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  • 101.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    van Duren, JKJ
    Eindhoven University of Technology, Netherlands.
    Jonkheijm, P
    Eindhoven University of Technology, Netherlands.
    Pasveer, WF
    Eindhoven University of Technology, Netherlands.
    Koenraad, PM
    Eindhoven University of Technology, Netherlands.
    Janssen, RAJ
    Eindhoven University of Technology, Netherlands.
    Salemink, HWM
    Eindhoven University of Technology, Netherlands.
    Wolter, JH
    Eindhoven University of Technology, Netherlands.
    Relating substitution to single-chain conformation and aggregation in poly(p-phenylene vinylene) films2003In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 3, no 9, p. 1191-1196Article in journal (Refereed)
    Abstract [en]

    The morphology of films of PPV derivatives is studied with molecular (single chain) resolution by phase-imaging scanning force microscopy. It is found that the symmetry of substitution is directly related to surface morphology and aggregation behavior. The molecular resolution in the phase contrast is shown to result from van der Waals interaction between the conjugated backbone of the polymer chains and the metallic tip, and can quantitatively be described by a simple harmonic oscillator model.

  • 102.
    Kemerink, Martijn
    et al.
    Eindhoven University of Technology, Netherlands.
    van Duren, JKJ
    Eindhoven University of Technology, Netherlands.
    van Breemen, AJJM
    Eindhoven University of Technology, Netherlands.
    Wildeman, J
    Eindhoven University of Technology, Netherlands.
    Wienk, MM
    Eindhoven University of Technology, Netherlands.
    Blom, PWM
    Eindhoven University of Technology, Netherlands.
    Schoo, HFM
    Eindhoven University of Technology, Netherlands.
    Janssen, RAJ
    Eindhoven University of Technology, Netherlands.
    Substitution and preparation effects on the molecular-scale morphology of PPV films2005In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 38, no 18, p. 7784-7792Article in journal (Refereed)
    Abstract [en]

    The morphology of spin-cast films of poly(p-phenylenevinylene) (PPV) derivatives is studied as a function of the substitution pattern of the conjugated backbone. Moreover, the influence of concentration in the casting solution, annealing, the choice of solvent, and the role of defects are addressed. By using a recently developed scanning-probe technique, we are able to visualize individual polymer chains and aggregates on the surface of spin-cast films. We find that a symmetric substitution pattern strongly promotes interchain aggregation in the surface layer, whereas an unsymmetric pattern in some cases leads to intrachain or self-aggregation. The nature of these intrachain aggregates is further investigated using molecular dynamics simulations. The observed molecular morphologies can in most cases be qualitatively related to macroscopic electrooptical properties. Therefore, our results strongly suggest that the surface morphology may be regarded as indicative of the morphology of the entire film.

  • 103.
    Khikhlovskyi, Vsevolod
    et al.
    Eindhoven University of Technology, Netherlands; TNO Dutch Org Appl Science Research, Netherlands.
    Gorbunov, Andrey V.
    Eindhoven University of Technology, Netherlands.
    van Breemen, Albert J. J. M.
    TNO Dutch Org Appl Science Research, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    Gelinck, Gerwin H.
    TNO Dutch Org Appl Science Research, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Multi-bit organic ferroelectric memory2013In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 14, no 12, p. 3399-3405Article in journal (Refereed)
    Abstract [en]

    Storage of multiple bits per element is a promising alternative to miniaturization for increasing the information data density in memories. Here we introduce a multi-bit organic ferroelectric-based non-volatile memory with binary readout from a simple capacitor structure. The functioning of our multi-bit concept is quite generally applicable and depends on the following properties for the data storage medium: (a) The data storage medium effectively consists of microscopic switching elements (hysterons). (b) The positive and negative coercive fields of each hysteron are equal in magnitude. (c) The distribution of hysteron coercive fields has substantial width. We show that the organic ferroelectric copolymer P(VDF-TrFE) meets these requirements. All basic properties of our device were measured and modeled in the framework of the dipole switching theory (DST). As a first example we show the possibility to independently program and subsequently read out the lower, middle and upper parts of the hysteron distribution function, yielding a 3-bit memory in a single capacitor structure. All measured devices show good state reproducibility, high endurance and potentially great scalability.

  • 104.
    Khikhlovskyi, Vsevolod
    et al.
    Eindhoven University of Technology, Netherlands.
    van Breemen, Albert J. J. M.
    Holst Centre, TNO, Eindhoven, The Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    Gelinck, Gerwin H.
    Eindhoven University of Technology, Netherlands; TNO, Eindhoven, Netherlands.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering. Eindhoven University of Technology, Netherlands.
    Data retention in organic ferroelectric resistive switches2016In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 31, p. 56-62Article in journal (Refereed)
    Abstract [en]

    Solution-processed organic ferroelectric resistive switches could become the long-missing non-volatile memory elements in organic electronic devices. To this end, data retention in these devices should be characterized, understood and controlled. First, it is shown that the measurement protocol can strongly affect the apparent retention time and a suitable protocol is identified. Second, it is shown by experimental and theoretical methods that partial depolarization of the ferroelectric is the major mechanism responsible for imperfect data retention. This depolarization occurs in close vicinity to the semiconductor-ferroelectric interface, is driven by energy minimization and is inherently present in this type of phase-separated polymer blends. Third, a direct relation between data retention and the charge injection barrier height of the resistive switch is demonstrated experimentally and numerically. Tuning the injection barrier height allows to improve retention by many orders of magnitude in time, albeit at the cost of a reduced on/off ratio. (c) 2016 Elsevier B.V. All rights reserved.

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  • 105.
    Khikhlovskyi, Vsevolod
    et al.
    Eindhoven University of Technology, Netherlands; TNO, Netherlands.
    van Breemen, Albert J. J. M.
    Holst Centre, TNO-The Dutch Organization for Applied Scientific Research, The Netherlands.
    Michels, Jasper J.
    Max Planck Institute for Polymer Research (MPI), Germany.
    Janssen, Rene A. J.
    Department of Applied Physics, Eindhoven University of Technology, The Netherlands.
    Gelinck, Gerwin H.
    Department of Applied Physics, Eindhoven University of Technology, The Netherlands; Holst Centre, TNO-The Dutch Organization for Applied Scientific Research, The Netherlands.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, The Institute of Technology. Department of Applied Physics, Eindhoven University of Technology, The Netherlands.
    3D-Morphology Reconstruction of Nanoscale Phase-Separation in Polymer Memory Blends2015In: Journal of Polymer Science Part B: Polymer Physics, ISSN 0887-6266, E-ISSN 1099-0488, Vol. 53, no 17, p. 1231-1237Article in journal (Refereed)
    Abstract [en]

    In many organic electronic devices functionality is achieved by blending two or more materials, typically polymers or molecules, with distinctly different optical or electrical properties in a single film. The local scale morphology of such blends is vital for the device performance. Here, a simple approach to study the full 3D morphology of phase-separated blends, taking advantage of the possibility to selectively dissolve the different components is introduced. This method is applied in combination with AFM to investigate a blend of a semiconducting and ferroelectric polymer typically used as active layer in organic ferroelectric resistive switches. It is found that the blend consists of a ferroelectric matrix with three types of embedded semiconductor domains and a thin wetting layer at the bottom electrode. Statistical analysis of the obtained images excludes the presence of a fourth type of domains. The criteria for the applicability of the presented technique are discussed. (c) 2015 Wiley Periodicals, Inc.

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  • 106.
    Khikhlovskyi, Vsevolod
    et al.
    Eindhoven University of Technology, Netherlands; TNO, Netherlands.
    Wang, Rui
    TNO, Netherlands.
    van Breemen, Albert J. J. M.
    TNO, Netherlands.
    Gelinck, Gerwin H.
    TNO, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Department of Applied Physics, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Nanoscale Organic Ferroelectric Resistive Switches2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 6, p. 3305-3312Article in journal (Refereed)
    Abstract [en]

    Organic ferroelectric resistive switches function by grace of nanoscale phase separation in a blend of a semiconducting and a ferroelectric polymer that is sandwiched between metallic electrodes. In this work, various scanning probe techniques are combined with numerical modeling to unravel their operational mechanism. Resistive switching is shown to result from modulation of the charge injection barrier at the semiconductor-electrode interfaces. The modulation is driven by the stray field of the polarization charges in the ferroelectric phase and consequently is restricted to regions where semiconductor and ferroelectric phases exist in close vicinity. Since each semiconductor domain can individually be switched and read out, a novel, nanoscale memory element is demonstrated. An ultimate information density of similar to 30 Mb/cm(2) is estimated for this bottom-up defined memory device.

