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  • 1.
    Barbero, David
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Skrypnychuck, Vasyl
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Stella, Antonio
    Confinement effects in thin semiconducting organic films2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    Understanding and controlling crystallite formation and orientation in thin semiconducting polymer films is paramount to building more efficient organic electronic devices for renewable energies. Indeed, chain packing and crystallization in such films determines to a large extent their electronic and optical properties [1-6]. Surprinsingly, little work has been done on the influence of confinement in semiconducting films. In this talk, we present results on the effect of confinement under applied pressure in one of the highest performing and most widely used organic semiconductor: regio-regular poly-3-hexylthiophene (rr-P3HT) thin films. We studied films with thickness ranging from ≈15-100 nm, and processed in various conditions of annealing and nano-confinement. Using X-ray diffraction techniques, atomic force microscopy (AFM) and UV vis spectroscopy we show that crystalline orientation, crystal density, kinetics and optical absorbance are affected by confinement. We expect these findings to help better understand the role of confinement on crytallization in semiconducting films, and to have strong implications for organic electronic applications and photovoltaics.

  • 2.
    Barbero, David
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Skrypnychuk, Vasyl
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boulanger, Nicolas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Yu, Victor
    Hilke, Michael
    Mannsfeld, Stefan
    Toney, Mike
    Improved Crystallinity and Increased Vertical Charge Transport in a P3HT Film Deposited on Single Layer  Graphene2014Konferensbidrag (Refereegranskat)
  • 3.
    Iakunkov, Artem
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Skrypnychuk, Vasyl
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nordenström, Andreas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shilayeva, Elizaveta A.
    Korobov, Mikhail
    Prodana, Mariana
    Enachescu, Marius
    Larsson, Sylvia H.
    Talyzin, Aleksandr V.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Activated graphene as a material for supercapacitor electrodes: effects of surface area, pore size distribution and hydrophilicity2019Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Activated reduced graphene oxide (a-rGO) is a material with a rigid 3D porous structure and high specific surface area (SSA). Using variation of activation parameters and post-synthesis mechanical treatment we prepared two sets of materials with a broad range of BET (N2) SSA ∼1000–3000 m2 g−1, and significant differences in pore size distribution and oxygen content. The performance of activated graphene as an electrode in a supercapacitor with KOH electrolyte was correlated with the structural parameters of the materials and water sorption properties. a-rGO is a hydrophobic material as evidenced by the negligibly small BET (H2O) SSA determined using analysis of water vapor sorption isotherms. However, the total pore volume determined using water vapor sorption and sorption of liquid water is almost the same as the one found by analysis of nitrogen sorption isotherms. Ball milling is found to provide an improved bulk density of activated graphene and collapse of all pores except the smallest ones (<2 nm). A decrease in the activation temperature from 850 °C to 550 °C is found to result in materials with a narrow micropore size distribution and increased oxygen content. Elimination of mesopores using ball milling or a lower activation temperature provided materials with better specific capacitance despite a significant decrease (by ∼30%) of the BET (N2) SSA. The best gravimetric and volumetric capacitances in KOH electrolyte were achieved not for samples with the highest value of the BET (N2) SSA but for materials with 80–90% of the total pore volume in micropores and an increased BET (H2O) SSA. Comparing the performance of electrodes prepared using rGO and a-rGO shows that a more hydrophilic surface is favorable for charge storage in supercapacitors with KOH electrolyte.

  • 4. Kan, Zhipeng
    et al.
    Colella, Letizia
    Canesi, Eleonora V.
    Vorobiev, Alexei
    Skrypnychuk, Vasyl
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Terraneo, Giancarlo
    Barbero, David R.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Bertarelli, Chiara
    MacKenzie, Roderick C. I.
    Keivanidis, Panagiotis E.
    Charge transport control via polymer polymorph modulation in ternary organic photovoltaic composites2016Ingår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 4, nr 4, s. 1195-1201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The control on the charge transport properties of ternary organic photovoltaic P3HT : PCBM : QBT devices is enabled by modulating the distribution of P3HT polymorphs in the device photoactive layers. Negligible amounts of QBT induce striking modifications in the P3HT lamellar stacking direction, forming both densely packed and non-densely packed P3HT chains. The former reduce the charge carrier recombination rate, enabling an increased fill factor and short-circuit device photocurrent.

  • 5.
    Skrypnychuk, Vasyl
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Vertical charge transport in conjugated polymers2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Conjugated polymers are novel organic electronic materials highly important for organic photovoltaic applications. Charge transport is one of the key properties which defines the performance of conjugated polymers in electronic devices.

    This work aims to explore the charge transport anisotropy in thin films of P3HT, one of the most common conjugated polymers. Using X-ray diffraction techniques and charge transport measurements, the relation between vertical charge transport through thin P3HT films and structure of the films was established.

    It was shown that particular orientations of crystalline domains of P3HT, namely face-on and chain-on, are beneficial for vertical charge transport. These orientations provide the efficient pathways for the charges to be transported vertically, either via π-π stacking interaction between the adjacent conjugated chains, or via the conjugated chain backbones. It was also demonstrated that particular orientations of crystallites are favourable for the formation of interconnected percolated pathways providing enhanced vertical charge transport across the film.

    Deposition of P3HT on most commonly used silicon substrates typically results in the formation of mostly edge-on orientation of crystallites which is unfavourable for vertical charge transport. Nanoimprint lithography was demonstrated as a powerful processing method for reorienting the edge-on crystalline domains of P3HT into chain-on (vertical) orientation. It is also shown that thin P3HT films with preferentially face-on orientations of crystallites can be deposited on graphene surface by spin coating.

