Studies on Growth Kinetics of Electrodeposited Znin₂se₄ Thin Films

Anuradha C. Pawar¹, A. V. Kokate², Pradnya S. Raut³, J. A. Borase², B. G. Wagh⁴ and H. R. Kulkarni²

¹Department of Physics, Brahma Valley Polytechnic, Anjaneri, Nashik - 422 213, India. 

²Department of Physics, MET's Institute of Engineering, Adgaon, Nashik, India.

³Department of Chemistry, MET's Institute of Engineering, Adgaon, Nashik, India.

⁴Department of Physics, KAANMS Arts, Commerce, Science College, Satana, Nashik, India.

DOI : http://dx.doi.org/10.13005/msri/070141

ABSTRACT:

ZnIn₂Se₄ thin film were prepared by pulsed electro deposition technique over stainless steel substrates in galvanostatics mode from an aqueous acidic bath containing ZnSO₄, In Cl₃, and SeO₂. The growth kinetics of the film was studied and the deposition parameters such as electrolyte bath concentration, deposition time, current density, and pH of electrolyte bath are optimized. The X-ray diffraction (XRD) analysis of the deposited film showed presence of polycrystalline nature. The surface morphology studied by Scanning electron microscope (SEM) shows that the deposited film are well adherent and grains are uniformly distributed over the surface of substrate.

KEYWORDS: Electrodeposition; XRD; SEM; Kinetics; ZnIn2Se4

Copy the following to cite this article: Pawar A. C, Kokate A. V, Raut P. S, Borase J. A, Wagh B. G, Kulkarni H. R. Studies on Growth Kinetics of Electrodeposited Znin2se4 Thin Films. Mat.Sci.Res.India;7(1)

Copy the following to cite this URL: Pawar A. C, Kokate A. V, Raut P. S, Borase J. A, Wagh B. G, Kulkarni H. R. Studies on Growth Kinetics of Electrodeposited Znin2se4 Thin Films. Mat.Sci.Res.India;7(1). Available from: http://www.materialsciencejournal.org/?p=2336

Introduction

For the last couple of decade’s interest in the use of photo electrochemical solar cells lead to large amount of research in the search for thin film polycrystalline material with acceptable efficiency. Some time approaching that of single crystals. In recent years, thin films have attracted much interest because of their varied application such as semi conducting devices, photovoltaic, optoelectronic devices, radiation detectors, laser materials, thermoelectric devices, solar energy converters. etc.^1-4

Interest in the use of photo electrochemical (PEC) solar cells for low-cost energy conversion has lead to an extensive research in the field for novel and suitable thin film semiconductor materials.^5-8 Recent investigation has shown that layered type semi conducting zinc chalcogenide group (ZnSe, ZnS, ZnTe) which absorb visible and near IR light are particularly promising materials for photo electrochemical solar energy conversion. The polycrystalline electrodes are economically desirable for solar cell applications. Hence this study has been directed towards obtaining ZnIn₂Se₄ in polycrystalline thin films.

Many workers investigated the photo electrochemical property of ZnIn₂Se₄ single crystal. The structural and optical properties of electrodeposited ZnIn₂Se₄ thin films have been reported. Many workers have been succeeded in depositing thin film of Z_nI_n2Se₄by vacuum evaporation.

In this report an attempt is made to prepare ZnIn₂Se₄ films through electrodeposition technique on stainless steel substrate which enables the film to be used for characterization studies like structural, surface composition, surface morphology and optical properties.

Material and Methods For Thin Film Synthesis

The thin films of ZnIn₂Se₄ were pulsed electro deposited on stainless steel substrate. The stainless steel plates were used as the cathode in three electrodes cell with graphite as the counter electrode and saturated calomel electrode (SCE) was the reference electrode. The electrolyte was prepared by mixing solution of ZnSO₄ (0.1M), InCl₃ (0.1M), and SeO₂ (0.1M) in the ratio of 1:2:4 respectively. The pH of electrolyte solution was varied by dilute HCl. Double distilled water was used for preparation of aqueous solution of above precursor chemicals. Before deposition the substrate were thoroughly cleaned with double distilled water. The distance between the working electrode and counter electrode way kept constant as 1 cm during deposition. From visual observation it was observed that a formation of reddish films of ZnIn₂Se₄ take place. These pulsed plated ZnIn₂Se₄ films were found to be well adherent and uniform. The detailed growth kinetics was studies by changing the deposition parameters, the pH of solution and current density

Results and Discussion

The polarization curve were plotted to determine the deposition potential of ZnIn₂Se₄ thin film are shown in fig 1.

