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Abstract: The crystallization of poly(3-hexylthiophene) (P3HT) to form nanowires has attracted considerable interest because this process significantly increases the hole mobility when compared to amorphous P3HT, leading to improved performance in photovoltaic and other organic electronic devices. However, full characterization of the crystallization self-assembly of the polymer chains in solution has not been achieved yet, due to limited use of in−situ not destructive techniques. Here, we investigate the ageing-driven formation and evolution of regioregular (rr) P3HT nanostructures in chlorobenzene solution using small angle neutron scattering (SANS) and UV–Vis spectroscopy. We have monitored how the shape of the rr-P3HT aggregates evolves. The initial states for rr-P3HT chains are the random coils, which straighten to form rods. These subsequently π - π stack to form 2D lamellae, which further stack to create nanowires. The formation of nanowires is promoted both by the length of ageing and by low temperatures ( 4∘C ). Temperatures above >40∘C reverse the formation of nanowires. Additionally, atomic force microscopy (AFM) and grazing incidence wide angle x-ray scattering (GIWAXS) reveal that the nanowires can be successfully aligned during deposition by off-axis spin coating. Finally, the anisotropic conductivity of the aligned rr-P3HT nanowire films is reported. This is significant for applications such as gas sensing or organic thin film transistors, where increased conductivity and controlled nanostructure are desirable.

Open Access

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Abstract: Due to the characteristic chain rigidity and weak intermolecular interactions of perfluorinated substances, the phase diagram of Langmuir monolayer formed by perfluorinated molecules has been interpreted so far as displaying only two phases, a 2D gas (G) and a liquid condensed (LC). However, in this work, we presented Grazing Incidence X-ray Diffraction measurements, which exhibit two diffraction peaks on the transition plateau: One is the signature of the hexagonal structure of the LC phase, the second one is associated to the low-density fluid phase and is thus more ordered than expected for a 2D gas or a typical fluid phase. Atomistic molecular dynamics simulations, performed on the transition plateau, revealed the existence of clusters in which domains of vertical molecules organized in a hexagonal lattice coexist with domains of parallel lines formed by tilted molecules, a new structure that could be described as a “2D smectic C” phase. Moreover, the diffraction spectrum calculated from the simulation trajectories compared favorably with the experimental spectra, fully validating the simulations and the proposed interpretation. The results were also in agreement with the thermodynamic analysis of the fluid phase and X-ray Reflectivity experiments performed before and after the transition between these two phases.

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Abstract: Clupeine, a cationic antimicrobial peptide found in fish, is of interest as a food additive but non-specific binding of the peptide to anionic molecules reduces its antimicrobial activity. The overall positive charge of clupeine can be reduced by blocking 10% of its arginine residues with 1,2-cyclohexanedione (CHD). The modified peptide retains antimicrobial activity but it is not known if its effect on the structure of Gram-negative model membranes is the same as the native peptide. In the presented paper, neutron reflectometry (NR) and X-ray reflectometry were used to investigate the effect of native and modified clupeine on the structure of model monolayer membranes composed of Phosphatidylethanolamine (PE), Phosphatidylglycerol (PG), and Cardiolipin (CL). The effect of the peptides on the structure of 1,2-dipalmitoyl (d62)-sn-glycero-3-phosphocholine (DPPC)/PE:PG:CL bilayers were also examined by NR. In both model systems, modified clupeine demonstrated a greater effect on the lipid structure. Charge reduction in the modified sample also resulted in improved hydrophobicity, and the formation of thicker peptide layers in the membrane models. Some lipid translocation was observed in the inner tail region (∼69 ± 0.24% DPPC and ∼24 ± 0.02% PE:PG:CL); and in the outer tail region (∼24 ± 0.02% DPPC and ∼56 ± 0.01% PE:PG:CL). Improved hydrophobicity and electrostatic interactions with lipid head groups, strongly suggests that the modified clupeine may use the carpet mechanisms to exert its effect on model membranes. These findings suggest that changing the charge on the native peptide changes the way in which the modified peptide disrupts Gram-negative model membranes.

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Abstract: Fluorinated non-fullerene acceptors (NFAs) usually have planar backbone and a higher tendency to crystallize compared to their non-fluorinated counterparts, which leads to enhanced charge mobility in organic solar cells (OSCs). However, this self-organization behavior may result in excessive phase separation with electron donors and thereby deteriorate device efficiency. Herein, we demonstrate an effective approach to tune the molecular organization of a fluorinated NFA (INPIC-4F), and its phase separation with the donor PBDB-T, by varying the casting solvent. A prolonged film drying time encourages the crystallization of INPIC-4F into spherulites and consequently results in excessive phase separation, leading to a low device power conversion efficiency (PCE) of 8.1%. Contrarily, a drying time leads to fine mixed domains with inefficient charge transport properties, resulting in a moderate device PCE of 11.4%. An intermediate film drying time results in the formation of face-on π-π stacked PBDB-T and INPIC-4F domains with continuous phase-separated networks, which facilitates light absorption, exciton dissociation as well as balanced charge transport towards the electrode, and achieves a remarkable PCE of 13.1%. This work provides a rational guide for optimizing the molecular ordering of NFAs and electron donors for high device efficiency.

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Abstract: The insufficient phase separation between polymer donors and non-fullerene acceptors (NFAs) featuring with low-structural orders disrupts efficient charge transport and increases charge recombination, consequently limits the maximum achievable power conversion efficiency (PCE) of organic solar cells (OSCs). Herein, an NFA IT-M has been added as the third component into the PBDB-T:m-INPOIC OSCs, and is shown to effectively tune the phase separation between donor and acceptor molecules, although all components in the ternary system exhibit low degrees of structural orders. The incorporation of 10 wt% IT-M into a PBDB-T:m-INPOIC binary host blend appreciably increases the length scale of phase separation, creating continuous pathways which increase and balance charge transport. This leads to an enhanced photovoltaic performance from 12.8% in the binary cell to 13.9% for the ternary cell with simultaneously improved open-circuit voltage, short-circuit current and fill factor. This work highlights the beneficial role of ternary components in controlling the morphology of the active layer for high performance OSCs.