  • 107.
    Kiefer, David
    et al.
    Chalmers Univ Technol, Sweden.
    Kroon, Renee
    Chalmers Univ Technol, Sweden.
    Hofmann, Anna I.
    Chalmers Univ Technol, Sweden.
    Sun, Hengda
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Liu, Xianjie
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Giovannitti, Alexander
    Imperial Coll London, England; Imperial Coll London, England.
    Stegerer, Dominik
    Chalmers Univ Technol, Sweden; Tech Univ Chemnitz, Germany.
    Cano, Alexander
    Chalmers Univ Technol, Sweden.
    Hynynen, Jonna
    Chalmers Univ Technol, Sweden.
    Yu, Liyang
    Chalmers Univ Technol, Sweden.
    Zhang, Yadong
    Georgia Inst Technol, GA 30332 USA; Georgia Inst Technol, GA 30332 USA.
    Nai, Dingqi
    Univ Calif Davis, CA 95616 USA.
    Harrelson, Thomas F.
    Univ Calif Davis, CA 95616 USA.
    Sommer, Michael
    Tech Univ Chemnitz, Germany.
    Moule, Adam J.
    Univ Calif Davis, CA 95616 USA.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Marder, Seth R.
    Georgia Inst Technol, GA 30332 USA; Georgia Inst Technol, GA 30332 USA.
    McCulloch, Iain
    Imperial Coll London, England; Imperial Coll London, England; King Abdullah Univ Sci and Technol, Saudi Arabia.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Fabiano, Simone
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Mueller, Christian
    Chalmers Univ Technol, Sweden.
    Double doping of conjugated polymers with monomer molecular dopants2019In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 18, no 2, p. 149-+Article in journal (Refereed)
    Abstract [en]

    Molecular doping is a crucial tool for controlling the charge-carrier concentration in organic semiconductors. Each dopant molecule is commonly thought to give rise to only one polaron, leading to a maximum of one donor: acceptor charge-transfer complex and hence an ionization efficiency of 100%. However, this theoretical limit is rarely achieved because of incomplete charge transfer and the presence of unreacted dopant. Here, we establish that common p-dopants can in fact accept two electrons per molecule from conjugated polymers with a low ionization energy. Each dopant molecule participates in two charge-transfer events, leading to the formation of dopant dianions and an ionization efficiency of up to 200%. Furthermore, we show that the resulting integer charge-transfer complex can dissociate with an efficiency of up to 170%. The concept of double doping introduced here may allow the dopant fraction required to optimize charge conduction to be halved.

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  • 108.
    Koopmans, Bert
    et al.
    Eindhoven University of Technology, Netherlands; Eindhoven University of Technology, Netherlands.
    Wagemans, Wiebe
    Eindhoven University of Technology, Netherlands; Eindhoven University of Technology, Netherlands.
    Bloom, Francisco L.
    Eindhoven University of Technology, Netherlands; Eindhoven University of Technology, Netherlands.
    Bobbert, Peter A.
    Eindhoven University of Technology, Netherlands; Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands; Eindhoven University of Technology, Netherlands.
    Wohlgenannt, Markus
    University of Iowa, IA 52242 USA; University of Iowa, IA 52242 USA.
    Spin in organics: a new route to spintronics2011In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 369, no 1951, p. 3602-3616Article, review/survey (Refereed)
    Abstract [en]

    New developments in the nascent field of organic spintronics are discussed. Two classes of phenomena can be discerned. In hybrid organic spin valves (OSVs), an organic semiconducting film is sandwiched between two ferromagnetic (FM) thin films, aiming at magnetoresistive effects as a function of the relative alignment of the respective magnetization directions. Alternatively, organic magnetoresistance (OMAR) is achieved without any FM components, and is an intrinsic property of the organic semiconductor material. Some of the exciting characteristics of OMAR, in both electrical conductance and photoconductance, are presented. A systematic, combined experimental-theoretical study of sign changes between positive and negative magnetoresistance is shown to provide important insight about the underlying mechanisms of OMAR. A simple explanation of experimental observations is obtained by combining a spin-blocking mechanism, an essential ingredient in the recently proposed bipolaron model, with specific features of the device physics of space charge limited current devices in the bipolar regime. Finally, we discuss possible links between the physics relevant for OMAR and that for OSVs. More specifically, weak hyperfine fields from the hydrogen atoms in organic materials are thought to be crucial for a proper understanding of both types of phenomena.

  • 109.
    Lakhwani, Girish
    et al.
    Eindhoven University of Technology, Netherlands.
    Gielen, Jeroen C.
    Radboud University of Nijmegen, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Christianen, Peter C. M.
    Radboud University of Nijmegen, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    Meskers, Stefan C. J.
    Eindhoven University of Technology, Netherlands.
    Intensive Chiroptical Properties of Chiral Polyfluorenes Associated with Fibril Formation2009In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 113, no 43, p. 14047-14051Article in journal (Refereed)
    Abstract [en]

    Thin films of chiral poly {9,9-bis[(3S)-3,7-dimethyloctyl]-2,7-fluorene} (1) were studied using circular dichroism (CD) spectroscopy. Films spin coated from chloroform solution, show CD with a degree of polarization g(abs) (= +4 x 10(-4) at 400 nm) that is independent of film thickness (50-290 nm). This implies that gabs is an intensive property of the material and related to the chiral organization of the molecules on a length scale less than 50 nm. Atomic force microscopy (AFM) on the films reveals fibrils. Addition of nonsolvent methanol to a solution of 1 in chloroform leads to fibril formation in solution and results in CD similar in band shape to that of the pristine spin coated films from chloroform solution and a g(abs) comparable in magnitude. Thus the chiral molecular arrangement leading to circular dichroism is part of the internal structure of these fibrils.

  • 110.
    Lee, Jiyoul
    et al.
    Holst Centre TNO, Netherlands; Pukyong National University, South Korea.
    van Breemen, Albert J. J. M.
    Holst Centre TNO, Netherlands.
    Khikhlovskyi, Vsevolod
    Holst Centre TNO, Netherlands; Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering. Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    Gelinck, Gerwin H.
    Holst Centre TNO, Netherlands; Eindhoven University of Technology, Netherlands.
    Pulse-modulated multilevel data storage in an organic ferroelectric resistive memory diode2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, no 24407Article in journal (Refereed)
    Abstract [en]

    We demonstrate multilevel data storage in organic ferroelectric resistive memory diodes consisting of a phase-separated blend of P(VDF-TrFE) and a semiconducting polymer. The dynamic behaviour of the organic ferroelectric memory diode can be described in terms of the inhomogeneous field mechanism (IFM) model where the ferroelectric components are regarded as an assembly of randomly distributed regions with independent polarisation kinetics governed by a time-dependent local field. This allows us to write and non-destructively read stable multilevel polarisation states in the organic memory diode using controlled programming pulses. The resulting 2-bit data storage per memory element doubles the storage density of the organic ferroelectric resistive memory diode without increasing its technological complexity, thus reducing the cost per bit.

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  • 111.
    Lenz, Thomas
    et al.
    Max Planck Institute Polymer Research, Germany; Grad School Mat Science Mainz, Germany.
    Zhao, Dong
    Max Planck Institute Polymer Research, Germany.
    Richardson, George
    University of London Imperial Coll Science Technology and Med, England; University of London Imperial Coll Science Technology and Med, England.
    Katsouras, Ilias
    Max Planck Institute Polymer Research, Germany; Holst Centre, Netherlands.
    Asadi, Kamal
    Max Planck Institute Polymer Research, Germany; Max Planck Grad Centre, Germany.
    Glasser, Gunnar
    Max Planck Institute Polymer Research, Germany.
    Zimmermann, Samuel T.
    University of London Imperial Coll Science Technology and Med, England; University of London Imperial Coll Science Technology and Med, England.
    Stingelin, Natalie
    University of London Imperial Coll Science Technology and Med, England; University of London Imperial Coll Science Technology and Med, England.
    Christian Roelofs, W. S.
    Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering. Eindhoven University of Technology, Netherlands.
    Blom, Paul W. M.
    Max Planck Institute Polymer Research, Germany; Grad School Mat Science Mainz, Germany.
    de Leeuw, Dago M.
    Max Planck Institute Polymer Research, Germany; King Abdulaziz University, Saudi Arabia.
    Microstructured organic ferroelectric thin film capacitors by solution micromolding2015In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 212, no 10, p. 2124-2132Article in journal (Refereed)
    Abstract [en]

    Ferroelectric nanostructures offer a promising route for novel integrated electronic devices such as non-volatile memories. Here we present a facile fabrication route for ferroelectric capacitors comprising a linear array of the ferroelectric random copolymer of vinylidenefluoride and trifluoroethylene (P(VDF-TrFE)) interdigitated with the electrically insulating polymer polyvinyl alcohol (PVA). Micrometer size line gratings of both polymers were fabricated over large area by solution micromolding, a soft lithography method. The binary linear arrays were realized by backfilling with the second polymer. We investigated in detail the device physics of the patterned capacitors. The electrical equivalent circuit is a linear capacitor of PVA in parallel with a ferroelectric capacitor of P(VDF-TrFE). The binary arrays are electrically characterized by both conventional Sawyer-Tower and shunt measurements. The dependence of the remanent polarization on the array topography is explained by numerical simulation of the electric field distribution.

