Polymer Solar Cells (PSCs) are extremely sensitive to oxygen and light exposure. While oxygen exposure can be reduced by packaging the devices with barrier materials, it is impossible to completely avoid oxygen diffusion during the envisaged especially when the encapsulation is supposed to be flexible and cost efficient. Therefore insights and strategies on PSCs materials stability upon light and oxygen exposure are required. Here, the photostability in air of several polymers was investigated by spectroscopic techniques (UV-vis and IR spectroscopy). The low band gap polymers were selected in order to have series with side chains variation with the same donor/acceptor units and series with different combination of donor/acceptor backbones (with similar side chains). So far, no clear rule of thumb was found for the pi-conjugated variation but a clear trend was observed for the side chain variation. The results are in very good agreement with recent predictions based on modelling. [1] The study was extended to the blend films (polymers blended with PC60BM). PC60BM stabilizes all the investigated polymers and interestingly the factor of stabilization as well as the PC60BM stability is related to the intrinsic stability of the polymer. This work provides new information regarding the complex topic of degradation and stabilization of polymer blend materials. [1] Silva HS, Tournebize A, Bégué D, Peisert H, Chassé T, Gardette JL, et al. A universal route to improving conjugated macromolecule photostability. RSC Adv. 2014;4:54919-23. The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2011 under grant agreement ESTABLIS n° 290022).