Conjugated polymer systems, including homopolymers, 1 alternating/random copolymers, 2 blends, 3 and block copolymers, 4,5 as semiconductors for electronic and optoelectronic applications are of continuing great interest. 6,7 In general, multicomponent conjugated polymer systems such as blends and block copolymers offer the opportunity to optimize and tailor electronic and optical properties while also having the potential to observe novel phenomena (e.g., energy transfer, charge transfer) not feasible in homopolymers and random/alternating copolymers.5 Compared to blends, 3 block copolymers are of special interest because of their superior self-assembly features and the improved control of the nanoscale domain sizes of their assembled structures. Indeed, the synthesis, self-assembly, and properties of rod-coil block copolymers, having a π-conjugated (rodlike) block and a coillike nonconjugated block, have been extensively studied. 4 Although experimental examples of allconjugated block copolymers have been known since 1996, 5a their synthesis, solution-phase self-assembly, melt-phase selfassembly, and properties remain to be fully investigated. 5,8 Recently, block copolythiophenes with crystalline-amorphous diblock architecture incorporating a crystalline poly(3-hexylthiophene) (P3HT) block were successfully synthesized by quasiliving chain growth polymerization, including poly{3-[2-(2-methoxyethoxy)ethoxy]methylthiophene}, 8b poly[3-(2-ethylhexylthiophene)], 8c or poly(3-phenoxymethylthiophene) 8d as the amorphous segment. The thin-film morphology of these crystalline-amorphous diblock copolythiophenes was shown by atomic force microscopy (AFM) to be microphase-separated into crystalline and amorphous domains. For many electronic and optoelectronic applications such as field-effect transistors and photovoltaic devices, where high carrier mobilities and high absorption coefficients are important, 6,7 amorphous domains are undesirable. We report herein the synthesis and self-assembly of crystalline-crystalline diblock copoly(3-alkylthiophene)s. Two compositions of the new regioregular poly(3-butylthiophene)-b-poly(3-octylthiophene) (P3BT-b-P3OT) were found to self-assemble into crystalline nanowires in solution and shown by wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) to be microphase-separated from the melt phase into two distinct crystalline domains with a lamellar structure.The synthesis of the diblock copoly(3-alkylthiophene)s was carried out by a modified Grignard metathesis method (GRIM), 1b,8 as illustrated in Scheme 1. The P3OT block was first synthesized by polymerization of 2,5-dibromo-3-octylthiophene, followed by the addition of activated 2,5-dibromo-3-butylthiophene monomer solution, giving the diblock copolymer system, poly(3-butylthiophene)-b-poly(3-octylthiophene). Two compositions, denoted BO50 and BO76, were synthesized by using the feed ratios of 2,5-dibromo-3-octylthiophene to 2,5-dibromo-3-butylthiophene of 1:1 and 1:2, respectively. The actual compositions...

We report the synthesis, characterization, solution-phase assembly of nanowires, field-effect charge transport, and photovoltaic properties of regioregular poly(3-pentylthiophene) (P3PT), the first regioregular poly(3-alkylthiophene) with an odd-numbered alkyl side chain length to be so investigated. Two samples of P3PT with weight-average molecular weights of 61 800 and 77 000 and 1.4−1.5 polydispersity index have comparable solubility and processability in organic solvents as regioregular poly(3-hexylthiophene) (P3HT) but have a higher melting transition at 259 °C. X-ray diffraction of P3PT films revealed a lamellar structure with an interlayer d 100 spacing of 1.51 nm and a π-stacking d 010 spacing of 0.374 nm, both smaller than in P3HT. Crystalline nanowires of 16−17 nm width and aspect ratios as high as 465 were assembled from P3PT solution. Field-effect transistors fabricated from P3PT thin films showed a mobility of holes of up to 0.10 cm2/(V s), and the carrier mobility increased with molecular weight. Bulk heterojunction solar cells based on P3PT/fullerene (PC71BM) blend thin films had a power conversion efficiency of 3.70% under 100 mW/cm2 AM1.5 solar illumination in air and a maximum external quantum efficiency of 69%. Similarly illuminated solar cells based on nanocomposites of P3PT nanowires/PC71BM had a 3.33% power conversion efficiency. These results demonstrate that P3PT is an attractive polymer semiconductor suitable for applications in thin-film and nanowire-based field-effect transistors and bulk heterojunction solar cells.

We describe bulk heterojunction (BHJ) solar cells containing blends of colloidal PbS nanocrystal quantum dots with several new donor-acceptor conjugated polymers. Using photoinduced absorption spectroscopy we found that blends of PbS quantum dots with one polymer, poly(2,3-didecyl-quinoxaline-5,8-diyl-alt-N-octyldithieno[3,2-b:2',3'-d]pyrrole) (PDTPQx), produce significantly more photoinduced charge than blends of PbS with the other donor-acceptor polymers or with traditionally studied polymers like [2-methoxy-5-(3',7'-dimethyloctyloxy)-para-phenylene vinylene] (MDMO-PPV) and poly(3-hexylthiophene) (P3HT). Photovoltaic devices made with PDTPQx/PbS blends exhibit power conversion efficiencies 10-100 times larger than previously reported BHJ blends made with IR-absorbing quantum dots.

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The photovoltaic properties, charge transport, and morphology of a series of diblock conjugated copolymers, poly(3-butylthiophene)-b-poly(3-octylthiophene) (P3BT-b-P3OT), were investigated as a function of block composition. Bulk heterojunction solar cells comprising blends of P3BT-b-P3OT and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) were found to have power conversion efficiencies as high as 3.0%, which represents factors of 1.6−9 enhancements compared to those of the homopolymers made under similar conditions. Imaging of P3BT-b-P3OT/PC71BM blends by atomic force microscopy and transmission electron microscopy revealed interpenetrating network with 11−18 nm crystalline polymer domains. The zero-field space charge limited current mobility of holes (∼(1−3) × 10−4 cm2 V−1 s−1) was similarly enhanced in the diblock copolymer solar cells compared to the homopolymers. These results demonstrate that block conjugated copolymers offer a promising approach to advanced materials for polymer solar cells and that the block composition is an attractive means to optimize the materials.