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  • 112.
    Li, Xiaoran
    et al.
    TNO, Netherlands; Eindhoven University of Technology, Netherlands.
    van Breemen, Albert J. J. M.
    TNO, Netherlands.
    Khikhlovskyi, Vsevolod
    Eindhoven University of Technology, Netherlands.
    Smits, Edsger C. P.
    TNO, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Broer, Dirk J.
    Eindhoven University of Technology, Netherlands.
    Gelinck, Gerwin H.
    TNO, Netherlands.
    Programmable polymer light emitting transistors with ferroelectric polarization-enhanced channel current and light emission2012In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 13, no 9, p. 1742-1749Article in journal (Refereed)
    Abstract [en]

    We present a voltage programmable polymer light emitting field-effect transistor (LEFET), consisting of a green emitting polymer (F8BT), and a ferroelectric polymer, P(VDF-TrFE), as the gate dielectric. We show by both experimental observations and numerical modeling that, when the ferroelectric gate dielectric is polarized in opposite directions at the drain and source sides of the channel, respectively, both electron and hole currents are enhanced, resulting in more charge recombination and similar to 10 times higher light emission in a ferroelectric LEFET, compared to the device with non-ferroelectric gate. As a result of the ferroelectric poling, our ferroelectric LEFETs exhibit repeated programmability in light emission, and an external quantum efficiency (EQE) of up to 1.06%. Numerical modeling reveals that the remnant polarization charge of the ferroelectric layer tends to pin the position of the recombination zone, paving the way to integrate specific optical out-coupling structures in the channel of these devices to further increase the brightness. (C) 2012 Elsevier B.V. All rights reserved.

  • 113.
    Mantovani Nardes, Alexandre
    et al.
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    A morphological model for the solvent-enhanced conductivity of PEDOT : PSS thin films2008In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 18, no 6, p. 865-871Article in journal (Refereed)
    Abstract [en]

    The well-known enhanced conductivity of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) thin films that is obtained by addition of high-boiling solvents like sorbitol to the aqueous dispersion used for film deposition is shown to be associated with a rearrangement of PEDOT-rich clusters into elongated domains, as evidenced from STM and AFM. Consistently, temperature dependent conductivity measurements for sorbitol-treated films reveal that charge transport occurs via quasi ID variable range hopping (VRH), in contrast to 3D VRH for untreated PEDOT:PSS films. The typical hopping distance of 60-90 nm, extracted from the conductivity measurements is consistent with hopping between the 30-40 nm sized grains observed with scanning probe microscopy.

  • 114.
    Mantovani Nardes, Alexandre
    et al.
    Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    Bastiaansen, Jolanda A. M.
    Eindhoven University of Technology, Netherlands.
    Kiggen, Nicole M. M.
    Eindhoven University of Technology, Netherlands.
    Langeveld, Bea M. W.
    Eindhoven University of Technology, Netherlands.
    van Breemen, Albert J. J. M.
    Eindhoven University of Technology, Netherlands.
    de Kok, Margreet M.
    Eindhoven University of Technology, Netherlands.
    Microscopic understanding of the anisotropic conductivity of PEDOT : PSS thin films2007In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 19, no 9, p. 1196-+Article in journal (Refereed)
    Abstract [en]

    The amsotropic conductivity of thin films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is correlated to the film morphology as obtained from scanning tunneling and atomic force microscopy images. The material was found to consist of layers of flattened PEDOT-rich particles that are separated by quasi-continuous PSS lamella (see figure).

  • 115.
    Mathijssen, S. G. J.
    et al.
    Eindhoven University of Technology, Netherlands.
    Coelle, M.
    Eindhoven University of Technology, Netherlands.
    Mank, A. J. G.
    Eindhoven University of Technology, Netherlands.
    Kemerink, M.
    Eindhoven University of Technology, Netherlands.
    Bobbert, P. A.
    Eindhoven University of Technology, Netherlands.
    de Leeuw, D. M.
    Eindhoven University of Technology, Netherlands.
    Scanning Kelvin probe microscopy on organic field-effect transistors during gate bias stress2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 19, article id 192104Article in journal (Refereed)
    Abstract [en]

    The reliability of organic field-effect transistors is studied using both transport and scanning Kelvin probe microscopy measurements. A direct correlation between the current and potential of a p-type transistor is demonstrated. During gate bias stress, a decrease in current is observed, that is correlated with the increased curvature of the potential profile. After gate bias stress, the potential changes consistently in all operating regimes: the potential profile gets more convex, in accordance with the simultaneously observed shift in threshold voltage. The changes of the potential are attributed to positive immobile charges, which contribute to the potential, but not to the current. (C) 2007 American Institute of Physics.

  • 116.
    Mathijssen, Simon G. J.
    et al.
    Eindhoven University of Technology, Netherlands; Philips Research Labs, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Sharma, Abhinav
    Eindhoven University of Technology, Netherlands.
    Coelle, Michael
    Merck Chemistry, England.
    Bobbert, Peter A.
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    de Leeuw, Dago M.
    Philips Research Labs, Netherlands.
    Charge trapping at the dielectric of organic transistors visualized in real time and space2008In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 20, no 5, p. 975-+Article in journal (Refereed)
    Abstract [en]

    Scanning Kelvin probe microscopy demonstrates that water-induced charge trapping at the SiO2 dielectric visualized in real time and space - is responsible for the commonly observed gate-bias-induced threshold-voltage shift in organic field-effect transistors. When a bias is applied to the electrodes, charges are injected onto the SiO2 (see background of the figure). When the contacts are grounded, the charges are released again (foreground picture).

  • 117.
    Mathijssen, Simon G. J.
    et al.
    Philips Research Labs, Netherlands; Eindhoven University of Technology, Netherlands.
    Smits, Edsger C. P.
    Philips Research Labs, Netherlands; Holst Centre TNO, Netherlands.
    van Hal, Paul A.
    Philips Research Labs, Netherlands.
    Wondergem, Harry J.
    Philips Research Labs, Netherlands.
    Ponomarenko, Sergei A.
    Russian Academic Science, Russia.
    Moser, Armin
    Graz University of Technology, Austria.
    Resel, Roland
    Graz University of Technology, Austria.
    Bobbert, Peter A.
    Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    de Leeuw, Dago M.
    Philips Research Labs, Netherlands; University of Groningen, Netherlands.
    Monolayer coverage and channel length set the mobility in self-assembled monolayer field-effect transistors2009In: Nature Nanotechnology, ISSN 1748-3387, E-ISSN 1748-3395, Vol. 4, no 10, p. 674-680Article in journal (Refereed)
    Abstract [en]

    The mobility of self-assembled monolayer field-effect transistors (SAMFETs) traditionally decreases dramatically with increasing channel length. Recently, however, SAMFETs using liquid-crystalline molecules have been shown to have bulk-like mobilities that are virtually independent of channel length. Here, we reconcile these scaling relations by showing that the mobility in liquid crystalline SAMFETs depends exponentially on the channel length only when the monalayer is incomplete. We explain this dependence both numerically and analytically, and show that charge transport is not affected by carrier injection, grain boundaries or conducting island size. At partial coverage, that is when the monolayer is incomplete, liquid-crystalline SAMFETs thus form a unique model system to study size-dependent conductance originating from charge percolation in two dimensions.

  • 118.
    Mathijssen, Simon G. J.
    et al.
    Philips Research Labs, Netherlands; Eindhoven University of Technology, Netherlands.
    Spijkman, Mark-Jan
    Philips Research Labs, Netherlands; University of Groningen, Netherlands.
    Andringa, Anne-Marije
    Philips Research Labs, Netherlands; University of Groningen, Netherlands.
    van Hal, Paul A.
    Philips Research Labs, Netherlands.
    McCulloch, Iain
    University of London Imperial Coll Science Technology and Med, England.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    de Leeuw, Dago M.
    Philips Research Labs, Netherlands; University of Groningen, Netherlands.
    Revealing Buried Interfaces to Understand the Origins of Threshold Voltage Shifts in Organic Field-Effect Transistors2010In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 22, no 45, p. 5105-+Article in journal (Refereed)
    Abstract [en]

    The semiconductor of an organic field-effect transistor is stripped with adhesive tape, yielding an exposed gate dielectric, accessible for various characterization techniques. By using scanning Kelvin probe microscopy we reveal that trapped charges after gate bias stress are located at the gate dielectric and not in the semiconductor. Charging of the gate dielectric is confirmed by the fact that the threshold voltage shift remains, when a pristine organic semiconductor is deposited on the exposed gate dielectric of a stressed and delaminated field-effect transistor.

