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A series of novel thiophene-flanked benzodipyrrolidone (BPT)-based alternating copolymers are synthesised, their optical and electrical properties evaluated. The BPT unit promotes a conjugated, planar polymer backbone, with a low bandgap, primarily due to low lying LUMO energy levels. Copolymerisation with thiophene exhibits well balanced ambipolar organic field-effect transistor performance, with electron and hole mobilities 0.1 and 0.2 cm(2) V(-1) s(-1), respectively.

Thieno[3,2-b]thienobis(silolothiophene), a new electron rich hexacyclic monomer has been synthesized and incorporated into three novel donor-acceptor low-bandgap polymers. By carefully choosing the acceptor co-monomer, the energy levels of the polymers could be modulated and high power conversion efficiencies of 5.52% were reached in OPV devices.

We report the first synthesis of a fused germaindacenodithiophene monomer and its polymerisation with 2,1,3-benzothiadiazole by Suzuki polycondensation. The resulting polymer, PGeTPTBT, is semicrystalline, despite the presence of four bulky 2-ethylhexyl groups. Blends with P(70)CBM afford solar cells with efficiencies of 5.02%.