The authors show that a photovoltaic device composed of a -donor-bridge–acceptor-bridge- type block copolymer thin film exhibits a significant performance improvement over its corresponding donor/acceptor blend (Voc increased from 0.14to1.10V and Jsc increased from 0.017 to 0.058mA∕cm2) under identical conditions, where donor is an alkyl derivatized poly-p-phenylenevinylene (PPV) conjugated block, acceptor is a sulfone-alkyl derivatized PPV conjugated block, and bridge is a nonconjugated and flexible unit. The authors attribute such improvement to the block copolymer intrinsic nanophase separation and molecular self-assembly that results in the reduction of the exciton and carrier losses.

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A novel class of light harvesting conjugated block copolymers, with electron-donating conjugated blocks (D) connected to electron-accepting conjugated blocks (A) via non conjugated and flexible bridge chains (B), has been designed, synthesized, and characterized. Specifically, D is a decyloxy-substituted polyphenylenevinylene (C10−PPV). A 1 and A 2 are PPVs with sulfone (SO2) acceptor moieties substituted on every other phenylene unit. A 1 carries two decyloxy groups on every phenylene unit, while in A 2 , half of the phenylene units are unsubstituted. The optical energy gaps are 2.24 eV for the donor block (D), 2.33 and 2.45 eV for A 1 and A 2 acceptor blocks. LUMO level offsets are 0.24 and 0.16 eV for D/A 1 and D/A 2 pairs, respectively. Comparing the photoluminescence from both films and solutions, very large red shifts (71 and 74 nm for A 1 and A 2 respectively) were observed in the two acceptor polymers. These red shifts in the emission spectra were more than twice as much as that observed for D (31 nm). The (DBA 1 B) n and (DBA 2 B) n block copolymer films exhibited improved processability and optoelectronic properties when compared with the corresponding films composed of donor/acceptor blends. Atomic force microscopic (AFM) studies of D, A 1 , and A 2 films were also undertaken to observe the degree of aggregation in the films. The results indicate the tendency of intermolecular aggregation increases as A 2 > D > A 1 . AFM topological images revealed that large aggregates of several hundreds of nanometers formed in donor/acceptor blend films, while in block copolymer films, domain sizes were similar to individual block sizes which are 1 order of magnitude smaller than in the blend.

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A series of evolving frontier energy levels and gaps sulfone-containing thienylenevinylene-based conjugated copolymers have been synthesized via the Horner-Emmons reactions between 2,5-bisdiethoxyphosphorylmethyl-3,4-dihexyl-1,1-dioxothiophene and a series of different donor type dialdehyde comonomers. The resulting polymers (SF-PTVs) contain alternating donor (benzene or thiophene ring with/without alkoxy substituents) and acceptor (1,1-dioxothiophene) units. A range of HOMO/LUMO levels and energy gaps (between 1.0 and 2.0 eV) were achieved in these new polymers. The use of oxidized thiophene moiety brings about 0.3 eV in reduction of energy gap. Computational study on the model oligomers of P(C6OTV-SFTV) and related structures reveals that the reduction is mainly due to the removal of aromaticity of the thiophene. The donor-acceptor interaction is also responsible for about one-third or less of the energy gap reduction. Theses polymers have very good thermal stability (dynamically, 258 °C or higher), and their decomposition starts with loss of mass as in contrast to regular PTVs which decompose initially by cross-linking.