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  • 1.
    Abdalla, Hassan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    van de Ruit, Kevin
    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.
    Effective Temperature and Universal Conductivity Scaling in Organic Semiconductors2015In: Scientific Reports, E-ISSN 2045-2322, Vol. 5, article id 16870Article in journal (Refereed)
    Abstract [en]

    We investigate the scalability of the temperature-and electric field-dependence of the conductivity of disordered organic semiconductors to universal curves by two different but commonly employed methods; by so-called universal scaling and by using the effective temperature concept. Experimentally both scaling methods were found to be equally applicable to the out-of-plane charge transport in PEDOT: PSS thin films of various compositions. Both methods are shown to be equivalent in terms of functional dependence and to have identical limiting behavior. The experimentally observed scaling behavior can be reproduced by a numerical nearest-neighbor hopping model, accounting for the Coulomb interaction, the high charge carrier concentration and the energetic disorder. The underlying physics can be captured in a simple empirical model, describing the effective temperature of the charge carrier distribution as the outcome of a heat balance between Joule heating and (effective) temperature-dependent energy loss to the lattice.

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  • 2.
    Christian Roelofs, W. S.
    et al.
    Eindhoven University of Technology, Netherlands; Philips Research Labs, Netherlands.
    Spijkman, Mark-Jan
    Philips Research Labs, Netherlands.
    Mathijssen, Simon G. J.
    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
    Eindhoven University of Technology, MB, Eindhoven, The Netherlands.
    Fundamental Limitations for Electroluminescence in Organic Dual-Gate Field-Effect Transistors2014In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 26, no 26, p. 4450-+Article in journal (Refereed)
    Abstract [en]

    A dual-gate organic field-effect transistor is investigated for electrically pumped lasing. The two gates can independently accumulate electrons and holes, yielding current densities exceeding the lasing threshold. Here, the aim is to force the electrons and holes to recombine by confining the charges in a single semiconducting film. It is found that independent hole and electron accumulation is mutually exclusive with vertical recombination and light emission.

  • 3.
    Cox, M.
    et al.
    Eindhoven University of Technology, Netherlands.
    Wijnen, M. H. A.
    Eindhoven University of Technology, Netherlands.
    Wetzelaer, G. A. H.
    University of Groningen, Netherlands.
    Kemerink, Martijn
    Molecular Materials and Nanosystems, Eindhoven University of Technology, MB Eindhoven, The Netherlands.
    Blom, P. W. M.
    University of Groningen, Netherlands; Max Planck Institute Polymer Research, Germany.
    Koopmans, B.
    Eindhoven University of Technology, Netherlands.
    Spectroscopic evidence for trap-dominated magnetic field effects in organic semiconductors2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 15, article id 155205Article in journal (Refereed)
    Abstract [en]

    Polaron traps are ubiquitous in organic semiconductors and recent evidence suggests they might be crucial for the large observed magnetic field effects (MFEs) in organic semiconductors. Here we measure MFEs in polymer thin-film devices with engineered, radiative trap sites in order to spectroscopically investigate the influence of the traps. Surprisingly, the luminescence at the trap sites and the polymer backbone is found to have an opposite response to a magnetic field. All our results are compatible with a mechanism in which spin mixing at the traps can create the large MFEs observed on the backbone. This scenario is quantitatively confirmed by numerical drift-diffusion modeling with magnetic-field-dependent exciton densities at the traps. These insights solve an outstanding controversy within the research field.

  • 4.
    Felekidis, Nikolaos
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Wang, E.
    Chalmers University of Technology, Göteborg, Sweden.
    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.
    Open circuit voltage and efficiency in ternary organic photovoltaic blends2016In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 9, no 1, p. 257-266Article in journal (Refereed)
    Abstract [en]

    Organic bulk heterojunction solar cells based on ternary blends of two donor absorbers and one acceptor are investigated by experiments and modeling. The commonly observed continuous tunability of the open circuit voltage V-OC with the donor1 : donor2 ratio can quantitatively be explained as quasi-Fermi level splitting due to photocreated charges filling a joint density of states that is broadened by Gaussian disorder. On this basis, a predictive model for the power conversion efficiency that accounts for the composition-dependent absorption and the shape of the current-voltage characteristic curve is developed. When all other parameters, most notably the fill factor, are constant, we find that for state-of-the-art absorbers, having a broad and strong absorption spectrum, ternary blends offer no advantage over binary ones. For absorbers with a more narrow absorption spectrum ternary blends of donors with complementary absorption spectra, offer modest improvements over binary ones. In contrast, when, upon blending, transport and/or recombination kinetics are improved, leading to an increased fill factor, ternaries may offer significant advantages over binaries.

