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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 10⁵ cm⁻¹, an order of magnitude higher than previously reported anthradithiophene−dialkylfluorene copolymers. Short-circuit currents exceeding 5 mA/cm² 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.