Preparation and Studies of Chemically Deposited Cu4sns4 Thin Films in The

Indian Journal of Engineering & Materials Sciences Vol. 17, August 2010, pp. 295-298

Preparation and studies of chemically deposited Cu 4SnS 4 thin films in the presence of complexing agent Na 2EDTA

Anuar Kassim a*, Zulkefly Kuang a, Atan Sharif a, Tan Wee Tee a, Ho Soon Min a & Saravanan Nagalingam b aDepartment of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia bDepartment of Bioscience and Chemistry, Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, 53300 Kuala Lumpur, Malaysia Received 13 March 2009; accepted 28 June 2010

The Cu 4SnS 4 thin films are deposited onto indium tin oxide glass substrate by chemical bath deposition method. The disodium ethylenediaminetetraacetic acid is used as a complexing agent during deposition process. The structural, morphological and optical properties of the deposited films have been studied using X-ray diffraction, atomic force microscopy and UV-Vis spectrophotometer, respectively. The presence of Na 2EDTA promotes the deposition of better quality films. The XRD analysis shows that these films have a high crystallinity with orthorhombic structure. The AFM images indicated that these films are uniform, compact with larger grains. The absorption spectra confirmed that the thicker film has higher absorption properties. The band gap of 1.6 eV with direct transition is observed.

Keywords: C hemical bath deposition, Semiconducting material, Solar cells, Thin films

In recent years, polycrystalline thin films have received a complexing agent. The properties of thin films much attention due to their very important role in the which deposited in the absence and in the presence of fabrication of solar cells, photoconductors, sensors, Na 2EDTA were studies. X-ray diffraction is used to infrared detectors and temperature control of satellites. study the structural properties of films. Meanwhile, The thin films can be prepared by various techniques the morphological and optical properties of Cu 4SnS 4 such as chemical bath deposition 1-6, vacuum thin films were investigated by using atomic force evaporation 7, electrodeposition 8, successive ionic layer microscope and UV-visible spectrophotometer, adsorption reaction 9, close spaced sublimation 10 , respectively. thermal evaporation 11 , spray pyrolysis 12 , sputter deposition 13 and metal organic chemical vapor 14 Experimental Procedure deposition . Among these, the chemical bath All the chemicals used for the deposition were deposition method is most commonly used because it is analytical grade and all the solutions were prepared in a simple, cost effective and economically reproducible deionised water (Alpha-Q Millipore). The Cu 4SnS 4 method that can be applied in large area deposition at thin films were prepared from an acidic bath using low temperature. This method is based on the copper sulfate (CuSO ), tin chloride (SnCl ) and controlled precipitation from solution of a compound 4 2 sodium thiosulfate (Na 2S2O3) act as a source of on a suitable substrate. The substrate are immersed copper, tin and sulfide ion, respectively. The either in an alkaline or acidic solution which containing disodium ethylenediaminetetraacetic acid (Na 2EDTA) the metal ion, chalcogenide source, the added acid or is used as a complexing agent during deposition base and a complexing agent. Several complexing process. 10 mL of 0.05 M CuSO solution was added agents have been utilized in the deposition of thin film 4 15 16-18 into 10 mL of 0.05 M SnCl 2 solution in 100 mL such as NH 3 , triethanolamine , nitrilotriacetic 19 20,21 beaker. To it, 10 mL of 0.1 M Na 2EDTA solution was acid , disodium ethylene diamine tetra-acetate , added and then solution was continuously stirred. 10 benzotriazole 22 and tartaric acid 23,24 . mL of 0.05 M Na 2S2O3 solution was then added into a In this paper, we prepare Cu 4SnS 4 thin films by beaker slowly. The resultant solution was stirred for chemical bath deposition method using Na 2EDTA as few minutes. The pH of the chemical bath was ______maintained at 1.5 by using hydrochloric acid. The *Corresponding author (E-mail: [email protected]) indium doped tin oxide (ITO) glass was used as the 296 INDIAN J ENG. MATER. SCI., AUGUST 2010

substrate. The ultrasonically cleaned glass substrates 28.4 °, 30.2 °, 42.8 °, 47.0 ° and 50.6 ° corresponding to were immersed vertically into acidic bath. The inter-planar distances of 3.99, 3.13, 2.96, 2.09, 1.93 deposition process was carried out for 120 min at and 1.80 Å which corresponds well with the standard 50 °C. The deposited films were tested for adhesion by JCPDS data (Reference code: 010710129). As can be subjecting it to a steady stream of distilled water. observed in Fig. 1b, the intensity of the peaks The crystal structure of the film was monitored by increased, indicating better crystalline phase for the X-ray diffraction (XRD) with a Philips PM 11730 films deposited in presence of Na 2EDTA. This could diffractometer equipped with a CuK α ( λ=1.5418 Å) be clearly seen in the (221) peak, which is more radiation source. Data were collected by step scanning intense. The appearance of three other peaks attribute θ θ from 20° to 60° (2 ) with a step size of 0.05° (2 ) and to Cu 4SnS 4 thin films at 2 θ = 35.1 °, 39.1 °, 56.6 ° 1 s counting time per step. Surface morphologies of the corresponding to (420), (222), (712) planes were films were observed by using a Q-Scope 250 (Quesant detected.

