 eV. The photo electrochemical study showed p-type electrical conductivity.
INTRODUCTION The synthesis of metal chalcogenide materials for optoelectronic application has becoming the growing research subject in recent few years. Among the various metal chalcogenide materials, tin selenide (SnSe) is one of the interesting material. SnSe belongs to group IV-VI that has potential application in the field of solar energy conversion. Bulk SnSe has an indirect band gap of 0.90 eV and a direct band gap of 1.30 eV, which makes it an attractive material for photovoltaic application [1]. It crystallizes in orthorhombic structure (space group Pnma) and exists as a layered compound with the lattice parameters a=1.149 nm, b=0.415 nm, and c= 0.4444 nm. In SnSe, tightly bound layers of Sn and Se atoms are stacked along the crystallographic c axis. The weak Vander walls bonding exhibit in these layers leads to the highly pronounced layered type of structure which leads to the prominent anisotropy of physical properties of this compound, making it attractive from both applicative and fundamental aspects [2]. It has applications in optoelectronic devices [3], radiation detectors [4], electrical switching, memory switching devices, holographic recording systems [5] and in photovoltaic devices [1]. Various methods have been reported for deposition of SnSe in bulk and also in thin film form such as chemical bath deposition [6, 7], thermal Co precipitation [1] electrodeposition [8, 9]. In the present paper, thin films of SnSe have been prepared by SILAR method and studied for their structural, morphological, optical, and photo electrochemical properties.
EXPERIMENTAL DETAILS Thin film preparation For the deposition of SnSe thin films, 0.1 M stannous chloride (SnCl2.2H2O) with pH~11 made by adding 1 M NaOH solution is used as the cationic precursor solution, and anionic precursor solution is sodium selenosulfate (Na2SeSO3). The preparation method of Na 2SeSO3 is described elsewhere [10]. The glass substrates were immersed in cationic precursor solution [SnCl2.2H2O] for 10 s for the adsorption of stannous (Sn2+) ions on the substrate surface. The substrate was rinsed in double distilled water for 10 s to remove loosely bound species of Sn 2+ ions. Then, the substrate was immersed in anionic precursor solution (Na 2SeSO3) for 10 s, for the selenide (Se 2-) ions to react with
2nd International Conference on Condensed Matter and Applied Physics (ICC 2017) AIP Conf. Proc. 1953, 050055-1–050055-4; https://doi.org/10.1063/1.5032710 Published by AIP Publishing. 978-0-7354-1648-2/$30.00
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the preadsorbed Sn2+ ions to form a layer of SnSe material. The unreacted Se 2− ions were removed by rinsing the substrate again in double distilled water for 10 s. Thus, one SILAR growth cycle of SnSe deposition was completed. This growth cycle was repeated to get desired SnSe film thickness. For the structural analysis, Philips PW-3710 X-ray diffractometer using Cr Kα (λ=2.28 Å) radiations was used. The SEM images were obtained using JEOL JSM model 6330. The optical absorption spectrum of thin films was recorded using spectrophotometer SHIMADZU 1800, in the wavelength range 350–1000 nm in the presence of other similar glass substrate as a reference. Photo electrochemical (PEC) experiments were performed in [Fe(CN) 6] 3−/[Fe(CN)6]4− redox system, by running linear sweep voltammetry (LSV) between −0.30 and −1.00 V in a conventional three-electrode cell. Saturated calomel electrode (SCE) was used as a reference electrode, SnSe film on stainless steel substrate was used as a working electrode, and platinum was used as a counter electrode. A tungsten filament lamp (500 W) was used for illuminating the electrode.
RESULTS AND DISCUSSION Film formation mechanism The deposition of SnSe thin films by SILAR method is carried out using four beaker systems. The 1st beaker contains SnCl2 solution containing Sn2+ ions. When the substrate is immersed in it, Sn2+ ions are adsorbed on the substrate surface. The loosely adsorbed Sn2+ ions are separated out by rinsing the substrate in double distilled water placed in a 2nd beaker. Beaker 3rd contains sodium selenosulphite which hydrolyzes to give Se 2- ions according to equation [11], Na2 SeSO3 +OH- ↔Na2 SO4 +HSe(1) HSe- +OH- ↔H2 O+Se2(2) When the substrate with pre-adsorbed Sn2+ ions is immersed in third beaker, these Se2- ions react with Sn2+ ions and forms SnSe as [7], Sn2+ +Se2- →SnSe (3) The substrate is then rinsed in double distilled water kept in a 4th beaker to remove loosely adsorbed SnSe particles and unreacted Se2- ions. This contains one SILAR cycle for deposition of SnSe layer. Several such cycles were repeated to increase the film thickness. The films are brown-black color and spectacularly reflecting. A maximum thickness of 0.2 µm is observed, for 100 cycles
Structural study Fig. 1 shows XRD pattern of SnSe film onto a glass substrate.