  • 119.
    Mathijssen, Simon G. J.
    et al.
    Eindhoven University of Technology, Netherlands; Philips Research Labs, Netherlands.
    van Hal, Paul A.
    Philips Research Labs, Netherlands.
    van den Biggelaar, Ton J. M.
    Philips Research Labs, Netherlands.
    Smits, Edsger C. P.
    Philips Research Labs, Netherlands; University of Groningen, Netherlands.
    de Boer, Bert
    University of Groningen, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    de Leeuw, Dago M.
    Philips Research Labs, Netherlands; University of Groningen, Netherlands.
    Manipulating the local light emission in organic light-emitting diodes by using patterned self-assembled monolayers2008In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 20, no 14, p. 2703-+Article in journal (Refereed)
    Abstract [en]

    Patterned organic light-emitting diodes are fabricated by using microcontactDrinted self-assembled monolayers on a gold anode (see background figure). Molecules with dipole moments in opposite directions result in an increase or a decrease of the local work function (foreground picture), providing a direct handle on charge injection and enabling local modification of the light emission

  • 120.
    Maturova, K.
    et al.
    Eindhoven University of Technology, Netherlands.
    van Bavel, S. S.
    Eindhoven University of Technology, Netherlands.
    Wienk, M. M.
    Eindhoven University of Technology, Netherlands.
    Janssen, R. A. J.
    Eindhoven University of Technology, Netherlands; Eindhoven University of Technology, Netherlands.
    Kemerink, M.
    Eindhoven University of Technology, Netherlands.
    Morphological Device Model for Organic Bulk Heterojunction Solar Cells2009In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 9, no 8, p. 3032-3037Article in journal (Refereed)
    Abstract [en]

    We present a numerical model for calculating current-voltage characteristics of polymer:fullerene bulk hetrojunction solar cells at different degrees of nanoscale phase separation. We show that the short-circuit current enhancement with finer phase separation is due to a reduction in bimolecular recombination caused by lateral movement of photogenerated electrons to the fullerene-rich phase. At high bias, vertical electron transport is enhanced and lateral movement is reduced, causing a significant field-dependent carrier extraction for coarse morphologies.

  • 121.
    Maturova, Klara
    et al.
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Connecting Scanning Tunneling Spectroscopy to Device Performance for Polymer: Fullerene Organic Solar Cells2010In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 4, no 3, p. 1385-1392Article in journal (Refereed)
    Abstract [en]

    Scanning tunneling microscopy and spectroscopy have been used to measure the local photovoltaic performance of prototypical polymer:fullerene (MDMO-PPV:PCBM) bulk heterojunction films with similar to 10 nm resolution. Fullerene-rich clusters are found to act as sinks, extracting electrons from a shell layer of a homogeneously mixed polymer:fullerene matrix, surrounding the fullerene cluster. The experimental results were quantitatively modeled with a drift-diffusion model that in first order accounts for the specific morphology. The same model has subsequently been used to calculate performance indicators of macroscopic solar cells as a function of film composition and characteristic size of the phase separation. As such, a first step has been set toward a quantitative correlation between nanoscopic and macroscopic device photovoltaic performance.

  • 122.
    Maturova, Klara
    et al.
    University of Eindhoven, Netherlands.
    Kemerink, Martijn
    University of Eindhoven, Netherlands.
    Wienk, Martijn M.
    University of Eindhoven, Netherlands.
    Charrier, Dimitri S. H.
    University of Eindhoven, Netherlands.
    Janssen, Rene A. J.
    University of Eindhoven, Netherlands.
    Scanning Kelvin Probe Microscopy on Bulk Heterojunction Polymer Blends2009In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 19, no 9, p. 1379-1386Article in journal (Refereed)
    Abstract [en]

    Here, correlated AFM and scanning Kelvin probe microscopy measurements with sub-100 nm resolution on the phase-separated active layer of polymer-fullerene (MDMO-PPV:PCBM) bulk heterojunction solar cells in the dark and under illumination are described. Using numerical modeling a fully quantitative explanation for the contrast and shifts of the surface potential in dark and light is provided. Under illumination an excess of photogenerated electrons is present in both the donor and acceptor phases. From the time evolution of the surface potential after switching off the light the contributions of free and trapped electrons can be identified. Based on these measurements the relative 3D energy level shifts of the sample are calculated. Moreover, by comparing devices with fine and coarse phase separation, it is found that the inferior performance of the latter devices is, at least partially, due to poor electron transport.

  • 123.
    Maturova, Klara
    et al.
    Eindhoven University of Technology, Netherlands.
    van Bavel, Svetlana S.
    Eindhoven University of Technology, Netherlands.
    Wienk, Martijn M.
    [Maturova, Netherlands.
    Janssen, Rene A. J.
    [Maturova, Netherlands.
    Kemerink, Martijn
    [Maturova, Netherlands.
    Description of the Morphology Dependent Charge Transport and Performance of Polymer:Fullerene Bulk Heterojunction Solar Cells2011In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 21, no 2, p. 261-269Article in journal (Refereed)
    Abstract [en]

    We present a combined numerical charge transport and morphology model to describe the current density-voltage (j-V) characteristics of three different, benchmark polymer: fullerene bulk heterojunction organic solar cells in which the device performance critically depends on the processing conditions or composition of the active layer. We find that an accurate description of the j-V characteristics over a broad bias range can be obtained when the actual complex, three-dimensional (3D) phase separation is represented by a simplified 2D or even 1D description. The morphological device model allows predicting the potential for increasing device performance by further optimizing the morphology. The optimal simplified morphology consists of two, relatively thin alternating vertically oriented slabs, that allow for fast lateral separation of photocreated holes and electrons. This morphology can effectively be described as 1D.

  • 124.
    Matyba, Piotr
    et al.
    Umeå University, Umeå, Sweden.
    Maturova, Klara
    Eindhoven University of Technology, Eindhoven, The Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Eindhoven, The Netherlands.
    Robinson, Nathaniel D
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Edman, Ludvig
    Umeå University, Umeå, Sweden.
    The dynamic organic p-n junction2009In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 8, no 8, p. 672-676Article in journal (Refereed)
    Abstract [en]

    Static p-n junctions in inorganic semiconductors are exploited in a wide range of todays electronic appliances. Here, we demonstrate the in situ formation of a dynamic p-n junction structure within an organic semiconductor through electrochemistry. Specifically, we use scanning kelvin probe microscopy and optical probing on planar light-emitting electrochemical cells (LECs) with a mixture of a conjugated polymer and an electrolyte connecting two electrodes separated by 120 mu m. We find that a significant portion of the potential drop between the electrodes coincides with the location of a thin and distinct light-emission zone positioned andgt;30 mu m away from the negative electrode. These results are relevant in the context of a long-standing scientific debate, as they prove that electrochemical doping can take place in LECs. Moreover, a study on the doping formation and dissipation kinetics provides interesting detail regarding the electronic structure and stability of the dynamic organic p-n junction, which may be useful in future dynamic p-n junction-based devices.

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  • 125.
    Meier, Sebastian B.
    et al.
    University of Erlangen Nurnberg, Germany; Siemens AG, Germany.
    van Reenen, Stephan
    Eindhoven University of Technology, Netherlands.
    Lefevre, Bastien
    Siemens AG, Germany.
    Hartmann, David
    Siemens AG, Germany.
    Bolink, Henk J.
    University of Valencia, Spain.
    Winnacker, Albrecht
    University of Erlangen Nurnberg, Germany.
    Sarfert, Wiebke
    Siemens AG, Germany.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Dynamic Doping in Planar Ionic Transition Metal Complex-Based Light-Emitting Electrochemical Cells2013In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 23, no 28, p. 3531-3538Article in journal (Refereed)
    Abstract [en]

    Using a planar electrode geometry, the operational mechanism of iridium(III) ionic transition metal complex (iTMC)-based light-emitting electrochemical cells (LECs) is studied by a combination of fluorescence microscopy and scanning Kelvin probe microscopy (SKPM). Applying a bias to the LECs leads to the quenching of the photoluminescence (PL) in between the electrodes and to a sharp drop of the electrostatic potential in the middle of the device, far away from the contacts. The results shed light on the operational mechanism of iTMC-LECs and demonstrate that these devices work essentially the same as LECs based on conjugated polymers do, i.e., according to an electrochemical doping mechanism. Moreover, with proceeding operation time the potential drop shifts towards the cathode coincident with the onset of light emission. During prolonged operation the emission zone and the potential drop both migrate towards the anode. This event is accompanied by a continuous quenching of the PL in two distinct regions separated by the emission line.

