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The role of CdCl2 in prompting recrystallization, grain growth and interdiffusion between CdS and CdTe layers in physical vapor-deposited CdS/CdTe thin-film solar cells is presented. Several CdTe/CdS thin-film samples with different CdTe film thicknesses were treated in air at 415°C for different times with and without a surface coating of CdCl2. The samples were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffractometry and optical absorption. The results show that CdCl2 treatment enhances the recrystallization and diffusion processes, leading to a compositional variation within the CdTe layer due to diffusion of sulfur from the CdS. The highest sulfur concentrations observed after 30 min treatments with CdCl2 at 415°C are near the solubility limit for sulfur in CdTe. The compositional distributions indicated by x-ray diffraction measurements of samples with different CdTe thickness show that the S-rich CdTe1−xSx region lies near the CdTe/CdS interface. A multiple-step mixing process must be inferred to account for the diffraction profiles obtained. © 1997 John Wiley & Sons, Ltd.
McCandless et al. (1997) studied this question.