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Diffusion of Cu in ZnS thin films was investigated in the temperature range 80–400 °C using the energy‐dispersive X‐ray fluorescence (EDXRF) technique. ZnS thin films were deposited by spray pyrolysis on a glass substrate. The temperature dependence of the Cu diffusion coefficient is described by the equation D = 1.4 × 10−10 exp [–(0.18 eV)/kT]. It is shown that diffusion doping of n‐type ZnS by Cu is accompanied by a significant increase in resistivity and a slight decrease in the band gap of the ZnS films. The observed results are attributed to the migration of Cu in polycrystalline ZnS films by means of diffusion both along grain boundaries and into grains. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A new fabrication technique of p-type CdS thin films by He-Ne laser illumination of bilayer Cu-nCdS structures at room temperature was investigated. The n-type CdS films were obtained by vacuum evaporation in a quasi-closed volume. X-ray diffraction was used to provide crystalline structure and composition data of CdS films and Cu-CdS structures. The band gap of CdS films was estimated from the optical transmission spectra. The hot probe and Hall effect studies were used for the determination of conductivity type and concentration of charge carriers in films. The formation of a p-n homojunction in CdS films or conversion of the film all over to the p-type, depending on the duration of laser illumination, was shown by I-V characteristics, the photovoltaic, the hot probe and Hall effect measurements. Analysis of concentration distributions of Cu in CdS films, arising as a result of laser-accelerated diffusion, by energy dispersive x-ray spectroscopy gave the effective diffusion coefficient of copper, D = 8 × 10-12 cm2 s-1 at T = 25 °C.

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The effects of white light illumination during the deposition of CdS thin films in a quasi-closed volume on the structural, photoelectrical and optical properties are investigated. The films were highly c-axis oriented with an increasing intensity of (002) reflection as the illumination increases. The room temperature resistivity values of the CdS films decreased in the range of 107-104 Ω cm. The photosensitivity in the fundamental absorption region and the transparency in the transmission region considerably increased as the illumination increased. Under 100 mW cm-2 insolation, the efficiencies of the CdS/CdTe solar cells based on CdS window materials which were deposited: (1) in the dark; and (2) under an illumination of 150 mW cm-2; were found to be 1.8% and 7.3%, respectively.

Low-temperature vacuum deposition instead of the commonly used vacuum deposition at high substrate temperatures has been applied to prepare high efficiency (CdS/CdTe) solar cells. CdS and CdTe thin films have been subsequently deposited on SnO 2 / Corning 7059 glass substrates and examined by using scanning electron microscopy (SEM) and grazing incidence X-ray diffraction (GIXRD) techniques. It has been found that CdTe and CdS films deposited at low substrate temperature (218 K) have very similar grain sizes and surface morphology, necessary for high efficiency photovoltaic performance of the resultant device structures. Particularly, the obtained solar cells have shown efficiencies of more than 14%. The applied preparation method can be regarded as promising for high efficiency CdTe-based solar cell fabrication.