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We synthesized anthradithiophene−cyclopentadithiophene conjugated copolymers via Stille coupling. The anthradithiophene core was verified to be superior in stability compared to pentacene toward Diels−Alder cycloaddition and therefore more compatible with fullerenes, acceptor material commonly used in bulk heterojunction (BHJ) photovoltaic cells. The polymers exhibit high film absorption coefficients of 105 cm−1, an order of magnitude higher than previously reported anthradithiophene−dialkylfluorene copolymers. Short-circuit currents exceeding 5 mA/cm2 and a BHJ device efficiency close to 1% were achieved when device morphology was improved with diiodooctane as a solvent additive. This is the highest power conversion efficiency achieved by an acene-containing polymer so far.

We have synthesized new types of pentacene− and anthradithiophene−dialkylfluorene conjugated copolymer via Suzuki cross-coupling polymerization. The polymer chemical structures and molecular weights were characterized by 1H NMR, 13C NMR, and gel permeation chromatography (GPC). Fundamental properties, such as electrochemical and optical behavior, were studied using cyclic voltammetry (CV) and UV−vis absorption (UV−vis) to estimate the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels as well as their optical bandgaps. Both polymers exhibit relatively low bandgaps and their high solubility in common halogenated organic solvents. They were successfully incorporated into photovoltaic cells, giving a power efficiency up to 0.68%. This is the first acene-containing conjugated polymer solar cell.

Morphological characterization has been used to explain the previously observed strong correlation between charge carrier mobility measured with thin-film transistors and the number-average molecular weight (MW) of the conjugated polymer regioregular poly(3-hexylthiophene). Atomic force microscopy and X-ray diffraction show that the low-mobility, low-MW films have a highly ordered structure composed of nanorods and the high-mobility, high-MW films have a less ordered, isotropic nodule structure. Modifying the morphology for a constant MW by changing the casting conditions or annealing the samples strongly affects the charge transport and morphology in the low-mobility, low-MW films, but has little effect on the high-MW films. In-plane grazing incidence X-ray scattering shows the in-plane π-stacking peak increases when the mobility increases for a constant MW. When the MW is changed, this correlation breaks down, confirming that in-plane π-stacking does not cause the mobility−MW relationship. We believe a ...