Toward Practical Useful Polymers for Highly Efficient Solar Cells via a Random Copolymer Approach

Using benzo­[1,2-b:4,5-b′]­dithiophene and two matched 5,6-difluorobenzo­[2,1,3]­thiadiazole-based monomers, we demonstrate that random copolymerization of two electron deficient monomers, alternating with one electron rich monomer, forms a successful approach to synthesize state-of-the-art semiconducting copolymers for organic solar cells. Over a range of compositions, these random copolymers provide impressive power conversion efficiencies (PCEs) of about 8.0%, higher than those of their binary parent polymers, and with little batch-to-batch variation. A PCE over 8% could also be achieved when the active layer was deposited from nonhalogenated solvents at room temperature.