Amide functionalized anthradithiophenes (ADTs) play active acceptor roles in polymer bulk-heterojunction solar cells. The first separation of ADT isomers is reported, and the regiochemistry of the ADT has significant impact on crystal packing and solar cell performance. Cell efficiency up to 0.80%, due in large part to high open-circuit voltage (V(OC) > 1.0 V), is achieved in bulk-heterojunction solar cells comprising syn-ADT and poly(3-hexylthiophene).