Inert gas cluster formation in sputter-deposited thin film CdTe solar cells

Magnetron sputtering is widely used for thin film deposition because it is a relatively low temperature process which also produces films with excellent uniformity. Unfortunately, in its use for the deposition of thin film CdTe devices, the inert working gas from the magnetron can incorporate into the film during the growth process and aggregate into large subsurface clusters during post processing. The gas clusters often occur at the CdS/CdTe interface causing delamination and blisters up to about 30 µm in diameter are readily observable on the film’s surface. The surface blisters are observed after post processing with CdCl2 at an elevated temperature but smaller inert gas clusters of several nanometres in diameter can be observed using high resolution transmission electron microscopy before the CdCl2 treatment. In this paper, these effects are investigated both experimentally and using molecular dynamics modelling. Some suggestions are also made as to how the effect might be minimised and higher efficiency solar devices fabricated.