Applications In Organic Field-effect Transistors Research Articles

Solution‐Processable Multifused Thiophene Small Molecules and Conjugated Polymer Semiconducting Blend for Organic Field Effect Transistor Application

AbstractThree new solution‐processable organic semiconductors (1–3) are synthesized and characterized for p‐type organic field effect transistors (OFETs). The backbone of these small molecules is modified by expanding the central core conjugation from thienothiophene (TT) to dithienothiophene (DTT) and tetrathienoacene (TTA), which are end‐capped with soluble β‐substituted alkyl chains dithienothiophenes (DTTR) to generate DTTR‐TT (1), DTTR‐DTT (2), and DTTR‐TTA (3). The highest mobility of 0.016 cm2 V−1 s−1 is achieved using solution‐sheared DTTR‐TTA film due to the extended conjugated TTA core, which enhances the intermolecular interaction and generates an efficient percolation for the OFET channel. Solution blending of crystalline DTTR‐TT small molecules with oriented‐packing polymer dithienothiophene‐thioalkylbithiophene (PDTT‐SBT) polymer leads to significantly enhanced mobilities from 0.0009 up to 0.22 cm2 V−1 s−1, occurring at an optimized 30% DTTR‐TT composition in the blend. Hole mobility of 30% DTTR‐TT blend is 0.22 cm2 V−1 s−1 which is higher than pristine small molecule DTTR‐TT (0.0009 cm2 V−1 s−1) and polymer PDTT‐SBT (0.067 cm2 V−1 s−1), respectively. An efficient strategy to enhance the mobility of small molecule DTTR‐TT by blending with easily synthesizable PDTT‐SBT polymer is reported.

Two-step direct heteroarylation reaction towards 2,5-bis(alkoxy)benzene polymer for organic field-effect transistors processed with tetrahydrofuran

A 2,5-bis(alkoxy)benzene polymer POB-TNT has been newly designed and synthesized via very convenient two-step direct heteroarylation reaction. Its physicochemical properties have been investigated. POB-TNT demonstrates typical [Formula: see text]-type carrier transport characteristic in unencapsulated bottom-gate and top-contact organic field-effect transistors (OFETs) processed with relatively green tetrahydrofuran solvent. The results highlight a readily accessible and low-cost-oriented polymer semiconductor for non-halogenated solvent-processed OFET application.

Simple synthesis of alkyl derivatives of tetrathienoacene and their application in organic field-effect transistors

Friedel–Crafts acylation of tetrathienoacene (TTA) followed by a reduction reaction led to promising organic semiconductor C8-TTA-C8, which was preliminarily tested as an active layer in OFETs.

Bis-isatin based polymers with tunable energy levels for organic field-effect transistor applications

Two bis-isatin based building blocks have been synthesized with the aid of non-covalent intramolecular interactions. Their polymers showed p-type or ambipolar charge transport in OFETs.

Highly Ordered Adlayer Formation of Water-Insoluble Nanographenes on Gold Using "Molecular Container"

Carbon materials such as graphene have been extensively studied for their application in electronic devices,electrocatalysis, and sensors. In contrast, polycyclic aromatic hydrocarbons (PAHs), the so-called nanographenes, are excellent materials for the creation of two-dimensional (2D) nanosheets.[1] The formation of adlayers on electrode surfaces is challenging because PAHs without peripheral substituents are used as 2D molecular templates and applications in conductance enhancement and organic field-effect transistors.[2] However, large PAHs tend to exhibit poor or no solubilities in organic solvents and water.To overcome this issue, in this study, we employed water-soluble micellar capsules consisting of V-shaped amphiphilic molecules. Characteristic electrochemical behaviors were observed in 0.1 M H2SO4 in the presence of the water-soluble capsules containing PAHs such as dicoronylene. Furthermore, under these conditions, PAHs were released from the capsules, resulting in the formation of a 2D adlayer of PAHs at the electrochemical interface. Finally, using electrochemical scanning tunneling microscopy (EC-STM), we demonstrate that our molecular containers based on the water-soluble molecular capsules allow the facile preparation of 2D PAH adlayers in addition to structurally controlling nanostructure formation on Au surfaces.In particular, dicoronylene molecules formed a highly ordered adlayer with c(4 x 8√3)rect adlattice.[3]

