We demonstrate that nanotubular networks formed by enzyme-triggered self-assembly of Fmoc-L₃ (9-fluorenylmethoxycarbonyl-tri-leucine) show significant charge transport. FT-IR, fluorescence spectroscopy and wide angle X-ray scattering (WAXS) data confirm formation of β-sheets that are locked together via π-stacking interactions. Molecular dynamics simulations confirmed the π–π stacking distance between fluorenyl groups to be 3.6–3.8 Å. Impedance spectroscopy demonstrated that the nanotubular xerogel networks possess minimum sheet resistances of 0.1 MΩ/sq in air and 500 MΩ/sq in vacuum (pressure: 1.03 mbar) at room temperature, with the conductivity scaling linearly with the mass of peptide in the network. These materials may provide a platform to interface biological components with electronics.

The principle remaining challenge in the research area of organic photovoltaic (OPV) materials is to develop solar cells that combine high efficiency, stability and reproducibility. Here, we demonstrate an experimental strategy which has successfully addressed this challenge. We produced a number of samples of the highly efficient PTB7 polymer with various molecular weights (M_n ∼ 40–220k). OPV cells fabricated with this polymer demonstrated significant improvement of the cell efficiency (by ∼90% relative) and lifetime (by ∼300% relative) with the M_n increase. We attribute these effects to the lower density of recombination centers (persistent radical defects revealed by EPR spectroscopy) and better photoactive layer morphology in the samples with higher M_n. Relevance of the observed correlation between the OPV efficiency and stability is discussed.

The chemical degradation of the Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] or ‘ PTB7’ has been studied using X-ray Photoelectron Spectroscopy (XPS). This material system appears to be intrinsically unstable especially when illuminated in air and XPS studies confirm the rapid photo-degradation is related to changes in chemical structure of the polymer. In particular, XPS spectra show an initial reduction in relative C-C intensity, suggests loss of the alkoxy side chains. This is followed by a dramatic increase in the level of oxygen-bonded species, especially C-O at ~286.5 eV and C(=O)O at 289.2 eV, indicative of COOH and OH group formation, and oxidation of S. The XPS results support the view that using processing additives reduces the chemical stability of the polymer and provides insight into strategies to improve molecular design to ensure higher chemical stability