Polymer Organic Field-effect Transistors Research Articles

Optimized Incorporation of Furan into Diketopyrrolopyrrole-Based Conjugated Polymers for Organic Field-Effect Transistors.

Flexible electronics have received considerable attention in the past decades due to their promising application in rollable display screens, wearable devices, implantable devices, and other electronic applications. In particular, conjugated polymers are favored for flexible electronics due to their mechanical flexibility and potential for solution-processed fabrication techniques, such as blade-coating, roll-to-roll printing, and high-throughput printing allowing for high-performance transistor devices. Thiophene is the prevailing conjugated unit to construct these conjugated polymers due to its favorable electronic properties. On the other hand, furans are among the few conjugated moieties that are easily derived from bio renewable resources. To promote sustainability, we selectively introduced furan into the conjugated backbone of a high-mobility polymer scaffold and systematically studied the effect on the microstructure and charge transport. We show that partially and selectively replacing thiophene units with furan can yield nearly comparable performance compared to the all-thiophene polymer. This strategy offers an improvement in the sustainability of the polymer by incorporating bio-sourced furan without sacrificing the high-performance characteristics. Meanwhile, polymers with incorrect or complete furan incorporation show reduced mobilities. This work serves to develop coherent structure-morphology-performance relationships; such knowledge will establish guidelines for the future development of sustainable, furan-based conjugated materials.

Aza-anthradithiophene-based conjugated polymers: Synthesis and field-effect transistor application

Acenedithiophenes are classical fused-ring units for constructing conjugated polymers. In this work, a new aza-anthradithiophene unit has been designed and was for the first time employed as building unit to constructing conjugated polymers for organic field-effect transistors. Two conjugated polymers based on thiophthene (P1) and benzothiadiazole (P2) as co-units were synthesized by Stille and Suzuki coupling reactions, respectively. The thermal stability, optical and electrochemical properties, and microstructure were investigated. Organic field-effect transistor devices based on conjugated polymers as semiconductor layer were also fabricated and two polymers exhibited typical hole transport characteristics with the average field-effect mobility up to 7.9 × 10−4 cm2V−1s−1 and Ion/Ioff ratios over 104.

DPP-based polymers with linear/branch side chain for organic field-effect transistors.

For polymer semiconductors, the packing ability and molecular weight of polymers play a very critical role in their optoelectronic properties and carrier transport properties. In this work, two polymers, named linear and branch, are designed and synthesized with donor–acceptor (D-A) structure, based on diketopyrrolopyrrole as an electron acceptor and carbazole as an electron donor, and applied these two polymers in organic field-effect transistors. Linear and branch have similar conjugated backbones but different molecular weights and alkyl chains. The effects of molecular weight and molecular aggregation ability on the carrier transfer efficiency are investigated. As a result, linear exhibits better aggregation ability, but due to its smaller molecular weight than branch molecule, the hole transfer efficiency of linear (1.1 × 10−2 cm2 V −1 s−1) is slightly lower than that of branch (2.3 × 10−2 cm2 V −1 s−1). This work proves that molecular weight is more important than molecular aggregation ability when designing organic field-effect transistors for polymer semiconductors.

A thriving decade: rational design, green synthesis, and cutting-edge applications of isoindigo-based conjugated polymers in organic field-effect transistors

A thriving decade: rational design, green synthesis, and cutting-edge applications of isoindigo-based conjugated polymers in organic field-effect transistors

Electrohydrodynamic-Jet-Printed Phthalimide-Derived Conjugated Polymers for Organic Field-Effect Transistors and Logic Gates.

A π-conjugated polymer semiconductor, PBDTTTffPI, was synthesized for use as an organic semiconductor suitable for electrohydrodynamic (EHD) jet printing technology. Bulky alkylation of the polymer gave PBDTTTffPI good solubility in several organic solvents. EHD jet printing using PBDTTTffPI ink produced direct patterns of polymer semiconductors while maintaining smooth surface morphologies and crystal structures similar to those of spin-coated PBDTTTffPI films. EHD-jet-printed PBDTTTffPI was appropriate for use as a semiconductor layer in organic field-effect transistors (OFETs) and logic gates. OFETs that used EHD-jet-printed PBDTTTffPI had better electrical characteristics than devices that used spin-coated semiconductor films. When a dielectric material (Al2O3) with a high dielectric constant was introduced, the jet-printed PBDTTTffPI operated well at low voltages. Integrated devices such as inverters, NAND gates, and NOR gates were fabricated by printing PBDTTTffPI patterns and showed good switching behaviors. Therefore, the use of printable PBDTTTffPI provides an advance toward fabrication of practical integrated arrays in next-generation devices.

