16 research outputs found

    Conductive Polymer Work Function Changes due toResidual Water: Impact of Temperature-DependentDielectric Constant

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    Solution‐processed conducting polymer thin films are key components in organic and flexible electronic and optoelectronic devices. An archetypal conducting polymer is poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS), which can feature a high work function and thus helps achieving Ohmic contacts for holes with many semiconductors. However, it is known that residual water in PEDOT:PSS films lowers their work function and is detrimental for device lifetime. Our photoelectron spectroscopy experiments reveal that the work function of PEDOT:PSS films containing residual water shows the same trend as function of temperature as does the dielectric constant (Δ) of water, in the range between 25 °C and ‐100 °C. Consistently, it is found from impedance spectroscopy measurements that Δ of residual water containing PEDOT:PSS films increases with decreasing temperature. After removal of residual water from PEDOT:PSS films by annealing in ultrahigh vacuum, the work function of thin films is much higher than before (reaching 6.1 eV) and, notably, independent of temperature. In contrast, no indication is found that the presence of residual water has any impact on the electrical conductivity. For a nominally water‐free molecularly doped conjugated donor/acceptor copolymer films, a correlation between sample work function and temperature similar to those seen for PEDOT:PSS is found.Peer Reviewe

    Modeling G2019S-LRRK2 Sporadic Parkinson's Disease in 3D Midbrain Organoids

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    Summary: Recent advances in generating three-dimensional (3D) organoid systems from stem cells offer new possibilities for disease modeling and drug screening because organoids can recapitulate aspects of in vivo architecture and physiology. In this study, we generate isogenic 3D midbrain organoids with or without a Parkinson's disease-associated LRRK2 G2019S mutation to study the pathogenic mechanisms associated with LRRK2 mutation. We demonstrate that these organoids can recapitulate the 3D pathological hallmarks observed in patients with LRRK2-associated sporadic Parkinson's disease. Importantly, analysis of the protein-protein interaction network in mutant organoids revealed that TXNIP, a thiol-oxidoreductase, is functionally important in the development of LRRK2-associated Parkinson's disease in a 3D environment. These results provide proof of principle for the utility of 3D organoid-based modeling of sporadic Parkinson's disease in advancing therapeutic discovery. : H. Kim and colleagues generated 3D midbrain organoids containing a G2019S mutation in LRRK2 and used this system for sporadic Parkinson’s disease (PD) modeling in vitro. Their results demonstrate that these 3D midbrain organoids can recapitulate the pathological features of LRRK2-associated sporadic PD. These results demonstrate that the 3D midbrain organoids are invaluable for recapitulating PD phenotypes and understanding the molecular underpinnings of these phenotypes. Keywords: Parkinson's disease, iPSC, organoids, disease modeling, midbrai

    Improved order and transport in C60 thin films grown on SiO2 via use of transient templates

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    The performance of C60_{60} semiconducting films is linked to the degree of crystallinity and ordering, properties that strongly depend on the substrate, and growth conditions. Substrate–molecule interactions can be specifically tailored by employing growth templates to achieve a desired thin film structure. However, the presence of a growth template after the film deposition is usually not desirable as it may change the properties of the layer of interest. The ability to remove a growth template without any disruption to the active layer would be highly beneficial. A simple method of template removal by annealing is presented here. A variety of small organic molecules (perfluoropentacene, [6]phenacene, and α-sexithiophene) were used as a growth template to obtain a high-quality well-ordered C60_{60} thin film. In situ grazing-incidence wide-angle x-ray scattering was employed to study the structural changes of C60_{60} thin films during template removal. While a slight disturbance of the thin film structure was observed during template removal caused by evaporated molecules from the growth template escaping through the C60_{60} layer, the disruption is only temporary. When the annealing process is concluded, only the well-ordered C60_{60} thin film directly on top of SiO2_2 is left, which is not achievable without the use of a growth template. Improved crystallinity and grain size of such a thin film, when compared to preparation without a growth template, lead to a significant improvement of the charge carrier mobility. Importantly, template removal prevents the formation of undesired ambipolar transistor characteristics

    Influence of alkyl chain variation on cocrystal formation and molecular charge transfer in DIP:perylene diimide binary systems

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    We present a comprehensive investigation of cocrystal formation and charge transfer effects in weakly interacting organic semiconductor mixtures. As a model system, we choose diindenoperylene (DIP) as a donor molecule and several perylene diimide derivatives (PDI) as acceptor molecules that differ in the n-alkyl side chain in the imide position and in the cyano (CN) group in the bay position. We identified the optimized side groups for the acceptors in thin films with the donor DIP concerning the mixing behavior and molecular charge transfer (CT) effects. The two systems, which form a well-defined cocrystal and show excited-state charge transfer effects, are DIP:PTCDI-C3_3 with an n-propyl side chain and DIP:PTCDI-C8_8-CN2_2 with incorporated cyano groups. Important for the mixing behavior and the charge transfer effects with DIP are the intermolecular interactions of the pure perylene diimide derivatives and the orientation of these molecules on the substrate (SiO2_2). For the DIP:PTCDI-C3_3 system, a sharp CT peak in absorption with a well-defined CT energy is observed. In contrast, the DIP:PTCDI-C8_8-CN2_2 mixed films show a broad CT band in absorption and two different CT energies. The mixing behavior and charge transfer effects with DIP are strongly influenced by the structure of the acceptors, which are easily chemically tunable in the desired way
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