Degradation process of the organic solar cells (OSCs) with Al and LiF/Al cathodes was studied using time of flight-secondary ion mass spectroscopy (TOF-SIMS) depth profile analysis and the lifetime of OSCs was improved using a bilayer cathode of organic interlayer/Al. The dissociation of LiF and diffusion of the Li were critical to the degradation of the organic solar cells with LiF/Al cathode and induced the significant reduction of open circuit voltage, short circuit current and power conversion efficiency during lifetime test. The degradation process was suppressed in the organic solar cells with organic interlayer/Al bilayer cathode, resulting in improved lifetime in organic solar cells. (C) 2012 Elsevier B.V. All rights reserved.