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Advanced Materials 12/2004; 16(23‐24):2174 - 2179. · 13.88 Impact Factor
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ABSTRACT: A systematic study of the hole mobility in hole-only diodes and field-effect transistors based on poly(2-methoxy-5-(3('),7(')-dimethyloctyloxy)-p-phenylene vinylene) and on amorphous poly(3-hexyl thiophene) has been performed as a function of temperature and applied bias. The experimental hole mobilities extracted from both types of devices, although based on a single polymeric semiconductor, can differ by 3 orders of magnitude. We demonstrate that this apparent discrepancy originates from the strong dependence of the hole mobility on the charge carrier density in disordered semiconducting polymers.
Physical Review Letters 12/2003; 91(21):216601. · 7.37 Impact Factor
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ABSTRACT: There is ample evidence that organic field-effect transistors have reached a stage where they can be industrialized, analogous to standard metal oxide semiconductor (MOS) transistors. Monocrystalline silicon technology is largely based on complementary MOS (CMOS) structures that use both n-type and p-type transistor channels. This complementary technology has enabled the construction of digital circuits, which operate with a high robustness, low power dissipation and a good noise margin. For the design of efficient organic integrated circuits, there is an urgent need for complementary technology, where both n-type and p-type transistor operation is realized in a single layer, while maintaining the attractiveness of easy solution processing. We demonstrate, by using solution-processed field-effect transistors, that hole transport and electron transport are both generic properties of organic semiconductors. This ambipolar transport is observed in polymers based on interpenetrating networks as well as in narrow bandgap organic semiconductors. We combine the organic ambipolar transistors into functional CMOS-like inverters.
Nature Material 11/2003; 2(10):678-82. · 32.84 Impact Factor
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ABSTRACT: Electronics based on organic transistors is steadily progressing towards higher levels of integration and better performance. In this work we discussed the operation of organic field-effect transistors and the charge transport properties of organic conjugated semiconductors. We also presented a simple analysis of some basic building blocks used in organic digital electronics, focusing on the relation between device and circuit performance. An overview of the main applications and of the state of the art of organic integrated circuits concluded the paper.
Solid-State Circuits Conference, 2003. ESSCIRC '03. Proceedings of the 29th European; 10/2003
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ABSTRACT: The scaling behavior of the transfer characteristics of solution-processed disordered organic thin-film transistors with channel length is investigated. This is done for a variety of organic semiconductors in combination with gold injecting electrodes. From the channel-length dependence of the transistor resistance in the conducting ON-state, we determine the field-effect mobility and the parasitic series resistance. The extracted parasitic resistance, typically in the MΩ range, depends on the applied gate voltage, and we find experimentally that the parasitic resistance decreases with increasing field-effect mobility. © 2003 American Institute of Physics.
Applied Physics Letters 06/2003; 82(25):4576-4578. · 3.84 Impact Factor
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ABSTRACT: We demonstrate that, by using a concentric device geometry, the dopant density and the bulk charge-carrier mobility can simultaneously be estimated from the transfer characteristics of a single disordered organic transistor. The technique has been applied to determine the relation between the mobility and the charge density in solution-processed poly(2,5-thienylene vinylene) and poly(3-hexyl thiophene) thin-film field-effect transistors. The observation that doping due to air exposure takes place already in the dark, demonstrates that photoinduced oxygen doping is not the complete picture. © 2003 American Institute of Physics.
Journal of Applied Physics 04/2003; 93(8):4831-4835. · 2.17 Impact Factor
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ABSTRACT: The switch-on voltage for disordered organic field-effect transistors is defined as the flatband voltage, and is used as a characterization parameter. The transfer characteristics of the solution processed organic semiconductors pentacene, poly(2,5-thienylene vinylene) and poly(3-hexyl thiophene) are modeled as a function of temperature and gate voltage with a hopping model in an exponential density of states. The data can be described with reasonable values for the switch-on voltage, which is independent of temperature. This result also demonstrates that the large threshold voltage shifts as a function of temperature reported in the literature constitute a fit parameter without a clear physical basis. © 2002 American Institute of Physics.
