Organic Field-effect Transistors (organic + field-effect_transistor)

Distribution by Scientific Domains

Kinds of Organic Field-effect Transistors

  • ambipolar organic field-effect transistor


  • Selected Abstracts


    A Water-Gate Organic Field-Effect Transistor

    ADVANCED MATERIALS, Issue 23 2010
    Loig Kergoat
    High-dielectric-constant insulators, organic monolayers, and electrolytes have been successfully used to generate organic field-effect transistors operating at low voltages. Here, we report on a device gated with pure water. By replacing the gate dielectric by a simple water droplet, we produce a transistor that entirely operates in the field-effect mode of operation at voltages lower than 1,V. This result creates opportunities for sensor applications using water-gated devices as transducing medium. [source]


    Organic Field-Effect Transistors: Planarization of Polymeric Field-Effect Transistors: Improvement of Nanomorphology and Enhancement of Electrical Performance (Adv. Funct.

    ADVANCED FUNCTIONAL MATERIALS, Issue 14 2010
    Mater.
    Contact geometry plays an important role in charge injection and transport in organic field-effect transistors. On page 2216, T. Kowalewski, L. M. Porter, et al. show a dramatic effect of electrode planarization on the polymer morphology at the contact edges and a resulting increase in fi eld-effect mobility in short channel length devices, and a corresponding decrease in contact resistance. The cover image shows atomic force micrograph of individual polymer nanofi brils spanning the length of a 10 µm channel transistor with planarized contacts. [source]


    Dual-Gate Organic Field-Effect Transistors as Potentiometric Sensors in Aqueous Solution

    ADVANCED FUNCTIONAL MATERIALS, Issue 6 2010
    Mark-Jan Spijkman
    Abstract Buried electrodes and protection of the semiconductor with a thin passivation layer are used to yield dual-gate organic transducers. The process technology is scaled up to 150-mm wafers. The transducers are potentiometric sensors where the detection relies on measuring a shift in the threshold voltage caused by changes in the electrochemical potential at the second gate dielectric. Analytes can only be detected within the Debye screening length. The mechanism is assessed by pH measurements. The threshold voltage shift depends on pH as ,Vth,=,(Ctop/Cbottom),×,58,mV per pH unit, indicating that the sensitivity can be enhanced with respect to conventional ion-sensitive field-effect transistors (ISFETs) by adjusting the ratio of the top and bottom gate capacitances. Remaining challenges and opportunities are discussed. [source]


    Air-Stable n-Type Organic Field-Effect Transistors Based on Carbonyl-Bridged Bithiazole Derivatives

    ADVANCED FUNCTIONAL MATERIALS, Issue 6 2010
    Yutaka Ie
    Abstract An electronegative conjugated compound composed of a newly designed carbonyl-bridged bithiazole unit and trifluoroacetyl terminal groups is synthesized as a candidate for air-stable n-type organic field-effect transistor (OFET) materials. Cyclic voltammetry measurements reveal that carbonyl-bridging contributes both to lowering the lowest unoccupied molecular orbital energy level and to stabilizing the anionic species. X-ray crystallographic analysis of the compound shows a planar molecular geometry and a dense molecular packing, which is advantageous to electron transport. Through these appropriate electrochemical properties and structures for n-type semiconductor materials, OFET devices based on this compound show electron mobilities as high as 0.06,cm2 V,1 s,1 with on/off ratios of 106 and threshold voltages of 20,V under vacuum conditions. Furthermore, these devices show the same order of electron mobility under ambient conditions. [source]


    Solution Processable Fluorenyl Hexa- peri -hexabenzocoronenes in Organic Field-Effect Transistors and Solar Cells

