Showing papers on "Organic semiconductor published in 2005"
TL;DR: It is demonstrated that the use of an appropriate hydroxyl-free gate dielectric—such as a divinyltetramethylsiloxane-bis(benzocyclobutene) derivative (BCB; ref. 6)—can yield n-channel FET conduction in most conjugated polymers, revealing that electrons are considerably more mobile in these materials than previously thought.
Abstract: Organic semiconductors have been the subject of active research for over a decade now, with applications emerging in light-emitting displays and printable electronic circuits. One characteristic feature of these materials is the strong trapping of electrons but not holes1: organic field-effect transistors (FETs) typically show p-type, but not n-type, conduction even with the appropriate low-work-function electrodes, except for a few special high-electron-affinity2,3,4 or low-bandgap5 organic semiconductors. Here we demonstrate that the use of an appropriate hydroxyl-free gate dielectric—such as a divinyltetramethylsiloxane-bis(benzocyclobutene) derivative (BCB; ref. 6)—can yield n-channel FET conduction in most conjugated polymers. The FET electron mobilities thus obtained reveal that electrons are considerably more mobile in these materials than previously thought. Electron mobilities of the order of 10-3 to 10-2 cm2 V-1 s-1 have been measured in a number of polyfluorene copolymers and in a dialkyl-substituted poly(p-phenylenevinylene), all in the unaligned state. We further show that the reason why n-type behaviour has previously been so elusive is the trapping of electrons at the semiconductor–dielectric interface by hydroxyl groups, present in the form of silanols in the case of the commonly used SiO2 dielectric. These findings should therefore open up new opportunities for organic complementary metal-oxide semiconductor (CMOS) circuits, in which both p-type and n-type behaviours are harnessed.
2,191 citations
TL;DR: In this article, the materials, charge-transport, and device physics of solution-processed organic field-effect transistors are reviewed, focusing in particular on the physics of the active semiconductor/dielectric interface.
Abstract: Field-effect transistors based on solution-processible organic semiconductors have experienced impressive improvements in both performance and reliability in recent years, and printing-based manufacturing processes for integrated transistor circuits are being developed to realize low-cost, large-area electronic products on flexible substrates. This article reviews the materials, charge-transport, and device physics of solution-processed organic field-effect transistors, focusing in particular on the physics of the active semiconductor/dielectric interface. Issues such as the relationship between microstructure and charge transport, the critical role of the gate dielectric, the influence of polaronic relaxation and disorder effects on charge transport, charge-injection mechanisms, and the current understanding of mechanisms for charge trapping are reviewed. Many interesting questions on how the molecular and electronic structures and the presence of defects at organic/organic heterointerfaces influence the device performance and stability remain to be explored.
1,651 citations
TL;DR: In this paper, a non-volatile memory device with flexible plastic active layers deposited from solution is presented, and the memory device is a ferroelectric field effect transistor (FeFET) made with a Ferroelectric fluoropolymer and a bisalkoxy-substituted poly(pphenylene vinylene) semiconductor material.
Abstract: We demonstrate a rewritable, non-volatile memory device with flexible plastic active layers deposited from solution. The memory device is a ferroelectric field-effect transistor (FeFET) made with a ferroelectric fluoropolymer and a bisalkoxy-substituted poly(p-phenylene vinylene) semiconductor material. The on- and off-state drain currents differ by several orders of magnitude, and have a long retention time, a high programming cycle endurance and short programming time. The remanent semiconductor surface charge density in the on-state has a high value of 18 mC m−2, which explains the large on/off ratio. Application of a moderate gate field raises the surface charge to 26 mC m−2, which is of a magnitude that is very difficult to obtain with conventional FETs because they are limited by dielectric breakdown of the gate insulator. In this way, the present ferroelectric–semiconductor interface extends the attainable field-effect band bending in organic semiconductors.
862 citations
TL;DR: In this paper, a thermal annealing process was applied to a blend of regioregular poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) to achieve a power conversion efficiency of 3% under air mass 1.5 simulated solar illumination.
Abstract: Here we report enhanced efficiency bulk heterojunction organic solar cells using blend films of regioregular poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) that are subjected to a thermal annealing process. Blend films (P3HT:PCBM=1:1 by weight) were prepared using chlorobenzene and 1,2-dichlorobenzene in order to investigate the role of the solvent. Irrespective of the chosen solvent, the optimal device annealing temperature was found to be 140 °C. The highest power conversion efficiency, 3% under air mass 1.5 simulated solar illumination (100mW∕cm2), was achieved by device annealing at 140 °C for 15 min using blend films prepared from chlorobenzene (2.3% for 1,2-dichlorobenzene).