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  • 5.
    Garcia-Iglesias, Miguel
    et al.
    Eindhoven University of Technology, Netherlands.
    de Waal, Bas F. M.
    Eindhoven University of Technology, Netherlands.
    Gorbunov, Andrey V.
    Eindhoven University of Technology, Netherlands.
    Palmans, Anja R. A.
    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.
    Meijer, E. W.
    Eindhoven University of Technology, Netherlands.
    A Versatile Method for the Preparation of Ferroelectric Supramolecular Materials via Radical End-Functionalization of Vinylidene Fluoride Oligomers2016In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 138, no 19, p. 6217-6223Article in journal (Refereed)
    Abstract [en]

    A synthetic method for the end-functionalization of vinylidene fluoride oligomers (OVDF) via a radical reaction between terminal olefins and I-OVDF is described. The method shows a wide substrate scope and excellent conversions, and permits the preparation of different disc-shaped cores such as benzene-1,3,5-tricarboxamides (BTAs), perylenes bisimide and phthalocyanines (Pc) bearing three to eight ferroelectric oligomers at their periphery. The formation, purity, OVDF conformation, and morphology of the final adducts has been assessed by a combination of techniques, such as NMR, size exclusion chromatography, differential scanning calorimetry, polarized optical microscopy, and atomic force microscopy. Finally, PBI-OVDF and Pc-OVDF materials show ferroelectric hysteresis behavior together with high remnant polarizations, with values as high as P-r approximate to 37 mC/m(2) for Pc-OVDF. This work demonstrates the potential of preparing a new set of ferroelectric materials simply by attaching OVDF oligomers to different small molecules. The use of carefully chosen small molecules paves the way to new functional materials in which ferroelectricity and electrical conductivity or light-harvesting properties coexist in a single compound.

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  • 6.
    Gorbunov, Andrey V.
    et al.
    Eindhoven University of Technology, Netherlands.
    Haedler, Andreas T.
    Eindhoven University of Technology, Netherlands.
    Putzeys, Tristan
    Katholieke University of Leuven, Belgium.
    Zha, R. Helen
    Eindhoven University of Technology, Netherlands.
    Schmidt, Hans-Werner
    University of Bayreuth, Germany.
    Kivala, Milan
    University of Erlangen Nurnberg, Germany.
    Urbanaviciute, Indre
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Wubbenhorst, Michael
    Katholieke University of Leuven, Belgium.
    Meijer, E. W.
    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.
    Switchable Charge Injection Barrier in an Organic Supramolecular Semiconductor2016In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 24, p. 15535-15542Article in journal (Refereed)
    Abstract [en]

    We disclose a supramolecular material that combines semiconducting and dipolar functionalities. The material consists of a discotic semiconducting carbonyl-bridged triarylamine core, which is surrounded by three dipolar amide groups. In thin films, the material self-organizes in a hexagonal columnar fashion through Jr-stacking of the molecular core and hydrogen bonding between the amide groups. Alignment by an electrical field in a simple metal/semiconductor/metal geometry induces a polar order in the interface layers near the metal contacts that can be reversibly switched, while the bulk material remains nonpolarized. On suitably chosen electrodes, the presence of an interfacial polarization field leads to a modulation of the barrier for charge injection into the semiconductor. Consequently, a reversible switching is possible between a high-resistance, injection-limited off-state and a low-resistance, space-charge-limited on-state. The resulting memory diode shows switchable rectification with on/off ratios of up to two orders of magnitude. This demonstrated multifunctionality of a single material is a promising concept toward possible application in lowcost, large-area, nonvolatile organic memories.

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  • 7.
    Howard, Ian A.
    et al.
    Max Planck Institute Polymer Research, Germany .
    Etzold, Fabian
    Max Planck Institute Polymer Research, Mainz, Germany.
    Laquai, Frederic
    Max Planck Institute Polymer Research, Mainz, Germany.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, The Institute of Technology. Eindhoven University of Technology, MB, Netherlands.
    Nonequilibrium Charge Dynamics in Organic Solar Cells2014In: Advanced Energy Materials, ISSN 1614-6832, E-ISSN 1614-6840, Vol. 4, no 9, article id 1301743Article in journal (Refereed)
    Abstract [en]

    The dynamics of charge carriers after their creation at, or near, an interface play a critical role in determining the efficiency of organic solar cells as they dictate, via mechanisms that are not yet fully understood, the pathways for charge separation and recombination. Here, a combination of ultrafast transient spectroscopy and kinetic Monte Carlo simulations based on a minimalistic model are used to examine various aspects of these charge dynamics in a typical donor-acceptor copolymer:methanofullerene blend. The observed rates of charge carrier energetic relaxation and recombination for a sequence of charge densities can be all consistently described in terms of the extended Gaussian disorder model. The physical picture that arises is a) that initial charge motion is highly diffusive and boosted by energetic relaxation in the disordered density of states and b) that mobile charge carriers dissociate from and re-associate into Coulombically associated pairs faster than they recombine, especially at early times. A simple analytical calculation confirms this picture and can be used to identify sub-Langevin recombination as the cause for quantitative deviations between the Monte Carlo calculations and the measured concentration dependence of the charge recombination.

  • 8.
    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.