Toward Efficient Charge Transport of Polymer-Based Organic Field-Effect Transistors: Molecular Design, Processing, and Functional Utilization

ConspectusPolymer-based organic field-effect transistors (OFETs) have attracted great attention owing to their significantly improved performance and the recently emerged prospects for broad applications. The charge carrier mobility of polymer-based OFETs has been improved from 10–5 to more than 10 cm2 V–1 s–1 over the past three decades. With the carrier mobility close to or higher than that of amorphous silicon, the application fields of polymer-based OFETs have been extended from sensing to logic or drive circuits. During OFET operation, the charge carriers are successively injected in and then transferred across the semiconducting channel under an external electric field. The behavior of the charge carriers is determined by both charge injection and charge transport. Well-matched frontier molecular orbital (FMO) energy levels and optimized hierarchical structures of semiconducting polymers are essential for the realization of high-performance polymer-based OFETs.In this Account, we mainly demonstrate our recent progress in molecular design strategies and fabrication processing methods for high-performance semiconducting polymers. Moreover, we provide some examples of integrated applications of polymer-based OFETs. The convenient FMO energy level modulation and excellent molecular designability of donor–acceptor (D–A) conjugated polymers facilitate studies on their performance enhancement in OFETs. Proper molecular design of the D–A polymer backbone and side chain can significantly contribute to charge injection enhancement, transport pathway establishment, and trap reduction, thereby resulting in efficient charge transport. Moreover, special fabrication processes of OFET devices can further enhance the charge transport by optimizing the hierarchical structures of semiconducting polymers, thereby enhancing their carrier mobility and stability. By employing high-performance semiconducting polymers as the semiconducting channel of OFETs, various applications can be implemented. These applications range from small-scale logic signal processing and periodic signal generation to complex visual perception systems, indicating broad application prospects in human life. The works on performance improvement and functional utilization of the semiconducting polymers in OFETs might provide insights for molecular design strategies and applications for future plastic electronics.

An unprecedented quinoid–donor–acceptor strategy to boost the carrier mobilities of semiconducting polymers for organic field-effect transistors

A novel quinoid–donor–acceptor strategy to design a quinoidal–aromatic conjugated polymer PAQM-BT is established. A hole mobility of up to 5.10 cm2 V−1 s−1 in OFETs is realized, which is among the highest values for quinoidal–aromatic polymers.

3,4-Ethylenedioxythiophene-Based Isomer-Free Quinoidal Building Block and Conjugated Polymers for Organic Field-Effect Transistors

Since quinoidal molecules have double-bond linkages between aromatic rings, they have many advantages for efficient charge transport resulting from high planarity and extended π-conjugation length. However, they unavoidably generate some isomers, which cause difficulty in purification and characterization. In this study, sulfur–oxygen conformation locking and steric repulsion approach is introduced to manipulate syn- and anti-isomerization of a quinoidal building block (bis-QEDOT). As a result, isomer-free bis-QEDOT is synthesized by introducing the 3,4-ethylenedioxy group, and the geometrical structure of bis-QEDOT is identified by thin-layer chromatography, 1H NMR, and density functional theory calculation. Furthermore, thiophene (T), bithiophene (2T), and thienylene vinylene (TV) as π-conjugated building blocks are polymerized with bis-QEDOT. Due to the quinoid structure, PQEDOT-T, PQEDOT-2T, and PQEDOT-TV show an intensified near-IR absorption and a low band gap around ∼1.16 eV. Grazing incidence wide-angle X-ray diffraction reveals that three quinoidal polymers show in the (h00) diffraction peaks up to third order after thermal annealing at 250 °C, demonstrating high crystallinity of the films. Finally, the electrical properties of the three polymers are investigated as an active layer in organic field-effect transistors showing hole mobilities of 4.3 × 10–2 (PQEDOT-T), 1.8 × 10–2 (PQEDOT-2T), and 7.8 × 10–3 cm2 V–1 s–1 (PQEDOT-TV).