Figure 1: Variation of current density with voltage

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The concentration of Zinc sulphide (ZnSO₄), Indium trichloride (InCl₃), and selenium dioxide (SeO₂) were 0.1M. The films were grown at the optimized deposition potential of 1100 mV with respect to SCE and at the current density 1.5 mA/ cm^-2_. When an electric field is applied between the working and counter electrode a fine ZnIn₂Se₄ thin film formation occurs on the surface of the substrate. The process of film formation is observed to be time dependent. The deposited film have been dried and preserved in desiccators for further study. The current density varied from 0.6 to 4.6 mA/cm–² during deposition. The film deposited at current density 1.5 mA/cm^-2 was found to be uniform thick. And well adherent to substrate. For other higher and lower values of current density thickness of film was less as compared to 1.5 mA/cm^-2.

The PEC cell n-ZnIn₂Se₄ /polysulphide/c is illuminated with 200 w tungsten filament lamps. The photons having energy equal to or greater than band gap energy of ZnIn₂Se₄ are absorbed in semiconductor and the electron-holes pairs are generated these electron hole pair are separated by local electric field. Present across the interface between semiconductor and polysulphide electrolyte. This leads to generation of photo voltage under open circuit and photocurrent under short circuit condition. The variation of Isc and Voc as a function of deposition time at constant pH is presented in fig 2.

Figure 2: Variation of Isc and Voc with deposition time

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It can be seen that the Isc and Voc are relatively higher at deposition time 30 min. at pH 2 this may be due to formation of nearly stoichiometric ZnIn₂Se₄ thin film material at 30 min.and optimum thickness of ZnIn₂Se₄ for the effective absorption of the photons. Fig 2 shows the variation of Isc and Voc with deposition time and the optimum values of Isc and Voc are found to be for the film deposited for 30 min. this may be attributed to the optimum thickness of the film.

Fig 3 Shows that variation of Isc and Voc with different pH at constant deposition time. It can be seen that the Isc and Voc are relatively higher at pH =1 at deposition time 30 min and optimum pH of ZnIn₂Se₄ film for the effective absorption of photons. The grown ZnIn₂Se₄ film deposited at the optimized preparation parameter was further characterized by analyzing the X-ray diffraction (XRD) pattern. The XRD pattern of ZnIn₂Se₄ film deposited on stainless steel substrate is shown in fig.4.

Figure 3: Variation of Isc and Voc with pH of bath

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Figure 4: The X-ray diffraction pattern (XRD) of electrodeposited ZnIn₂Se₄ thin film

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The XRD analysis reveals that film is polycrystalline and the sharp peaks are identified at (112), (211), (204) planes of ZnIn₂Se₄ film. The standard‘d’ values and observed ‘d’ values for ZnIn₂Se₄ thin film are matching with each other. (Table 2). This confirms that material is ZnIn₂Se₄

Table 1: Optimized parameters of deposited ZnIn₂Se₄ thin film

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Table 2: The standard ‘d’ values and observed ‘d’ values for ZnIn₂Se₄ thin film are tabulated along with ASTM data [Fig. 5]

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Table 3: Particle size

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The surface morphology of ZnIn₂Se₄ thin film was studied by SEM picture.The SEM micrograph shows well adherent, smooth film surface without cracks. The surface morphology of ZnIn₂Se₄ film prepared under optimized conditions exhibits spherical grains of uniform size about 12A⁰ spread all over the surface.

Conclusions

Almost stoichiometric ZnIn₂Se₄ thin films formation by electro deposition technique was taken from acidic bath. The film grown at the optimized pH and time is polycrystalline with tetragonal structure and the particle sizes are found to be 10.705 A⁰ , 12.9429 A⁰ ,13.7332 A⁰ with lattice parameter a=5.709, b=5.709, c=11.44. SEM analysis is shown by Fig.5,6,7 indicating that the deposited film is uniform , well adherent and grains are uniformly distributed over the surface of substrate.

Figure 5: SEM of ZnIn₂Se₄ thin film for 20 kV and magnification is 1000

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Figure 6(a): SEM of ZnIn₂Se₄ thin film for 20 kV and magnification is 5000

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Figure 6(b): SEM of ZnIn₂Se₄ thin film for 20 kV and magnification is 10000

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 Acknowledgements

I would like to thank Prin. Prof. C.K.Patil, Prin. Dr.A.A.Kulkarni, all of my colleagues, staff members, and research scholars of the institute. 

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