Publications (19)171.32 Total impact
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Article: Photophysics of self-assembled monolayers of a π-conjugated quinquethiophene derivative.
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ABSTRACT: The photophysics of fully and partially covered self-assembled monolayers (SAMs) of a quinquethiophene (5T) derivative have been investigated. The monolayers behave as H-aggregates. The fluorescence of fully covered SAMs is weak and red-shifted, and the extinction is blue-shifted as compared to that of single molecules. The fluorescence of partially covered SAMs is dominated by that of single molecules on the surface. The extinction spectra are similar for fully and partially covered monolayers, which show that even the smallest islands are H-aggregates. The extinction spectra furthermore closely resemble those for 5T single crystals, which demonstrates that in oligothiophene crystals the intermolecular interactions within one layer molecules are stronger than the interlayer electronic coupling.The Journal of Physical Chemistry A 06/2012; 116(29):7645-50. · 2.95 Impact Factor -
Article: Operational stability of organic field-effect transistors.
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ABSTRACT: Organic field-effect transistors (OFETs) are considered in technological applications for which low cost or mechanical flexibility are crucial factors. The environmental stability of the organic semiconductors used in OFETs has improved to a level that is now sufficient for commercialization. However, serious problems remain with the stability of OFETs under operation. The causes for this have remained elusive for many years. Surface potentiometry together with theoretical modeling provide new insights into the mechanisms limiting the operational stability. These indicate that redox reactions involving water are involved in an exchange of mobile charges in the semiconductor with protons in the gate dielectric. This mechanism elucidates the established key role of water and leads in a natural way to a universal "stress function", describing the stretched exponential-like time dependence ubiquitously observed. Further study is needed to determine the generality of the mechanism and the role of other mechanisms.Advanced Materials 03/2012; 24(9):1146-58. · 13.88 Impact Factor -
Article: Microstructure and Phase Behavior of a Quinquethiophene-Based Self-Assembled Monolayer as a Function of Temperature
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ABSTRACT: The self-assembly of monolayers is a highly promising approach in organic electronics but most systems show weak device performances probably due to a lack of long range order of the molecules. The present self assembled monolayer is formed by a molecule which consists of a dimethylchlorosilyl group combined with a quinquethiophene unit through an undecane spacer. This system is the first reported self assembled monolayer on silicon oxide surfaces which forms two-dimensional crystals. A detailed structural solution is presented based on grazing incidence x-ray scattering experiments and theoretical packing analysis. By transverse shear microscopy the shape and size of the crystallites are determined - polygonal shapes of lateral size of several µm are observed. In-situ temperature studies reveal gradual changes of the molecular packing which are irreversible. Melting of the crystal structure is found at 520 K, while the self assembled monolayer remains stable up to 620 K. This work presents unknown structural properties of a self assembled monolayer revealing insights into layer formation and irreversible evolution by temperature treatment. The self-assembly of monolayers is a highly promising approach in organic electronics but most systems show weak device performances probably due to a lack of long range order of the molecules. The present self assembled monolayer is formed by a molecule which consists of a dimethylchlorosilyl group combined with a quinquethiophene unit through an undecane spacer. This system is the first reported self assembled monolayer on silicon oxide surfaces which forms two-dimensional crystals. A detailed structural solution is presented based on grazing incidence x-ray scattering experiments and theoretical packing analysis. By transverse shear microscopy the shape and size of the crystallites are determined - polygonal shapes of lateral size of several µm are observed. In-situ temperature studies reveal gradual changes of the molecular packing which are irreversible. Melting of the crystal structure is found at 520 K, while the self assembled monolayer remains stable up to 620 K. This work presents unknown structural properties of a self assembled monolayer revealing insights into layer formation and irreversible evolution by temperature treatment.The Journal of Physical Chemistry C 10/2011; 115(46):22925-22930. · 4.80 Impact Factor -
Article: Revealing buried interfaces to understand the origins of threshold voltage shifts in organic field-effect transistors.
Advanced Materials 12/2010; 22(45):5105-9. · 13.88 Impact Factor -
Article: Efficient solar cells based on an easily accessible diketopyrrolopyrrole polymer.
Advanced Materials 09/2010; 22(35):E242-6. · 13.88 Impact Factor -
Article: Synthesis of Monochlorosilyl Derivatives of Dialkyloligothiophenes for Self-Assembling Monolayer Field-Effect Transistors
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ABSTRACT: Unsymmetrical dimethylchlorosilyl-substituted α,α'-dialkylquater-, quinque-, and sexithiophenes were designed and successfully synthesized by a combination of Kumada and Suzuki cross-coupling reactions followed by hydrosilylation. Optimization possibilities of the hydrosilylation of low-soluble linear oligothiophenes by dimethylchlorosilane as well as the nonreactive byproducts formed are described. The molecular structures of the obtained dimethylchlorosilyl-functionalized oligothiophenes were proven by NMR and DCI MS techniques. These compounds were found to be stable and reactive enough, even in the presence of the nonreactive byproducts, to form semiconducting monolayers on dielectric hydroxylated SiO2 surfaces by self-assembly from solution. The semiconducting properties of these oligothiophene SAMs were as good as those of bulk oligothiophenes. This allowed the production of stable, even under ambient conditions, SAMFETs with a mobility of up to 0.04 cm2/(V s) and an on/off ratio up to 1 × 10^8.Organometallics 09/2010; 29(19):4213–4226. · 3.96 Impact Factor -
Article: Ordered semiconducting self-assembled monolayers on polymeric surfaces utilized in organic integrated circuits.