709 citations
TL;DR: In this paper, a relationship between the energy of the highest occupied molecular orbital (HOMO) and the oxidation potential of molecular organic semiconductors is presented, based on an analysis of image charge forces on spherical molecules positioned near a conductive plane formed by the electrode in an electrochemical cell.
705 citations
TL;DR: New spin-coatable, ultrathin (<20 nm) cross-linked polymer blends exhibiting excellent insulating properties, large capacitances, and enabling low-voltage OTFT functions are reported, and complementary invertors have been fabricated which function at 2 V.
Abstract: The quest for high-performance organic thin-film transistor (OTFT) gate dielectrics is of intense current interest. Beyond having excellent insulating properties, such materials must meet other stringent requirements for optimum OTFT function: efficient low-temperature solution fabrication, mechanical flexibility, and compatibility with diverse gate materials and organic semiconductors. The OTFTs should function at low biases to minimize power consumption, hence the dielectric must exhibit large gate capacitance. We report the realization of new spin-coatable, ultrathin (<20 nm) cross-linked polymer blends exhibiting excellent insulating properties (leakage current densities approximately 10(-)(8) Acm(-)(2)), large capacitances (up to approximately 300 nF cm(-)(2)), and enabling low-voltage OTFT functions. These dielectrics exhibit good uniformity over areas approximately 150 cm(2), are insoluble in common solvents, can be patterned using standard microelectronic etching methodologies, and adhere to/are compatible with n(+)-Si, ITO, and Al gates, and with a wide range of p- and n-type semiconductors. Using these dielectrics, complementary invertors have been fabricated which function at 2 V.
453 citations
TL;DR: The highly organized molecular packing (uniaxial crystalline phase) has been deduced from the measurement of electron diffraction and polarized microscopy imaging and the detected optical axis is consistent with the one-dimensional stacking of the molecules.
Abstract: Nanobelt structures have been fabricated for an n-type semiconductor molecule, N,N‘-di(propoxyethyl)perylene-3,4,9,10-tetracarboxylic diimide (PTCDI). The short alkyloxy side chain not only affords effective π−π stacking in polar solvents for self-assembling but also provides sufficient solubility in nonpolar solvents for solution processing. As revealed by both AFM and electron microscopies, the nanobelts have an approximately rectangular cross section, with a typical thickness of about 100 nm and a width in the range of 300−500 nm. The length of the nanobelts ranges from 10 to a few tens of micrometers. The highly organized molecular packing (uniaxial crystalline phase) has been deduced from the measurement of electron diffraction and polarized microscopy imaging. The detected optical axis is consistent with the one-dimensional stacking of the molecules.
425 citations
TL;DR: In this paper, the authors demonstrate bilayer source-drain (S-D) electrodes for organic thin film transistors (OTFTs), which consists of a transition metal oxide (MoO3,WO3 or V2O5) layer and a metal layer.
Abstract: We demonstrate bilayer source-drain (S-D) electrodes for organic thin film transistors (OTFT). The bilayer consists of a transition metal oxide (MoO3,WO3, or V2O5) layer and a metal layer. The metal oxide layer, directly contacting the organic semiconducting layer, serves as the charge-injection layer. The overcoated metal layer is responsible for the conduction of charge carriers. We found that the metal oxide layer coupled between pentacene and metal layers played an important role in improving the field-effect transistor characteristics of OTFTs. Devices with the bilayer S-D electrodes showed enhanced hole-injection compared to those with only metal electrode. High field-effect mobility of 0.4cm2∕Vs and on/off current ratios of 104 were obtained in the pentacene based TFTs using the bilayer S-D electrodes at a gate bias of −40V. The improvement is attributed to the reduction in the contact barrier and the prevention of metal diffusion into the organic layer and/or unfavorable chemical reaction between ...
386 citations
TL;DR: The Hall effect in the field-induced accumulation layer on the surface of single-crystal samples of a small-molecule organic semiconductor rubrene is observed and the Hall mobility muH increases with decreasing temperature in both the intrinsic and trap-dominated conduction regimes.
Abstract: After several decades of intensive research, our understanding of the charge transport in small-molecule organic semiconductors remains incomplete. The complexity of the transport phenomena in these systems is due to the polaronic nature of charge carriers [1] and the strong interaction of small polarons with defects. For the emerging field of organic electronics [2], it is especially important to develop an adequate model of the polaronic transport at room temperature. This is a challenging task because the energy of thermal excitations at room temperature may be comparable to the width of the conduction band in these van der Waals-bonded materials. The recent theories [3‐7] show that the high-T polaronic transport in organic semiconductors is governed by the competition between the bandwidth narrowing that would lead to a
385 citations
TL;DR: In this paper, the authors performed a comprehensive magnetoresistance study on a set of organic semiconductor sandwich devices made from different conjugated polymers and small molecules, including a range of materials that show greatly different chemical structure, mobility, and spin-orbit coupling strength.
