Semiconductors In Organic Field-effect Transistors Research Articles

Synthesis and electrical properties of novel oligomer semiconductors for organic field-effect transistors (OFETs): Asymmetrically end-capped acene-heteroacene conjugated oligomers

Noble small molecules composed of an aromatic phenylene-trithiophene and naphthalene-trithiophene conjugated core were synthesized and examined for their property in p-type OFET devices. The phenylene and naphthalene moieties were combined with a trithiophene to introduce torsional structures into the conjugated core and improve the solubility compared with the solubility of the quaterthiophene core containing molecule. Although phenylene-trithiophene and naphthalene-trithiophene containing molecules showed lower mobilities (2.9 × 10−3 and 1.04 × 10−2 cm2/V, respectively) than quaterthiophene containing molecule (3.21 × 10−2 cm2/V), they showed more film uniformity caused by improved solubility. The thermal stability, photochemical properties, and morphological characteristics were investigated using TGA, DSC, cyclic voltammetry, and XRD techniques.

Synthesis of dibenzothiophenes by Pd-catalyzed dual C-H activation from diaryl sulfides.

Palladium-catalyzed dual C-H functionalization of diaryl sulfides to form dibenzothiophenes (DBTs) by oxidative dehydrogenative cyclization is reported. This protocol afforded various DBTs in moderate to good yields with tolerance of a wide variety of substrates. Benzo[1,2-b:4,5-b']bis[b]benzothiophene was successfully synthesized by this method, which was used as an organic semiconductor for field-effect transistors.

New Organic Semiconductors with Imide/Amide‐Containing Molecular Systems

Due to their high electron affinities, chemical and thermal stabilities, π-conjugated molecules with imide/amide frameworks have received considerable attentions as promising candidates for high-performance optoelectronic materials, particularly for organic semiconductors with high carrier mobilities. The purpose of this Research News is to give an overview of recent advances in development of high performance imide/amide based organic semiconductors for field-effect transistors. It covers naphthalene diimide-, perylene diimide- and amide-based conjugated molecules and polymers for organic semiconductors.

Integrated Materials Design of Organic Semiconductors for Field-Effect Transistors

The past couple of years have witnessed a remarkable burst in the development of organic field-effect transistors (OFETs), with a number of organic semiconductors surpassing the benchmark mobility of 10 cm(2)/(V s). In this perspective, we highlight some of the major milestones along the way to provide a historical view of OFET development, introduce the integrated molecular design concepts and process engineering approaches that lead to the current success, and identify the challenges ahead to make OFETs applicable in real applications.

Organic field-effect transistor sensors: a tutorial review

The functioning principles of electronic sensors based on organic semiconductor field-effect transistors (OFETs) are presented. The focus is on biological sensors but also chemical ones are reviewed to address general features. The field-induced electronic transport and the chemical and biological interactions for the sensing, each occurring at the relevant functional interface, are separately introduced. Once these key learning points have been acquired, the combined picture for the FET electronic sensing is proposed. The perspective use of such devices in point-of-care is introduced, after some basics on analytical biosensing systems are provided as well. This tutorial review includes also a necessary overview of the OFET sensing structures, but the focus will be on electronic rather than electrochemical detection. The differences among the structures are highlighted along with the implications on the performance level in terms of key analytical figures of merit such as: repeatability, sensitivity and selectivity.

Performance Characteristics of Organic Photovoltaic Cells using Pentacene as a Hole Conducting Layer Material

The performance characteristics of organic photovoltaic cells using pentacene as a hole conducting material have been investigated. Pentacene has been extensively studied as a p-type semiconductor in organic field-effect transistors. In this study, pentacene was incorporated into PEDOT:PSS Film to improve mobility in the hole conducting layer. Organic photovoltaic cells have been fabricated with the structure of ITO/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS)-pentacene/CuPc/CuPc:C60/C60/BCP(bathocuproine)/Al. The power conversion efficiency was strongly dependent on the doping amount of pentacene in the PEDOT:PSS-pentacene films. Fabrication parameters also affected on the performance of pentacene-based photovoltaic cells.

The effect of Au Nanoparticle on Metal Organic Semiconductor Field effect Transistor on Plastic Substrate by Transfer Method

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A Soluble α-Dithienotetrathiafulvalene Derivative for Organic Field-effect Transistors

Abstract Bis(octylthio) derivative of α-dithienotetrathiafulvalene (α-DT-TTF) was synthesized, characterized, and examined as a semiconductor for organic field-effect transistors (OFETs). In contrast to no field-effect responses of devices based on evaporated thin-film of the parent α-DT-TTF, the octylthio derivative afforded solution-processed OFETs showing apparent normally-on behaviors with field-effect mobility of up to 0.6 cm2 V−1 s−1. Characterization of the thin-film revealed that the octylthio groups had significant impact on self-assembly, affording high quality thin films with well-oriented molecular array.