    ADVANCED FUNCTIONAL MATERIALS, Issue 6 2010
    Wallace W. H. Wong
    Abstract The organization of organic semiconductor molecules in the active layer of organic electronic devices has important consequences to overall device performance. This is due to the fact that molecular organization directly affects charge carrier mobility of the material. Organic field-effect transistor (OFET) performance is driven by high charge carrier mobility while bulk heterojunction (BHJ) solar cells require balanced hole and electron transport. By investigating the properties and device performance of three structural variations of the fluorenyl hexa- peri -hexabenzocoronene (FHBC) material, the importance of molecular organization to device performance was highlighted. It is clear from 1H NMR and 2D wide-angle X-ray scattering (2D WAXS) experiments that the sterically demanding 9,9-dioctylfluorene groups are preventing ,,, intermolecular contact in the hexakis-substituted FHBC 4. For bis-substituted FHBC compounds 5 and 6, ,,, intermolecular contact was observed in solution and hexagonal columnar ordering was observed in solid state. Furthermore, in atomic force microscopy (AFM) experiments, nanoscale phase separation was observed in thin films of FHBC and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) blends. The differences in molecular and bulk structural features were found to correlate with OFET and BHJ solar cell performance. Poor OFET and BHJ solar cells devices were obtained for FHBC compound 4 while compounds 5 and 6 gave excellent devices. In particular, the field-effect mobility of FHBC 6, deposited by spin-casting, reached 2.8,×,10,3,cm2 V,1 s and a power conversion efficiency of 1.5% was recorded for the BHJ solar cell containing FHBC 6 and PC61BM. [source]


    Variable Temperature Mobility Analysis of n-Channel, p-Channel, and Ambipolar Organic Field-Effect Transistors

    ADVANCED FUNCTIONAL MATERIALS, Issue 1 2010
    Joseph A. Letizia
    Abstract The temperature dependence of field-effect transistor (FET) mobility is analyzed for a series of n-channel, p-channel, and ambipolar organic semiconductor-based FETs selected for varied semiconductor structural and device characteristics. The materials (and dominant carrier type) studied are 5,5,,,-bis(perfluorophenacyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (1, n-channel), 5,5,,,-bis(perfluorohexyl carbonyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (2, n-channel), pentacene (3, p-channel); 5,5,,,-bis(hexylcarbonyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (4, ambipolar), 5,5,,,-bis-(phenacyl)-2,2,: 5,,2,:5,,2,,,-quaterthiophene (5, p-channel), 2,7-bis((5-perfluorophenacyl)thiophen-2-yl)-9,10-phenanthrenequinone (6, n-channel), and poly(N -(2-octyldodecyl)-2,2,-bithiophene-3,3,-dicarboximide) (7, n-channel). Fits of the effective field-effect mobility (µeff) data assuming a discrete trap energy within a multiple trapping and release (MTR) model reveal low activation energies (EAs) for high-mobility semiconductors 1,3 of 21, 22, and 30,meV, respectively. Higher EA values of 40,70,meV are exhibited by 4,7 -derived FETs having lower mobilities (µeff). Analysis of these data reveals little correlation between the conduction state energy level and EA, while there is an inverse relationship between EA and µeff. The first variable-temperature study of an ambipolar organic FET reveals that although n-channel behavior exhibits EA,=,27,meV, the p-channel regime exhibits significantly more trapping with EA,=,250,meV. Interestingly, calculated free carrier mobilities (µ0) are in the range of ,0.2,0.8,cm2,V,1 s,1 in this materials set, largely independent of µeff. This indicates that in the absence of charge traps, the inherent magnitude of carrier mobility is comparable for each of these materials. Finally, the effect of temperature on threshold voltage (VT) reveals two distinct trapping regimes, with the change in trapped charge exhibiting a striking correlation with room temperature µeff. The observation that EA is independent of conduction state energy, and that changes in trapped charge with temperature correlate with room temperature µeff, support the applicability of trap-limited mobility models such as a MTR mechanism to this materials set. [source]


    Sensing of Alkylating Agents Using Organic Field-Effect Transistors

    ADVANCED FUNCTIONAL MATERIALS, Issue 1 2010
    Yair Gannot
    Abstract Alkylating agents are simple and reactive molecules that are commonly used in many and diverse fields, such as organic synthesis, medicine, and agriculture. Some highly reactive alkylating species are also being used as blister chemical warfare agents. The detection and identification of alkylating agent is not a trivial issue because of their high reactivity and simple structure. Here, a novel polythiophene derivative that is capable of reacting with alkylating agents is reported, along with its application in direct electrical sensing of alkylators using an organic field-effect transistor, OFET, device. Upon reacting with alkylators, the OFET containing the new polythiophene analogue as its channel becomes conductive, and the gate effect is lost; this is in marked contrast to the response of the OFET to "innocent" vapors, such as alcohols and acetone. By following the drain,source current under gate bias, one can easily follow the processes of absorption of the analyte to the polythiophene channel and their subsequent reaction. [source]


