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Abstract: We show that both the morphology and crystal structure of regioregular poly(3-hexylthiophene) (RR-P3HT) films in organic field effect transistor (OFET) devices with top surface contacts are altered, when an electric field is applied. Grazing incidence X-ray diffraction (GIXD) analysis reveals a dramatic decrease in structural order in the non-linear current regime and, by contrast, much less pronounced structural changes of the (h 00) peaks in the linear current regime. Using for the first time resonance soft X-ray reflectivity (RSoXR) on RR-P3HT to avoid radiation damaged and to enhance the scope of the attained depth resolved information, we show that these changes are located in a several tens of nanometer thin sub-surface layer of the active polymer in the device. Furthermore, the RSoXR data reveal that the changes are strongly related to the C 1s→ π ∗ and C 1s→ σ ∗-resonances. In situ AFM measurements of the RR-P3HT device surface support the reciprocal space analysis results by showing a substantial softening and lateral expansion of the RR-P3HT films, when 20V are applied between the contacts. These morphological and structural changes are partially reversible in nature. [Copyright &y& Elsevier]

The synthesis of a series of novel A-π-D-π-A oligomers bearing either electron-donating dithieno[3,2- b :2′,3′- d ]silole (DTS) or dithieno[3,2- b :2′,3′- d ]pyrrole (DTP) units linked through a bithiophene π-bridge with the electron-withdrawing methyldicyanovinyl (DCV) or N-ethylrhodanine (Rh) groups is described. In order to evaluate the effects of different donor-acceptor combinations on various physical properties of the oligomers they are comprehensively studied by UV–Vis spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and cyclic voltammetry (CV). Replacing the DTS by DTP as well as the DCV by Rh leads to increasing of HOMO energy levels and slight decreasing of LUMO energy levels, respectively. The DTP-based oligomers have a red shift in absorption spectra and an increased solubility as compared to the DTS-based analogs. Replacing the acceptor DCV unit by Rh also results in significantly higher solubility, but the Rh-based oligomers exhibit weaker intermolecular interactions, poorer optical absorption of sun light as well as lower charge carrier mobility in blends. Altogether, the structural improvement of the DTS-DCV and DTP-DCV blends upon annealing correlates well with the observed photovoltaic performances in organic solar cells. These results give more insight how to fine-tune and predict physical properties and photovoltaic performance of small A-π-D-π-A molecules having different donor-acceptor combinations in their chemical structures and thus providing a molecular design guideline for the next generation of high-performance photovoltaic materials. [ABSTRACT FROM AUTHOR]

In the present work the role of the thermal treatment on the reorganization of gold nanoparticles (AuNPs) functionalized with a π-conjugated dithiol ligand, namely 9,9-didodecyl-2,7-bis-thiofluorene, is studied by grazing incidence X-ray diffraction technique. For a detailed investigation of the structural changes and reorganization occurring in the AuNPs network and of the monitoring of complex interactions between nanoparticles, the line profiles are analyzed in out-of-plane and in-plane directions. The obtained data support the idea of the formation of a uniform network of nanoparticles that after annealing are extended from hexagonal to cubic arrangement. [ABSTRACT FROM AUTHOR]

X-ray and electron diffraction analyses were carried out under various geometries to investigate the role of alkyl side chain length on the structural properties of regioregular poly(3-alkylthiophene) (RR-P3AT) thin films by sequentially increasing the alkyl side chain length from n-pentyl till n-octyl. P3AT thin films with different thicknesses were drop cast at room temperature (RT) and low temperature (−30 °C) for the structural analysis. A thorough X-ray diffraction, transmission electron microscopic, field effect transistor and photoluminescence (PL) investigations revealed the following: (i) texturing of RT cast P3AT thin films along the out-of-plane direction on decreasing the alkyl side chain length, (ii) poor π–π stacking of P3AT crystallites on increasing the alkyl side chain length, which results from the increased steric hindrance between the grafted alkyl side chains, (iii) such poor π–π stacking of P3ATs on increasing the alkyl side chain length eventually found to hinder the mobility of charge carriers, and (iv) evolution of well defined vibronic side bands in the PL spectra of −30 °C cast films confirm the formation of highly crystalline films as compared to the RT cast ones. Highly edge-on oriented and uniform thin films can be fabricated by optimizing the cast temperature and concentration of the solution. [ABSTRACT FROM AUTHOR]