Compatibility of C60 grafted polystyrene/P3OT: Towards the extrusion of photoactive materials

To develop a new solventless and environment-friendly processing method for large-scale production of organic photovoltaic cells, the processability by extrusion of two photoactive polymers was studied. Poly(3-octylthiophene) was chosen as donor polymer and polystyrene grafted by fullerene C-60 as acceptor polymer. In the molten state, poly(3-octylthiophene) exhibits a similar behavior to that of typical flexible polymers and then could be processed by extrusion at temperatures above 180 degrees C. An appropriate range of grafted C-60 (from 4 to 12 vol%) has been determined in previous works from functional properties, thermal behavior and morphology observations displayed by a series of polystyrenes grafted by various fullerene C-60 contents. The rheological properties (storage and loss moduli, melt viscosity) of the synthesized C-60 grafted polystyrenes series are investigated. Two successive transitions in the viscosity are observed at 3-4 and 12-13 vol% of grafted C-60, related to the percolation of C-60 molecules and to the formation, growth and percolation of C-60 aggregates, respectively. For extrusion Compatibility with poly(3-octylthiophene), the optimal content of grafted C-60 ranges from 7 to 12 vol% according to the theological behavior. Thus, the processing of donor/acceptor heterojunctions by extrusion could now be considered to produce active layers of photovoltaic organic solar cells.