Optical and electrical properties of bi-layers organic devices Hager Trad, Ahlem Rouis, Jöel Davenas and Mustapha Majdoub Eur. Phys. J. Appl. Phys., 68 1 (2014) 10103 Published online: 13 October 2014 DOI: 10.1051/epjap/2014140069