Abstract This paper reports on the stability of encapsulated ITO-free bulk heterojunction organic solar cells (BHJ-OSC) 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-C60 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 1000h of aging under damp heat condition (85°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. 1800h of aging under damp heat condition. Similar devices encapsulated between glass plate and flexible barrier film showed almost no degradation after ca. 10,000h under thermal stress of 85°C (dark and ambient air). Further, remarkable stability of more than 12,000h with less than 10% reduction in the device performance was achieved under continuous illumination of 1000W/m2 (similar to AM1.5G spectrum but with lower UV content).