Properties of the CdCl2 Air-annealed CSS CdTe Thin Films

Thin 7-9 μm CdTe films have been deposited on soda lime glass by close-spaced sublimation (CSS). By controlling the CSS temperature-time profile of source and substrate the pinhole-free CdTe films with a good adhesion on roughened glass were prepared. The classical solution-based CdCl2 was applied to enhance the film crystallinity and optoelectronic properties of the CdTe layers. The layers were characterized by X-ray diffraction, Raman and Photoluminescence spectroscopy, scanning microscopy (SEM), energy dispersive X-ray microanalysis and Van der Paw method. CdCl2 heat treatment is a key step in CdTe device processing. Howeverthe process leaves a significant amount of chlorine-rich residue on the CdTe surface that decreases performance of the solar cell.Annealing of the CdCl2-treated polycrystalline CdTeimproves the optoelectronic properties and thus enhances the performance of CdTe/CdS solar cells. A correlation between the structural and optoelctronic properties of CdTe layers and annealing conditions in nitrogen atmosphere at 250, 400 and 450oC for 60 min of the CdCl2treated layers has been found.