  • 126.
    Melianas, Armantas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Etzold, Fabian
    Max Planck Institute Polymer Research, Germany.
    Savenije, Tom J.
    Delft University of Technology, Netherlands.
    Laquai, Frederic
    Max Planck Institute Polymer Research, Germany; King Abdullah University of Science and Technology, Saudi Arabia.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering. Eindhoven University of Technology, Netherlands.
    Photo-generated carriers lose energy during extraction from polymer-fullerene solar cells2015In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, no 8778Article in journal (Refereed)
    Abstract [en]

    In photovoltaic devices, the photo-generated charge carriers are typically assumed to be in thermal equilibrium with the lattice. In conventional materials, this assumption is experimentally justified as carrier thermalization completes before any significant carrier transport has occurred. Here, we demonstrate by unifying time-resolved optical and electrical experiments and Monte Carlo simulations over an exceptionally wide dynamic range that in the case of organic photovoltaic devices, this assumption is invalid. As the photo-generated carriers are transported to the electrodes, a substantial amount of their energy is lost by continuous thermalization in the disorder broadened density of states. Since thermalization occurs downward in energy, carrier motion is boosted by this process, leading to a time-dependent carrier mobility as confirmed by direct experiments. We identify the time and distance scales relevant for carrier extraction and show that the photo-generated carriers are extracted from the operating device before reaching thermal equilibrium.

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  • 127.
    Melianas, Armantas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Felekidis, Nikolaos
    Dept Phys Chem and Biol, Complex Mat and Devices, S-58183 Linkoping, Sweden.
    Puttisong, Yuttapoom
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Meskers, Stefan C. J.
    Eindhoven Univ Technol, Netherlands.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Nonequilibrium site distribution governs charge-transfer electroluminescence at disordered organic heterointerfaces2019In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 116, no 47, p. 23416-23425Article in journal (Refereed)
    Abstract [en]

    The interface between electron-donating (D) and electron-accepting (A) materials in organic photovoltaic (OPV) devices is commonly probed by charge-transfer (CT) electroluminescence (EL) measurements to estimate the CT energy, which critically relates to device open-circuit voltage. It is generally assumed that during CT-EL injected charges recombine at close-to-equilibrium energies in their respective density of states (DOS). Here, we explicitly quantify that CT-EL instead originates from higher-energy DOS site distributions significantly above DOS equilibrium energies. To demonstrate this, we have developed a quantitative and experimentally calibrated model for CT-EL at organic D/A heterointerfaces, which simultaneously accounts for the charge transport physics in an energetically disordered DOS and the Franck-Condon broadening. The 0-0 CT-EL transition lineshape is numerically calculated using measured energetic disorder values as input to 3-dimensional kinetic Monte Carlo simulations. We account for vibrational CT-EL overtones by selectively measuring the dominant vibrational phonon-mode energy governing CT luminescence at the D/A interface using fluorescence line-narrowing spectroscopy. Our model numerically reproduces the measured CT-EL spectra and their bias dependence and reveals the higher-lying manifold of DOS sites responsible for CT-EL. Lowest-energy CT states are situated similar to 180 to 570 meV below the 0-0 CT-EL transition, enabling photogenerated carrier thermalization to these low-lying DOS sites when the OPV device is operated as a solar cell rather than as a light-emitting diode. Nonequilibrium site distribution rationalizes the experimentally observed weak current-density dependence of CT-EL and poses fundamental questions on reciprocity relations relating light emission to photovoltaic action and regarding minimal attainable photovoltaic energy conversion losses in OPV devices.

  • 128.
    Melianas, Armantas
    et al.
    Stanford Univ, CA 94305 USA.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Photogenerated Charge Transport in Organic Electronic Materials: Experiments Confirmed by Simulations2019In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 31, no 22, article id 1806004Article, review/survey (Refereed)
    Abstract [en]

    The performance of organic optoelectronic devices, such as organic photovoltaic (OPV) cells, is to a large extent dictated by their ability to transport the photogenerated charge, with relevant processes spanning a wide temporal (fs-mu s) and spatial (1-100 nm) range. However, time-resolved techniques can access only a limited temporal window, and often contradict steady-state measurements. Here, commonly employed steady-state and time-resolved techniques are unified over an exceptionally wide temporal range (fs-mu s) in a consistent physical picture. Experimental evidence confirmed by numerical simulations shows that, although various techniques probe different time scales, they are mutually consistent as they probe the same physical mechanisms governing charge motion in disordered media-carrier hopping and thermalization in a disorder-broadened density of states (DOS). The generality of this framework is highlighted by time-resolved experimental data obtained on polymer:fullerene, polymer:polymer, and small-molecule blends with varying morphology, including recent experiments revealing that low donor content OPV devices operate by long-range hole tunneling between non-nearest-neighbor molecules. The importance of nonequilibrium processes in organic electronic materials is reviewed, with a particular focus on experimental data and understanding charge transport physics in terms of material DOS.

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  • 129.
    Melianas, Armantas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Pranculis, Vytenis
    Center for Physical Sciences and Technology, Lithuania.
    Devižis, Andrius
    Center for Physical Sciences and Technology, Lithuania.
    Gulbinas, Vidmantas
    Center for Physical Sciences and Technology, Lithuania.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, The Institute of Technology. Department of Applied Physics, Eindhoven University of Technology, MB, Eindhoven, The Netherlands.
    Dispersion-Dominated Photocurrent in Polymer:Fullerene Solar Cells2014In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 24, no 28, p. 4507-4514Article in journal (Refereed)
    Abstract [en]

    Organic bulk heterojunction solar cells are often regarded as near-equilibrium devices, whose kinetics are set by well-defined charge carrier mobilities, and relaxation in the density of states is commonly ignored or included purely phenomenologically. Here, the motion of photocreated charges is studied experimentally with picosecond time resolution by a combination of time-resolved optical probing of electric field and photocurrent measurements, and the data are used to define parameters for kinetic Monte Carlo modelling. The results show that charge carrier motion in a prototypical polymer:fullerene solar cell under operational conditions is orders of magnitude faster than would be expected on the basis of corresponding near-equilibrium mobilities, and is extremely dispersive. There is no unique mobility. The distribution of extraction times of photocreated charges in operating organic solar cells can be experimentally determined from the charge collection transients measured under pulsed excitation. Finally, a remarkable distribution of the photocurrent over energy is found, in which the most relaxed charge carriers in fact counteract the net photocurrent.

  • 130.
    Melianas, Armantas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Pranculis, Vytenis
    Center for Physical Sciences and Technology, Vilnius, Lithuania.
    Spoltore, Donato
    Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Dresden, Germany.
    Benduhn, Johannes
    Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Dresden, Germany.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Gulbinas, Vidmantas
    Center for Physical Sciences and Technology, Vilnius, Lithuania / Department of General Physics and Spectroscopy, Faculty of Physics, Vilnius University, Vilnius, Lithuania.
    Vandewal, Koen
    Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Dresden, Germany.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Charge Transport in Pure and Mixed Phases in Organic Solar Cells2017In: Advanced Energy Materials, ISSN 1614-6840, Vol. 7, no 20Article in journal (Refereed)
    Abstract [en]

    In organic solar cells continuous donor and acceptor networks are considered necessary for charge extraction, whereas discontinuous neat phases and molecularly mixed donor–acceptor phases are generally regarded as detrimental. However, the impact of different levels of domain continuity, purity, and donor–acceptor mixing on charge transport remains only semiquantitatively described. Here, cosublimed donor–acceptor mixtures, where the distance between the donor sites is varied in a controlled manner from homogeneously diluted donor sites to a continuous donor network are studied. Using transient measurements, spanning from sub-picoseconds to microseconds photogenerated charge motion is measured in complete photovoltaic devices, to show that even highly diluted donor sites (5.7%–10% molar) in a buckminsterfullerene matrix enable hole transport. Hopping between isolated donor sites can occur by long-range hole tunneling through several buckminsterfullerene molecules, over distances of up to ≈4 nm. Hence, these results question the relevance of “pristine” phases and whether a continuous interpenetrating donor–acceptor network is the ideal morphology for charge transport.

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  • 131.
    Melianas, Armantas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Pranculis, Vytenis
    Center for Physical Sciences and Technology Savanoriu, Lithuania.
    Xia, Yuxin
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Felekidis, Nikolaos
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Gulbinas, Vidmantas
    Center for Physical Sciences and Technology Savanoriu, Lithuania.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Photogenerated Carrier Mobility Significantly Exceeds Injected Carrier Mobility in Organic Solar Cells2017In: Advanced Energy Materials, ISSN 1614-6840, Vol. 7, no 9, article id 1602143Article in journal (Refereed)
    Abstract [en]

    Charge transport in organic photovoltaic (OPV) devices is often characterized by space-charge limited currents (SCLC). However, this technique only probes the transport of charges residing at quasi-equilibrium energies in the disorder-broadened density of states (DOS). In contrast, in an operating OPV device the photogenerated carriers are typically created at higher energies in the DOS, followed by slow thermalization. Here, by ultrafast time-resolved experiments and simulations it is shown that in disordered polymer/fullerene and polymer/polymer OPVs, the mobility of photogenerated carriers significantly exceeds that of injected carriers probed by SCLC. Time-resolved charge transport in a polymer/polymer OPV device is measured with exceptionally high (picosecond) time resolution. The essential physics that SCLC fails to capture is that of photo­generated carrier thermalization, which boosts carrier mobility. It is predicted that only for materials with a sufficiently low energetic disorder, thermalization effects on carrier transport can be neglected. For a typical device thickness of 100 nm, the limiting energetic disorder is σ ≈71 (56) meV for maximum-power point (short-circuit) conditions, depending on the error one is willing to accept. As in typical OPV materials the disorder is usually larger, the results question the validity of the SCLC method to describe operating OPVs.