  • 9.
    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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  • 10.
    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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  • 11.
    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.

  • 12.
    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, 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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  • 13.
    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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  • 14.
    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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  • 15.
    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, 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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  • 16.
    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.

  • 17.
    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 1614-6832, E-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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  • 18.
    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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  • 19.
    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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  • 20.
    Tang, Shi
    et al.
    The Organic Photonics and Electronics Group, Department of Physics, Umeå University, Sweden; LunaLEC AB, Sweden.
    Sandström, Andreas
    The Organic Photonics and Electronics Group, Department of Physics, Umeå University, Sweden; LunaLEC AB, Sweden.
    Lundberg, Petter
    The Organic Photonics and Electronics Group, Department of Physics, Umeå University, Sweden.
    Lanz, Thomas
    The Organic Photonics and Electronics Group, Department of Physics, Umeå University, Sweden.
    Larsen, Christian
    The Organic Photonics and Electronics Group, Department of Physics, Umeå University, Sweden; LunaLEC AB, Sweden.
    van Reenen, Stephan
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Edman, Ludvig
    The Organic Photonics and Electronics Group, Department of Physics, Umeå University, Umeå, SE-901 87, Sweden. L.E.ludvig.edman@umu.se; LunaLEC AB, Linnaeus väg 24, Umeå, SE-901 87, Sweden. L.E.ludvig.edman@umu.se.
    Author Correction: Design rules for light-emitting electrochemical cells delivering bright luminance at 27.5 percent external quantum efficiency2020In: Nature Communications, E-ISSN 2041-1723, Vol. 11, no 1Article in journal (Other academic)
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  • 21.
    Upreti, Tanvi
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering. Centre of Advanced Materials, Heidelberg University, Heidelberg, Germany.
    Wang, Yuming
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering. Centre of Advanced Materials, Heidelberg University, Heidelberg, Germany.
    On the Device Physics of High-Efficiency Ternary Solar Cells2022In: Solar RRL, E-ISSN 2367-198X, Vol. 6, no 11, article id 2200450Article in journal (Refereed)
    Abstract [en]

    Mixing a third compound into the active layer of an organic bulk heterojunction solar cell to form a ternary system has become an established way to improve performance. Various models, based on different assumptions regarding the active layer morphology and the energetics, have been proposed but there is neither consensus on the applicability of the various assumptions to different experimental systems, nor on the actual device physics of these, mostly qualitative, models. Kinetic Monte Carlo simulations are used to investigate the role of morphology and relative energy levels of the constituent materials. By comparing with experimental current–voltage characteristics, a consistent picture arises when the (minority) third compound is predominantly incorporated between the other (majority) compounds and has energy levels that are intermediate to those of the binary host. Even if morphologically imperfect, the resulting energy cascade promotes charge separation and reduces recombination, leading to higher fill factors and short-circuit current densities. The open-circuit voltage sits between that of the binary extremes, in agreement with data from an extensive literature review. This leads to selection criteria for third compounds in terms of energetics and miscibility that promote the formation of a cascade morphology in real and energy space.

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  • 22.
    Urbanaviciute, Indre
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Meng, Xiao
    Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, Eindhoven, The Netherlands .
    Biler, Michal
    Department of Chemistry – BMC, Uppsala University, Uppsala, Sweden.
    Wei, Yingfen
    Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands .
    Cornelissen, Tim D.
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Bhattacharjee, Subham
    Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Linares, Mathieu
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering. Swedish e-Science Research Centre (SeRC), Stockholm, Sweden.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Negative piezoelectric effect in an organic supramolecular ferroelectric2019In: Materials Horizons, ISSN 2051-6347, E-ISSN 2051-6355, Vol. 6, p. 1688-1698Article in journal (Refereed)
    Abstract [en]

    The vast majority of ferroelectric materials demonstrate a positive piezoelectric effect. Theoretically, the negative piezoelectric coefficient d33 could be found in certain classes of ferroelectrics, yet in practice, the number of materials showing linear longitudinal contraction with increasing applied field (d33 < 0) is limited to few ferroelectric polymers. Here, we measure a pronounced negative piezoelectric effect in the family of organic ferroelectric small-molecular BTAs (trialkylbenzene-1,3,5-tricarboxamides), which can be tuned by mesogenic tail substitution and structural disorder. While the large- and small-signal strain in highly-ordered thin-film BTA capacitor devices are dominated by intrinsic contributions and originates from piezostriction, rising disorder introduces additional extrinsic factors that boost the large-signal d33 up to −20 pm V’1 in short-tailed molecules. Interestingly, homologues with longer mesogenic tails show a large-signal electromechanical response that is dominated by the quadratic Maxwell strain with significant mechanical softening upon polarization switching, whereas the small-signal strain remains piezostrictive. Molecular dynamics and DFT calculations both predict a positive d33 for defect-free BTA stacks. Hence, the measured negative macroscopic d33 is attributed to the presence of structural defects that enable the dimensional effect to dominate the piezoelectric response of BTA thin films.

