Out-door testing and long-term stability of plastic solar cells E. A. Katz, S. Gevorgyan, M. S. Orynbayev and F. C. Krebs Eur. Phys. J. Appl. Phys., 36 3 (2006) 307-311 Published online: 10 January 2007 DOI: 10.1051/epjap:2006159