Recent advances in the orientation of conjugated polymers for organic field-effect transistors

This review summarizes recent advancements in various orientation techniques for conjugated polymers for use in high performance organic field effect transistors.

Alkoxy-Substituted Anthra[1,2-c:5,6-c′]bis([1,2,5]thiadiazole) (ATz): A New Electron-Acceptor Unit in the Semiconducting Polymers for Organic Electronics

A new type of thiadiazole-based acceptor unit and its donor–acceptor copolymers were synthesized and characterized to develop the high-performance semiconducting polymers for organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). We successfully synthesized an anthra[1,2-c:5,6-c′]bis([1,2,5]thiadiazole) (ATz) core and ATz-quaterthiophene copolymers. These copolymers possess a wide energy gap of ca. 1.8 eV and a deeper HOMO energy levels around −5.4 eV than that of typical thiadiazole–oligothiophene copolymers. Such weak electron-accepting nature may be due to the decreased electron affinity of the ATz core by an existence of alkoxy groups with strong electron-donating ability. The ATz copolymers exhibited good semiconducting properties with hole mobility of up to 0.03 cm2 V–1 s–1 and photovoltaic response with PCE of up to 5.7%, despite the unfavorable molecular orders, thin-film structure, and/or amorphous structure.

Hydrocarbons‐Driven Crystallization of Polymer Semiconductors for Low‐Temperature Fabrication of High‐Performance Organic Field‐Effect Transistors

AbstractWhile many high‐performance polymer semiconductors are reported for organic field‐effect transistors (OFETs), most require a high‐temperature postdeposition annealing of channel semiconductors to achieve high performance. This negates the fundamental attribute of OFETs being a low‐cost alternative to conventional high‐cost silicon technologies. A facile solution process is developed through which high‐performance OFETs can be fabricated without thermal annealing. The process involves incorporation of an incompatible hydrocarbon binder or wax into the channel semiconductor composition to drive rapid phase separation and instantaneous crystallization of polymer semiconductor at room temperature. The resulting composite channel semiconductor film manifests a nano/microporous surface morphology with a continuous semiconductor nanowire network. OFET mobility of up to about 5 cm2 V−1 s−1 and on/off ratio ≥ 106 are attained. These are hitherto benchmark performance characteristics for room‐temperature, solution‐processed polymer OFETs, which are functionally useful for many impactful applications.

Recent progress in thermally stable and photosensitive polymers

Thermally stable and photosensitive polymers (TSPSPs), such as photosensitive polyimides (PSPIs) and polybenzoxazoles (PSPBOs), have been widely developed in recent years for their applications in electronic packaging (for example, buffer coating, passivation layers, and insulation layers) and redistribution in microelectronics due to their excellent thermal and reasonable dielectric properties. This review describes recent advances in TSPSPs during the last decade and focuses on related design concepts. Following a brief introduction of the basic patterning procedure, various chemistries used for the design of TSPSPs are highlighted along with two major patterning methodologies: positive- and negative-working PSPIs/PSPBOs. Furthermore, new applications of TSPSPs (for example, low dielectric materials, high refractive index lenses, resists for indium tin oxide patterning, and π-conjugated polymers for organic-field effect transistors) are introduced. Thermally stable and photosensitive polymers have been widely developed in recent years for their applications in the electronic packaging such as buffer coating, passivation layers, and insulation layers for redistribution in microelectronics due to their excellent thermal and reasonable dielectric properties. This review describes the recent progress of TSPSPs in the last decade and focuses on their design concept. After a brief introduction of the basic patterning procedure, various chemistries on the design of TSPSPs are highlighted along with two major patterning methodologies such as positive- and negative-working polymers. Furthermore, new applications of TSPSPs, such as low dielectric materials, high refractive index lenses, resists for ITO patterning, and π-conjugated polymers for organic-field effect transistors, are also introduced.