Abstract: Following the recent observation of large magnetoresistance at room temperature in polyfluorene sandwich devices, we have performed a comprehensive magnetoresistance study on a set of organic semiconductor sandwich devices made from different $\ensuremath{\pi}$-conjugated polymers and small molecules The study includes a range of materials that show greatly different chemical structure, mobility, and spin-orbit coupling strength We study both hole and electron transporters at temperatures ranging from 10 K to 300 K We observe large negative or positive magnetoresistance (up to 10% at 300 K and 10 mT) depending on material and device operating conditions We discuss our results in the framework of known magnetoresistance mechanisms and find that none of the existing models can explain our results
350 citations
TL;DR: Weak intermolecular interactions, low dielectric constants, and the availability of a nearly unlimited number of different molecules determine the scope of organic semiconductors as systems for exploring and exploiting solid-state phenomena as discussed by the authors.
Abstract: Weak intermolecular interactions, low dielectric constants, and the availability of a nearly unlimited number of different molecules determine the scope of organic semiconductors as systems for exploring and exploiting solid-state phenomena.
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01 Aug 2005
TL;DR: In this article, the effect of Gaussian disorder on charge carrier transport and recombination in organic semiconductors was investigated and shown to be an important factor in the performance of organic semiconductor devices.
Abstract: Foreword (R.H. Friend) Preface (W. Brutting, C. Adachi) FILM GROWTH, ELECTRONIC STRUCTURE AND INTERFACES 1 Organic molecular beam deposition (F. Schreiber, Tubingen Univ., Germany) 2 Electronic structure of interfaces with conjugated organic materials (N. Koch, HU Berlin, Germany) 3 Electronic structure of molecular solids: Bridge to the electrical conduction (N. Ueno, Chiba Univ., Japan) 4 Interfacial doping for efficient charge injection (J.J. Kim, Seoul National Univ., South Korea) 5 Displacement current measurement for exploring charge carrier dynamics in organic semiconductor devices (Y. Noguchi, Y. Tanaka, Y. Miyazaki, N. Sato, Y. Nakayama, H. Ishii, Chiba Univ., Japan) CHARGE TRANSPORT 6 Effects of Gaussian disorder on charge carrier transport and recombination in organic semiconductors (R. Coehoorn, P.A. Bobbert, Philips Research & Eindhoven Univ. Techn., The Netherlands) 7 Charge transport physics of high mobility molecular semiconductors (H. Sirringhaus, T. Sakanoue, J.-F. Chang, Univ. Cambridge, U.K.) 8 Ambipolar charge carrier transport in molecular field-effect transistors (A. Opitz, W. Brutting, Augsburg Univ., Germany) 9 Organic magnetoresistance (M. Wohlgenannt, Univ. Iowa, U.S.A.) PHOTOPHYSICS 10 Excitons at polymer interfaces (N. Greenham, Univ. Cambridge, U.K.) 11 Electronic processes at organic semiconductor heterojunctions: The mechanism of exciton dissociation in semicrystalline solid-state microstructures (F. Paquin, G. Latini, M. Sakowicz, P.-L. Karsenti, L. Wang, D. Beljonne, N. Stingelin, C. Silva, Univ. Montreal, Canada & Imperial College London, U.K.) 12 Recent progress in the understanding of exciton dynamics within phosphorescentOLEDs (S. Reineke, M. Baldo, MIT, U.S.A.) 13 Organometallic Emitters for OLEDs. Triplet Harvesting, Singlet Harvesting, Case Structures, and Trends (H. Yersin, Regensburg Univ., Germany) DEVICE PHYSICS 14 Doping of organic semiconductors (B. Lussem, M. Riede, K. Leo, Dresden Univ., Germany) 15 Device efficiency of organic LEDs (W. Brutting, J. Frischeisen, Augsburg Univ., Germany) 16 Light outcoupling in organic LEDs (C.-H. Tsai, C.-C. Wu, National Taiwan Univ., Taiwan) 17 Photogeneration and Recombination in Polymer Solar Cells (C. Deibel, A. Baumann, V. Dyakonov, Wurzburg Univ., Germany) 18 Light-emitting organic crystal field-effect transistors for future organic injection lasers (H. Nakanotani, C. Adachi, Kyushu Univ., Japan)
TL;DR: This class of organic semiconductors has relatively low HOMO levels and large band gaps, they also displayed good environmental stability even with prolonged exposure to amber light, an appealing characteristic for OTFT applications.