Dynamic character of charge transport parameters in disordered organic semiconductor field-effect transistors

In this perspective article, we discuss the dynamic instability of charge carrier transport in a range of popular organic semiconductors. We observe that in many cases field-effect mobility, an important parameter used to characterize the performance of organic field-effect transistors (OFETs), strongly depends on the rate of the gate voltage sweep during the measurement. Some molecular systems are so dynamic that their nominal mobility can vary by more than one order of magnitude, depending on how fast the measurements are performed, making an assignment of a single mobility value to devices meaningless. It appears that dispersive transport in OFETs based on disordered semiconductors, those with a high density of localized trap states distributed over a wide energy range, is responsible for the gate voltage sweep rate dependence of nominal mobility. We compare such rate dependence in different materials and across different device architectures, including pristine and trap-dominated single-crystal OFETs, as well as solution-processed polycrystalline thin-film OFETs. The paramount significance given to a single mobility value in the organic electronics community and the practical importance of OFETs for applications thus suggest that such an issue, previously either overlooked or ignored, is in fact a very important point to consider when engaging in fundamental studies of charge carrier mobility in organic semiconductors or designing applied circuits with organic semiconductors.

Single-step solution processing of small-molecule organic semiconductor field-effect transistors at high yield

Here, we report a simple, alternative route towards high-mobility structures of the small-molecular semiconductor 5,11-bis(triethyl silylethynyl) anthradithiophene that requires one single processing step without the need for any post-deposition processing. The method relies on careful control of the casting temperature of the semiconductor and allows rapid production of transistors with uniform and reproducible device performance over large areas.

Thienoacene‐Based Organic Semiconductors

Thienoacenes consist of fused thiophene rings in a ladder-type molecular structure and have been intensively studied as potential organic semiconductors for organic field-effect transistors (OFETs) in the last decade. They are reviewed here. Despite their simple and similar molecular structures, the hitherto reported properties of thienoacene-based OFETs are rather diverse. This Review focuses on four classes of thienoacenes, which are classified in terms of their chemical structures, and elucidates the molecular electronic structure of each class. The packing structures of thienoacenes and the thus-estimated solid-state electronic structures are correlated to their carrier transport properties in OFET devices. With this perspective of the molecular structures of thienoacenes and their carrier transport properties in OFET devices, the structure-property relationships in thienoacene-based organic semiconductors are discussed. The discussion provides insight into new molecular design strategies for the development of superior organic semiconductors.

Modulated intermolecular electrostatic interaction and morphology transition in squarylium dyes based organic field-effect transistors

A series of indolium squarine dyes were studied as air-stable semiconductors in organic field-effect transistors. By modulating substituted groups and structural rigidity, a mobility of 4.8 × 10 −3 cm 2/Vs was achieved in solution processed device and the highest mobility of 0.2 cm 2/Vs was obtained in single crystal devices. By structural analysis and theoretical calculation, crystal packing mode was found to be associated with the electrostatic attraction and repulsion between positive and negative charge centers of the molecule. This electrostatic interaction drove the spontaneous intermolecular ordering in the film, and resulted in performance enhancement for ISQ transistors. Quantitative research between mobility and the area of polycrystalline regions revealed the dependence of transport ability on the continuity and uniformity of the crystalline phase.

Dianthra[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DATT): Synthesis, Characterization, and FET Characteristics of New π-Extended Heteroarene with Eight Fused Aromatic Rings

A novel highly π-extended heteroarene with eight fused aromatic rings, dianthra[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DATT), was selectively synthesized via a newly developed synthetic strategy, fully characterized by means of single crystal X-ray structural analysis, and examined as an organic semiconductor in thin film transistors. Even with its highly extended acene-like π-system, DATT is a fairly air-stable compound with IP of 5.1 eV. Single crystal X-ray structural analysis revealed its planar molecular structure and the lamella-like layered structure with typical herringbone packing. Theoretical calculations of the solid state electronic structure based on the bulk single crystal structure suggest that DATT affords almost comparable intermolecular orbital couplings between HOMOs (t(HOMO)) with those of dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT), implying its good potential as an organic semiconductor for organic field-effect transistors. In fact, field-effect mobilities as high as 3.0 cm(2) V(-1) s(-1) were achieved with vapor-processed DATT-based devices, which is comparable with that of DNTT-based devices. The molecular ordering of DATT in the thin film state, however, turned out to be not completely uniform; as elucidated by in-plane and out-of-plane XRD measurements, the face-on molecular orientation was contaminated in the edge-on orientation, the former of which is not optimal for efficient carrier transport and thus could limit the mobility.

Organic Charge-transfer Salts and the Component Molecules in Organic Transistors

Abstract Electron donors and acceptors such as tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ), which have been long known as components of organic metals, act as p- and n-channel organic semiconductors in organic field-effect transistors. High performance, good thin-film properties, and long-term stability have been achieved on the basis of appropriate molecular design. In addition, their charge-transfer complexes work as the active layers as well as conducting electrode materials showing low contact resistance.