Self-condensation-type direct arylation synthesis of naphthalene bisimide-bithiophene alternating copolymers

The self-condensation-type direct arylation of naphthalene bisimide (NBI)-bithiophene alternating copolymers (PNBI2T), which was classified as one of high-performance acceptor polymers in organic field-effect transistors and organic photovoltaics, was developed. A new AB-type NBI monomer (NBI2T-Br) was designed for the self-condensation-type direct arylation. A PNBI2T was successfully synthesized by using NBI2T-Br; as a result of screening of the reaction conditions, the PNBI2T with M n = 13,000 was obtained in the high yield (87 %) in the presence of Pd(OAc)2, PCy3·HBF4, PivOH, and K2CO3. Furthermore, analyses of spectroscopy, optical, electrochemical, and thermal properties indicated that the PNBI2T with the desired structure was synthesized by the self-condensation-type direct arylation.

Characterization of ohmic contacts in polymer organic field-effect transistors

It is well known that contact resistance Rc limits the performance of organic field-effect transistors (OFETs) that have high field-effect mobilities (μFET ≳ 0.3 cm2 V−1 s−1) and short channel lengths (Lch ≲ 30 μm). The usual transfer-line method (TLM) to analyze Rc calls for extrapolation of total resistance to zero Lch at constant drain and gate voltages. This requires an unrealistic assumption that Rc does not vary with source−drain current Isd (nor with channel carrier density σ). Here we describe a self-consistent TLM analysis that instead imposes the condition of constant Isd and σ. The results explicitly reveal the dependence of Rc on Isd and σ. We further describe how this Rc(Isd, σ) surface can be modelled to yield the specific contact resistivity ρc of the metal/organic semiconductor (OSC) interface, a key parameter that has so far been neglected in OFETs. We illustrate the application of these analyses to high-performance staggered top-gate bottom-contact poly(2,5-bis(alkyl)-1,4-dioxopyrrolo [3,4-c]pyrrole-3,6-diyl-terthiophene-2,5″-diyl) (DPPT2-T) OFETs fabricated on bottom Au source–drain electrode arrays, with high contact-corrected μFET of 0.5 cm2 V−1 s−1. We show that when these electrodes are modified to impose weak, and then strong hole-doping of the DPPT2-T interface, Rc diminishes and its dispersion, i.e. dependence on Isd and σ, weakens. The ultimate ρc attained for the strongly hole-doped contact is ca. 1 Ω cm2, broadly independent of Isd and σ, which we propose is a hallmark of a true metal/OSC ohmic contact. For comparison, the bare Au/DPPT2-T contact gives ρc of the order of 10 Ω cm2 with a marked σ dependence. The lowest ρc reached here shortens the current transfer length down to ca. 5 μm, enabling short electrode lengths to be advantageously employed in technology.

Solution-processed high-LUMO-level polymers in n-type organic field-effect transistors: a comparative study as a semiconducting layer, dielectric layer, or charge injection layer

In solution-processed organic field-effect transistors (OFETs), the polymers with high level of lowest unoccupied molecular orbitals (LUMOs, > −3.5 eV) are especially susceptible to electron-trapping that causes low electron mobility and strong instability in successive operation. However, the role of high-LUMO-level polymers could be different depending on their locations relative to the semiconductor/insulator interface, or could even possibly benefit the device in some cases. We constructed unconventional polymer heterojunction n-type OFETs to control the location of the same polymer with a high LUMO level, to be in, under, or above the accumulation channel. We found that although the devices with the polymer in the channel suffer from dramatic instability, the same polymer causes much less instability when it acts as a dielectric modification layer or charge injection layer. Especially, it may even improve the device performance in the latter case. This result helps to improve our understanding of the electron-trapping and explore the value of these polymers in OFETs.

Incorporation of polycyclic azaborine compounds into polythiophene-type conjugated polymers for organic field-effect transistors.

A thiophene-fused polycyclic azaborine skeleton was employed into conjugated polymers for organic field-effect transistors for the first time. Two polythiophene-type polymers were developed, which exhibited low HOMO levels and strong intermolecular interactions, leading to a hole mobility of up to 0.38 cm(2) V(-1) s(-1).

Regulating charge injection in ambipolar organic field-effect transistors by mixed self-assembled monolayers.