Applied Physics Letters 06/2002; · 3.84 Impact Factor
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ABSTRACT: Metal–insulator–semiconductor diodes with poly(3-hexyl thiophene) as the semiconductor were characterized with impedance spectroscopy as a function of bias, frequency, and temperature. We show that the standard Mott–Schottky analysis gives unrealistic values for the dopant density in the semiconductor. From modeling of the data, we find that this is caused by the relaxation time of the semiconductor, which increases rapidly with decreasing temperature due to the thermally activated conductivity of the poly(3-hexyl thiophene). © 2001 American Institute of Physics.
Applied Physics Letters 06/2001; 78(24):3902-3904. · 3.84 Impact Factor
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ABSTRACT: We have measured and analyzed the temperature and gate voltage dependencies of the field-effect mobility in organic thin-film transistors. We find that the mobility prefactor increases exponentially with the activation energy in agreement with the Meyer–Neldel rule. This behavior is demonstrated in the mobility data of solution-processed pentacene, poly(2,5-thienylene vinylene) and in mobility data reported in literature. Surprisingly, the characteristic Meyer–Neldel energy for all analyzed materials is close to 40 meV. Possible implications for the charge transport mechanism in these materials are discussed. © 2000 American Institute of Physics.
Applied Physics Letters 06/2000; 76(23):3433-3435. · 3.84 Impact Factor
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ABSTRACT: We demonstrate that charge-transport in partially-ordered thin films of poly(3- hexylthiophene) is strongly dependent on the charge-carrier density in the film, which we relate to the localized nature of the charge carriers. We base our conclusions on measurements in which the charge-carrier density is varied by electrostatic means (in a transistor geometry) and by in- situ thermal removal of oxygen dopants. For the doping levels investigated, we argue that the removal of oxygen does not induce structural changes in the conjugated polymer, and that it only shifts the Fermi-level of the film.
MRS Proceedings. 12/1999; 660.
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ABSTRACT: The kinetics of acid doping of the semiconductor regioregular poly-3-hexylthiophene with vaporized chlorosilane have been investigated using field-effect transistors. The dopant density has been derived as a function of temperature and exposure time from the shift in the pinch-off voltage, being the gate bias where current starts to flow. The doping kinetics are perfectly described by empirical stretched exponential time dependence with a saturation dopant density of 1±0.5×10^26 m−3 and a thermally activated relaxation time. We show that a similar relationship holds for previously reported kinetics of poly-thienylene-vinylene doped with molecular oxygen.
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ABSTRACT: We have investigated the field dependence of the in-plane conductivity in poly(2,5-thienylene vinylene) thin films. The conductivity is found to have a square root dependence on the lateral electric field with values of the activation energy, Δ=0.46 eV, B=2.3·10-5 eV(m/V)^½ and the characteristic temperature T0=5.2·10^2 K. A similar value (T0=4.9·10^2 K) is found for the isokinetic temperature in Meyer-Neldel experiments on poly(2,5-thienylene vinylene) field-effect transistors. Based on these results, we argue that entropy changes due to hopping of charge carriers should be incorporated in theoretical descriptions of the field dependent mobility in disordered organic semiconductors.
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ABSTRACT: We have measured and analyzed the temperature and gate voltage dependencies of the field-effect mobility in organic thin-film transistors. We find that the mobility prefactor increases exponentially with the activation energy in agreement with the Meyer–Neldel rule. This behavior is demonstrated in the mobility data of solution-processed pentacene, poly(2,5-thienylene vinylene) and in mobility data reported in literature. Surprisingly, the characteristic Meyer–Neldel energy for all analyzed materials is close to 40 meV. Possible implications for the charge transport mechanism in these materials are discussed.
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[show abstract]
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ABSTRACT: We demonstrate that, by using a concentric device geometry, the dopant density and the bulk charge-carrier mobility can simultaneously be estimated from the transfer characteristics of a single disordered organic transistor. The technique has been applied to determine the relation between the mobility and the charge density in solution-processed poly(2,5-thienylene vinylene) and poly(3-hexyl thiophene) thin-film field-effect transistors. The observation that doping due to air exposure takes place already in the dark, demonstrates that photoinduced oxygen doping is not the complete picture.