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  • 132.
    Meng, Xiao
    et al.
    Eindhoven University of Technology, Netherlands.
    Gorbunov, Andrey V.
    Eindhoven University of Technology, Netherlands.
    Christian Roelofs, W. S.
    Eindhoven University of Technology, Netherlands.
    Meskers, Stefan C. J.
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands; Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering. Eindhoven University of Technology, Netherlands.
    Sijbesma, Rint P.
    Eindhoven University of Technology, Netherlands.
    Ferroelectric Switching and Electrochemistry of Pyrrole Substituted Trialkylbenzene-1,3,5-Tricarboxamides2017In: Journal of Polymer Science Part B: Polymer Physics, ISSN 0887-6266, E-ISSN 1099-0488, Vol. 55, no 8, p. 673-683Article in journal (Refereed)
    Abstract [en]

    We explore a new approach to organic ferroelectric diodes using a benzene-tricarboxamide (BTA) core connected with C10 alkyl chains to pyrrole groups, which can be polymerized to provide a semiconducting ferroelectric material. The compound possesses a columnar hexagonal liquid crystalline (LC) phase and exhibits ferroelectric switching. At low switching frequencies, an additional process occurs, which leads to a high hysteretic charge density of up to similar to 1000 mC/m(2). Based on its slow rate, the formation of gas bubbles, and the emergence of characteristic polypyrrole absorption bands in the UV-Vis-NIR, the additional process is identified as the oxidative polymerization of pyrrole groups, enabled by the presence of amide groups. Polymerization of the pyrrole groups, which is essential to obtain semiconductivity, is limited to thin layers at the electrodes, amounting to similar to 17 nm after cycling for 21 h. (C) 2017 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc.

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  • 133.
    MOLENKAMP, LW
    et al.
    RHEIN WESTFAL TH AACHEN, DENMARK.
    FLENSBERG, K
    RHEIN WESTFAL TH AACHEN, DENMARK.
    KEMERINK, MARTIJN
    RHEIN WESTFAL TH AACHEN, DENMARK.
    SCALING OF THE COULOMB ENERGY DUE TO QUANTUM FLUCTUATIONS IN THE CHARGE ON A QUANTUM-DOT1995In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 75, no 23, p. 4282-4285Article in journal (Refereed)
    Abstract [en]

    The charging energy of a quantum dot is measured through the effect of its potential on the conductance of a second dot. This technique allows a measurement of the scaling of the dots charging energy with the conductance of the tunnel barriers leading to the dot. We find that the charging energy scales quadratically with the reflection probability of the barriers. The observed power law agrees with a recent theory.

  • 134.
    MOLENKAMP, LW
    et al.
    Philips Research Labs., Eindhoven, the Netherlands.
    KEMERINK, MARTIJN
    Philips Research Labs., Eindhoven, the Netherlands.
    STOCHASTIC COULOMB-BLOCKADE AND SCALING OF CHARGING ENERGY IN A DOUBLE-QUANTUM DOT SYSTEM1994In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 16, no 3, p. 275-278Article in journal (Refereed)
    Abstract [en]

    We have studied the transport properties of a device consisting of two quantum dots, defined electrostatically in a (Al,Ga)As heterostructure. In the series conductance of the two dots, we observe irregularly spaced conductance peaks of fluctuating amplitude. This behaviour results from transport in the stochastic Coulomb blockade regime. In a second experiment, we measure the charging energy of one dot through the effect of its potential (which varies in a saw-tooth fashion with gate voltage) on the conductance of the other dot. We find that the charging energy scales quadratically with the reflection probability of the tunnel barriers, in agreement with a recent theory.

  • 135.
    Nardes, A. M.
    et al.
    Eindhoven University of Technology, Netherlands.
    Kemerink, M.
    Eindhoven University of Technology, Netherlands.
    de Kok, M. M.
    Philips Research Labs, Netherlands.
    Vinken, E.
    Eindhoven University of Technology, Netherlands.
    Maturova, K.
    Eindhoven University of Technology, Netherlands.
    Janssen, R. A. J.
    Eindhoven University of Technology, Netherlands.
    Conductivity, work function, and environmental stability of PEDOT : PSS thin films treated with sorbitol2008In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 9, no 5, p. 727-734Article in journal (Refereed)
    Abstract [en]

    The electrical properties of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) thin films deposited from aqueous dispersion using different concentrations of sorbitol have been studied in detail. Although it is well known that sorbitol enhances the conductivity of PEDOT:PSS thin films by three orders of magnitude, the origin and consequences of sorbitol treatment are only partly understood and subject of further study. By thermal annealing of spin coated PEDOT:PSS/sorbitol films and simultaneously monitoring the conductivity, we demonstrate that the strong increase in conductivity coincides with evaporation of sorbitol from the film. Hence, sorbitol is a processing additive rather than a (secondary) dopant. Scanning Kelvin probe microscopy reveals that sorbitol treatment causes a reduction of the work function from 5.1 eV to 4.8-4.9 eV. Sorbitol also influences the environmental stability of the films. While the conductivity of the pristine PEDOT:PSS films increases by about one order of magnitude at similar to 50% RH due to an ionic contribution to the overall conductivity, films prepared using sorbitol exhibit an increased environmental stability with an almost constant conductivity up to 45% RH and a slight decrease at 50% RH. The higher stability results from a reduced tendency to take up water from the air, which is attributed to a denser packing of the PEDOT:PSS after sorbitol treatment. (C) 2008 Elsevier B.V. All rights reserved.

  • 136.
    Nardes, A. M.
    et al.
    Eindhoven University of Technology, Netherlands.
    Kemerink, M.
    Eindhoven University of Technology, Netherlands.
    Janssen, R. A. J.
    Eindhoven University of Technology, Netherlands.
    Anisotropic hopping conduction in spin-coated PEDOT : PSS thin films2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, no 8, article id 085208Article in journal (Refereed)
    Abstract [en]

    The charge transport in spin-coated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been investigated as a function of temperature and electric field. Both the magnitude and the transport mechanism are found to be strongly anisotropic. This striking behavior is quantitatively explained in terms of a morphological model in which flattened, quasimetallic PEDOT-rich grains are organized in horizontal layers that are separated by continuous insulating PSS lamellas. In this model, the in-plane conductivity is described by three-dimensional variable range hopping between similar to 25 nm sized PEDOT-rich particles separated by subnanometer PSS barriers, while the out-of-plane conductivity is described by nearest-neighbor hopping between more widely spaced molecular sites. These length scales are supported by previously reported scanning probe measurements.

  • 137.
    Pilet, N.
    et al.
    PSI, Switzerland.
    Khikhlovskyi, V.
    Eindhoven University of Technology, Netherlands.
    van Breemen, A. J. J. M.
    TNO Dutch Org Appl Science Research, Netherlands.
    Michels, J. J.
    TNO Dutch Org Appl Science Research, Netherlands; Max Planck Institute Polymer Research, Germany.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering. Eindhoven University of Technology, Netherlands.
    Gelinck, G.
    Eindhoven University of Technology, Netherlands; TNO Dutch Org Appl Science Research, Netherlands.
    Warnicke, P.
    PSI, Switzerland.
    Bernard, L.
    Swiss Federal Labs Mat Science and Technology, Switzerland.
    Piezoelectricity enhancement of P(VDF/TrFE) by X-ray irradiation2016In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 37, p. 257-262Article in journal (Refereed)
    Abstract [en]

    Organic electronics is becoming more and more important because the low level of fabrication and deposition complexity even at large scale makes it a good candidate for future low cost technological product development. P(VDF-TrFE) is a co-polymer of special interest due its ferroelectric property enabling usage in re-programmable non-volatile organic memory and magnetoelectric sensors. Piezo force microscopy (PFM) provides access to the technologically relevant ferroelectric polarisability and its remanent polarization via imaging of the piezoelectric property. Here we use PFM to show that piezoelectric response of a P(VDF-TrFE) film can be enhanced by up to 260 % after soft X-ray irradiation. This enhancement correlates with morphological change of part of the film, from amorphous to crystalline. An optimal irradiation dose is found above which the film gets eroded and the piezoelectric response gets lowered. (C) 2016 Elsevier B.V. All rights reserved.