We report on a technique using mixed self-assembled monolayers (SAMs) to finely regulate ambipolar charge injection in polymer organic field-effect transistors. Differing from the other works that employ single SAM specifically for efficient charge injection in p-type and n-type transistors, we blend two different SAMs of alkyl- and perfluoroalkyl thiols at different ratios and apply them to ambipolar OFETs and inverter. Thanks to the utilization of ambipolar semiconductor and one SAM mixture, the device and circuit fabrications are facile with only one step for semiconductor deposition and another for SAM treatment. This is much simpler with respect to the conventional scheme for the unipolar-device-based complementary circuitry that demands separate deposition and processing for individual p-channel and n-channel transistors. Our results show that the mixed-SAM treatments not only improve ambipolar charge injection manifesting as higher hole- and electron-mobility and smaller threshold voltage but also gradually tune the device characteristics to reach a desired condition for circuit application. Therefore, this simple but useful approach is promising for ambipolar electronics.

Tuning Packing and Solubility of Donor (D)–Acceptor (A) Polymers by cis–trans Isomerization within Alkenyl Side Chains

The impact of alkenyl substituents on the behavior of cyclopentadithiophene–benzothiadiazole (CDT–BTZ) donor (D)–acceptor (A) polymers in organic field-effect transistors (OFETs) and on the supramolecular organization was investigated. Linear cis- and trans-alkenes were attached to the donor unit of CDT–BTZ polymers to demonstrate the dependence of supramolecular ordering and solubility in organic solvents on chemical conformation. The layer interdigitation of the substituents differed due to shape disparities between cis- and trans-alkenes. While trans-alkenes exhibit zigzag structures that are beneficial for close packing, cis-alkenes are curved and thus possess a less regular shape that is disadvantageous to thin film ordering. This was proven by grazing incidence wide-angle X-ray scattering (GIWAXS) studies, which revealed shorter intermolecular distances for the polymer with trans-alkene substituents even in comparison to analogous polymers with saturated alkyl substituents. Furthermore, the isomeriz...

Controlling Conformations of Diketopyrrolopyrrole-Based Conjugated Polymers: Role of Torsional Angle

Transport of charge carriers through conjugated polymers is strongly influenced by the presence and distribution of structural disorders. In the present work, structural defects caused by the presence of torsional angle were investigated in a diketopyrrolopyrrole (DPP)-based conjugated polymer. Two new copolymers of DPP were synthesized with varying torsional angles to trace the role of structural disorder. The optical properties of these copolymers in solution and thin film reveal the strong influence of torsional angle on their photophysical properties. A strong influence was observed on carrier transport properties of polymers in organic field-effect transistors (OFET) device geometry. The polymers based on phenyl DPP with higher torsional angle (PPTDPP-OD-TEG) resulted in high threshold voltage with less charge carrier mobility as compared to the polymer based on thiophene DPP (2DPP-OD-TEG) bearing a lower torsional angle. Carrier mobility and the molecular orientation of the conjugated polymers were correlated on the basis of grazing incidence X-ray scattering measurements showing the strong role of torsional angle introduced in the form of structural disorder. The results presented in this Article provide a deep insight into the sensitivity of structural disorder and its impact on the device performance of DPP-based conjugated polymers.

Perfluorinated polymer with unexpectedly efficient deep blue electroluminescence for full-colour OLED displays and light therapy applications

The fluorinated phenylene unit is used as a building block for an all-conjugated fluorene-based alternating copolymer (PFO–TFP). The synthesis, carried out by an optimized Suzuki cross-coupling, produces an extremely high purity compound with a series of intriguing properties. Firstly, a blue-shift of the absorption and emission spectra with respect to the parent polymer is achieved. Secondly, the photoluminescence (PL) quantum yields (QYs) of the solution, as high as 68%, are surprisingly retained in the solid-state. Finally, an improved colour stability of the film with respect to unsubstituted polymers, investigated by means of cyclic voltammetry and exposure to ultraviolet radiation, is observed. The PFO–TFP tested as an undoped active layer in a polymer light-emitting diode (PLED) shows a highly desirable pure deep blue 405 nm electroluminescence, CIE = (0.17; 0.06) and a remarkable 5.03% external quantum efficiency, thus fulfilling the requirements for both full-colour displays and biomedical applications. To date, fluorine atom incorporation has been successfully employed in the synthesis of high-performing polymers for organic field-effect transistors and photovoltaics. We give the first unambiguous proof of its efficacy in achieving pure deep blue electroluminescence in a highly efficient and stable PLED, which is competitive with the best reported conjugated oligomer-based devices.