Poly(p-xylylene)-graft-poly(butylacrylate-g-fullerene) or PPX-g-PBAFu was synthesized by using Wessling route and atom transfer radical addition (ATRA) techniques. The graft copolymers were used as a compatibilizer in the bulk heterojunction (BHJ) polymer solar cells of poly(3-hexylthiophene) (P3HT) and fullerene (C60). The results from AFM micrographs showed that the phase size of P3HT and the aggregated C60in the blended system was decreased from 300 to 30 nm after adding the copolymer (20 pph). Furthermore, the efficiencies of the BHJ cells fromJ-Vcurve were remarkably increased five times after adding the copolymer. [ABSTRACT FROM AUTHOR]