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    Negative piezoelectric effect in an organic supramolecular ferroelectric
  • 23.
    van Breemen, Albert J. J. M.
    et al.
    Holst Centre TNO, Netherlands.
    van der Steen, Jan-Laurens
    Holst Centre TNO, Netherlands.
    van Heck, Geri
    Holst Centre TNO, Netherlands.
    Wang, Rui
    Holst Centre TNO, Netherlands; Eindhoven University of Technology, Netherlands.
    Khikhlovskyi, Vsevolod
    Holst Centre TNO, Netherlands; Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Eindhoven, The Netherlands.
    Gelinck, Gerwin H.
    Holst Centre TNO, Netherlands.
    Crossbar arrays of nonvolatile, rewritable polymer ferroelectric diode memories on plastic substrates2014In: APPLIED PHYSICS EXPRESS, ISSN 1882-0778, Vol. 7, no 3, article id 031602Article in journal (Refereed)
    Abstract [en]

    In this paper, we demonstrate a scalable and low-cost memory technology using a phase separated blend of a ferroelectric polymer and a semiconducting polymer as data storage medium on thin, flexible polyester foils of only 25 mu m thickness. By sandwiching this polymer blend film between rows and columns of metal electrode lines where each intersection makes up one memory cell, we obtained 1 kbit cross bar arrays with bit densities of up to 10 kbit/cm(2). (C) 2014 The Japan Society of Applied Physics

  • 24.
    van Breemen, Albert
    et al.
    Holst Centre/TNO, Eindhoven, The Netherlands.
    Zaba, Tomasz
    Holst Centre/TNO, Eindhoven, The Netherlands.
    Khikhlovskyi, Vsevolod
    Holst Centre/TNO, Eindhoven, The Netherlands; Eindhoven University of Technology, MB, Eindhoven, The Netherlands.
    Michels, Jasper
    Holst Centre/TNO, Eindhoven, The Netherlands.
    Janssen, Rene
    Eindhoven University of Technology, MB, Eindhoven, The Netherlands.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, The Institute of Technology. Eindhoven University of Technology, MB, Eindhoven, The Netherlands.
    Gelinck, Gerwin
    Holst Centre/TNO, Eindhoven, The Netherlands.
    Surface Directed Phase Separation of Semiconductor Ferroelectric Polymer Blends and their Use in Non-Volatile Memories2015In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 25, no 2, p. 278-286Article in journal (Refereed)
    Abstract [en]

    The polymer phase separation of P(VDF-TrFE):F8BT blends is studied in detail. Its morphology is key to the operation and performance of memory diodes. In this study, it is demonstrated that it is possible to direct the semiconducting domains of a phase-separating mixture of P(VDF-TrFE) and F8BT in a thin film into a highly ordered 2D lattice by means of surface directed phase separation. Numerical simulation of the surface-controlled de-mixing process provides insight in the ability of the substrate pattern to direct the phase separation, and hence the regularity of the domain pattern in the final dry blend layer. By optimizing the ratio of the blend components, the number of electrically active semiconductor domains is maximized. Pattern replication on a cm-scale is achieved, and improved functional device performance is demonstrated in the form of a 10-fold increase of the ON-current and a sixfold increase in current modulation. This approach therefore provides a simple and scalable means to higher density integration, the ultimate target being a single semiconducting domain per memory cell.

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  • 25.
    van de Ruit, Kevin
    et al.
    Eindhoven University of Technology, Netherlands.
    Itzhak Cohen, Racheli
    Ben Gurion University of Negev, Israel.
    Bollen, Dirk
    Agfa Gevaert NV, Belgium.
    van Mol, Ton
    Holst Centre TNO, Netherlands.
    Yerushalmi-Rozen, Rachel
    Ben Gurion University of Negev, Israel; Ben Gurion University of Negev, Israel.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Quasi-One Dimensional in-Plane Conductivity in Filamentary Films of PEDOT:PSS2013In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 23, no 46, p. 5778-5786Article in journal (Refereed)
    Abstract [en]

    The mechanism and magnitude of the in-plane conductivity of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) thin fi lms is determined using temperature dependent conductivity measurements for various PEDOT: PSS weight ratios with and without a high boiling solvent (HBS). Without the HBS the in-plane conductivity of PEDOT: PSS is lower and for all studied weight ratios well described by the relation s = s0exp[-T0 T 0.5] with T 0 a characteristic temperature. The exponent 0.5 indicates quasi-one dimensional (quasi-1D) variable range hopping (VRH). The conductivity prefactor s 0 varies over three orders of magnitudes and follows a power law s 0. c 3.5 PEDOT with c PEDOT the weight fraction of PEDOT in PEDOT: PSS. The fi eld dependent conductivity is consistent with quasi-1D VRH. Combined, these observations suggest that conductance takes place via a percolating network of quasi-1D fi laments. Using transmission electron microscopy (TEM) fi lamentary structures are observed in vitrifi ed dispersions and dried fi lms. For PEDOT: PSS fi lms with HBS, the conductivity also exhibits quasi-1D VRH behavior when the temperature is less than 200 K. The low characteristic temperature T 0 indicates that HBStreated fi lms are close to the critical regime between a metal and an insulator. In this case, the conductivity prefactor scales linearly with c PEDOT, indicating the conduction is no longer limited by a percolation of fi laments. The lack of observable changes in TEM upon processing with the HBS suggests that the changes in conductivity are due to a smaller spread in the conductivities of individual fi laments, or a higher probability for neighboring fi laments to be connected rather than being caused by major morphological modifi cation of the material.

