This paper reports on the stability of encapsulated ITO-free bulk heterojunction organic solar cells (BHJOSC) with the layer sequence of Cr/Al/Cr/photoactive layer (PAL)/poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonate) (PEDOT:PSS)/metal-grid under different aging conditions. The PAL consisted of poly (3-hexylthiophene) (P3HT) as donor and (6,6)-phenyl-C-60 butyric acid methyl ester (PCBM) as acceptor. Completely flexible devices (encapsulated between two flexible barrier films) were able to maintain >95% of their initial device performance after 1000 h of aging under damp heat condition (85 degrees C/85% relative humidity) according to standard IEC 61646. Suns-Voc measurements reveal that there is a slight increase in both the transport resistance of the photoactive layer as well as the series resistance of the PEDOT:PSS electrode. Devices encapsulated between two glass plates were able to retain more than 90% of their initial device performance after ca. 1800 h of aging under damp heat condition. Similar devices encapsulated between two glass plates and between a glass plate and flexible barrier film showed almost no degradation after ca. 10,000 h under thermal stress of 85 degrees C (dark and ambient air). Further, remarkable stability of more than 12,000 h with less than 10% reduction in the device performance was achieved under continuous illumination of 1000 W/m(2) (similar to AM1.5G spectrum but with lower UV content). (C) 2014 Elsevier B.V. All rights reserved.