    Insulator Polarization Mechanisms in Polyelectrolyte-Gated Organic Field-Effect Transistors

    ADVANCED FUNCTIONAL MATERIALS, Issue 20 2009
    Oscar Larsson
    Abstract Electrolyte-gated organic field-effect transistors (OFETs) hold promise for robust printed electronics operating at low voltages. The polarization mechanism of thin solid electrolyte films, the gate insulator in such OFETs, is still unclear and appears to limit the transient current characteristics of the transistors. Here, the polarization response of a thin proton membrane, a poly(styrenesulfonic acid) film, is controlled by varying the relative humidity. The formation of the conducting transistor channel follows the polarization of the polyelectrolyte, such that the drain transient current characteristics versus the time are rationalized by three different polarization mechanisms: the dipolar relaxation at high frequencies, the ionic relaxation (migration) at intermediate frequencies, and the electric double-layer formation at the polyelectrolyte interfaces at low frequencies. The electric double layers of polyelectrolyte capacitors are formed in ,1,µs at humid conditions and an effective capacitance per area of 10,µF cm,2 is obtained at 1,MHz, thus suggesting that this class of OFETs might operate at up to 1,MHz at 1,V. [source]


    Controlling Electron and Hole Charge Injection in Ambipolar Organic Field-Effect Transistors by Self-Assembled Monolayers

    ADVANCED FUNCTIONAL MATERIALS, Issue 15 2009
    Xiaoyang Cheng
    Abstract Controlling contact resistance in organic field-effect transistors (OFETs) is one of the major hurdles to achieve transistor scaling and dimensional reduction. In particular in the context of ambipolar and/or light-emitting OFETs it is a difficult challenge to obtain efficient injection of both electrons and holes from one injecting electrode such as gold since organic semiconductors have intrinsically large band gaps resulting in significant injection barrier heights for at least one type of carrier. Here, systematic control of electron and hole contact resistance in poly(9,9-di- n -octylfluorene- alt -benzothiadiazole) ambipolar OFETs using thiol-based self-assembled monolayers (SAMs) is demonstrated. In contrast to common believe, it is found that for a certain SAM the injection of both electrons and holes can be improved. This simultaneous enhancement of electron and hole injection cannot be explained by SAM-induced work-function modifications because the surface dipole induced by the SAM on the metal surface lowers the injection barrier only for one type of carrier, but increases it for the other. These investigations reveal that other key factors also affect contact resistance, including i) interfacial tunneling through the SAM, ii) SAM-induced modifications of interface morphology, and iii) the interface electronic structure. Of particular importance for top-gate OFET geometry is iv) the active polymer layer thickness that dominates the electrode/polymer contact resistance. Therefore, a consistent explanation of how SAM electrode modification is able to improve both electron and hole injection in ambipolar OFETs requires considering all mentioned factors. [source]


    Monitoring the Channel Formation in Organic Field-Effect Transistors via Photoinduced Charge Transfer

    ADVANCED FUNCTIONAL MATERIALS, Issue 5 2009
    Thokchom Birendra Singh
    Abstract Conducting channel formation in organic field-effect transistors (OFETs) is considered to happen in the organic semiconductor layer very close to the interface with the gate dielectric. In the gradual channel approximation, the local density of accumulated charge carriers varies as a result of applied gate bias, with the majority of the charge carriers being localized in the first few semiconductor monolayers close to the dielectric interface. In this report, a new concept is employed which enables the accumulation of charge carriers in the channel by photoinduced charge transfer. An OFET employing C60 as a semiconductor and divinyltetramethyldisiloxane-bis(benzocyclobutene) as the gate dielectric is modified by a very thin noncontinuous layer of zinc-phthalocyanine (ZnPc) at the semiconductor/dielectric interface. With this device geometry, it is possible to excite the phthalocyanine selectively and photogenerate charges directly at the semiconductor/dielectric interface via photoinduced electron transfer from ZnPc onto C60. Thus the formation of a gate induced and a photoinduced channel in the same device can be correlated. [source]


    Ambipolar Organic Field-Effect Transistors from Cross-Conjugated Aromatic Quaterthiophenes; Comparisons with Quinoidal Parent Materials