  • 26.
    van de Ruit, Kevin
    et al.
    Eindhoven University of Technology, Netherlands.
    Katsouras, Ilias
    University of Groningen, Netherlands.
    Bollen, Dirk
    Agfa Gevaert NV, Belgium.
    van Mol, Ton
    Holst Centre TNO, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    de Leeuw, Dago M.
    Max Planck Institute Polymer Research, Germany.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    The Curious Out-of-Plane Conductivity of PEDOT:PSS2013In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 23, no 46, p. 5787-5793Article in journal (Refereed)
    Abstract [en]

    For its application as transparent conductor in light-emitting diodes and photovoltaic cells, both the in-plane and out-of-plane conductivity of PEDOT:PSS are important. However, studies into the conductivity of PEDOT:PSS rarely address the out-of-plane conductivity and those that do, report widely varying results. Here a systematic study of the out-of-plane charge transport in thin films of PEDOT:PSS with varying PSS content is presented. To this end, the PEDOT:PSS is enclosed in small interconnects between metallic contacts. An unexpected, but strong dependence of the conductivity on interconnect diameter is observed for PEDOT:PSS formulations without high boiling solvent. The change in conductivity correlates with a diameter dependent change in PEDOT:PSS layer thickness. It is suggested that the order of magnitude variation in out-of-plane conductivity with only a 3-4-fold layer thickness variation can quantitatively be explained on basis of a percolating cluster model.

  • 27.
    van Reenen, S.
    et al.
    Eindhoven University of Technology, Netherlands.
    Scheepers, M.
    Eindhoven University of Technology, Netherlands.
    van de Ruit, K.
    Eindhoven University of Technology, Netherlands.
    Bollen, D.
    Agfa Gevaert NV, Belgium.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, The Institute of Technology.
    Explaining the effects of processing on the electrical properties of PEDOT:PSS2014In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 15, no 12, p. 3710-3714Article in journal (Refereed)
    Abstract [en]

    By simultaneously measuring the Seebeck coefficient and the conductivity in differently processed PEDOT:PSS films, fundamental understanding is gained on how commonly used processing methods improve the conductivity of PEDOT:PSS. Use of a high boiling solvent (HBS) enhances the conductivity by 3 orders of magnitude, as is well-known. Simultaneously, the Seebeck coefficient S remains largely unaffected, which is shown to imply that the conductivity is improved by enhanced connectivity between PEDOT-rich filaments within the film, rather than by improved conductivity of the separate PEDOT filaments. Post-treatment of PEDOT: PSS films by washing with H2SO4 leads to a similarly enhanced conductivity and a significant reduction in the layer thickness. This reduction strikingly corresponds to the initial PSS ratio in the PEDOT:PSS films, which suggests removal and replacement of PSS in PEDOT:PSS by HSO4- or SO42- after washing. Like for the HBS treatment, this improves the connectivity between PEDOT filaments. Depending on whether the H2SO4 treatment is or is not preceded by an HBS treatment also the intra-filament transport is affected. We show that by characterization of S and sigma it is possible to obtain more fundamental understanding of the effects of processing on the (thermo) electrical characteristics of PEDOT:PSS.

  • 28.
    van Reenen, S.
    et al.
    Eindhoven University of Technology, The Netherlands.
    Vitorino, M.V.
    Eindhoven University of Technology, The Netherlands; University of Lisbon, Portugal .
    Meskers, S.C.J.
    Eindhoven University of Technology, The Netherlands.
    Janssen, R.A.J.
    Eindhoven University of Technology, The Netherlands.
    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.
    Photoluminescence quenching in films of conjugated polymers by electrochemical doping2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 20, p. 205206-Article in journal (Refereed)
    Abstract [en]

    An important loss mechanism in organic electroluminescent devices is exciton quenching by polarons. Gradual electrochemical doping of various conjugated polymer films enabled the determination of the doping density dependence of photoluminescence quenching. Electrochemical doping was achieved by contacting the film with a solid electrochemical gate and an injecting contact. A sharp reduction in photoluminescence was observed for doping densities between 1018 and 1019 cm(-3). The doping density dependence is quantitatively modeled by exciton diffusion in a homogeneous density of polarons followed by either F "orster resonance energy transfer or charge transfer. Both mechanisms need to be considered to describe polaron-induced exciton quenching. Thus, to reduce exciton-polaron quenching in organic optoelectronic devices, both mechanisms must be prevented by reducing the exciton diffusion, the spectral overlap, the doping density, or a combination thereof.

