International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 04 Special Issue: 09 | Sep -2017
p-ISSN: 2395-0072
www.irjet.net
One Day International Seminar on Materials Science & Technology (ISMST 2017) 4th August 2017 Organized by
Department of Physics, Mother Teresa Women’s University, Kodaikanal, Tamilnadu, India
Effect of precursor on the efficient formation of ZnS thin films for buffer layer G. Genifer Silvena1, Bincy John1, A. Leo Rajesh1* 1Department
of Physics, St. Joseph’s College, Tiruchirappalli, Tamilnadu, India Corresponding author’s e-mail id: aleorajesh@gmail.com ---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract - ZnS thin films were found to be a promising
deposition [6] because it is large scale applicable economically and convenient for ambient conditions. Other deposition techniques such as sputtering [7], thermal evaporation [8], pulsed lased deposition [9] and sol-gel [10]. Wide range of investigations is being done on this material such as pH variation, temperature variation and variation in molar ratio, etc.
replacement for the toxic CdS buffer layers in thin film photovoltaic cells in the recent years. The ZnS thin films were prepared using chemical spray pyrolysis technique with an equimolar ratio of Zn-S precursors. The effect of different precursors Zinc (II) chloride dihydrate, Zinc acetate dihydrate, Zinc Nitrate hexahydrate and Zinc sulphate heptahydrate were taken as precursors for Zinc and thiourea was taken as sulfur source in the preparation of ZnS thin films. The films were deposited at a temperature of 400˚C and with a flow rate of 1.5ml/min. The deposited films were characterized using Xray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), UV-Visible spectroscopy and photoluminescence. The XRD pattern confirmed the polycrystalline film formation with the intensed (111) phase. The morphological images showed sphere like shapes of the particles. The UV-Visible spectrum showed maximum transmittance value for a buffer layer and a wide bandgap for the photons to pass through. The optical emission spectrum and purity of the material was analyzed from the photoluminescence study.
In the present study ZnS thin films are deposited onto glass substrates with four different Zinc precursor materials and their structural, morphological and optical properties are studied. This work helps in identifying the suitable starting material to deposit ZnS thin films using chemical spray pyrolysis technique.
2. EXPERIMENTAL ZnS thin films were prepared using aqueous solutions of four precursor materials Zinc Nitrate hexahydrate (Zn (NO3)2.6H2O), Zinc (II) chloride dihydrate (ZnCl2.2H2O), Zinc acetate dihydrate (Zn (CH3COO)2.2H2O) and Zinc sulphate heptahydrate (ZnSO4.7H2O) for Zinc source and Thiourea (CH4N2S) for Sulphur source. The films were deposited using spray pyrolysis technique at a temperature of 400˚C, pressure of 1.2 kg/cm2 and a solution flow rate of 1.5 ml/min. The concentrations were constantly taken at 1:1 molar ratios for Zn and S materials in 40 ml of aqueous solution. The solutions were sprayed continuously onto the cleaned and preheated glass substrates. Four types of films were prepared named as ZnS-1, ZnS-2, ZnS-3 and ZnS-4 in the above precursor order respectively.
Key Words: ZnS, thin films, precursors, spray pyrolysis, buffer layer.
1. INTRODUCTION ZnS thin films are promising replacements for CdS buffer layers in thin film solar cells. Though CdS layers are suitable and available in application level in efficient photovoltaic cells a requirement for replacement is CdS buffer layers is due to its toxic nature and less transparency [1]. Replacement of ‘Zn’ in the place of ‘Cd’ makes it as a toxic free material which is useful for the eco-friendly fabrication of thin film solar cells. ZnS has high transmittance in the Visible and IR region and has an optimum bandgap of ~3.7 eV [2].
The prepared films were characterized using X-ray diffractometer (XPERT-PRO) with a scan range of 10˚ to 80˚ with CuKα radiation to study the structural formation. The surface morphology was studied using FESEM (Carl Zeiss) at 10kV source voltage. The optical properties were studied using UV-Visible spectroscopy (Perkin Elmer Lambda 576) for a wavelength region of 300-1100 nm and Photoluminescence spectrometer (Fluorimeter LS45) with an excitation wavelength of 270 nm.
Various deposition techniques are followed to deposit buffer layers in thin film solar cells. The most common methods among them is spray pyrolysis [3-5] and chemical bath
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