Diketopyrrolopyrrole–thiophene–methoxythiophene based random copolymers for organic field effect transistor applications

Abstract Methoxy-substituted thiophene units were incorporated into a diketopyrrolopyrrole and quaterthiophene based copolymer to produce random copolymers. Inclusion of the methoxy group narrowed the optical energy gap of the resulting copolymers owing to the enhanced planar backbone that results in more effective conjugation. At a low loading ratio of 25mol% random copolymer exhibited a hole mobility of ~0.3 cm2 V−1 s−1 comparable to that of the diketopyrrolopyrrole and quaterthiophene based original polymer. Although increasing the methoxy-substituted thiophene ratio in the polymers resulted in decreased molecular weights, it was concluded that incorporation of the methoxy-substituted thiophenes enhanced the hole mobility from 0.02 cm2 V−1 s−1 for 50mol% loading to 0.07 cm2 V−1 s−1 for 100mol% loading. The enhancement was attributed to the formation of pre-aggregates with stronger interchain interactions with increasing backbone coplanarity, resulting in edge-on dominant and bimodal edge-on/face-on molecular packing orientations. The addition of tetramethylammonium iodide as an ionic additive proved not to be an effective method for improving the performance of polymers containing the methoxy-substituted thiophenes, whereas the original polymer displayed a noticeable improvement of the charge transport properties.

Synthesis, characterization and organic field-effect transistors applications of novel tetrathienoacene derivatives

Two novel organic semiconductors with tetrathienoacene (TTA) as the central core end-capped with 5-hexyl-2-thiophene, (Hex-T)2-TTA, and 4-hexyl-phenyl, (Hex-Ph)2-TTA, have been synthesized and investigated for organic field effect transistor (OFET) applications. The novel TTA derivatives were characterized by thermal gravimetric analysis, differential scanning calorimetry, UV–Vis spectroscopy, and cyclic voltammetry as well as studied by density functional theory calculations. Two types of OFETs with the solution and vacuum-deposited active layer were fabricated and characterized. Both TTA-derivatives demonstrated electroluminescence in OFETs, and (Hex-Ph)2-TTA showed ambipolar charge transport with the hole mobility as high as 0.68 cm2 V−1s−1.

Diketopyrrolopyrrole (DPP)-Based Materials and Its Applications: A Review.

Diketopyrrolopyrrole (DPP) and its derivatives have been widely studied in the past few years due to its intrinsic physical and chemical properties, such as strong electron-withdrawing, deep color, high charge carrier mobility, strong aggregation, good thermal-/photo-stability. In the 1970s, DPP was developed and used only in inks, paints, and plastics. Later, DPP containing materials were found to have potential other applications, typically in electronic devices, which attracted the attention of scientists. In this feature article, the synthesis pathway of DPP-based materials and their applications in organic field-effect transistors, photovoltaic devices, sensors, two photo-absorption materials, and others are reviewed, and possible future applications are discussed. The review outlines a theoretical scaffold for the development of conjugated DPP-based materials, which have multiple potential applications.

Pyrrole-Containing Semiconducting Materials: Synthesis and Applications in Organic Photovoltaics and Organic Field-Effect Transistors.

Organic semiconducting materials derived from π-electron-rich pyrroles have garnered attention in recent years for the development of organic semiconductors. Although pyrrole is the most electron-rich five-membered heteroaromatic ring, it has found few applications in organic photovoltaics and organic field-effect transistors due to synthetic challenges and instability. However, computational modeling assisted screening processes have indicated that relatively stable materials containing pyrrolic units can be synthesized without compromising their inherent electron-donating properties. In this work, we provide a complete, up-to-date review of pyrrole-containing semiconducting materials used for organic photovoltaics and organic field-effect transistors and highlight recent advances in the synthesis of these materials.

