Enhanced Performance of Bulk Heterojunction Solar Cells Using Block Copoly(3-alkylthiophene)s

The photovoltaic properties, charge transport, and morphology of a series of diblock conjugated copolymers, poly(3-butylthiophene)-b-poly(3-octylthiophene) (P3BT-b-P3OT), were investigated as a functional of block composition. Bulk heterojunction solar cells comprising blends of P3BT-b-P3OT and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) were found to have power conversion effeciencies as high as 3.0% which represents factors of 1.6-9 enhancements compared to those of the homopolymers made under simiar conditions. Imaging of P3BT-b-P3OT/PC71BM blends by atomic force microscopy and transmission electron microscopy revealed interpenetrating network with 11-18 nm crystalline polymer domains. The zero-field spae charge limited current mobility of holes(similar to(1-3) x 10(-4) cm(2) V-1 s(-1)) was similarly enhanced in the diblock copolymer solar cells compared to the homopolymers. These results demonstrate that block conjugated copolymers offer a promising approach to advanced materials for polymer solar cells and that the block composition is an attractive means to optimize the materials.