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  • 29.
    van Reenen, Stephan
    et al.
    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, The Institute of Technology. Eindhoven University of Technology, Netherlands.
    Fundamental Tradeoff between Emission Intensity and Efficiency in Light-Emitting Electrochemical Cells2015In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 25, no 20, p. 3066-3073Article in journal (Refereed)
    Abstract [en]

    The characteristic doping process in polymer light-emitting electrochemical cells (LECs) causes a tradeoff between luminescence intensity and efficiency. Experiments and numerical modeling on thin film polymer LECs show that, on the one hand, carrier injection and transport benefit from electrochemical doping, leading to increased electron-hole recombination. On the other hand, the radiative recombination efficiency is reduced by exciton quenching by polarons involved in the doping. Consequently, the quasi-steady-state luminescent efficiency decreases with increasing ion concentration. The transient of the luminescent efficiency shows a characteristic roll-off while the current continuously increases, attributed to ongoing electrochemical doping and the associated exciton quenching. Both effects can be modeled by exciton polaron-quenching via diffusion-assisted Forster resonance energy transfer. These results indicate that the tradeoff between efficiency and intensity is fundamental, suggesting that the application realm of future LECs should be sought in high-brightness, low-production cost devices, rather than in high-efficiency devices.

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  • 30.
    van Reenen, Stephan
    et al.
    Eindhoven University of Technology, The Netherlands.
    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.
    Correcting for contact geometry in Seebeck coefficient measurements of thin film devices2014In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 15, no 10, p. 2250-2255Article in journal (Refereed)
    Abstract [en]

    Driven by promising recent results, there has been a revived interest in the thermoelectric properties of organic (semi) conductors. Concomitantly, there is a need to probe the Seebeck coefficient S of modestly conducting materials in thin film geometry. Here we show that geometries that seem desirable from a signal-to-noise perspective may induce systematic errors in the measured value of S, S-m, by a factor 3 or more. The enhancement of S-m by the device geometry is related to competing conduction paths outside the region between the electrodes. We derive a universal scaling curve that allows correcting for this and show that structuring the semiconductor is not needed for the optimal electrode configuration, being a set of narrow, parallel strips.

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  • 31.
    van Reenen, Stephan
    et al.
    University of Oxford, England.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Snaith, Henry J.
    University of Oxford, England.
    Modeling Anomalous Hysteresis in Perovskite Solar Cells2015In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 6, no 19, p. 3808-3814Article in journal (Refereed)
    Abstract [en]

    Organic inorganic lead halide perovskites are distinct from most other semiconductors because they exhibit characteristics of both electronic and ionic motion. Accurate understanding of the optoelectronic impact of such properties is important to fully optimize devices and be aware of any limitations of perovskite solar cells and broader optoelectronic devices. Here we use a numerical drift-diffusion model to describe device operation of perovskite solar cells. To achieve hysteresis in the modeled current voltage characteristics, we must include both ion migration and electronic charge traps, serving as recombination centers. Trapped electronic charges recombine with oppositely charged free electronic carriers, of which the density depends on the bias-dependent ion distribution in the perovskite. Our results therefore show that reduction of either the density of mobile ionic species or carrier trapping at the perovskite interface will remove the adverse hysteresis in perovskite solar cells. This gives a clear target for ongoing research effort and unifies previously conflicting experimental observations and theories.

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  • 32.
    van Reenen, Stephan
    et al.
    Eindhoven University of Technology, Netherlands.
    Kouijzer, Sandra
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands; Eindhoven University of Technology, Netherlands.
    Wienk, Martijn M.
    Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, The Institute of Technology. Eindhoven University of Technology, Netherlands.
    Origin of Work Function Modification by Ionic and Amine-Based Interface Layers2014In: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 1, no 8, p. 1400189-Article in journal (Refereed)
    Abstract [en]

    Work function modification by polyelectrolytes and tertiary aliphatic amines is found to be due to the formation of a net dipole at the electrode interface, induced by interaction with its own image dipole in the electrode. In polyelectrolytes differences in size and side groups between the moving ions lead to differences in approach distance towards the surface. These differences determine magnitude and direction of the resulting dipole. In tertiary aliphatic amines the lone pairs of electrons are anticipated to shift towards their image when close to the interface rather than the nitrogen nuclei, which are sterically hindered by the alkyl side chains. Data supporting this model is from scanning Kelvin probe microscopy, used to determine the work function modification by thin layers of such materials on different substrates. Both reductions and increases in work function by different materials are found to follow a general mechanism. Work function modification is found to only take place when the work function modification layer (WML) is deposited on conductors or semiconductors. On insulators no effect is observed. Additionally, the work function modification is independent of the WML thickness or the substrate work function in the range of 3 to 5 eV. Based on these results charge transfer, doping, and spontaneous dipole orientation are excluded as possible mechanisms. This understanding of the work function modification by polyelectrolytes and amines facilitates design of new air-stable and solution-processable WMLs for organic electronics.