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ABSTRACT: We report on a two-dimensional highly ordered self-assembled monolayer (SAM) directly grown on a bare polymer surface. Semiconducting SAMs are utilized in field-effect transistors and combined into integrated circuits as 4-bit code generators. The driving force to form highly ordered SAMs is packing of the liquid crystalline molecules caused by the interactions between the linear alkane moieties and the pi-pi stacking of the conjugated thiophene units. The fully functional circuits demonstrate long-range order over large areas, which can be regarded as the start of flexible monolayer electronics.Nano Letters 06/2010; 10(6):1998-2002. · 13.20 Impact Factor -
Article: Gas sensing with self-assembled monolayer field-effect transistors
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ABSTRACT: A new sensitive gas sensor based on a self-assembled monolayer field-effect transistor (SAMFET) was used to detect the biomarker nitric oxide. A SAMFET based sensor is highly sensitive because the analyte and the active channel are separated by only one monolayer. SAMFETs were functionalised for direct NO detection using iron porphyrin as a specific receptor. Upon exposure to NO a threshold voltage shift towards positive gate biases was observed. The sensor response was examined as a function of NO concentration. High sensitivity has been demonstrated by detection of ppb concentrations of NO. Preliminary measurements have been performed to determine the selectivity.Organic Electronics 02/2010; 11(5):895-898. · 4.05 Impact Factor -
Article: Poly(diketopyrrolopyrrole-terthiophene) for ambipolar logic and photovoltaics.
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ABSTRACT: A new semiconducting polymer, PDPP3T, with alternating diketopyrrolopyrrole and terthiophene units is presented. PDPP3T has a small band gap of 1.3 eV and exhibits nearly balanced hole and electron mobilities of 0.04 and 0.01 cm(2) V(-1) s(-1), respectively, in field-effect transistors (FETs). By the combination of two identical ambipolar transistors, an inverter was constructed that exhibits a gain of approximately 30. When PDPP3T was combined with [60]PCBM or [70]PCBM in a 1:2 weight ratio, photovoltaic cells were made that provide a photoresponse up to 900 nm and an AM1.5 power conversion efficiency of 3.8 or 4.7%, respectively. In contrast to the almost constant FET mobility, the efficiency of the photovoltaic cells was found to be strongly dependent on the molecular weight of PDPP3T and the use of diiodooctane as a processing agent.Journal of the American Chemical Society 11/2009; 131(46):16616-7. · 9.91 Impact Factor -
Article: Monolayer coverage and channel length set the mobility in self-assembled monolayer field-effect transistors.
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ABSTRACT: The mobility of self-assembled monolayer field-effect transistors (SAMFETs) traditionally decreases dramatically with increasing channel length. Recently, however, SAMFETs using liquid-crystalline molecules have been shown to have bulk-like mobilities that are virtually independent of channel length. Here, we reconcile these scaling relations by showing that the mobility in liquid crystalline SAMFETs depends exponentially on the channel length only when the monolayer is incomplete. We explain this dependence both numerically and analytically, and show that charge transport is not affected by carrier injection, grain boundaries or conducting island size. At partial coverage, that is when the monolayer is incomplete, liquid-crystalline SAMFETs thus form a unique model system to study size-dependent conductance originating from charge percolation in two dimensions.Nature Nanotechnology 08/2009; 4(10):674-680. · 27.27 Impact Factor -
Article: Monolayer coverage and channel length set the mobility in self-assembled monolayer field-effect transistors
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ABSTRACT: The mobility of self-assembled monolayer field-effect transistors (SAMFETs) traditionally decreases dramatically with increasing channel length. Recently, however, SAMFETs using liquid-crystalline molecules have been shown to have bulk-like mobilities that are virtually independent of channel length. Here, we reconcile these scaling relations by showing that the mobility in liquid crystalline SAMFETs depends exponentially on the channel length only when the monolayer is incomplete. We explain this dependence both numerically and analytically, and show that charge transport is not affected by carrier injection, grain boundaries or conducting island size. At partial coverage, that is when the monolayer is incomplete, liquid-crystalline SAMFETs thus form a unique model system to study size-dependent conductance originating from charge percolation in two dimensions.Nature Nanotechnology 08/2009; 4(10):674-680. · 27.27 Impact Factor -
Article: Bottom-up organic integrated circuits.