Abstract: Proper functionalization of indolo[3,2-b]carbazole led to a new class of high-performance organic semiconductors suitable for organic thin-film transistor (OTFT) applications. While 5,11-diaryl-substituted indolo[3,2-b]carbazoles without long alkyl side chains provided amorphous thin films upon vacuum deposition, those with sufficiently long alkyl side chains such as 5,11-bis(4-octylphenyl)indolo[3,2-b]carbazole self-organized readily into highly crystalline layered structures under similar conditions. OTFTs using channel semiconductors of this nature exhibited excellent field-effect properties, with mobility up to 0.12 cm2 V-1 s-1 and current on/off ratio to 107. As this class of organic semiconductors has relatively low HOMO levels and large band gaps, they also displayed good environmental stability even with prolonged exposure to amber light, an appealing characteristic for OTFT applications.
TL;DR: The synthesis and characterization of a fused-ring compound, dithieno[2,3-d:2',3'-d']thieno [3,2-b:4,5-b']dithiophene (pentathienoacene, PTA), demonstrating the potential of PTA for application in future organic electronics.
Abstract: We present the synthesis and characterization of a fused-ring compound, dithieno[2,3-d:2‘,3‘-d‘]thieno[3,2-b:4,5-b‘]dithiophene (pentathienoacene, PTA). In contrast to pentacene, PTA has a larger band gap than most semiconductors used in organic field-effect transistors (OFETs) and therefore is expected to be stable in air. The large π-conjugated and planar molecular structure of PTA would also form higher molecular orders that are conductive for carrier transport. X-ray diffraction and atomic force microscopy experiments on its films show that the molecules stack in layers with their long axis upright from the surface. X-ray photoelectron spectroscopy suggests that there are no chemical bonds at the PTA/Au interface. OFETs based on the PTA have been constructed, and their performances as p-type semiconductors are also presented. A high mobility of 0.045 cm2/V s and an on/off ratio of 103 for a PTA OFET have been achieved, demonstrating the potential of PTA for application in future organic electronics.
TL;DR: In this article, a thin poly(styrenesulphonate)-doped poly(3,4-ethylenedioxythiophene) (PEDT:PSS) hole transporter and an emissive semiconductor significantly improves the device efficiency of polymer light-emitting diodes (LEDs).
Abstract: We report that adding a thin (∼10nm) semiconducting polymer interlayer between apoly(styrenesulphonate)-doped poly(3,4-ethylenedioxythiophene) (PEDT:PSS) hole transporter and an emissive semiconductor significantly improves the device efficiency of polymer light-emitting diodes (LEDs). With the interlayer, the external quantum efficiency (EQE) increases from 0.7%(0.4cd∕A at 3.7V) to 1.9% (1.0cd∕A at 3.3V) at 100cd∕m2 for red LEDs and from 1.9%(6.2cd∕A at 3.4V) to 3.0% (10.1cd∕A at 3.0V) at 1000cd∕m2 for green LEDs. An EQE of 4.0% is also observed in blue LEDs (35% increase). The interlayer is spin-coated directly on top of the PEDT:PSS layer from a poly(2,7-(9,9-di-n-octylfluorene)-alt-(1,4-phenylene-((4-sec-butylphenyl)imino)-1,4-phenylene)) (TFB) solution. This interlayer prevents significant quenching of radiative excitons at the PEDT:PSS interface by acting as an efficient exciton blocking layer.
TL;DR: In this article, the first few pentacene layers on a dielectric substrate are strongly dependent on the surface properties, directly affecting the charge mobility of Pentacene thin film OTFTs.
Abstract: Among all organic semiconductors, pentacene has been shown to have the highest thin film mobility reported to date. The crystalline structure of the first few pentacene layers deposited on a dielectric substrate is strongly dependent on the dielectric surface properties, directly affecting the charge mobility of pentacene thin film OTFTs. Herein, we report that there is a direct correlation between the crystalline structure of the initial submonolayer of a pentacene film and the mobility of the corresponding 60-nm-thick films showing terrace-like structure, as confirmed by 2D grazing-incidence X-ray diffraction and atomic force microscopy. Specifically, multilayered pentacene films, grown from single crystal-like faceted islands on HMDS-treated surface, have shown much higher charge mobility (μ = 3.4 ± 0.5 cm2/Vs) than those with polycrystalline dendritic islands (μ = 0.5 ± 0.15 cm2/Vs) on OTS-treated ones.
TL;DR: In this paper, a sheet image scanner was successfully manufactured on a plastic film by integrating high-quality organic transistors and organic photodetectors and the effective sensing area of the integrated device is 5/spl times/5 cm/sup 2/; the resolution, 36 dots per inch (dpi); and the total number of sensor cells, 5184.