FIGURE 1 The X-ray diffraction pattern of SnSe thin film on glass substrate
The observed pattern shows the polycrystalline nature of the SnSe film. The observed peaks at 2θ=24.190, 37.470, 45.920, and 57.410 correspond to the (200), (201), (111) and (311) planes of the SnSe orthorhombic phase respectively. It indicates that the preferred orientation lies along (200). The cell constants are calculated to be a=1.09 nm, b=0.4
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nm, and c= 0.46 nm. The results are close to JCPDS card no. 89-0233. No other peaks than SnSe were observed confirming high product purity. The crystallite size for (200), (201) and (111) peaks are calculated by using the formula, 0.9λ
d= βcosθ
(4)
Where d is average crystallite size, λ wavelength of X-rays used (λ=2.28 Å Cr target), ß is full width at halfmaximum (FWHM), and θ is Bragg’s angle. The crystallite size observed are 13.5, 11.71 and 19.26 nm for (200), (201) and (111) planes, respectively. The average crystallite size found to be about 15 nm.
Surface morphological and wettability study Fig. 2 (a) shows the low magnification image of SnSe film on glass substrate.
FIGURE 2: The SEM images of SnSe thin film at (a) X10, 000 and (b) X30,000 magnifications.
The low magnification (X10, 000) image shows the distribution of granular particles covering the entire surface of the substrate. Fig. 2 (b) shows the high magnification (X30, 000) image from which the elongated shape of particles with random orientations.
Optical study
FIGURE 3: The variation of (αhυ)2 vs. hυ of SnSe thin film. (Inset shows variation of absorbance with wavelength).
Optical absorption of the films absorption of the films deposited on glass substrates was performed in the wavelength region 350 to 1000 nm using glass as a reference. Inset of fig. 3 shows the absorbance plot of SnSe film as a function of wavelength. The optical band gap of the thin film was determined by applying the Tauc relationship given by: αhϑ=A0 [hϑ-Eg ]n (6) Where hυ is the photon energy, E g is the band gap energy, and Ao is a constant which is related to the effective masses associated with the bands. The value of n is equal to 1/2 for a direct band gap material and 2 for the indirect
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gap. The optical band gap of the film determined from the extrapolation of the linear plot of (αhυ) 2 versus hυ at α= 0 (fig. 3 ) was found to be 1.55 eV. The present value of band gap energy is close to that reported by Pejova and Grozdanov [6] and Franzman et al. [12] by chemical synthesis methods.
Photoelectrochemical study
FIGURE 4: Photoresponse of SnSe film under the chopped light.
Fig. 4 shows the photoresponse for a photoelectrochemical cell formed with SnSe film upon illumination and constant chopping with a tungsten lamp (500 W). An increase in the photo current (Ip) has observed after illumination. The current change upon illumination indicates semiconductor behavior of the material. The photo current obtained on the negative (cathode) potential side indicates that the film prepared is of p-type (positive) and such films have been used as a photocathode in a photo electrochemical cell for reduction reactions [7].
CONCLUSIONS Polycrystalline thin films of SnSe have been prepared using the SILAR method. SEM images have observed the uniform distribution of nanoparticles with an elongated shape. The SnSe thin film showed an optical band gap of 1.55 eV. The films showed photoresponse in cathodic region indicating p-type electrical behavior.
REFERENCES 1.
Giuk Jeong, Jekyung Kim, Oki Gunawan, Seong Ryul Pae, Soo Hyun Kim, Jae Yong Song, Yun Seog Lee, Byungha Shin, J. Alloys and Com. 722, 474-481 (2017). 2. B. Pejova, A. Tanusevski, J. Phys. Chem. C 112, 3525-3537 (2008). 3. B. B. Nariya, A. K. Dasadia, M. K. Bhayani, A. J. Patel, A. R. Jani, Chalcogenide Lett. 6, 549-554 (2009). 4. A. Bernardes-Silva,A.F. Mesquita, E. de MouraNeto, A.O. Porto, G.M. de Lima, J.D. Ardisson, F.S. Lameiras, Sol. State Commun. 135, 677-682 (2005). 5. T. Lindgren,M. Larsson, S. Lindquist, Sol. Energy Mater. Sol. Cells 73, 377-389 (2002). 6. B. Pejova, I. Grozdanov, Thin Solid Films, 515, 5203-5211, (2007). 7. Z. Zainal, N. Saravanan, K. Anuar, M.Z. Hussein, W.M.M. Yunus, Mater. Sci. Eng.B 107, 181-185 (2004). 8. Z. Zainal, N. Saravanan, K. Anuar, M.Z. Hussein, W.M.M. Yunus, Sol. Energy Mater. Sol. Cells 81, 261-268 (2004). 9. M. Bicer, I. Sisman, Appl. Surf. Sci. 257, 2944-2949 (2011). 10. R.B. Kale, C.D. Lokhande, Appl. Surf. Sci. 223, 343-351 (2004). 11. R.B. Kale, C.D. Lokhande, Mater. Res. Bull. 39, 1829-1839 (2004). 12. M. A. Franzman, C. W. Schlenker, M. E. Thompson, R. L. Brutchey, J. Am. Chem. Soc. 132, 4060-1 (2010).
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