Tuning the Emission Color of Indolo[3,2‐b]carbazole‐Based Boron Complexes and their Application in Organic Field Effect Transistors and Bioimaging

AbstractSynthetic strategies were developed for the preparation of indolo‐imine boron difluoride (IIBD) dyes based on indolo[3,2‐b]carbazole structures. Four new IIBD dyes were synthesized and were subsequently converted into the corresponding ‐BPh2/‐BOR2 and N‐t‐Boc/N‐benzoyl derivatives. The photophysical properties of all dyes were determined in both solution and solid media. All dyes absorb in the UV/Vis region, show negative solvatochromism, and are fluorescent in both media. The absorbance and fluorescence properties of the dyes can be tuned over a wide range by synthetic modifications. These findings are rationalized by theoretical calculations that correspond well to the experimental shifts, explain the negative solvatochromism, and allow quantification of charge transfer (CT). Similarly, the HOMO–LUMO energies measured by CV are in good agreement with the theoretically calculated values. Interestingly, the energy gaps of the dyes can also be tuned by structural modulations using the developed chemical route. Charge transport properties of the dyes were checked and showed that the N‐benzoyl derivative has the highest hole mobility which is useful for organic field effect transistor (OFET) applications. In addition, easy cellular uptake of the dyes, their low toxicity and high stability inside the cells associated with bright fluorescence in the cytoplasm will be useful for their future application as cellular imaging agents. All of these aspects highlight the interest of this new class of dyes.

Flurorinated isomeric polymer semiconductors for air-stable unencapsulated transistors

Two flurorinated isomeric polymeric semiconductors (P1 and P2) containing benzo[[Formula: see text]][1,2,5]thiadiazole units have been newly designed and synthesized. Basic physicochemical properties, surface morphology and crystallinity features have been investigated. Both polymers show typical [Formula: see text]-type charge transport characteristics. P1 displays better average hole mobility of ‘[Formula: see text][Formula: see text]cm2[Formula: see text][Formula: see text] with high on/off ratio of [Formula: see text] and low threshold voltage of [Formula: see text]. Both polymers exhibit good hole transport stability in ambient condition based on the result of continuously monitoring unencapsulated device performances for 110 days. The results demonstrate the isomeric effect on optoelectronic properties of new flurorinated polymers, which are promising semiconductors for air-stable unencapsulated organic field-effect transistor application.

Hysteresis-Free, High-Performance Polymer-Dielectric Organic Field-Effect Transistors Enabled by Supercritical Fluid.

Organic field-effect transistors (OFETs) are of the core units in organic electronic circuits, and the performance of OFETs replies critically on the properties of their dielectric layers. Owing to the intrinsic flexibility and natural compatibility with other organic components, organic polymers, such as poly(vinyl alcohol) (PVA), have emerged as highly interesting dielectric materials for OFETs. However, unsatisfactory issues, such as hysteresis, high subthreshold swing, and low effective carrier mobility, still considerably limit the practical applications of the polymer-dielectric OFETs for high-speed, low-voltage flexible organic circuits. This work develops a new approach of using supercritical CO2 fluid (SCCO2) treatment on PVA dielectrics to achieve remarkably high-performance polymer-dielectric OFETs. The SCCO2 treatment is able to completely eliminate the hysteresis in the transfer characteristics of OFETs, and it can also significantly reduce the device subthreshold slope to 0.25 V/dec and enhance the saturation regime carrier mobility to 30.2 cm2 V−1 s−1, of which both the numbers are remarkable for flexible polymer-dielectric OFETs. It is further demonstrated that, coupling with an organic light-emitting diode (OLED), the SCCO2-treated OFET is able to function very well under fast switching speed, which indicates that an excellent switching behavior of polymer-dielectric OFETs can be enabled by this SCCO2 approach. Considering the broad and essential applications of OFETs, we envision that this SCCO2 technology will have a very broad spectrum of applications for organic electronics, especially for high refresh rate and low-voltage flexible display devices.

Novel and asymmetric S,N-heterocyclics with fused six-membered rings for organic field effect transistor applications

Three novel ladder-type and asymmetric S,N-heterocyclics with fused six-membered rings have been designed and synthesised, their packing modes, opto-electronic property and charge transport abilities have also been evaluated systematically.