Abstract: A large-area, flexible, and lightweight sheet image scanner has been successfully manufactured on a plastic film by integrating high-quality organic transistors and organic photodetectors. The effective sensing area of the integrated device is 5/spl times/5 cm/sup 2/; the resolution, 36 dots per inch (dpi); and the total number of sensor cells, 5184. The pentacene transistors with top contact geometry have a channel length of 18 /spl mu/m and mobility of 0.7 cm/sup 2//Vs. Organic photodetectors composed of copper phthalocyanine and 3,4,9,10-perylene-tetracarboxylic-diimide distinguish between black and white parts on paper based on the difference in their reflectivity. Since this new area-type image-capturing device does not require any optics or mechanical scanning devices, the present sheet image scanners are mechanically flexible, lightweight, shock resistant, and potentially inexpensive to manufacture; therefore, they are suitable for human-friendly mobile electronics.
TL;DR: The design, synthesis, and device stability data for novel bis-5'-alkylthiophen-2'yl-2,6-anthracene organic semiconductors are presented and there is no decrease in performance during continuous operation of the devices over several thousand cycles.
Abstract: The development of new organic semiconductors with improved electrical performance and enhanced environmental stability is the focus of considerable research activity. This communication presents the design, synthesis, and device stability data for novel bis-5‘-alkylthiophen-2‘yl-2,6-anthracene organic semiconductors. When incorporated into thin-film field-effect transistors, mobilities as high as 0.5 cm2/Vs and on/off current ratios greater than 107 are observed. We have investigated device stability in terms of both shelf life and operating lifetime. Devices incorporating the reported semiconductors display an average field-effect mobility of 0.4 cm2/Vs for DHTAnt and an on/off current ratio of 106 even after 15 months of storage. Furthermore, there is no decrease in performance during continuous operation of the devices over several thousand cycles.
TL;DR: Very thin (2.3-5.5 nm) self-assembled organic dielectric multilayers have been integrated into organic thin-film transistor structures to achieve sub-1-V operating characteristics.
Abstract: Very thin (2.3-5.5 nm) self-assembled organic dielectric multilayers have been integrated into organic thin-film transistor structures to achieve sub-1-V operating characteristics. These new dielectrics are fabricated by means of layer-by-layer solution phase deposition of molecular silicon precursors, resulting in smooth, nanostructurally well defined, strongly adherent, thermally stable, virtually pinhole-free, organosiloxane thin films having exceptionally large electrical capacitances (up to ≈2,500 nF·cm-2), excellent insulating properties (leakage current densities as low as 10-9 A·cm-2), and single-layer dielectric constant (k)of ≈16. These 3D self-assembled multilayers enable organic thin-film transistor function at very low source-drain, gate, and threshold voltages (<1 V) and are compatible with a broad variety of vapor- or solution-deposited p- and n-channel organic semiconductors.
gate insulator
molecular multilayer
organic dielectric
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TL;DR: In this article, the authors present a mechanism that explains the energy-level alignment at organic-organic (OO) semiconductor heterojunctions, which is driven by the alignment of the charge neutrality level (CNL) of the two organic semiconductors.
Abstract: We present a mechanism that explains the energy-level alignment at organic-organic (OO) semiconductor heterojunctions. Following our work on metal/organic interfaces, we extend the concepts of charge neutrality level (CNL) and induced density of interface states to OO interfaces, and propose that the energy-level alignment is driven by the alignment of the CNLs of the two organic semiconductors. The initial offset between the CNLs gives rise to a charge transfer across the interface, which induces an interface dipole and tends to align the CNLs. The initial CNL difference is reduced according to the screening factor $S$, a quantity related to the dielectric functions of the organic materials. Good quantitative agreement with experiment is found. Our model thus provides a simple and intuitive, yet general, explanation of the energy-level alignment at organic semiconductor heterojunctions.
TL;DR: In this paper, a hybrid photovoltaic cell based on a blend of inorganic nanocrystals and polymers has been proposed for low-cost, scalable solar power conversion.
Abstract: Recent results have demonstrated that hybrid photovoltaic cells based on a blend of inorganic nanocrystals and polymers possess significant potential for low-cost, scalable solar power conversion. Colloidal semiconductor nanocrystals, like polymers, are solution processable and chemically synthesized, but possess the advantageous properties of inorganic semiconductors such as a broad spectral absorption range and high carrier mobilities. Significant advances in hybrid solar cells have followed the development of elongated nanocrystal rods and branched nanocrystals, which enable more effective charge transport. The incorporation of these larger nanostructures into polymers has required optimization of blend morphology using solvent mixtures. Future advances will rely on new nanocrystals, such as cadmium telluride tetrapods, that have the potential to enhance light absorption and further improve charge transport. Gains can also be made by incorporating application-specific organic components, including electroactive surfactants which control the physical and electronic interactions between nanocrystals and polymer.
