Evidence is presented for the formation of a weak ground‐state charge‐transfer complex in the blend films of poly[9,9‐dioctylfluorene‐co‐N‐(4‐methoxyphenyl)diphenylamine] polymer (TFMO) and [6,6]‐phenyl‐C61 butyric acid methyl ester (PCBM), using photothermal deflection spectroscopy (PDS) and photoluminescence (PL) spectroscopy. Comparison of this polymer blend with other polyfluorene polymer/PCBM blends shows that the appearance of this ground‐state charge‐transfer complex is correlated to the ionization potential of the polymer, but not to the optical gap of the polymer or the surface morphology of the blend film. Moreover, the polymer/PCBM blend films in which this charge‐transfer complex is observed also exhibit efficient photocurrent generation in photovoltaic devices, suggesting that the charge‐transfer complex may be involved in charge separation. Possible mechanisms for this charge‐transfer state formation are discussed as well as the significance of this finding to the understanding and optimization of polymer blend solar cells.

The microstructure of MDMO-PPV:PCBM blends as used in bulk hetero-junction organic solar cells was studied by Atomic Force Microscopy (AFM) and Kelvin Force Microscopy (KFM) to image the surface morphology and by means of Transmission Electron Microscopy (TEM) to reveal images of the film's interior.By introducing KFM, it was possible to demonstrate that phase separated domains have different local electrical properties than the surrounding matrix. Since blend morphology clearly influences global electrical properties and photovoltaic performance, an attempt to control the morphology by means of casting conditions was undertaken. By using AFM, it has been proven that not only the choice of solvent, but also drying conditions dramatically influence the blend structure. Therefore, the possibility of discovering the blend morphology by AFM, KFM and TEM makes them powerful tools for understanding today's organic photovoltaic performances and for screening new sets of materials.

In this work we report on the eco-friendly processing of PBDTTPD:PC71BM organic solar cells using water-based nanoparticle (NP) dispersions. The polymer:fullerene NPs are prepared using the miniemulsion-solvent evaporation method, despite employing high-boiling solvents. Polymer solar cells are fabricated from these blend NPs and the device characteristics are studied in function of annealing time and temperature. The photoactive layer formation is carefully analyzed using atomic force microscopy (AFM). Annealing for longer times significantly increases the power conversion efficiency (PCE), up to 3.8%, the highest value reported for surfactant based NP solar cells. Our work shows that the low bandgap polymer PBDTTPD has the ability to afford reasonable efficiencies in NP solar cells in combination with PC71BM and paves the way to a truly eco-friendly processing of organic photovoltaics (OPVs).

Filamentous cable bacteria display unrivalled long-range electron transport, generating electrical currents over centimeter distances through a highly ordered network of fibers embedded in their cell envelope. The conductivity of these periplasmic wires is exceptionally high for a biological material, but their chemical structure and underlying electron transport mechanism remain unresolved. Here, we combine high-resolution microscopy, spectroscopy, and chemical imaging on individual cable bacterium filaments to demonstrate that the periplasmic wires consist of a conductive protein core surrounded by an insulating shell layer. The core proteins contain a sulfur-ligated nickel cofactor, and conductivity decreases when nickel is oxidized or selectively removed. The involvement of nickel as the active metal in biological conduction is remarkable, and suggests a hitherto unknown form of electron transport that enables efficient conduction in centimeter-long protein structures.

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