Optimization of Deposition Time and Optical Constants
of CuInSe2 Polycrystalline Thin Films grown
by Close-Spaced Vapour Transport without vacuum
K. Konan1, J. K. Saraka2*, P. Gbaha2, K. D. Konan2, B. Hadjoudja3
1 Laboratoire de Conversion Photovoltaïque, Centre d’Electronique et de Micro-Optoélectronique,
Université de Montpellier 2, F-34095 Montpellier Cedex 05, France
2 Institut National Polytechnique de Yamoussoukro BP 1093 Yamoussoukro, Côte d’Ivoire
3 Laboratoire des semiconducteurs, Département de Physique, Université d’Annaba, BP 12, Sidi Amar, Annaba, Algérie.
* Corresponding author. E-mail: Joseph_Saraka@yahoo.fr
Received: 06 March 2007; revised version accepted: 24April 2009
CuInSe2 thin films were deposited on glass substrates from a source heated at a temperature of 500°C by vacuum free CSVT process. The corresponding substrate temperature was 318°C. The deposition time was varied from one to five hours. For its optimization, composition and structure of the films were analysed by Energy Dispersive Spectrometry (EDS) and X-ray diffraction (XRD) respectively. EDS analysis showed a quasi- stoichiometric composition of all the films. For three and four hours of deposition, the ratio Cu/In was found to be the same as the characteristic value of the starting CuInSe2 powder. (XRD) spectra revealed that all the films were polycrystalline. The lattice parameters a and c evaluated from these spectra corroborated the nature of chalcopyrite structure. The intensity of the suitable (112) diffraction peak depended strongly on the deposition time. It was found that films deposited during three hours exhibited (112) peak with a maximum intensity. Therefore, the optimal deposition time to produce CuInSe2 thin films for solar cells is about three hours. For this deposition time, the transmittance (T) and the reflectance (R) of the films were characterized using a spectrophotometer in the wavelength range 1 – 2 mm and the optical constants refractive index (n) and extinction coefficient (k) were evaluated.
Keywords: Vacuum free CSVT; deposition time; (112) peak intensity; CuInSe2; thin films; optical constants.