Organic solar cells have recently experienced tremendous efficiency improvements, but their longevity is still limited by morphological degradation, among other factors. We demonstrate in this work that small amounts of amphiphilic small molecules such as perylene monoimide-diamine (PMIDA-C12) admixed to the active layer can dramatically improve the longevity of classical polymer solar cells (P3HT:PC60BM). While fill factors and efficiencies of classical reference solar cells without amphiphile dropped to 35 and 4% of their original values after 588 h of artificial aging (at 80 °C), respectively, these values are stable at 80% of their initial values for the solar cells containing 0.01 wt % PMIDA-C12. Spectroscopic and atomic force microscopy studies indicate that the amphiphiles stabilize the morphology of the active layers. Hence, the presented approach of doping the active layer with an amphiphilic molecule appears to be promising for improving the long-term stability of organic solar cells.