  • 138.
    Ponseca, Carlito
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Arlauskas, Andrius
    Ctr Phys Sci and Technol, Lithuania.
    Yu, Hongling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Wang, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Nevinskas, Ignas
    Ctr Phys Sci and Technol, Lithuania.
    Duda, Eimantas
    Ctr Phys Sci and Technol, Lithuania.
    Vaicaitis, Virgilijus
    Vilnius Univ, Lithuania.
    Eriksson, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Bergqvist, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Liu, Xiaoke
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Krotkus, Arunas
    Ctr Phys Sci and Technol, Lithuania.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Pulsed Terahertz Emission from Solution-Processed Lead Iodide Perovskite Films2019In: ACS Photonics, E-ISSN 2330-4022, Vol. 6, no 5, p. 1175-1181Article in journal (Refereed)
    Abstract [en]

    We report pulsed terahertz (THz) emission from solution-processed metal halide perovskite films with electric field 1 order of magnitude lower than p-InAs, an efficient THz emitter. Such emission is enabled by a unique combination of efficient charge separation, high carrier mobilities, and more importantly surface defects. The mechanism of generation was identified by investigating the dependence of the THz electric field amplitude on surface defect densities, excess charge carriers, excitation intensity and energy, temperature, and external electric field. We also show for the first time THz emission from a curved surface, which is not possible for any crystalline semiconductor and paves the way to focus high-intensity sources. These results represent a possible new direction for perovskite optoelectronics and for THz emission spectroscopy as a complementary tool in investigating surface defects on metal halide perovskites, of fundamental importance in the optimization of solar cells and light-emitting diodes.

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  • 139.
    Riera-Galindo, Sergi
    et al.
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Orbelli Biroli, Alessio
    CNR, Italy.
    Forni, Alessandra
    CNR, Italy.
    Puttisong, Yuttapoom
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Tessore, Francesca
    Univ Milan, Italy.
    Pizzotti, Maddalena
    Univ Milan, Italy.
    Pavlopoulou, Eleni
    Univ Bordeaux, France.
    Solano, Eduardo
    ALBA Synchrotron Light Source, Spain.
    Wang, Suhao
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Wang, Gang
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ruoko, Tero-Petri
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Berggren, Magnus
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    di Carlo, Gabriele
    Univ Milan, Italy.
    Fabiano, Simone
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Impact of Singly Occupied Molecular Orbital Energy on the n-Doping Efficiency of Benzimidazole Derivatives2019In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, no 41, p. 37981-37990Article in journal (Refereed)
    Abstract [en]

    We investigated the impact of singly occupied molecular orbital (SOMO) energy on the n-doping efficiency of benzimidazole derivatives. By designing and synthesizing a series of new air-stable benzimidazole-based dopants with different SOMO energy levels, we demonstrated that an increase of the dopant SOMO energy by only similar to 0.3 eV enhances the electrical conductivity of a benchmark electron-transporting naphthalenediimide-bithiophene polymer by more than 1 order of magnitude. By combining electrical, X-ray diffraction, and electron paramagnetic resonance measurements with density functional theory calculations and analytical transport simulations, we quantitatively characterized the conductivity, Seebeck coefficient, spin density, and crystallinity of the doped polymer as a function of the dopant SOMO energy. Our findings strongly indicate that charge and energy transport are dominated by the (relative) position of the SOMO level, whereas morphological differences appear to play a lesser role. These results set molecular-design guidelines for next-generation n-type dopants.

    The full text will be freely available from 2020-09-20 12:58
  • 140.
    Roeling, Erik M.
    et al.
    ;.
    Chr Germs, Wijnand
    Smalbrugge, Barry
    Geluk, Erik Jan
    de Vries, Tjibbe
    Janssen, Rene A. J.
    Kemerink, Martijn
    Correction: Organic electronic ratchets doing work (vol 10, pg 51, 2011)2011In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 10, no 2Article in journal (Refereed)
    Abstract [en]

    n/a

  • 141.
    Roeling, Erik M.
    et al.
    Eindhoven University of Technology, Netherlands.
    Chr Germs, Wijnand
    Eindhoven University of Technology, Netherlands.
    Smalbrugge, Barry
    Eindhoven University of Technology, Netherlands.
    Geluk, Erik Jan
    Eindhoven University of Technology, Netherlands.
    de Vries, Tjibbe
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Scaling of characteristic frequencies of organic electronic ratchets2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 4, article id 045430Article in journal (Refereed)
    Abstract [en]

    The scaling of the characteristic frequencies of electronic ratchets operating in a flashing mode is investigated by measurements and numerical simulations. The ratchets are based on organic field effect transistors operated in accumulation mode. Oscillating potentials applied to asymmetrically spaced interdigitated finger electrodes embedded in the gate dielectric create a time-dependent, spatially asymmetric perturbation of the transistor channel potential. As a result, a net dc current can flow between source and drain despite zero source-drain bias. The frequency at current maximum is linearly dependent on the charge carrier density and the charge carrier mobility and inversely proportional to the squared length of the ratchet period, which can be related to the RC time of one asymmetric unit. Counterintuitively, it is independent of driving amplitude. Furthermore, the frequency at current maximum depends on the asymmetry of the ratchet potential, whereas the frequency of maximum charge pumping efficiency does not.

  • 142.
    Roeling, Erik M.
    et al.
    [Smalbrugge, Netherlands.
    Chr Germs, Wijnand
    [Smalbrugge, Netherlands.
    Smalbrugge, Barry
    Eindhoven University of Technology, Netherlands.
    Jan Geluk, Erik
    Eindhoven University of Technology, Netherlands.
    de Vries, Tjibbe
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    [Smalbrugge, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    The performance of organic electronic ratchets2012In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 2, no 1, article id 012106Article in journal (Refereed)
    Abstract [en]

    Organic electronic ratchets rectify time-correlated external driving forces, giving output powers that can drive electronic circuitry. In this work their performance characteristics are investigated using numerical modeling and measurements. It is shown how the characteristic parameters of the time-varying asymmetric potential like length scales and amplitude, as well as the density and mobility of the charge carriers in the device influence the performance characteristics. Various ratchet efficiencies and their relations are discussed. With all settings close to optimum, a ratchet with charge displacement and power efficiencies close to 50% and 7% respectively is obtained. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [doi:10.1063/1.3677934]

  • 143.
    Roeling, Erik M.
    et al.
    Eindhoven University of Technology, Netherlands.
    Germs, Wijnand Chr.
    [Roeling, Netherlands.
    Smalbrugge, Barry
    Eindhoven University of Technology, Netherlands.
    Jan Geluk, Erik
    Eindhoven University of Technology, Netherlands.
    de Vries, Tjibbe
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    [Roeling, Netherlands.
    Kemerink, Martijn
    [Roeling, Netherlands.
    Organic electronic ratchets doing work2011In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 10, no 1, p. 51-55Article in journal (Refereed)
    Abstract [en]

    The possibility to extract work from periodic, undirected forces has intrigued scientists for over a century-in particular, the rectification of undirected motion of particles by ratchet potentials, which are periodic but asymmetric functions. Introduced by Smoluchowski and Feynman(1,2) to study the (dis)ability to generate motion from an equilibrium situation, ratchets operate out of equilibrium, where the second law of thermodynamics no longer applies. Although ratchet systems have been both identified in nature(3,4) and used in the laboratory for the directed motion of microscopic objects(5-9), electronic ratchets(10-13) have been of limited use, as they typically operate at cryogenic temperatures and generate subnanoampere currents and submillivolt voltages(10-14). Here, we present organic electronic ratchets that operate up to radio frequencies at room temperature and generate currents and voltages that are orders of magnitude larger. This enables their use as a d.c. power source. We integrated the ratchets into logic circuits, in which they act as the d.c. equivalent of the a. c. transformer, and generate enough power to drive the circuitry. Our findings show that electronic ratchets may be of actual use.