    Using patterning of thin P3HT films by nanoimprint lithography, unprecedentedly high average vertical mobilities in the range of 3.1-10.6 cm2 V-1 s-1 were achieved in undoped P3HT.

    These results demonstrate that charge transport in thin films of a relatively simple and well-known conjugated polymer P3HT can be significantly improved using optimization of crystallinity,orientation of crystallites, polymer chain orientation and alignment in the films.

  • 6.
    Skrypnychuk, Vasyl
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boulanger, Nicolas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Yu, Victor
    Hilke, Michael
    Mannsfeld, Stefan C. B.
    Toney, Michael F.
    Barbero, David R.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Enhanced Vertical Charge Transport in a Semiconducting P3HT Thin Film on Single Layer Graphene2015Ingår i: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 25, nr 5, s. 664-670Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The crystallization and electrical characterization of the semiconducting polymer poly(3-hexylthiophene) (P3HT) on a single layer graphene sheet is reported. Grazing incidence X-ray diffraction revealed that P3HT crystallizes with a mixture of face-on and edge-on lamellar orientations on graphene compared to mainly edge-on on a silicon substrate. Moreover, whereas ultrathin (10 nm) P3HT films form well oriented face-on and edge-on lamellae, thicker (50 nm) films form a mosaic of lamellae oriented at different angles from the graphene substrate. This mosaic of crystallites with - stacking oriented homogeneously at various angles inside the film favors the creation of a continuous pathway of interconnected crystallites, and results in a strong enhancement in vertical charge transport and charge carrier mobility in the thicker P3HT film. These results provide a better understanding of polythiophene crystallization on graphene, and should help the design of more efficient graphene based organic devices by control of the crystallinity of the semiconducting film.

  • 7.
    Skrypnychuk, Vasyl
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boulanger, Nicolas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Yu, Victor
    Hilke, Michael
    Toney, Michael
    Barbero, David R.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Reduced crystallinity and enhanced charge transport by melt annealing of an organic semiconductor on single layer graphene2016Ingår i: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 4, nr 19, s. 4143-4149Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on the effect of the annealing temperature on the crystallization and the electrical properties of the semiconducting polymer poly(3-hexylthiophene) (P3HT) on single layer graphene. Electrical characterization showed that heating the P3HT film above the melting point (Tm) resulted in a higher vertical charge carrier mobility. Grazing incidence X-ray diffraction (GIXD) revealed that the film was actually less crystalline overall, but that it consisted of a much higher number of face-on crystallites. We moreover show that annealing above Tm removes the existing seeds still present in the film at lower temperatures and enhances face-on formation. These results provide a better understanding of the influence of the annealing temperature on polythiophene crystallization on graphene, and it shows that the annealing at higher temperature induces a more favorable crystalline orientation which enhances charge transport, despite the reduction in the overall crystallinity. These results should help in the design of more efficient graphene based organic electronic devices by controlling the crystalline morphology of the semiconducting film.

  • 8.
    Skrypnychuk, Vasyl
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wetzelaer, Gert-Jan A. H.
    Gordiichuk, Pavlo I.
    Mannsfeld, Stefan C. B.
    Herrmann, Andreas
    Toney, Michael F.
    Barbero, David R.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ultrahigh Mobility in an Organic Semiconductor by Vertical Chain Alignment2016Ingår i: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 28, nr 12, s. 2359-2366Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method to produce highly efficient and long-range vertical charge transport is demonstrated in an undoped polythiophene thin film, with average mobilities above 3.1 cm(2) V-1 s(-1). These record high mobilities are achieved by controlled orientation of the polymer crystallites enabling the most efficient and fastest charge transport along the chain backbones and across multiple chains. The significant increase in mobility shown here may present a new route to producing faster and more efficient optoelectronic devices based on organic materials. [GRAPHICS] .

  • 9. Vorobiev, Alexei
    et al.
    Dennison, Andrew
    Chernyshov, Dmitry
    Skyrpnychuck, Vasyl
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Barbero, David
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Graphene oxide hydration and solvation: an in situ neutron reflectivity study2014Ingår i: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 6, nr 20, s. 12151-12156Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Graphene oxide membranes were recently suggested for applications in separation of ethanol from water using a vapor permeation method. Using isotope contrast, neutron reflectivity was applied to evaluate the amounts of solvents intercalated into a membrane from pure and binary vapors and to evaluate the selectivity of the membrane permeation. Particularly, the effect of D2O, ethanol and D2O–ethanol vapours on graphene oxide (GO) thin films (25 nm) was studied. The interlayer spacing of GO and the amount of intercalated solvents were evaluated simultaneously as a function of vapour exposure duration. The significant difference in neutron scattering length density between D2O and ethanol allows distinguishing insertion of each component of the binary mixture into the GO structure. The amount of intercalated solvent at saturation corresponds to 1.4 molecules per formula unit for pure D2O (1.4 monolayers) and 0.45 molecules per formula unit (one monolayer) for pure ethanol. This amount is in addition to H2O absorbed at ambient humidity. Exposure of the GO film to ethanol–D2O vapours results in intercalation of GO with both solvents even for high ethanol concentration. A mixed D2O–ethanol layer inserted into the GO structure is water enriched compared to the composition of vapours due to slower ethanol diffusion into GO interlayers

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