The recent progress in the field of organic conducting polymers were best regarded as an alternative to conventional silicon based solar cells for low-cost energy source. However, these organic based materials are sensitive towards moisture and oxygen in the ambient; it needs hermitic protection (WVTR of 10-6g/m2/d and OTR of 10-5g/cm2/d). The use of high barrier polymeric materials can greatly reduce the permeability of ingress gases to the active device layer and also suitable for large area applications. In the present study, reduced graphene oxide (r-GO) was synthesized by modified Hummer’s method. Poly(vinyl butyral) with various degree of acetalization and r-GO content were synthesized with different butyraldehyde mole ratio with poly(vinyl alcohol) of two different molecular weights in-situ with graphene oxide. These nanocomposite films were solvent casted in to a film thickness of 70±5 µm. Calcium degradation technique was used to access the moisture permeability behavior of these films under various levels of humidity and temperatures. These films were encapsulated with organic solar cells. The performance evaluations of these solar cells under natural aging conditions were carried out for efficiency degradation of these devices after aging. The level of r-GO content and acetalization degree to the thermal stability, glass-transition behavior, UV stability and dynamic mechanical properties in poly(vinyl butyral) matrix were also presented in the light existing mechanism of the moisture – nanofillers-polymer matrix interaction. Keywords: Poly(vinyl butyral); moisture barrier studies; graphene nanocomposites References 1. J. S. Park, H. Chae, H. K. Chung and S. I Sang, Semicond. Sci. Technol 26, 034001 (2011) 2. S. Saravanan, P.C. Ramamurthy and G. Madras, Compos. Sci. Technol. 96, 80-87 (2014)