Charge transport and electronic properties of N-heteroquinones: quadruple weak hydrogen bonds and strong π–π stacking interactions

The charge transport and photophysical properties of N-heteroquinones, which can function as n-type organic semiconductors in organic field-effect transistors (OFETs) with high electron mobility, were systematically investigated using hopping model, band theory, and time-dependent density functional theory (TDDFT). The calculated absorption spectra and electron mobility are in good agreement with experimental results. To the studied compounds, subtle structural modifications can greatly reduce the reorganization energy. There are two main kinds of intermolecular interaction forces of the studied compounds in the crystal, which result from intermolecular π–π and hydrogen bonds interactions, respectively. The results of hopping model show that the electron transport properties are mainly determined by pathways containing intermolecular π–π interactions, and hole transport properties are mainly determined by pathways containing intermolecular hydrogen bonds from the standpoint of transfer integral. Moreover, electronic transfer integral value increases with the enhancement of intermolecular overlap corresponding to the overlap extent of π–π packing. Hole transfer integral value decreases with decreasing the number of hydrogen bonds. This means that charge transport properties can be efficiently tuned by controlling the relative positions of the molecules and the number of hydrogen bonds. The analysis of band structure also supports the conclusion of hopping model.

Polythiophenes: Important Conjugated Semiconducting Polymers for Organic Field-Effect Transistors

Polythiophenes (PTs) are one of the most important classes of conjugated polymers employed as semiconductors in organic field-effect transistors (OFETs). In the last few years, versatile thiophene-based polymers have received great interest for applications in large-area, flexible, and low-cost electronics attributing to their excellent optoelectronic properties. Significant progress has been made in PT-based semiconductors for high performance transistors. We review here the achievements gained in conjugated PT-based semiconductors and demonstrate their structural modifications and design principles. We highlight the most important semiconducting polymers created from PT derivatives obtained through rational monomer design, controlled π-conjugation and appropriately positioned pendant side-chain distribution. Finally, we discuss remaining challenges and outline our views on future developments. Keywords: Polythiophenes, organic field-effect transistors

Semiconducting Organic Molecular Materials

Semiconducting Organic Molecular MaterialsThis feature article gives an overview of recent advances in development of high performance molecular organic semiconductors for field-effect transistors with emphasis on the structure of molecular materials and requirements for high-performance.

Effect of interface roughness on the carrier transport in germanium MOSFETs investigated by Monte Carlo method

Interface roughness strongly influences the performance of germanium metal–organic–semiconductor field effect transistors (MOSFETs). In this paper, a 2D full-band Monte Carlo simulator is used to study the impact of interface roughness scattering on electron and hole transport properties in long- and short- channel Ge MOSFETs inversion layers. The carrier effective mobility in the channel of Ge MOSFETs and the in non-equilibrium transport properties are investigated. Results show that both electron and hole mobility are strongly influenced by interface roughness scattering. The output curves for 50 nm channel-length double gate n and p Ge MOSFET show that the drive currents of n- and p-Ge MOSFETs have significant improvement compared with that of Si n- and p-MOSFETs with smooth interface between channel and gate dielectric. The 82% and 96% drive current enhancement are obtained for the n- and p-MOSFETs with the completely smooth interface. However, the enhancement decreases sharply with the increase of interface roughness. With the very rough interface, the drive currents of Ge MOSFETs are even less than that of Si MOSFETs. Moreover, the significant velocity overshoot also has been found in Ge MOSFETs.

Chrysene Derivatives as New Organic Semiconductors for Organic Field-effect Transistors

Organic field-effect transistors based on vapor deposited films of 2,8-dioctylchrysene (C8-CR), 2,8-diphenylchrysene (Ph-CR), 2,8-dinaphthylchrysene (Nap-CR) and 2,8-bis(octylstyryl)chrysene (C8S-CR) were successfully fabricated. All the chrysene derivatives based OFETs showed typical p-channel FET characteristics, and the best field-effect mobility of 4.1 x 10^-2 cm^2V^-1s^-1 with on/off current ratio of 10^5 was obtained for the Ph-CR based OFET. Interestingly, the field-effect characteristics were strongly affected by substrate temperatures (Tsub). According to the AFM and XRD measurements, molecular packing and morphology of the deposited films were drastically changed by substrate temperatures.

High performance organic semiconductors for field-effect transistors

The purpose of this feature article is to give an overview of recent advances in development of high performance organic semiconductors for field-effect transistors, especially those with mobility of/over amorphous silicon, since they are believed to be promising candidates with practical applications in the near future's organic electronic industry. We hope this comprehensive summary of high performance organic semiconductors will provide guidelines for the design and synthesis of novel, high performance organic field-effect semiconductors.