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International Journal of Photoenergy
Volume 2012, Article ID 723714, 7 pages
Research Article

In Situ and Ex Situ Studies of Molybdenum Thin Films Deposited by rf and dc Magnetron Sputtering as a Back Contact for CIGS Solar Cells

1Department of Electrical and Computer Engineering, Old Dominion University, Norfolk, VA 23529, USA
2Wright Center for Photovoltaic Innovation and Commercialization, University of Toledo, Toledo, OH 43606, USA

Received 16 December 2011; Accepted 31 January 2012

Academic Editor: Bhushan Sopori

Copyright © 2012 K. Aryal et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Molybdenum thin films were deposited by rf and dc magnetron sputtering and their properties analyzed with regards to their potential application as a back contact for CIGS solar cells. It is shown that both types of films tend to transition from tensile to compressive strain when the deposition pressure increases, while the conductivity and the grain size decreas. The nucleation of the films characterized by in situ and real time spectroscopic ellipsometry shows that both films follow a Volmer-Weber growth, with a higher surface roughness and lower deposition rate for the rf deposited films. The electronic relaxation time was then extracted as a function of bulk layer thickness for rf and dc films by fitting each dielectric function to a Drude free-electron model combined with a broad Lorentz oscillator. The values were fitted to a conical growth mode and demonstrated that the rf-deposited films have already smaller grains than the dc films when the bulk layer thickness is 30 nm.