Solution-Processable Unsymmetrical Triarylamines: Towards High Mobility and ON/OFF Ratio in Bottom-Gated OFETs.

Self-assembly of organic small molecules into an ordered thin film has been the key strategy towards efficient charge transport for organic field-effect transistors (OFETs). Solution processing is a feasible and economic way to enhance pi-pi interaction. Herein, nitrile-substituted unsymmetrical triarylamines for OFET applications with high mobility are reported. The compounds were constructed by Suzuki cross-coupling reactions under inert conditions. The HOMO level of about 5.3 eV indicates good hole-transporting ability. OFETs were assembled in bottom-gate, top-contact architecture. Devices fabricated from a binary solvent system exhibited excellent p-channel characteristics, with impressively high charge-carrier mobility of up to 2.58 cm2 V-1 s-1 and ION/OFF current ratios of 106 -107 . SEM and AFM analysis showed the efficient molecular self-assembly attained by the simple and effective solvent-engineering method. Theoretical insights obtained by DFT calculations supported by single-crystal structures showed that the crystalline nature and packing modes of these compounds ensure high mobility. The results prove that these compounds have great potential for use in numerous electronic applications, such as sensors and logic switches.

Modulation of transversal conductivity of europium(III) bisphthalocyaninate ultrathin films by peripheral substitution

In the present work, we demonstrate that transversal conductivity and, consequently, electrochemical activity of ultrathin solid films of two structurally similar octa-butoxy and tetra-crown-ether substituted europium bisphthalocyaninates are quite different. It is shown that presence of the crown moieties allows excellent transfer of charge through monomolecular ultrathin films of respectively substituted complex. This enables their redox-multistability, which can be utilized in molecular logic and information storage devices. On the other hand, transversal charge transfer is inhibited in the films of octa-butoxy-substituted bisphthalocyaninate, which might be promising for organic field-effect transistor applications.

Understanding of Fluorination Dependence on Electron Mobility and Stability of Naphthalenediimide-Based Polymer Transistors in Environment with 100% Relative Humidity.

A family of copolymers (P(NDIOD-T2Fx)) based on naphthalenediimide (NDI) and 2,2'-bithiophene (T2) units with different amounts of 3,3'-difluoro-2,2'-bithiophene (T2F) decoration were synthesized, characterized, and used in n-type organic field-effect transistors (OFETs). With increasing T2F content in the backbone, we observe increased melting and crystallization transitions, blue-shifted absorptions, and deeper-lying highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels, together with improved hydrophobicity. The highest electron mobility of 4.48 × 10-1 cm2 V-1 s-1 was obtained for P(NDIOD-T2F0) without a T2F unit, which is attributed to the larger domain grains and crystallites, as well as a more tightly packed and oriented crystalline structure, as evidenced from the morphological study. In contrast, P(NDIOD-T2F100) with the highest T2F content has superior air stability, showing greater than 25% electron mobility retention after 30 days in wet conditions of 100% relative humidity without encapsulation. Even P(NDIOD-T2F100) is able to operate normally after 30 min of immersion in water, which is due to the synergistic contributions from the deep HOMO/LUMO levels and improved hydrophobicity. This study advances our fundamental understanding of how the morphology/crystallinity, device performance, and device stability of n-type copolymers are tuned by incorporating different concentrations of T2F in the backbone, shedding light on an important modification for air- and water-stable n-type materials for future OFET applications.

Large-Area MXene Electrode Array for Flexible Electronics.

MXenes, an emerging class of two-dimensional (2D) transition metal carbides and nitrides, have potential for application as high-performance, low-cost electrodes in organic field-effect transistors (OFETs) because of their water dispersibility, high conductivity, and work-function tunability. In this study, we successfully fabricated a large-scale, uniform Ti3C2Tx MXene electrode array on a flexible plastic substrate for application in high-performance OFETs. The work function of the Ti3C2Tx MXene electrodes was also effectively modulated via chemical doping with NH3. The fabricated OFETs with Ti3C2Tx MXene electrodes exhibited excellent device performance, such as a maximum carrier mobility of ∼1 cm2·V-1·s-1 and an on-off current ratio of ∼107 for both p-type and n-type OFETs, even though all the electrode and dielectric layers were fabricated on the plastic substrate by solution processing. Furthermore, MXene-electrode-based complementary logic circuits, such as NOT, NAND, and NOR, were fabricated via integration of p-type and n-type OFETs. The proposed approach is expected to expand the application range of MXenes to other OFET-based electronic devices, such as organic light-emitting displays and electronic skins.

