Effect of deposition pressure on the properties of magnetron-sputter-deposited molybdenum back contacts for CIGS solar cells

Abstract

Molybdenum (Mo) thin films were deposited onto soda-lime glass substrates by DC magnetron sputtering of a Mo target at various chamber pressures ranging from 1.5 × 10−3 to 7.5 × 10−3 mbar. The film properties were analysed with regards to their application as back electrode in copper indium gallium diselenide (CIGS) solar cells. It is observed that the resulting film morphology and microstructure were strongly affected by deposition pressure. Mo films deposited at a low pressure possess a high density and a low sheet resistance. These films also have a compact microstructure and a compressive strain, which lead to poor adhesion. The adhesion can be improved by increasing the chamber pressure, which has negative effects on the sheet resistance, optical reflection and porosity of the films. On the basis of these results, a method has been established to fabricate low-resistivity Mo films on soda-lime glass with very good adhesion for CIGS solar cell applications.