TL;DR: In this article, the degradation of electrical performance under high relative humidity was attributed to charge trapping at grain boundaries by polar water molecules reducing the rate of charge transport, and the moisture sensitivity of the OTFT saturation current depends on the device geometry (bottom or top contact device) and channel length.
Abstract: Humidity dependence of electrical performance of p-channel organic thin-film transistors (OTFTs) with various semiconductor compounds has been investigated. All devices showed decreased current output and mobility as the relative humidity (RH) was increased. The moisture sensitivity of the OTFT saturation current depends on the device geometry (bottom or top contact device) and channel length. The OTFT configuration with a short channel length and bottom contact was most affected by humidity compared to the top contact and larger channel length OTFT structures. The degradation of electrical performance under high RH is attributed to charge trapping at grain boundaries by polar water molecules reducing the rate of charge transport.
28 Jan 2005
TL;DR: In this article, the authors propose a method for synthesizing conjugated polymers by step-growth polymerization, which can be seen as an alternative to the traditional linear block copolymerization.
Abstract: Foreword. Preface. List of Contributors. VOLUME 1. Synthetic Methods. 1 Synthetic Methods for Semiconducting Polymers (Alberto Bolognesi and Maria Cecilia Pasini). 1.1 Introduction and Overview. 1.2 Synthetic Pathways for PA. 1.3 Conjugated Polymers by Step-Growth Polymerizations. 1.4 Block Copolymers. 1.5 Towards Autoorganized Devices. References. 2 Processable Semiconducting Polymers Containing Oligoconjugated Blocks (Joannis K. Kallitsis, Panagiotis K. Tsolakis, and Aikaterini K. Andreopoulou). 2.1 Introduction. 2.2 Rod-Coil Block Copolymers. 2.3 Alternating Conjugated-Nonconjugated Polymers. References. Structure/Morphology. 3 Interfacial Aspects of Semiconducting Polymer Devices (Richard A. L. Jones). 3.1 Introduction. 3.2 Some Basics of Polymer Blend Thermodynamics and Dynamics. 3.3 Surface Segregation, Surface-driven Phase Separation, Wetting and Self-Stratification. 3.4 Morphology in Thin Films of Semiconducting Polymer Blends. 3.5 Surface Segregation in Polymer-doped Conducting Polymers. 3.6 Interface Structure. 3.7 Conclusions. References. Electronic Structure of Interfaces. 4 Electronic Structure of Surfaces and Interfaces in Conjugated Polymers (Michael Logdlund, Mats Fahlman, Stina K.M. Jonsson, and William R. Salaneck). 4.1 Introduction. 4.2 Photoelectron Spectroscopy. 4.3 Theoretical Approaches. 4.4 Materials. 4.5 Charge Storage States in Conjugated Polymers. 4.6 Interface Formations in Conjugated Systems. 4.7 Summary. References. Photophysics. 5 Photophysics of Conjugated Polymers (Lewis Rothberg). 5.1 Introduction and Overview. 5.2 Definitions and Terminology. 5.3 Spectroscopy. 5.4 Photophysics. 5.5 Summary. 5.6 Conclusion. References. 6 Photophysics in Semiconducting Polymers: The Case of Polyfluorenes (Christoph Gadermaier, Larry Luer, Alessio Gambetta, Tersilla Virgili, Margherita Zavelani-Rossi, and Guglielmo Lanzani). 6.1 Introduction. 6.2 Experimental. 6.3 Low-Dimensional Physics in Conjugated Chains. 6.4 Ground-State Absorption and cw Photoluminescence. 6.5 Long-Lived Photoexcitation in Polyfluorenes (PFs). 6.6 Singlet Exciton Dynamics. 6.7 On-Chain Emissive Defects. 6.8 Charged Excitations and Their Photogeneration Mechanism. 6.9 Intrachain Dynamics. 6.10 Three-Pulse Time-Resolved Experiments. 6.11 Light-Emitting-Diode-Related Dynamics in the Ultrafast Timescale. References. 7 Spectroscopy of Photoexcitations in Conjugated Polymers (Z. Valy Vardeny and Markus Wohlgenannt). 7.1 Introduction. 7.2 Experimental Methods. 7.3 Experimental Results: cw PA Spectroscopy. 7.4 Transient Pump-and-Probe Spectroscopy. 7.5 Multiple-Pulse Transient Spectroscopy. 7.6 ODMR Spectroscopy: Measurement of Spin-Dependent Polaron Recombination Rates. 7.7 Summary. References. Transport/Injection. 8 Charge Transport in Neat and Doped Random Organic Semiconductors (Vladimir I. Arkhipov, Igor I. Fishchuk, Andriy Kadashchuk, and Heinz Bassler). 