Donor−acceptor diblock copolymers, composed of regioregular poly(3-hexylthiophene) (rrP3HT) as the electron donor block and poly(perylene diimide acrylate) (PPDA) as the electron acceptor block, were prepared and used to fabricate a solar cell. Vinyl-terminated rrP3HT was synthesized by Grignard metathesis polymerization and converted to an alkoxyamine macroinitiator. This polythiophene macroinitiator was used in controlled free radical polymerization of a perylene diimide-containing acrylate. The targeted donor−acceptor diblock copolymers were prepared with low-to-moderate polydispersity indices (1.2−1.4) and molecular weights sufficiently high for producing films by spin-coating. These copolymers showed efficient photoluminescence quenching in the solid state, indicative of charge separation, and were used to produce a solar cell with power conversion efficiency of 0.49%.