SULFUR DIFFUSION IN POLYCRYSTALLINE THIN-FILM CdTe SOLAR CELLS

X-ray diffraction and photoluminescence measurements have been used to characterize the diffusion of S into CdTe during post growth annealing of CdTe solar cells. For anneals at 410°C in the presence of CdCl2, evidence that both a CdTe1-xSx phase and nearly-pure CdTe are present near the back contact is observed. The ternary phase becomes more prominent and the S concentration increases with depth reaching roughly 4-5% near the CdS interface. Much less diffusion is observed at 350°C while for a 460°C anneal, CdTe1-xSx with a S concentration near 5% is found throughout the layer. The presence of CdCl2 during the anneal enhances the interdiffusion.