    ADVANCED FUNCTIONAL MATERIALS, Issue 3 2009
    Rocío Ponce Ortiz
    Abstract This contribution presents an electrochemical, Raman spectroscopic, and theoretical study probing the differences in molecular and electronic structure of two quinoidal oligothiophenes (3,,4,-dibutyl-5,5,-bis(dicyanomethylene)-5,5,-dihydro-2,2,:5,,2,-terthiophene and 5,5,-bis(dicyanomethylene)-3-hexyl-2,5-dihydro-4,4,-dihexyl-2,2,,5,5,-tetrahydro-tetrathiophene) with terminal tetracyanomethylene functionalization and aromatic oligothiophenes where acceptor moieties are positioned at lateral positions along the conjugated chain (6,6,-dibutylsulfanyl-[2,2,-bi-[4-dicyanovinylene-4H-cyclopenta[2,1-b:3,4-b,]dithiophene]). In this way, the consequences of linear and cross conjugation are compared and contrasted. From this analysis, it is apparent that organic field-effect transistors fabricated with cross-conjugated tetrathiophene semiconductors should combine the benefits of an electron-donor aromatic chain with strongly electron-accepting tetracyanomethylene substituents. The corresponding organic field-effect transistors exhibit ambipolar transport with rather similar hole and electron mobilities. Moreover, n-channel conduction is enhanced to yield one of the highest electron mobilities found to date for this type of material. [source]


    High-Performance Solution-Processable Poly(p -phenylene vinylene)s for Air-Stable Organic Field-Effect Transistors

    ADVANCED FUNCTIONAL MATERIALS, Issue 5 2005

    Abstract The influence of the substitution pattern (unsymmetrical or symmetrical), the nature of the side chain (linear or branched), and the processing of several solution processable alkoxy-substituted poly(p -phenylene vinylene)s (PPVs) on the charge-carrier mobility in organic field-effect transistors (OFETs) is investigated. We have found the highest mobilities in a class of symmetrically substituted PPVs with linear alkyl chains (e.g., R1, R2,=,n -C11H23, R3,=,n -C18H37). We have shown that the mobility of these PPVs can be improved significantly up to values of 10,2,cm2,V,1,s,1 by annealing at 110,°C. In addition, these devices display an excellent stability in air and dark conditions. No change in the electrical performance is observed, even after storage for thirty days in humid air. [source]


    Extracting Parameters from the Current,Voltage Characteristics of Organic Field-Effect Transistors

    ADVANCED FUNCTIONAL MATERIALS, Issue 11 2004
    G. Horowitz
    Abstract Organic field-effect transistors were fabricated with vapor-deposited pentacene on aluminum oxide insulating layers. Several methods are used in order to extract the mobility and threshold voltage from the transfer characteristic of the devices. In all cases, the mobility is found to depend on the gate voltage. The first method consists of deriving the drain current as a function of gate voltage (transconductance), leading to the so-called field-effect mobility. In the second method, we assume a power-law dependence of the mobility with gate voltage together with a constant contact resistance. The third method is the so-called transfer line method, in which several devices with various channel length are used. It is shown that the mobility is significantly enhanced by modifying the aluminum oxide layer with carboxylic acid self-assembled monolayers prior to pentacene deposition. The methods used to extract parameters yield threshold voltages with an absolute value of less than 2 V. It is also shown that there is a shift of the threshold voltage after modification of the aluminum oxide layer. These features seem to confirm the validity of the parameter-extraction methods. [source]


    High-Performance Single Crystal Organic Field-Effect Transistors Based on Two Dithiophene-Tetrathiafulvalene (DT-TTF) Polymorphs

    ADVANCED MATERIALS, Issue 37 2010
    Raphael Pfattner
    Solution prepared single crystal organic field-effect transistors (OFETs) combine low-cost with high performance due to structural ordering of molecules. However, in organic crystals polymorphism is a known phenomenon, which can have a crucial influence on charge transport. Here, the performance of solution-prepared single crystal OFETs based on two different polymorphs of dithiophene-tetrathiafulvalene, which were investigated by confocal Raman spectroscopy and X-ray diffraction, are reported. OFET devices prepared using different configurations show that both polymorphs exhibited excellent device performance, although the ,-phase revealed charge carrier mobility between two and ten times higher in accordance to the closer stacking of the molecules. [source]