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ABSTRACT: The hole transport in various poly(p-phenylene vinylene) (PPV) derivatives has been investigated in field-effect transistors (FETs) and light-emitting diodes (LEDs) as a function of temperature and applied bias. The discrepancy between the experimental hole mobilities extracted from FETs and LEDs based on a single disordered polymeric semiconductor originates from the strong dependence of the hole mobility on the charge carrier density. The microscopic charge transport parameters are directly related to the chemical composition of the analysed polymers. By chemically modifying the PPV, the hole mobility in both FETs and LEDs can be changed by orders of magnitude. For highly disordered PPVs it is demonstrated that the exponential density of states (DOS), which is used to describe the charge transport in FETs, is a good approximation of the tail states of the Gaussian DOS, which describes the charge transport in LEDs. Increase of the directional order in the PPV film enhances the mobility but also induces a strong anisotropy in the charge transport, thereby obscuring a direct comparison between sandwich and field-effect devices.
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ABSTRACT: Capacitance–voltage (C–V) characteristics of metal–insulator–semiconductor (MIS) diodes with poly(3-hexylthiophene) (P3HT) as p-type semiconductor were investigated as function of time, ambient, and illumination. P3HT is only stable under illumination with light in vacuum, while in the presence of oxygen it needs to be placed in the dark. P3HT is rapidly doped upon exposure to both oxygen and light. Temporal changes in acceptor density profiles were determined by using Mott–Schottky analysis of the capacitance–voltage (C−V) characteristics. The profiles were determined to be constant over the P3HT film thickness. Wavelength dependent photoimpedance measurements show that the acceptor creation efficiency peaks upon excitation of the molecular oxygen–polythiophene contact charge transfer complex at (1.9±0.1) eV.
Synthetic Metals.
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ABSTRACT: The switch-on voltage for disordered organic field-effect transistors is defined as the flatband voltage, and is used as a characterization parameter. The transfer characteristics of the solution processed organic semiconductors pentacene, poly(2,5-thienylene vinylene) and poly(3-hexyl thiophene) are modeled as a function of temperature and gate voltage with a hopping model in an exponential density of states. The data can be described with reasonable values for the switch-on voltage, which is independent of temperature. This result also demonstrates that the large threshold voltage shifts as a function of temperature reported in the literature constitute a fit parameter without a clear physical basis.
Applied Physics Letters, 80 (20), 2002 ; doi:10.1063/1.1479210.
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ABSTRACT: The scaling behavior of the transfer characteristics of solution-processed disordered organic thin-film transistors with channel length is investigated. This is done for a variety of organic semiconductors in combination with gold injecting electrodes. From the channel-length dependence of the transistor resistance in the conducting ON-state, we determine the field-effect mobility and the parasitic series resistance. The extracted parasitic resistance, typically in the MΩ range, depends on the applied gate voltage, and we find experimentally that the parasitic resistance decreases with increasing field-effect mobility.
Applied Physics Letters, 82 (25), 2003 ; doi:10.1063/1.1581389.
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ABSTRACT: Metal–insulator–semiconductor diodes with poly(3-hexyl thiophene) as the semiconductor were characterized with impedance spectroscopy as a function of bias, frequency, and temperature. We show that the standard Mott–Schottky analysis gives unrealistic values for the dopant density in the semiconductor. From modeling of the data, we find that this is caused by the relaxation time of the semiconductor, which increases rapidly with decreasing temperature due to the thermally activated conductivity of the poly(3-hexyl thiophene).
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ABSTRACT: In conventional field-effect transistors, the extracted mobility does not take into account the distribution of charge carriers. However, in disordered organic field-effect transistors, the local charge carrier mobility decreases from the semiconductor/insulator interface into the bulk, due to its dependence on the charge carrier density. It is demonstrated that the conventional field-effect mobility is a good approximation for the local mobility of the charge carriers at the interface.
Organic Electronics.
