Selenophene-thiophene block copolymer solar cells with thermostable nanostructures.

The nanostructure morphology and electron donor performance of a poly(3-hexylselenophene)-block-poly(3-hexylthiophene) (P3HS-b-P3HT) copolymer was studied in a photovoltaic device with a [6,6]-phenyl C61 butyric acid methyl ester (PCBM) acceptor. P3HS-b-P3HT forms fiberlike nanostructures spontaneously, which leads to an initial optimal device performance. Furthermore the nanostructure morphology is not greatly affected by annealing, which leads to a device stability that outperforms P3HT, P3HS, or a P3HS/P3HT mixture under identical conditions. External quantum efficiency, hole mobility, and current-voltage measurements show that the block copolymer also outperforms a ternary blend that consists of a physical mixture of P3HS, P3HT, and PCBM with the same overall composition. Overall, the observation of optimal device performance and morphology without annealing as well as enhanced thermal stability demonstrates the advantage of fully conjugated diblock copolymers in nanostructured devices.