Paper TF-WeM11
A Viable Magnetron Sputtering Process for Thin Film CdTe Solar Cells

Wednesday, November 1, 2017, 11:20 am, Room 20

The exceptional uniformity of deposition provides magnetron sputtering with potentially important advantages for the production of thin film CdTe solar cells. For example, the thickness of the absorber layer could be reduced to ~1um saving on material cost. The uniformity is also essential for glazing applications such as power producing semi-transparent windows. Efforts to develop a viable process for the deposition of thin film CdTe solar cells by magnetron sputtering have been hampered for many years by the formation of surface blistering following the cadmium chloride activation process. Delamination of the films at the cadmium sulphide junction is often observed and catastrophic void formation within the CdTe layer and at the junction has also been reported. As a result, the conversion efficiency of sputtered devices has not matched that obtained using lower energy deposition techniques such as Close Space Sublimation or Vapour Transport Deposition. We have discovered that blistering is caused by argon trapped in the CdTe layer during the sputtering process. High Resolution Transmission Electron Microscopy reveals that argon gas bubbles are formed by diffusion during the high temperature device activation process. The bubbles then coalesce to cause surface blistering. Here we report on the development of a viable sputtering process by replacing argon with xenon as the magnetron working gas. Using xenon avoids gas bubble and blister formation. The microstructural integrity of the devices is retained resulting in increased performance of sputtered thin film CdTe photovoltaic devices.