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 CuIn 1-x Al x Se 2 solar cells, were systematically investigated. The Mo 1-X Al X films fabricated by co-sputtering were exposed in a damp-heat (DH) chamber with 85C and 85 relativity humidity for 168 h to verify the reliability. The resistivity of the Mo 79 Al 21 films after DH exposure was only slightly increased from 2 10 -6 m to 2.3 10 -6 m; however, the pure Mo films after DH exposure became insulating due to the formation of the MoO x 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 Mo 1-X Al X 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 Al 2 O 3 layer may suppress the formation of the MoSe 2 layer at the interface between Mo and CIS-based films. Consequently, the Mo film with the optimized Al doping, for example, the Mo 79 Al 21 film may become a good candidate of the back electrode for CuIn 1-x Al x Se 2 solar cells to maintain good reliability as well as to achieve good adhesion and low series resistance. © 2011 The Electrochemical Society.