The lifetime of organic solar cells (OSCs) is a key point that has to be addressed to allow their commercial development. Ultra-barrier organic/inorganic multilayer encapsulation therefore has to be developed to improve OSC stability. Polymer nanocomposites are good candidates to be used as the organic layer in the multilayered structure. We report here an optimization of MMt-Na+ content up to 10 wt% in PVA nanocomposite to obtain the properties required for organic solar cell encapsulation, namely an exfoliated structure that has high gas barrier properties, transparency, wettability and planarity of the surface. The elaboration of these nanocomposites was performed through an environmentally friendly process in aqueous solution. The distribution of MMt-Na+ in PVA was first investigated, and the results showed that the transparency of the nanocomposite films was not affected by the presence of the clay in the visible region (400-700 nm). The morphology of nanocomposites was also investigated. A good distribution of the MMt-Na+ in PVA, with intercalated and exfoliated structures, was observed, especially for concentrations up to 5 wt%. Surface properties were also explored and it was shown that PVA/MMt-Na+ 5% nanocomposite permitted to obtain an improvement in wettability without increasing too much the surface roughness. Subsequently, the permeability of the nanocomposites was investigated and it was shown that 5 wt% of MMt-Na+ improved the helium permeability (by 70%) and also oxygen and water permeability. Finally, PVA/MMt-Na+ 5 wt% nanocomposite layer was used as encapsulation for organic solar cells and the improvement of the OSCs stability was evidenced. This work allowed selecting optimized nanocomposites with clay content up to 5 wt%, which will be incorporated into multilayer encapsulation structure to have the best compromise between the different required properties and to enhance organic solar cells stability. (C) 2011 Elsevier B.V. All rights reserved.