ELECTRICAL AND OPTICAL-PROPERTIES OF VACUUM-EVAPORATED CDS FILMS

Abstract

1 mum CdS films for the window layer of CdS/CuInSe2 solar cells have been prepared by vacuum evaporation at various deposition conditions. Deposition rates were 0.73 and 3.3 nm s-1, and substrate temperature ranged from 50 to 225-degrees-C. The effect of the deposition conditions on the properties of CdS films was investigated by measuring electrical resistivity, optical transmittance and reflectance. The resistivity of the evaporated CdS films strongly decreased as substrate temperature decreased and the films with high deposition rate showed lower resistivity compared to the films with low deposition rate. Interestingly, the combination of high deposition rate and very low substrate temperature resulted in an increase of resistivity. The optical transmittance of CdS films increased as substrate temperature decreased and then decreased with further decrease in substrate temperature. The transmittance strongly depended on deposition rate at low substrate temperature ( < 100-degrees-C), while it was independent of deposition rate at high substrate temperature ( > 100-degrees-C). In particular, high transmittance can be extended to lower substrate temperature by reducing deposition rate. Low optical reflectance can be obtained by lowering substrate temperature. The results indicate that CdS films of low resistivity and high transmittance can be produced by vacuum evaporation at low substrate temperature and low deposition rate.