Instrument Corporation) atomic force microscope in a The surface morphology of thin films was contact mode. Photoelectrochemical experiments were 3- 4- determined by atomic force microscopy (AFM). AFM performed in [Fe(CN) 6] /[Fe(CN) 6] redox system, by can give the structure, grain size and surface running linear sweep voltammetry between -0.4 to -1.0 roughness of thin films. Figures 2a and 2b show the V. The halogen lamp (100 W) was used for AFM images of the Cu 4SnS 4 thin film deposited in the illuminating the electrode. The optical properties of the absence and in the presence of Na 2EDTA. It is film were measured with a Perkin Elmer UV/Vis Lambda 20 Spectrophotometer. The data were registered from 300 to 800 nm with an uncoated glass as a reference. The absorption data were manipulated for the determination of the band gap energy.

Results and Discussion Figures 1a and 1b show the X-ray diffraction (XRD) patterns of the Cu 4SnS 4 thin films deposited in the absence and in the presence of Na 2EDTA. The XRD data indicate that the studied films are polycrystalline and have an orthorhombic structure with lattice constant ( a =1.3558 nm, b = 0.7681 nm, c = 0.6412 nm). The films deposited in the absence of

Na 2EDTA produced only six peaks at 2 θ = 22.3 °,

Fig. 1 −X-ray diffraction pattern of Cu 4SnS 4 thin films deposited Fig. 2 −Atomic force microscopy image of Cu 4SnS 4 thin films in (a) absence and (b) presence of Na 2EDTA deposited in (a) absence and (b) presence of Na 2EDTA KASSIM et al .: Cu 4SnS 4 THIN FILMS 297

observed that the films deposited using Na 2EDTA n/2 [k( hv− E g ) ] have a uniform surface, homogeneous and well cover A = … (1) hv the substrate. Its three-dimensional image shows that larger grain sizes were observed. The grains sizes where v is the frequency, h is the Planck’s constant, k were in the range from 0.9 to 1.2 µm. The thickness equals a constant while n carries the value of either 1 or and root mean square of the roughness is about 980 4. The value of n is 1 and 4 for the direct transition and nm and 106 nm, respectively. On the other hand, the indirect transition, respectively. Figures 4a and 4b show smaller grain sizes were obtained for the film the plot of (Ahv) 2/n versus hv for the films deposited in deposited in absence of Na 2EDTA. The grains sizes the absence and in the presence of Na 2EDTA. Since the were in the range from 0.1 to 0.2 µm. The thickness plot of (Ahv) 2 versus (hv) is a straight line indicating that and root mean square of the roughness is about 302 the involved transition is direct transition. The band gap nm and 27 nm, respectively. These results were value obtained by extrapolating the linear portion of the consistent with XRD analysis. plot of (Ahv) 2 versus (hv) to (Ahv) 2 = 0. As shown in

The optical properties of thin films were measured figure, the band gap energy of the films deposited in in the range of 350-800 nm by UV-Vis presence of Na 2EDTA (1.6 eV) is larger than that of the spectrophotometer. Figures 3a and 3b show the films deposited in the absence of Na 2EDTA (1.0 eV). This is due to the larger grain sizes were observed in absorption spectra of the Cu 4SnS 4 thin films deposited these films. in the absence and in the presence of Na 2EDTA. As it Figures 5a and 5b illustrate the results of can be seen, the thin films deposited with Na 2EDTA display high absorption characteristics in the visible photoactivity measurement of the Cu 4SnS 4 thin films region when compared with the films deposited in the deposited in the absence and in the presence of Na EDTA, respectively. The light was manually absence of Na 2EDTA. This is due to more Cu 4SnS 4 2 materials were formed under this condition. The chopped to describe the dark and the photocurrent. As spectra shows two regions, one for higher wavelength the electrode was illuminated, the current increases and with practically lower absorption and other for lower when the illumination was chopped, the current flow wavelength in which absorption increases gradually decreases. This current change with illumination starting from 700 nm downward. This makes it confirms that the film shows good respond towards possible for this material to be used in a light and posses semiconducting behavior. The photoelectrochemical cells.

Band gap energy and transition type can be derived from mathematical treatment of data obtained from optical absorbance versus wavelength with Stern relationship of near-edge absorption (Eq. (1)):

2 Fig. 3 −UV-Vis absorption spectra of Cu 4SnS 4 thin films deposited Fig. 4−Plot of (Ahv) versus hv of Cu 4SnS 4 thin films deposited in in (a) absence and (b) presence of Na 2EDTA (a) absence and (b) presence of Na 2EDTA 298 INDIAN J ENG. MATER. SCI., AUGUST 2010

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