    Chemical and Physical Sensing by Organic Field-Effect Transistors and Related Devices

    ADVANCED MATERIALS, Issue 34 2010
    Takao Someya
    Abstract Organic semiconductor films are susceptible to noncovalent interactions, trapping and doping, photoexcitation, and dimensional deformation. While these effects can be detrimental to the performance of conventional circuits, they can be harnessed, especially in field-effect architectures, to detect chemical and physical stimuli. This Review summarizes recent advances in the use of organic electronic materials for the detection of environmental chemicals, pressure, and light. The material features that are responsible for the transduction of the input signals to electronic information are discussed in detail. [source]


    Reliability of Organic Field-Effect Transistors

    ADVANCED MATERIALS, Issue 38-39 2009
    Henning Sirringhaus
    Abstract In this article, we review current understanding of the reliability of organic field-effect transistors, with a particular focus on degradation of device characteristics under bias stress conditions. We discuss the various factors that have been found to influence the operational stability of different material systems, including dependence on stress voltage and duty cycle, gate dielectric, environmental conditions, light exposure, and contact resistance. A key question concerns the role of extrinsic factors, such as oxidation or presence of moisture, and that of intrinsic factors, such as the inherent structural and electronic disorder that is present in thin organic semiconductor films. We also review current understanding of the microscopic defects that could play a role in charge trapping in organic semiconductors. [source]


    Patterned Graphene Electrodes from Solution-Processed Graphite Oxide Films for Organic Field-Effect Transistors

    ADVANCED MATERIALS, Issue 34 2009
    Shuping Pang
    A replacement for gold as the hole-injecting metal in organic electronic devices is presented: patterned graphene electrodes prepared from graphite oxide sheets by oxygen plasma etching. Solution-processed organic FETs with poly(3-hexylthiophene) as the semiconductor and these graphene electrodes are shown to perform as well as or even better than devices with gold contacts. [source]


    Extended Lifetime of Organic Field-Effect Transistors Encapsulated with Titanium Sub-Oxide as an ,Active' Passivation/Barrier Layer

    ADVANCED MATERIALS, Issue 19 2009
    Shinuk Cho
    A thin capping layer of titanium sub-oxide (TiOx) prepared by sol,gel synthesis from titanium alkoxides extends the lifetime of organic FETs. The TiOx layer functions as an ,active' passivation/barrier layer that actually removes oxygen and water vapor from the organic semiconductor. The results demonstrate a significant improvement in the lifetime of organic field-effect transistors when exposed to air. [source]


    High Electron Mobility and Ambient Stability in Solution-Processed Perylene-Based Organic Field-Effect Transistors

    ADVANCED MATERIALS, Issue 16 2009
    Claudia Piliego
    Bottom-contact n-channel OFETs based on spin-coated films of N,N, -1H,1H -perfluorobutyl dicyanoperylenediimide (PDI-FCN2) exhibit a saturation-regime mobility of 0.15,cm2 V,1 s,1 in vacuum and good air stability. These performances are attributed to the high crystallinity and to the edge-on orientation promoted by the thermal treatment, as showed by confocal laser microscopy. [source]


    High-Performance Organic Field-Effect Transistors

    ADVANCED MATERIALS, Issue 14-15 2009
    Daniele Braga
    Abstract With the advent of devices based on single crystals, the performance of organic field-effect transistors has experienced a significant leap, with mobility now in excess of 10,cm2 V,1 s,1. The purpose of this review is to give an overview of the state-of-the-art of these high-performance organic transistors. The paper focuses on the problem of parameter extraction, limitations of the performance by the interfaces, which include the dielectric,semiconductor interface, and the injection and retrieval of charge carriers at the source and drain electrodes. High-performance devices also constitute tools of choice for investigating charge transport phenomena in organic materials. It is shown how the combination of field-effect measurements with other electrical characterizations helps in elucidating this still unresolved issue. [source]


    Dithieno[2,3- d;2,,3,- d,]benzo[1,2- b;4,5- b,]dithiophene (DTBDT) as Semiconductor for High-Performance, Solution-Processed Organic Field-Effect Transistors,