  • 144.
    Roelofs, W. S. C.
    et al.
    Eindhoven University of Technology, Netherlands; Philips Research Labs, Netherlands.
    Mathijssen, S. G. J.
    Philips Research Labs, Netherlands; University of Groningen, Netherlands.
    Bijleveld, J. C.
    Eindhoven University of Technology, Netherlands.
    Raiteri, D.
    Eindhoven University of Technology, Netherlands.
    Geuns, T. C. T.
    Philips Research Labs, Netherlands.
    Kemerink, M.
    Eindhoven University of Technology, Netherlands.
    Cantatore, E.
    Eindhoven University of Technology, Netherlands.
    Janssen, R. A. J.
    Eindhoven University of Technology, Netherlands.
    de Leeuw, D. M.
    Philips Research Labs, Netherlands; University of Groningen, Netherlands.
    Fast ambipolar integrated circuits with poly(diketopyrrolopyrrole-terthiophene)2011In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 98, no 20, article id 203301Article in journal (Refereed)
    Abstract [en]

    Ambipolar integrated circuits were prepared with poly (diketopyrrolopyrrole-terthiophene) as the semiconductor. The field-effect mobility of around 0.02 cm(2)/V s for both electrons and holes allowed for fabrication of functional integrated complementary metal-oxide semiconductor (CMOS)-like inverters and ring oscillators. The oscillation frequency was found to have a near quadratic dependence on the supply bias. The maximum oscillation frequency was determined to be 42 kHz, which makes this ring oscillator the fastest CMOS-like organic circuit reported to date. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3589986]

  • 145.
    Roelofs, W. S. C.
    et al.
    Eindhoven University of Technology, Netherlands; Philips Research Labs, Netherlands.
    Mathijssen, S. G. J.
    Philips Research Labs, Netherlands.
    Janssen, R. A. J.
    Eindhoven University of Technology, Netherlands.
    de Leeuw, D. M.
    Philips Research Labs, Netherlands; University of Groningen, Netherlands.
    Kemerink, M.
    Eindhoven University of Technology, Netherlands.
    Accurate description of charge transport in organic field effect transistors using an experimentally extracted density of states2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 8, article id 085202Article in journal (Refereed)
    Abstract [en]

    The width and shape of the density of states (DOS) are key parameters to describe the charge transport of organic semiconductors. Here we extract the DOS using scanning Kelvin probe microscopy on a self-assembled monolayer field effect transistor (SAMFET). The semiconductor is only a single monolayer which has allowed extraction of the DOS over a wide energy range, pushing the methodology to its fundamental limit. The measured DOS consists of an exponential distribution of deep states with additional localized states on top. The charge transport has been calculated in a generic variable range-hopping model that allows any DOS as input. We show that with the experimentally extracted DOS an excellent agreement between measured and calculated transfer curves is obtained. This shows that detailed knowledge of the density of states is a prerequisite to consistently describe the transfer characteristics of organic field effect transistors.

  • 146.
    Roelofs, W. S. Christian
    et al.
    Eindhoven University of Technology, Netherlands; Philips Research Labs, Netherlands.
    Li, Weiwei
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    de Leeuw, Dago M.
    Max Planck Institute Polymer Research, Germany; King Abdulaziz University, Saudi Arabia.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, The Institute of Technology. Eindhoven University of Technology, Eindhoven, The Netherlands.
    Contactless charge carrier mobility measurement in organic field-effect transistors2014In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 15, no 11, p. 2855-2861Article in journal (Refereed)
    Abstract [en]

    With the increasing performance of organic semiconductors, contact resistances become an almost fundamental problem, obstructing the accurate measurement of charge carrier mobilities. Here, a generally applicable method is presented to determine the true charge carrier mobility in an organic field-effect transistor (OFET). The method uses two additional finger-shaped gates that capacitively generate and probe an alternating current in the OFET channel. The time lag between drive and probe can directly be related to the mobility, as is shown experimentally and numerically. As the scheme does not require the injection or uptake of charges it is fundamentally insensitive to contact resistances. Particularly for ambipolar materials the true mobilities are found to be substantially larger than determined by conventional (direct current) schemes.

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  • 147.
    Roelofs, W.S. Christian
    et al.
    Eindhoven University of Technology, The Netherlands; Philips Research Laboratories, Eindhoven, The Netherlands .
    Charrier, Dimitri S. H.
    Eindhoven University of Technology, The Netherlands .
    Dzwilewski, Andrzej
    Eindhoven University of Technology, The Netherlands .
    Janssen, Rene A. J.
    Eindhoven University of Technology, The Netherlands .
    de Leeuw, Dago M.
    Max Planck Institute Polymer Research, Mainz, Germany; King Abdulaziz University, Jeddah, Saudi Arabia .
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, The Institute of Technology. Eindhoven University of Technology, The Netherlands .
    Scanning tunnelling microscopy on organic field-effect transistors based on intrinsic pentacene2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 104, no 26, p. 263301-Article in journal (Refereed)
    Abstract [en]

    The full potential of scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy for in-situ characterization of organic semiconductors has so far not been accessible. Here, we demonstrate that the underlying problem, the low intrinsic conductivity, can be overcome by working in a field-effect geometry. We present high resolution surface topographies obtained by STM on pentacene organic field-effect transistors (OFETs). By virtue of the OFET geometry, the hole accumulation layer that is present at sufficiently negative gate bias acts as back contact, collecting the tunnelling current. The presence of a true tunnelling gap is established, as is the need for the presence of an accumulation layer. The tunnelling current vs. tip bias showed rectifying behaviour, which is rationalized in terms of the tip acting as a second gate on the unipolar semiconductor. An explanatory band diagram is presented. The measurements shown indicate that intrinsic organic semiconductors can be in-situ characterized with high spatial and energetic resolution in functional devices.

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  • 148.
    Rogowski, Rafal Z.
    et al.
    Eindhoven University of Technology, Netherlands; Dutch Polymer Institute, Netherlands.
    Dzwilewski, Andrzej
    Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Darhuber, Anton A.
    Eindhoven University of Technology, Netherlands.
    Solution Processing of Semiconducting Organic Molecules for Tailored Charge Transport Properties2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 23, p. 11758-11762Article in journal (Refereed)
    Abstract [en]

    We studied the charge transport characteristics of the organic semiconductor 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-PEN) deposited by dip-coating of a solution in an azeotropic solvent mixture. Arrays of crystalline ribbons were obtained with a morphology controllable by variation of the coating speed U. The charge carrier mobility mu, exhibited a systematic and reproducible dependence on the coating speed U and maximum values as high as mu approximate to 1.0 cm(2)/(V s).

  • 149.
    Roland, Steffen
    et al.
    Univ Potsdam, Germany; UP Transfer GmbH, Germany.
    Kniepert, Juliane
    Univ Potsdam, Germany.
    Love, John A.
    Univ Potsdam, Germany.
    Negi, Vikas
    Eindhoven Univ Technol, Netherlands.
    Liu, Feilong
    Eindhoven Univ Technol, Netherlands.
    Bobbert, Peter
    Eindhoven Univ Technol, Netherlands.
    Melianas, Armantas
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Stanford Univ, CA 94305 USA.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Hofacker, Andreas
    Tech Univ Dresden, Germany.
    Neher, Dieter
    Univ Potsdam, Germany.
    Equilibrated Charge Carrier Populations Govern Steady-State Nongeminate Recombination in Disordered Organic Solar Cells2019In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 6, p. 1374-1381Article in journal (Refereed)
    Abstract [en]

    We employed bias-assisted charge extraction techniques to investigate the transient and steady-state recombination of photogenerated charge carriers in complete devices of a disordered polymer-fullerene blend. Charge recombination is shown to be dispersive, with a significant slowdown of the recombination rate over time, consistent with the results from kinetic Monte Carlo simulations. Surprisingly, our experiments reveal little to no contributions from early time recombination of nonequilibrated charge carriers to the steady-state recombination properties. We conclude that energetic relaxation of photogenerated carriers outpaces any significant nongeminate recombination under application-relevant illumination conditions. With equilibrated charges dominating the steady-state recombination, quasi-equilibrium concepts appear suited for describing the open-circuit voltage of organic solar cells despite pronounced energetic disorder.

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  • 150.
    Scheunemann, Dorothea
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Heidelberg Univ, Germany.
    Non-Wiedemann-Franz behavior of the thermal conductivity of organic semiconductors2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 7, article id 075206Article in journal (Refereed)
    Abstract [en]

    Organic semiconductors have attracted increasing interest as thermoelectric converters in recent years due to their intrinsically low thermal conductivity compared to inorganic materials. This boom has led to encouraging practical results in which the thermal conductivity has predominantly been treated as an empirical number. However, in an optimized thermoelectric material, the electronic component can dominate the thermal conductivity, in which case the figure of merit ZT becomes a function of thermopower and Lorentz factor only. Hence the design of effective organic thermoelectric materials requires understanding the Lorenz number. Here, analytical modeling and kinetic Monte Carlo simulations are combined to study the effect of energetic disorder and length scales on the correlation of electrical and thermal conductivity in organic semiconductor thermoelectrics. We show that a Lorenz factor up to a factor similar to 5 below the Sommerfeld value can be obtained for weakly disordered systems, in contrast with what has been observed for materials with band transport. Although the electronic contribution dominates the thermal conductivity within the application-relevant parameter space, reaching ZT amp;gt; 1 would require minimization of both the energetic disorder and also the lattice thermal conductivity to values below kappa(1at) amp;lt; 0.2 W/mK.

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