The Influence of Interchain Branches on Solid State Packing, Hole Mobility and Photovoltaic Properties of Poly(3‐hexylthiophene) (P3HT)

The hole mobility and power conversion efficiency of bulk heterojunction solar cells based on P3HT-type donor polymers and the soluble fullerene derivative [6,6]-phenyl C 61 butyric acid methyl ester (PCBM) as an acceptor both show a strong sensitivity to the introduction of interchain branches into the P3HT backbones. Branched B-P3HT copolymers display a distinctly decreased hole mobility and reduced solar cell power conversion efficiency with increasing amount of interchain 3.3'-bithiophene branches within the polythiophene macromolecules. The results illustrate the primary importance of proper solid state packing towards optimum charge transport and solar cell performance.