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  • 33.
    Xu, Kai
    et al.
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering. Yanshan Univ, Peoples R China.
    Ruoko, Tero-Petri
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering. Tampere Univ, Finland.
    Shokrani, Morteza
    Heidelberg Univ, Germany.
    Scheunemann, Dorothea
    Heidelberg Univ, Germany.
    Abdalla, Hassan
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Sun, Hengda
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering. Donghua Univ, Peoples R China.
    Yang, Chiyuan
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Puttisong, Yuttapoom
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Kolhe, Nagesh B.
    Univ Washington, WA 98195 USA; Univ Washington, WA 98195 USA.
    Mendoza Figueroa, Silvestre
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Oshaug Pedersen, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Ederth, Thomas
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. 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. N Ink AB, Teknikringen 7, SE-58330 Linkoping, Sweden.
    Jenekhe, Samson A.
    Univ Washington, WA 98195 USA; Univ Washington, WA 98195 USA.
    Fazzi, Daniele
    Univ Bologna, Italy; Univ Cologne, Germany.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering. Heidelberg Univ, Germany.
    Fabiano, Simone
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering. N Ink AB, Teknikringen 7, SE-58330 Linkoping, Sweden.
    On the Origin of Seebeck Coefficient Inversion in Highly Doped Conducting Polymers2022In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 32, no 20, article id 2112276Article in journal (Refereed)
    Abstract [en]

    A common way of determining the majority charge carriers of pristine and doped semiconducting polymers is to measure the sign of the Seebeck coefficient. However, a polarity change of the Seebeck coefficient has recently been observed to occur in highly doped polymers. Here, it is shown that the Seebeck coefficient inversion is the result of the density of states filling and opening of a hard Coulomb gap around the Fermi energy at high doping levels. Electrochemical n-doping is used to induce high carrier density (&gt;1 charge/monomer) in the model system poly(benzimidazobenzophenanthroline) (BBL). By combining conductivity and Seebeck coefficient measurements with in situ electron paramagnetic resonance, UV-vis-NIR, Raman spectroelectrochemistry, density functional theory calculations, and kinetic Monte Carlo simulations, the formation of multiply charged species and the opening of a hard Coulomb gap in the density of states, which is responsible for the Seebeck coefficient inversion and drop in electrical conductivity, are uncovered. The findings provide a simple picture that clarifies the roles of energetic disorder and Coulomb interactions in highly doped polymers and have implications for the molecular design of next-generation conjugated polymers.

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  • 34.
    Zapata-Arteaga, Osnat
    et al.
    ICMAB CSIC, Spain.
    Marina, Sara
    POLYMAT, Spain; Univ Basque Country, Spain.
    Zuo, Guangzheng
    Univ Potsdam, Germany.
    Xu, Kai
    ICMAB CSIC, Spain.
    Dorling, Bernhard
    ICMAB CSIC, Spain.
    Alberto Perez, Luis
    ICMAB CSIC, Spain.
    Sebastian Reparaz, Juan
    ICMAB CSIC, Spain.
    Martin, Jaime
    POLYMAT, Spain; Univ Basque Country, Spain; Univ A Coruna, Spain; Basque Fdn Sci, Spain.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering. Heidelberg Univ, Germany.
    Campoy-Quiles, Mariano
    ICMAB CSIC, Spain.
    Design Rules for Polymer Blends with High Thermoelectric Performance2022In: Advanced Energy Materials, ISSN 1614-6832, E-ISSN 1614-6840, Vol. 12, no 19, article id 2104076Article in journal (Refereed)
    Abstract [en]

    A combinatorial study of the effect of in-mixing of various guests on the thermoelectric properties of the host workhorse polymer poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT) is presented. Specifically, the composition and thickness for doped films of PBTTT blended with different polymers are varied. Some blends at guest weight fractions around 10-15% exhibit up to a fivefold increase in power factor compared to the reference material, leading to zT values around 0.1. Spectroscopic analysis of the charge-transfer species, structural characterization using grazing-incidence wide-angle X-ray scattering, differential scanning calorimetry, Raman, and atomic force microscopy, and Monte Carlo simulations are employed to determine that the key to improved performance is for the guest to promote long-range electrical connectivity and low disorder, together with similar highest occupied molecular orbital levels for both materials in order to ensure electronic connectivity are combined.

