Solution-processed organic solar modules offer a promising approach for low-cost and flexible organic photovoltaic (OPV) technology. However, one of the key challenges of these devices is the degradation of materials over time, leading to overall limited module stability, which ultimately results in a decrease in efficiency. In this study, the environmental degradation mechanisms of roll-to-roll slot-die organic solar modules have been investigated by means of photovoltaic, spectroscopic and electron paramagnetic resonance (EPR) measurements. The degradation of modules based on blends of P3HT with PC61BM fullerene or with non-fullerene o-IDTBR acceptors has been analyzed following the ISOS-L-1 protocol. Moreover, two different encapsulating materials have also been studied. Our results indicate that the fullerene acceptor provides better stabilization to the donor polymer than the non-fullerene acceptor. Additionally, oxygen diffusion affects not only the photoactive layer components but also the hole transport layer. Finally, the encapsulation with adequate materials, such as a barrier foil offering UV protection, allows for longer lifetimes.