Photothermal Deflection Spectroscopy (PDS) technique was used to study undoped and copper (Cu) doped cadmium sulphide (CdS) thin films. Variation in grain size and lattice strain due to Cu doping were analysed using X-ray diffraction (XRD). Changes in mobility of carriers in CdS with Cu concentration was studied using PDS technique for the first time and results are compared with the earlier ones. Thickness of Cu diffused region in CdS was also calculated and compared with results from X-Ray Photoelectron Spectroscopy (XPS) and Ellipsometry. Results from PDS technique are found to be agreeing with those from other experiments. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

CdS homojunction solar cell having an improved efficiency of 3% has been fabricated. This is achieved by the uniform distribution of copper into the n-CdS film by repeated thermal annealing of copper coated on the n-CdS. The ESCA analysis (Electron Spectroscopy for Chemical Analysis) gives the idea that no copper compounds like CuxS has not been formed. The depth profile of the sample showed that the copper distribution on the top layer of the CdS is uniform and there existed n-CdS layer below the p-CdS:Cu layer, free of copper atoms. The optical absorption studies on the sample revealed that there is a slight modification of optical band gap, for the copper diffused p-CdS. The spectral response curve for the cell has also been drawn.

Trap levels in n- and p-type spray pyrolysed CdS thin films were analysed using thermally stimulated current (TSC) and dark-conductivity measurements. TSC measurements of the n-type sample revealed the presence of only one peak under light excitation for a short period due to mobility of sulphur vacancies, but longer excitation could give evidence of one more level which was due to a complex of cadmium and sulphur vacancies. TSC spectra of the p-type sample indicated the presence of two levels of comparable cross section irrespective of light excitation time, which correspond to mobility of the sulphur vacancy and copper impurity. TSC measurements on air annealed n-type samples indicated the presence of a level due to the sulphur vacancies and another level may be due to chemisorbed oxygen. However vacuum annealed samples showed results similar to those of as-prepared n-type samples. The dark-conductivity measurements of these samples were found to be in good agreement with the TSC measurement results.

PN homojunction has been fabricated for the first time in spray pyrolised CdS thin film. This is achieved by annealing CdS/Cu bilayer film. J-V characteristics of the homojunction are drawn; fill factor and efficiency are calculated to be 0.44% and 0.73% respectively. It is observed that there exists a minimum temperature at which the CdS/Cu bilayer has to be annealed for the formation of the junction. Interestingly increasing the annealing temperature does not result in any appreciable variations of open circuit voltage and short circuit current.

Top layer of spray pyrolyzedn-type CdS has been converted intop-type by diffusion of copper which resulted in the formation of homojunction. This is achieved by annealing CdS/Cu bilayer film. The nature of diffusion of copper atoms into CdS has been studied using auger electron spectroscopy (AES).