Precise Extraction of Charge Carrier Mobility for Organic Transistors

AbstractUnreliable mobility values, and particularly greatly overestimated values and severely distorted temperature dependences, have recently hampered the development of the organic transistor field. Given that organic field‐effect transistors (OFETs) have been routinely used to evaluate mobility, precise parameter extraction using the electrical properties of OFETs is thus of primary importance. This review examines the origins of the various mobilities that must be determined for OFET applications, the relevant extraction methods, and the data selection limitations, which help in avoiding conceptual errors during mobility extraction. For increased precision, the review also discusses device fabrication considerations, calibration of both the specific gate‐dielectric capacitance and the threshold voltage, the contact effects, and the bias and temperature dependences, which must actually be handled with great care but have mostly been overlooked to date. This review serves as a systematic overview of the OFET mobility extraction process to ensure high precision and will also aid in improving future research.

Influence of Al2O3 nanoparticles incorporation on the dielectric properties of solution processed PVA films for organic field effect transistor applications

We report, the influence of Al2O3 nanoparticles (NP) incorporation on the dielectric properties of solution processed polyvinylalcohol (PVA) films for organic field effect transistor applications. It was observed typical p-type organic field effect transistors. Devices processed using employing PVA films blended with 70 wt% of Al2O3 NP as gate dielectric layers demonstrated higher field effect mobility, better saturation behavior and reduced hysteresis phenomenon compared to the devices based on pure PVA films. Al2O3 NP:PVA blends based dielectric films with 0, 3, 5, 10, 20, 50 and 70 wt% concentrations of Al2O3 NP compared to the weight of PVA were prepared. Dielectric parameters such as dielectric constant and dielectric strength of the Al2O3 NP:PVA films were analyzed. It was found that real dielectric constant as well as dielectric strength of the films increase with increase of Al2O3 NP concentration. Cole–Cole plots of the films demonstrated depressed semi-circles which points non-Debye type behavior. We presume that the devices being investigated with promising results, may be utilized for some industrial applications such as large area sensor arrays in future.

High-Performance Organic Field-Effect Transistors Fabricated with High-k Composite Polymer Gel Dielectrics

This study presents a composite gel-like dielectric material for organic field-effect transistors (OFET) applications. Poly(methyl methacrylate) (PMMA) gelled with propylene carbonate was used as gel dielectric material. Copper phthalocyanine was used as active layer in the OFET structures. In order to enhance the performance of the PMMA-gel dielectric material, silicium dioxide (SiO2) was used as an additive material. Various ratios of SiO2 were added to the gel dielectric and the effect of SiO2 on the OFET performance was investigated. It was clearly observed that SiO2 enhanced the performance and source-drain current of the fabricated OFETs. SiO2 was added to the PMMA-gel with different doping ratios of 0%, 10%, 30%, 50% and 100% by using a solution-processing method. The dielectric properties of the PMMA-gel:SiO2 composite materials were analyzed with impedance spectroscopy in terms of their effective capacitance ©I), tangent factor (tan(δ)), phase angle and complex dielectric constant (e′ and e″). The hole mobility of the OFETs was enhanced by 50% SiO2 nanoparticles in PMMA-gel dielectric materials from 6.83 × 10−1 cm2 V−1 s−1 to 4.66 × 100 cm2 V−1 s−1 (at VDS = − 0.5 V). The time-dependent IDS curves were analyzed for OFETs fabricated with PMMA-gel:SiO2 composite dielectric layers. It was found that all the devices worked stably under bias stress and gave fast responses for all gate voltages.