CdTe1-xSx absorber layers for thin-film CdTe/CdS solar cells

Fabrication of high efficiency superstrate CdTe/CdS solar cells results in diffusion of CdS into the CdTe layer. Control of this diffusion is critical for processing cells with ultra-thin CdS layers. Two approaches are presented for retarding the diffusion of CdS into the CdTe-based absorber layer during chloride treatment of superstrate thin-film CdTe/CdS solar cells. One approach utilizes as-deposited CdTe1-xSx alloy absorber layers with x near the thermodynamic limit of CdS-CdTe alloys to reduce the driving force for CdS diffusion. The second approach employs an anneal at T > 550 degrees C prior to chloride heat treatment to reduce diffusion pathways near the absorber-window layer interface. X-ray diffraction, optical, and quantum efficiency measurements were used to quantify changes in CdS thickness and absorber layer composition.