Analysis of Microstructure and Surface Morphology of Sputter Deposited Molybdenum Back Contacts for CIGS Solar Cells

Abstract

Magnetron sputter-deposited molybdenum (Mo) thin films are widely used as back electrodes in thin-film copper indium gallium (di)selenide (CIGS) solar cells. In order to fabricate high-efficiency CIGS solar cells, the properties of the Mo back electrode need to be tailored. These properties are associated with the microstructure of the films and thus highly dependent on the deposition conditions. The microstructure of the Mo back electrode is critical to the adhesion and the efficiency of the device. In this work, approximately 900nm thick single-layer and bilayer Mo films are deposited at different pressure conditions while keeping the power constant at 2kW. The films are characterized by different methods for a detailed microstructure and morphology understanding. X-ray diffraction measurements reveal that the Mo grain orientation in the [110] direction is enhanced by the bilayer stack design, which is favourable for back contact applications in high-efficiency CIGS solar cells. The surface roughness of the bilayer Mo films is found to increase slightly with increasing bottom layer thickness, and is generally higher than that of single-layer Mo films.