Composite films of poly(3-hexylthiophene) and single-as well as multi-walled carbon nanotubes are demonstrated to offer a competitive thermoelectric performance. The power factor significantly exceeds values obtained with either constituent alone provided that the conjugated polymer is sufficiently pdoped. The use of single-walled carbon nanotubes consistently results in a higher electrical conductivity with a maximum value above 10 3 S cm À1 and thus gives rise to a power factor of 25 AE 6 mW m À1 K À2 for a filler content of only 8 wt% and a maximum 95 AE 12 mW m À1 K À2 for 42-81 wt%. Moreover, a carbon nanotube content of 8-10 wt% does not compromise the low bulk thermal conductivity of the polymer matrix, which promises a high figure of merit of at least ZT > 10 À2 at room-temperature. All samples are cast on plastic substrates, emphasising their suitability for large-area, flexible thermoelectric applications.

A detailed study of the interaction mechanism between carbon nanotubes and physically adsorbed block copolymers is presented. The combination of experimental observations, computer simulations and theory suggests that while the solvophobic blocks adsorb to the nanotubes by a nonwrapping mechanism, the dangling (solvophilic) blocks provide a steric barrier that leads to the formation of stable dispersions of individual single walled carbon nanotubes (SWNT) and multiwalled carbon nanotubes (MWNT) above a threshold concentration of the polymer. The observed threshold concentration depends on the length of the solvophobic blocks, and it is higher for MWNT as compared to SWNT. Theory suggests that the latter is a consequence of dimensional considerations. Spectroscopic characterization of the dispersions indicate that the dispersing block polymers do not alter the electronic structure of the well dispersed individual SWNT, supporting the model of nonspecific adsorption of the polymer to the tube driven by van der walls type interactions. The study presented here offers a generic scheme for optimization of the structure and composition of block copolymers used for dispersion of CNT in different media.

light-harvesting active layer is composed of bulk-heterojunctions, i.e., blends of a polymeric electron-donor (hole-conductor) and an electron-acceptor (electron-conductor), with fullerene derivatives yielding particularly promising results. Thanks to recent advances in the synthesis of donor materials, power-conversion effi ciencies of 8-10% can now be achieved with lab-scale devices. [ 1 ] The precise bulk-heterojunction nanostructure, i.e., the distribution of donor and acceptor molecules, is crucial for maximizing the photovoltaic performance for a given blend composition. This is because a compromise has to be made between two critical aspects: i) a large contact area between donor and acceptor molecules aids charge generation and thus a fi nely intermixed blend is favored, and ii) percolation of separated, relatively phase-pure donor and acceptor domains to improve charge transport to the electrodes. Therefore, the ideal nanostructure features an intermediate degree of phase separation, which has to be carefully optimized through processing parameters such as the choice of solvent or solvent mixture, the blend stoichiometry and polymer molecular weight as well as post-deposition thermal or vapor annealing.The bulk-heterojunction nanostructure of non-crystalline polymer:fullerene blends has the tendency to rapidly coarsen when heated above its glass transition temperature, which represents an important degradation mechanism. We demonstrate that fullerene nucleating agents can be used to thermally arrest the nanostructure of photovoltaic blends that comprise a non-crystalline thiophene-quinoxaline copolymer and the widely used fullerene derivative [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM). To this end, C 60 fullerene is employed to effi ciently nucleate PCBM crystallization. Sub-micrometersized fullerene crystals are formed when as little as 2 wt% C 60 with respect to PCBM is added to the blend. These reach an average size of only 200 nanometers upon introduction of more than 8 wt% C 60 . Solar cells based on C 60 -nucleated blends indicate signifi cantly improved thermal stability of the bulk-heterojunction nanostructure even after annealing at an elevated temperature of 130 °C, which lies above the glass transition temperature of the blend. Moreover, we fi nd that various other compounds, including C 70 fullerene, single-walled carbon nanotubes, and sodium benzoate, as well as a number of commercial nucleating agents-commonly used to clarify isotactic polypropylene-permit to control crystallization of the fullerene phase.

Conjugated polymers and carbon nanotubes (CNTs) are important constituents of modern functional hybrid materials. Their utilization as photoactive layers in organic solar cells requires better understanding of the relation between the structure and composition of the hybrids and their photovoltaic efficiency. While fullerenes‐conjugated polymer hybrids have been intensively studied over the last two decades, far less is known about the linkage between processing conditions, interfacial interactions, self‐assembled structures and functionality in CNT‐conjugated polymers composites. This article reviews some of the studies carried over the last decade and highlights the challenges in both fundamental understanding and technological manipulation of these materials. Copyright © 2012 John Wiley & Sons, Ltd.

We have demonstrated OPV accelerated degradation studies using concentrated sunlight, where the atmosphere, temperature and illumination intensity were independently controlled. Testing various schemes for controlling the sample temperature under concentrated sunlight showed that heating of P3HT:PCBM was caused by photons at the absorbed wavelength range and dissipation of excess photon energy, and not necessarily by IR photon absorption. Sunlight chopping was found to be an effective method for independent temperature control under illumination by concentrated sunlight.The first accelerated degradation tests using sunlight concentration applied to P3HT:PCBM blends were reported. P3HT:PCBM blends exposed to concentrated sunlight in the presence of traces of oxygen/ humidity showed degradation induced by photo-oxidation of the P3HT backbone within the P3HT:PCBM blend, which is significantly thermally accelerated, in agreement with previous observations. However, this could be demonstrated in a time scale of 1 Corresponding authors2 minutes and hours, i.e., significantly accelerated. Exposure of well encapsulated P3HT:PCBM films to concentrated sunlight demonstrated stability up to 3,600 sun*hours, corresponding to about 1.6 years of operating time. This result was obtained at 300 suns exposure after merely 12 hours, demonstrating the advantage of using concentrated sunlight for accelerated stability tests.These tests can therefore combine extremely high acceleration factors with profound understanding of the effect of various, independently controlled factors on the degradation mechanisms.