Well-defined donor-acceptor rod-coil diblock copolymers based on P3HT containing C60: the morphology and role as a surfactant in bulk-heterojunction solar cells

The synthesis of well-defined rod-coil block copolymers consisting of P3HT donor and C-60 acceptor chromophores (P3HT-b-P(S(x)A(y))-C-60) in a molecular architecture is reported for use in bulk-heterojunction (BHJ) solar cells. In thin films of the resulting block copolymer, reproducible self-assembly into well-defined "nanofibrils'' is observed. This is the first example of a block copolymer containing a C-60 derivative that shows exclusively a nanofibrilar structure. We have investigated the potential utility of the block copolymer as a "surfactant'' for controlling the interface morphology of the P3HT: PCBM donor-acceptor phase domains within the composite. We find a substantial improvement in device performance when 5% of block copolymer are introduced to the P3HT: PCBM blend system, resulting in ca. 35% improved efficiency relative to the P3HT: PCBM solar cell fabricated without the "surfactant''.