Recent work has demonstrated the potential of all-conjugated block copolymers for solution-processed photovoltaic devices, with power conversion efficiencies near 3%. However, optoelectronic properties and structure-property-processing relationships are poorly understood for this class of materials, and controlled synthetic approaches are lacking. Here, we present a new synthetic approach relying on click chemistry and structure-processing-property analysis of donor-acceptor block copolymers. The implementation of copper-catalyzed azide-alkyne click coupling in the synthesis of all-conjugated block copolymers provides control over the molecular weight of both polymer blocks independently. The morphology of a series of poly(3-hexylthiophene) (P3HT) and poly(3-dodecylthiophene) (P3DDT) all-conjugated block copolymers is analyzed by a combination of grazing-incidence wide- and small-angle X-ray scattering. While co-crystallization is inhibited in P3HT all-conjugated block copolymers, P3DDT block copolymers show significant co-crystallization and a rich processing-dependent morphology. Finally, we present optoelectronic measurements, including photovoltaic device results, of block copolymers incorporating ambipolar poly-((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(thiophen-5-yl)-2,1,3-benzothiadiazole]-2',2?-diyl) (PFTBT) polymer block and high-performance p-type PTB7 polymer. OPVs devices based on block copolymers and block copolymer additives are analyzed. These results provide guidelines for optimizing the morphology of all-conjugated block copolymers through materials design and processing. 

Synthesis, morphology, and optoelectronic properties of donor-acceptor all-conjugated block copolymers

247th National Meeting (2014)

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