Anti-Corroded Molybdenum Back Electrodes by Al Doping for CuIn1-xAlxSe2 Solar Cells

Abstract

The effects of Al doping into Mo films, used as back electrodes of CuIn1-xAlxSe2 solar cells, were systematically investigated. The Mo1-XAlX films fabricated by co-sputtering were exposed in a damp-heat (DH) chamber with 85°C and 85% relativity humidity for 168 h to verify the reliability. The resistivity of the Mo79Al21 films after DH exposure was only slightly increased from 2 × 10−6 Ω m to 2.3 × 10−6 Ω m; however, the pure Mo films after DH exposure became insulating due to the formation of the MoOx layer. Based on the analyses of the x-ray diffraction and x-ray photoelectron spectrum, we suggest that the Al atoms are dissolved into the Mo films in the as-deposited state and segregate to the surface of Mo1-XAlX films during DH exposure. A thin Al-oxide layer is formed on the surface and behaves as an anti-corrosion layer, which enhances reliability. On the other hand, with increasing the Al content, increased amount of the Al2O3 layer may suppress the formation of the MoSe2 layer at the interface between Mo and CIS-based films. Consequently, the Mo film with the optimized Al doping, for example, the Mo79Al21 film may become a good candidate of the back electrode for CuIn1-xAlxSe2 solar cells to maintain good reliability as well as to achieve good adhesion and low series resistance.