8.1 Introduction. 8.2 Charge Generation. 8.3 Charge-Carrier Hopping in Noncrystalline Organic Materials. 8.4 Experimental Techniques. 8.5 Experimental Results. 8.6 Conclusions. References. 9 Charge Transport and Injection in Conjugated Polymers (Paul W.M. Blom, Cristina Tanase, and Teunis van Woudenbergh). 9.1 Introduction. 9.2 Charge Transport. 9.3 Charge Injection. References. VOLUME 2. Applications. 10 Physics of Organic Light-Emitting Diodes (Ian H. Campbell, Brian K. Crone, and Darryl L. Smith). 10.1 Introduction. 10.2 Thin Films of Organic Semiconductors. 10.3 Device Electronic Structure. 10.4 Single-Layer Devices. 10.5 Multilayer Devices. 10.6 Conclusions. References. 11 Conjugated Polymer-Based Organic Solar Cells (Gilles Dennler, Niyazi Serdar Sariciftci, and Christoph J. Brabec). 11.1 Introduction. 11.2 Conjugated Polymers as Photoexcited Donors. 11.3 Bulk-Heterojunction Solar Cells. 11.4 Determining Parameters of Bulk-Heterojunction Solar Cells. 11.5 From Basics to Applications. 11.6 Conclusions. References. 12 Organic Thin-Film Transistors (Gilles Horowitz). 12.1 Introduction. 12.2 The MISFET - A Reminder. 12.3 The Organic Transistor - What's Different? 12.4 Charge-Transport Mechanisms. 12.5 Concluding Remarks. References. 13 n-Channel Organic Transistor Semiconductors for Plastic Electronics Technologies (Howard E. Katz). 13.1 Plastic Electronics Technology and Organic Semiconductors. 13.2 n-Channel OFET Semiconductors. 13.3 Conclusion. References. 14 Photochromic Diodes (Xavier Crispin, Peter Andersson, Nathaniel D. Robinson, Yoann Olivier, Jerome Cornil, and Magnus Berggren). 14.1 Introduction. 14.2 Photochromic Molecules. 14.3 Organic Diodes. 14.4 Electronic Switches - Device Concepts. 14.5 Conclusions. References. 15 Organic/Polymeric Thin-Film Memory Devices (Yang Yang, Jianyong Ouyang, Liping Ma, Jia-Hung Tseng, and Chih-Wei Chu). 15.1 Introduction. 15.2 Review of Polymer and Organic Memory. 15.3 OMO Nanoparticle Layered Memory Devices. 15.4 Polymer-Blend Composite System. 15.5 Advanced Memory Device Architecture. 15.6 Conclusion. References. 16 Biosensors Based on Conjugated Polymers (Hoang-Anh Ho and Mario Leclerc). 16.1 Introduction. 16.2 Different Types of CPs. 16.3 Colorimetric Methods. 16.4 Fluorometric Methods. 16.5 Electrochemical Methods. 16.6 Conclusions and Perspectives. References. Processing. 17 Manufacturing of Organic Transistor Circuits by Solution-Based Printing (Henning Sirringhaus, Christoph W. Sele, Timothy von Werne, and Catherine Ramsdale). 17.1 Introduction to Printed Organic Thin-Film Transistors. 17.2 Overview of Printing-Based Manufacturing Approaches for OTFTs. 17.3 High-Resolution, Self-Aligned Inkjet Printing. 17.4 Performance and Reliability of Solution-Processed OTFTs for Applications in Flexible Displays. 17.5 Conclusions. References. 18 High-Resolution Composite Materials for Organic Electronics (Graciela Blanchet). 18.1 Introduction. 18.2 Building Blocks. 18.3 Large-Area Printing Process and Devices. 18.4 Printable Materials. 18.5 Conclusion. References. Subject Index.
TL;DR: A rectifier based on a pentacene diode that can rectify an incoming a.c. signal at 50 MHz is reported, showing that even the ultra-high-frequency band at around 800 MHz is within reach.
Abstract: Amain focus of research on organic semiconductors is their potential application in passive organic radio-frequency identification (RF-ID) tags. First prototypes working at 125 kHz have been shown by industrial research groups1. However, to be commercially viable, the organic RF-ID tag would need to be compatible with the base-carrier frequency of 13.56 MHz (ref. 2). High-frequency operation has been out of reach for devices based on organic semiconducting material, because of the intrinsically low mobility of those materials. Here, we report on a rectifier based on a pentacene diode that can rectify an incoming a.c. signal at 50 MHz. At 14 MHz, a rectified voltage of 11 V for an a.c. voltage with a peak-to-peak amplitude of 36 V has been achieved. On the basis of those results, we estimate the frequency limits of an organic diode showing that even the ultra-high-frequency band at around 800 MHz is within reach.