    ADVANCED MATERIALS, Issue 2 2009
    Peng Gao
    The facile synthesis of a new five-ring-fused pentacene analog with four symmetrically fused thiophene ring units (Dithieno[2,3- d;2,,3,- d,]benzo[1,2- b;4,5- b,]dithiophene, Cn -DTBDT) is presented. After aligning this material from solution, thin films for organic field-effect transistors were obtained, resulting in excellent hole mobilities of up to 1.7 cm2V,1s,1, and on/off ratio of 107. [source]


    Novel Thiophene-Thiazolothiazole Copolymers for Organic Field-Effect Transistors,

    ADVANCED MATERIALS, Issue 23 2007
    I. Osaka
    A semiconducting polymer bearing the thiazolothiazole moiety in the polythiophene backbone (see figure) is synthesized. The polymer is found to have small bandgap and large ionization potential. Despite the low molecular weight, the polymer exhibited a high field-effect mobility after annealing. A high on/off ratio suggests the polymer possesses high stability against oxygen doping. The polymer device also showed good environmental stability. [source]


    Near-Infrared Light-Emitting Ambipolar Organic Field-Effect Transistors,

    ADVANCED MATERIALS, Issue 5 2007

    Near-IR light-emitting ambipolar OFETs are demonstrated, employing a squaraine derivative as the electroactive layer. Efficient control of the emission-region position in the channel is achieved by varying the drain/gate potentials. By using a transport model, combined with experimental results, strong metal-induced electroluminescence quenching is observed when light emission takes place in close proximity to the source,drain electrodes (see figure). [source]


    High Ambipolar Mobility in a Highly Ordered Smectic Phase of a Dialkylphenylterthiophene Derivative That Can Be Applied to Solution-Processed Organic Field-Effect Transistors,

    ADVANCED MATERIALS, Issue 3 2007
    M. Funahashi
    A phenylterthiophene derivative that exhibits a highly ordered smectic phase around room temperature is synthesized. In the bulk of the smectic phase, ambipolar carrier transport is observed and electron mobility exceeds 0.2,cm2,V,1,s,1. Thin-film transistors (see the AFM image in the figure) are fabricated by a spin-coating method and exhibit p-type operation, a field-effect mobility of 0.02,cm2,V,1,s,1, and an on/off ratio of 106. [source]


    Ambipolar Organic Field-Effect Transistors Based on a Solution-Processed Methanofullerene,

    ADVANCED MATERIALS, Issue 23-24 2004
    D. Anthopoulos
    Organic field-effect transistors (OFETs, see Figure), based on the solution- processible methanofullerene [6,6]-phenyl-C61 -butyric acid methyl ester (PCBM), have been fabricated in a bottom-contact device configuration using gold electrodes. The OFET functions either as a p- or n-channel device, depending upon the bias conditions. This is the first example of ambipolar charge transport in FETs based on pristine PCBM. [source]


    A Facile Synthesis of Linear Benzene-Fused Bis(tetrathiafulvalene) Compounds and Their Application for Organic Field-Effect Transistors.

    CHEMINFORM, Issue 45 2006
    Xike Gao
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


    Effect of Traps on Carrier Injection and Transport in Organic Field-effect Transistor

    IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 4 2010
    Martin Weis Non-member
    Abstract This study illustrates effect of traps on the charge injection and transport in the organic field-effect transistor (OFET). Here are included silicon nanoparticles (NPs) on a semiconductor-gate insulator interface, which work as trapping centers of charge carriers. Charge transport and injection phenomena are investigated by electrical measurements in presence of traps with designed densities. We find that OFETs with a low concentration of intrinsic carriers, such as a pentacene, are extremely sensitive to the internal electric fields. A significant threshold voltage shift due to trapped charge is observed, with a possibility to tune it by controlling the NP density. We demonstrate that the NP film can serve to design the amount of the accumulated charge in OFET and thus change the space-charge-limited conditions to the injection-limited conditions. A detailed analysis of pentacene OFET based on dielectric properties and the Maxwell-Wagner model reveals the internal electric field created by NPs. Additionally, the effect of NPs is discussed with respect to effective mobility, and its decrease is related to deceleration of carrier propagation by the trapping effect as well as low injection due to the increase of the carrier injection barrier by the internal field. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]


    Solution Processable Fluorenyl Hexa- peri -hexabenzocoronenes in Organic Field-Effect Transistors and Solar Cells

