An investigation into the effect of annealing on the microstructure of CdTe/CdS solar cells

Thin film CdTe/CdS heterojunction solar cells are subjected to two anneal processes; the first after the deposition of the CdS, the second after the subsequent CdTe deposition. The effect of the second heat treatment on vacuum evaporated CdTe was investigated. Samples were heat treated with and without a CdCl2 surface coating at 450 degrees C for various times. Recrystallization and interdiffusion occurred irrespective of the presence of CdCl2, but CdCl2 exacerbated the degree of interfacial mixing. The interdiffusion led to a reduction in the stress in the film, implying an accommodation of the interface mismatch, and thus a reduction in the number of defects. Similar interdiffusion characteristics were found when annealing at 400 degrees C and 450 degrees C, but interdiffusion was significantly reduced at the lower temperature of 350 degrees C.