TL;DR: In this article, the effect of doping on the density of states (DOS) distribution and charge-carrier transport in a disordered hopping system is considered analytically, and it is shown that doping such a system produces a random distribution of dopant ions, which Coulombically interact with carriers localized in intrinsic hopping sites.
Abstract: The effect of doping on the density-of-states (DOS) distribution and charge-carrier transport in a disordered hopping system is considered analytically. It is shown that doping such a system produces a random distribution of dopant ions, which Coulombically interact with carriers localized in intrinsic hopping sites. This interaction further increases the energy disorder and broadens the deep tail of the DOS distribution. Therefore, doping of a disordered organic semiconductor, on the one hand, increases the concentration of charge carriers and lifts up the Fermi level but, on the other hand, creates additional deep Coulombic traps of the opposite polarity. While the former effect facilitates conductivity, the latter strongly suppresses the carrier hopping rate. A model of hopping in a doped disordered organic semiconductor is suggested. It is shown that the doping efficiency strongly depends upon the energy disorder and external electric field.
TL;DR: This work advances a general route for facile fabrication of thin-film devices from solution by incorporating a glass-inducing diluent that enables controlled crystallization from an initial vitreous state of the organic semiconductor, formed in a selected area of the phase diagram of the two constituents.
Abstract: Electronic devices based on single crystals of organic semiconductors provide powerful means for studying intrinsic charge-transport phenomena and their fundamental electronic limits1–4. However, for technological exploitation, it is imperative not to be confined to the tedious growth and cumbersome manipulation of molecular crystals—which generally show notoriously poor mechanical properties—but to be able to process such materials into robust architectures by simple and efficient means. Here, we advance a general route for facile fabrication of thin-film devices from solution. The key beneficial feature of our process—and the principal difference from existing vapour deposition5–7 and solution-processing schemes7–10—is the incorporation of a glass-inducing diluent that enables controlled crystallization from an initial vitreous state of the organic semiconductor, formed in a selected area of the phase diagram of the two constituents. We find that the vitrifying diluent does not adversely affect device performance. Indeed, our environmentally stable, discrete rubrene-based transistors rival amorphous silicon devices, reaching saturated mobilities of up to 0.7 cm2 V−1 s−1, ON–OFF ratios of ≥106 and subthreshold slopes as steep as 0.5 V per decade. A nearly temperature-independent device mobility, indicative of a high crystalline quality of our solution-processed, rubrene-based films11, corroborates these findings. Inverter and ring-oscillator structures are also demonstrated.
TL;DR: In this article, the authors have fabricated very flexible pentacene field effect transistors with polyimide gate dielectric layers on plastic films with a mobility of 0.3cm2∕Vs and an on/off ratio of 105, and have measured their electrical properties under various compressive and tensile strains while changing the bending radius of the base plastic films systematically.
Abstract: We have fabricated very flexible pentacene field-effect transistors with polyimide gate dielectric layers on plastic films with a mobility of 0.3cm2∕Vs and an on/off ratio of 105, and have measured their electrical properties under various compressive and tensile strains while changing the bending radius of the base plastic films systematically. We have found that the change in source-drain current with bending radius is reproducible and reversible when the bending radius is above 4.6mm, which corresponds to strains of ∼1.4±0.1%. Furthermore, the change in source-drain current does not depend on the direction of strain versus direction of current flow.
TL;DR: The ability to control various aspects of crystal growth in one system provides a powerful technique for the bottom-up fabrication of organic single-crystal semiconductor devices.
Abstract: This work demonstrates a method for inducing site-specific nucleation and subsequent growth of large oriented organic semiconductor single crystals using micropatterned self-assembled monolayers (SAMs) We demonstrate growth of oriented, patterned, and large organic semiconductor single crystals for potential use in organic electronic devices The control over multiple parameters in a single system has not yet been reported The ability to control various aspects of crystal growth in one system provides a powerful technique for the bottom-up fabrication of organic single-crystal semiconductor devices
TL;DR: The electronic level alignment of various organic molecules on metal surfaces has been determined by a combined experimental and theoretical effort as mentioned in this paper using ab initio electronic structure calculations, and it is demonstrated that the commonly observed interface dipole is largely due to a quantum-mechanical phenomenon resulting from exchange repulsion.
Abstract: The electronic level alignment of various organic molecules on metal surfaces has been determined by a combined experimental and theoretical effort. Using ab initio electronic structure calculations, it is demonstrated that the commonly observed interface dipole is largely due to a quantum-mechanical phenomenon resulting from exchange repulsion. Surprisingly, this physical effect, also referred to as Pauli repulsion dominates even in the case of aromatic molecules on Cu and Au surfaces, i.e., on interfaces that are of key importance in molecular electronics.