    ADVANCED FUNCTIONAL MATERIALS, Issue 6 2010
    Wallace W. H. Wong
    Abstract The organization of organic semiconductor molecules in the active layer of organic electronic devices has important consequences to overall device performance. This is due to the fact that molecular organization directly affects charge carrier mobility of the material. Organic field-effect transistor (OFET) performance is driven by high charge carrier mobility while bulk heterojunction (BHJ) solar cells require balanced hole and electron transport. By investigating the properties and device performance of three structural variations of the fluorenyl hexa- peri -hexabenzocoronene (FHBC) material, the importance of molecular organization to device performance was highlighted. It is clear from 1H NMR and 2D wide-angle X-ray scattering (2D WAXS) experiments that the sterically demanding 9,9-dioctylfluorene groups are preventing ,,, intermolecular contact in the hexakis-substituted FHBC 4. For bis-substituted FHBC compounds 5 and 6, ,,, intermolecular contact was observed in solution and hexagonal columnar ordering was observed in solid state. Furthermore, in atomic force microscopy (AFM) experiments, nanoscale phase separation was observed in thin films of FHBC and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) blends. The differences in molecular and bulk structural features were found to correlate with OFET and BHJ solar cell performance. Poor OFET and BHJ solar cells devices were obtained for FHBC compound 4 while compounds 5 and 6 gave excellent devices. In particular, the field-effect mobility of FHBC 6, deposited by spin-casting, reached 2.8,×,10,3,cm2 V,1 s and a power conversion efficiency of 1.5% was recorded for the BHJ solar cell containing FHBC 6 and PC61BM. [source]


    Controllable Shifts in Threshold Voltage of Top-Gate Polymer Field-Effect Transistors for Applications in Organic Nano Floating Gate Memory

    ADVANCED FUNCTIONAL MATERIALS, Issue 2 2010
    Kang-Jun Baeg
    Abstract Organic field-effect transistor (FET) memory is an emerging technology with the potential to realize light-weight, low-cost, flexible charge storage media. Here, solution-processed poly[9,9-dioctylfluorenyl-2,7-diyl]-co-(bithiophene)] (F8T2) nano floating gate memory (NFGM) with a top-gate/bottom-contact device configuration is reported. A reversible shift in the threshold voltage (VTh) and reliable memory characteristics was achieved by the incorporation of thin Au nanoparticles (NPs) as charge storage sites for negative charges (electrons) at the interface between polystyrene and cross-linked poly(4-vinylphenol). The F8T2 NFGM showed relatively high field-effect mobility (µFET) (0.02,cm2 V,1 s,1) for an amorphous semiconducting polymer with a large memory window (ca. 30,V), a high on/off ratio (more than 104) during writing and erasing with an operation voltage of 80,V of gate bias in a relatively short timescale (less than 1,s), and a retention time of a few hours. This top-gated polymer NFGM could be used as an organic transistor memory element for organic flash memory. [source]


    The Influence of Film Morphology in High-Mobility Small-Molecule:Polymer Blend Organic Transistors

    ADVANCED FUNCTIONAL MATERIALS, Issue 14 2010
    Jeremy Smith
    Abstract Organic field-effect transistors (OFETs) based upon blends of small molecular semiconductors and polymers show promise for high performance organic electronics applications. Here the charge transport characteristics of high mobility p-channel organic transistors based on 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene:poly(triarylamine) blend films are investigated. By simple alteration of the film processing conditions two distinct film microstructures can be obtained: one characterized by small spherulitic grains (SG) and one by large grains (LG). Charge transport measurements reveal thermally activated hole transport in both SG and LG film microstructures with two distinct temperature regimes. For temperatures >115,K, gate voltage dependent activation energies (EA) in the range of 25,60 meV are derived. At temperatures <115,K, the activation energies are smaller and typically in the range 5,30 meV. For both film microstructures hole transport appears to be dominated by trapping at the grain boundaries. Estimates of the trap densities suggests that LG films with fewer grain boundaries are characterized by a reduced number of traps that are less energetically disordered but deeper in energy than for small SG films. The effects of source and drain electrode treatment with self-assembled monolayers (SAMs) on current injection is also investigated. Fluorinated thiol SAMs were found to alter the work function of gold electrodes by up to ,1,eV leading to a lower contact resistance. However, charge transport analysis suggests that electrode work function is not the only parameter to consider for efficient charge injection. [source]