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ABSTRACT: Self-assembly-the autonomous organization of components into patterns and structures-is a promising technology for the mass production of organic electronics. Making integrated circuits using a bottom-up approach involving self-assembling molecules was proposed in the 1970s. The basic building block of such an integrated circuit is the self-assembled-monolayer field-effect transistor (SAMFET), where the semiconductor is a monolayer spontaneously formed on the gate dielectric. In the SAMFETs fabricated so far, current modulation has only been observed in submicrometre channels, the lack of efficient charge transport in longer channels being due to defects and the limited intermolecular pi-pi coupling between the molecules in the self-assembled monolayers. Low field-effect carrier mobility, low yield and poor reproducibility have prohibited the realization of bottom-up integrated circuits. Here we demonstrate SAMFETs with long-range intermolecular pi-pi coupling in the monolayer. We achieve dense packing by using liquid-crystalline molecules consisting of a pi-conjugated mesogenic core separated by a long aliphatic chain from a monofunctionalized anchor group. The resulting SAMFETs exhibit a bulk-like carrier mobility, large current modulation and high reproducibility. As a first step towards functional circuits, we combine the SAMFETs into logic gates as inverters; the small parameter spread then allows us to combine the inverters into ring oscillators. We demonstrate real logic functionality by constructing a 15-bit code generator in which hundreds of SAMFETs are addressed simultaneously. Bridging the gap between discrete monolayer transistors and functional self-assembled integrated circuits puts bottom-up electronics in a new perspective.Nature 11/2008; 455(7215):956-959. · 36.28 Impact Factor -
Article: Unified description of potential profiles and electrical transport in unipolar and ambipolar organic field-effect transistors
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ABSTRACT: Validation of models for charge transport in organic transistors is fundamentally important for their technological use. Usually current-voltage measurements are performed to investigate organic transistors. In situ scanning Kelvin probe microscopy measurements provide a powerful complementary technique to distinguish between models based on band and hopping transports. We perform combined current-voltage and Kelvin probe microscopy measurements on unipolar and ambipolar organic field-effect transistors. We demonstrate that by this combination we can stringently test these two different transport models and come up with a unified description of charge transport in disordered organic semiconductors. -
Article: Dynamics of Threshold Voltage Shifts in Organic and Amorphous Silicon Field-Effect Transistors
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Article: Manipulating the Local Light Emission in Organic Light-Emitting Diodes by using Patterned Self-Assembled Monolayers
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Article: Unified description of potential profiles and electrical transport in unipolar and ambipolar organic field-effect transistors
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ABSTRACT: Validation of models for charge transport in organic transistors is fundamentally important for their technological use. Usually current-voltage measurements are performed to investigate organic transistors. In situ scanning Kelvin probe microscopy measurements provide a powerful complementary technique to distinguish between models based on band and hopping transports. We perform combined current-voltage and Kelvin probe microscopy measurements on unipolar and ambipolar organic field-effect transistors. We demonstrate that by this combination we can stringently test these two different transport models and come up with a unified description of charge transport in disordered organic semiconductors.Phys. Rev. B. 76(12). -
Article: Charge Trapping at the Dielectric of Organic Transistors Visualized in Real Time and Space
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Article: Small band gap copolymers based on furan and diketopyrrolopyrrole for field-effect transistors and photovoltaic cells
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ABSTRACT: Four small band gap semiconducting copolymers based on electron deficient diketopyrrolopyrrole alternating with electron rich trimers containing furan and benzene or thiophene have been synthesized via Suzuki polymerization. The polymers have optical band gaps between 1.4 and 1.6 eV, optimized for solar energy conversion, and exhibit ambipolar charge transport in field-effect transistors with hole and electron mobilities higher than 10-2 cm2 V-1 s-1. In solar cells the polymers are used as electron donors and provide power conversion efficiencies up to 3.7% in simulated solar light when mixed with [70]PCBM as acceptor. -
Article: Gate-Bias Controlled Charge Trapping as a Mechanism for NO2 Detection with Field-Effect Transistors
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ABSTRACT: Detection of nitrogen dioxide, NO2, is required to monitor the air-quality for human health and safety. Commercial sensors are typically chemiresistors, however field-effect transistors are being investigated. Although numerous investigations have been reported, the NO2 sensing mechanism is not clear. Here, the detection mechanism using ZnO field-effect transistors is investigated. The current gradually decreases upon NO2 exposure and application of a positive gate bias. The current decrease originates from the trapping of electrons, yielding a shift of the threshold voltage towards the applied gate bias. The shift is observed for extremely low NO2 concentrations down to 10 ppb and can phenomenologically be described by a stretched-exponential time relaxation. NO2 detection has been demonstrated with n-type, p-type, and ambipolar semiconductors. In all cases, the threshold voltage shifts due to gate bias induced electron trapping. The description of the NO2 detection with field-effect transistors is generic for all semiconductors and can be used to improve future NO2 sensors.
Top co-authors
Top Journals
Institutions
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2010
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Philips Research
Eindhoven, North Brabant, Netherlands
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2009–2010
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Technische Universiteit Eindhoven
Eindhoven, North Brabant, Netherlands
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2008
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University of Groningen
Groningen, Province of Groningen, Netherlands
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