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Optical properties of CuInS2 thin films prepared by spray pyrolysis

Transmission measurements were performed to examine the optical properties of the films; the absorption coefficient and the optical band gap of the films were calculated by transmission spectra. The absorption spectra of the films showed that this compound is a direct band gap one and its gap varied between 1.30 - 1.78eV. Those thin films were analyzed by X-ray diffraction in order to understand the effect of layers structure on their optical properties. | Communications in Physics, Vol. 22, No. 1 (2012), pp. 59-64 OPTICAL PROPERTIES OF CuInS2 THIN FILMS PREPARED BY SPRAY PYROLYSIS TRAN THANH THAI Institute of Physics Engineering, Hanoi University of Technology and Department of Technique and Technologies, Quy Nhon University, PHAM PHI HUNG AND VO THACH SON Institute of Physics Engineering, Hanoi University of Technology VU THI BICH Center for Quantum Electronics, Institute of Physics, VAST Abstract. Polycrystalline CuInS2 (CIS) absorber films for solar cells were prepared by spray pyrolysis of aqueuos solution of copper chloride, indium chloride and thiourea onto heated glass substrates. By optimizing the spray parameters, such as reducing/increasing the temperature of the substrate and molar ratio of Cu/In in the spraying solution, the optical characteristics of films, which are well matched to the solar spectrum, were identified. In all cases, those CIS thin films were of p-type conductivity. Transmission measurements were performed to examine the optical properties of the films; the absorption coefficient and the optical band gap of the films were calculated by transmission spectra. The absorption spectra of the films showed that this compound is a direct band gap one and its gap varied between 1.30 - 1.78eV. Those thin films were analyzed by X-ray diffraction in order to understand the effect of layers structure on their optical properties. I. INTRODUCTION The CuInS2 (CIS) compound belongs to the family of direct band gap I-III-IV2 chalcopyrite semiconductor. This compound exhibits a large fundamental absorption coefficient (α ∼105 cm−1 ) and a band gap (Eg ≈ 1.55eV) optimally close to the peak of the spectral distribution of solar energy [1-5]. No high toxic component is included in this compound semiconductor. The highest reported efficiency of CIS based solar cells is close to 12% [2,3,6-8]. However, at the present time, the main fundamental physical parameters important for practical application of this .