We synthesized anthradithiophene-cyclopentadithiophene conjugated copolymers via Stille coupling. The anthradithiophene core was verified to be superior in stability compared to pentacene toward Diels-Alder cycloaddition and therefore more compatible with fullerenes, acceptor material commonly used in bulk heterojunction (BHJ) photovoltaic cells. The polymers exhibit high film absorption coefficients of 10(5) cm(-1), an order of magnitude higher than previously reported anthradithiophene-dialkylfluorene copolymers. Short-circuit currents exceeding 5 mA/cm(2) and a BHJ device efficiency close to 1% were achieved when device morphology was improved with diiodooctane as a solvent additive. This is the highest power conversion efficiency achieved by an acene-containing polymer so far.