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  • 35.
    Zuo, Guangzheng
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Abdalla, Hassan
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. 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.
    Impact of doping on the density of states and the mobility in organic semiconductors2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 23, p. 235203-Article in journal (Refereed)
    Abstract [en]

    We experimentally investigated conductivity and mobility of poly(3-hexylthiophene) (P3HT) doped with tetrafluorotetracyanoquinodimethane (F(4)TCNQ) for various relative doping concentrations ranging from ultralow (10(-5)) to high (10(-1)) and various active layer thicknesses. Although the measured conductivity monotonously increases with increasing doping concentration, the mobilities decrease, in agreement with previously published work. Additionally, we developed a simple yet quantitative model to rationalize the results on basis of a modification of the density of states (DOS) by the Coulomb potentials of ionized dopants. The DOS was integrated in a three-dimensional (3D) hopping formalism in which parameters such as energetic disorder, intersite distance, energy level difference, and temperature were varied. We compared predictions of our model as well as those of a previously developed model to kinetic Monte Carlo (MC) modeling and found that only the former model accurately reproduces the mobility of MC modeling in a large part of the parameter space. Importantly, both our model and MC simulations are in good agreement with experiments; the crucial ingredient to both is the formation of a deep trap tail in the Gaussian DOS with increasing doping concentration.

  • 36.
    Zuo, Guangzheng
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Andersson, Olof
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Abdalla, Hassan
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. 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.
    High thermoelectric power factor from multilayer solution-processed organic films2018In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, no 8, article id 083303Article in journal (Refereed)
    Abstract [en]

    We investigate the suitability of the "sequential doping" method of organic semiconductors for thermoelectric applications. The method consists of depositing a dopant (F4TCNQ) containing solution on a previously cast semiconductor (P3HT) thin film to achieve high conductivity, while preserving the morphology. For very thin films (similar to 25 nm), we achieve a high power factor around 8 mu W/mK(-2) with a conductivity over 500 S/m. For the increasing film thickness, conductivity and power factor show a decreasing trend, which we attribute to the inability to dope the deeper parts of the film. Since thick films are required to extract significant power from thermoelectric generators, we developed a simple additive technique that allows the deposition of an arbitrary number of layers without significant loss in conductivity or power factor that, for 5 subsequent layers, remain at similar to 300 S/m and similar to 5 mu W/mK(-2), respectively, whereas the power output increases almost one order of magnitude as compared to a single layer. The efficient doping in multilayers is further confirmed by an increased intensity of (bi)polaronic features in the UV-Vis spectra. Published by AIP Publishing.

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  • 37.
    Zuo, Guangzheng
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Li, Zhaojun
    Chalmers University of Technology, Sweden.
    Wang, Ergang
    Chalmers University of Technology, Sweden.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    High Seebeck Coefficient and Power Factor in n-Type Organic Thermoelectrics2018In: Advanced Electronic Materials, E-ISSN 2199-160X, Vol. 4, no 1, article id 1700501Article in journal (Refereed)
    Abstract [en]

    The n-type thermoelectric properties of [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) are investigated for different solution-based doping methods. A novel inverse-sequential doping method where the semiconductor (PCBM) is deposited on a previously cast dopant 4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)-N,N-diphenylaniline film to achieve a very high power factor PF approximate to 35 mu W m(-1) K-2 with a conductivity sigma approximate to 40 S m(-1) is introduced. It is also shown that n-type organic semiconductors obey the -1/4 power law relation between Seebeck coefficient S and sigma that are previously found for p-type materials. An analytical model on basis of variable range hopping unifies these results. The power law for n-type materials is shifted toward higher conductivities by two orders of magnitude with respect to that of p-type, suggesting strongly that n-type organic semiconductors can eventually become superior to their p-type counterparts. Adding a small fraction lower lowest unoccupied molecular orbital material (core-cyanated naphthalene diimide) into PCBM leads to a higher S for inverse-sequential doping but not for bulk doping due to different morphologies.

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  • 38.
    Zuo, Guangzheng
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. 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.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. 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.
    High Seebeck Coefficient in Mixtures of Conjugated Polymers2018In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 28, no 15, article id 1703280Article in journal (Refereed)
    Abstract [en]

    A universal method to obtain record?high electronic Seebeck coefficients is demonstrated while preserving reasonable conductivities in doped blends of organic semiconductors through rational design of the density of states (DOSs). A polymer semiconductor with a shallow highest occupied molecular orbital (HOMO) level?poly(3?hexylthiophene) (P3HT) is mixed with materials with a deeper HOMO (PTB7, TQ1) to form binary blends of the type P3HTx:B1?x (0 ≤ x ≤ 1) that is p?type doped by F4TCNQ. For B = PTB7, a Seebeck coefficient S = 1100 µV K?1 with conductivity σ = 0.3 S m?1 at x = 0.10 is achieved, while for B = TQ1, S = 2000 µV K?1 and σ = 0.03 S m?1 at x = 0.05 is found. Kinetic Monte Carlo simulations with parameters based on experiments show good agreement with the experimental results, confirming the intended mechanism. The simulations are used to derive a design rule for parameter tuning. These results can become relevant for low?power, low?cost applications like (providing power to) autonomous sensors, in which a high Seebeck coefficient translates directly to a proportionally reduced number of legs in the thermogenerator, and hence in reduced fabrication cost and complexity.

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