Polymer Field-effect Transistors Research Articles

Boosting the performance of polymer field-effect transistors through fluorine atom substitutions and comparing the effect of various acceptor units and channel mobilities

Three conjugated copolymers, PDPP-2FTVT, PIID-2FTVT, and PNDI-2FTVT based on the 2,2′-(1E)-1,2-ethenediylbis[3-fluorothiophene] (2FTVT) core with varying acceptor units, diketopyrrolopyrrole (DPP), isoindigo (IID), and naphthalenediimide (NDI) were developed for organic field-effect transistors (OFETs). Combined electron-withdrawing fluorine atoms and vinyl linkage in the 2FTVT unit not only reduce the frontier molecular orbital energies but also extended the absorption profile and planarize the polymer backbone, manifesting synergetic effect on the strengthened molecular interactions and charge-carrier properties. The resulted copolymer, PDPP-2FTVT show highly reliable thin film transistor properties with highest hole mobility of 1.93 cm2 V−1 s−1 compared to PIID-2FTV and PNDI-2FTVT. PIID-2FTV copolymer show ambipolar characteristic with hole and electron mobilities of 0.71 and 0.03 cm2 V−1 s−1 respectively while PNDI-2FTVT exhibited the highest electron mobility of 0.20 cm2 V−1 s−1 among three copolymers. Thin film micro-structure characterization reveal that the three copolymers formed lamellar, edge-on molecular packing (for PDPP-2FTVT and PIID-2FTV), increased crystallinity with smaller π-π stacking distances, and strengthen the planarity after thermal annealing. These results contribute important progresses in solution-processed OFET and could provide a greater possibility of 2FTVT based copolymers for commercial application.

Polymer field-effect transistors with inkjet-printed silver electrodes: from device fabrication to circuit simulation

Polymer field-effect transistors with inkjet-printed silver electrodes: from device fabrication to circuit simulation

Facile Blending Strategy for Boosting the Conjugated Polymer Semiconductor Transistor's Mobility.

The optimization of field-effect mobility in polymer field-effect transistors (FETs) is a critical parameter for advancing organic electronics. Today, many challenges still persist in understanding the roles of the design and processing of semiconducting polymers toward electronic performance. To address this, a facile approach to solution processing using blends of PDPP-TVT and PTPA-3CN is developed, resulting in a 3.5-fold increase in hole mobility and retained stability in electrical performance over 3 cm2 V-1 s-1 after 20 weeks. The amorphous D-A conjugated structure and strong intramolecular polarity of PTPA-3CN are identified as major contributors to the observed improvements in mobility. Additionally, the composite analysis by X-ray photoelectron spectroscopy (XPS) and the flash differential scanning calorimetry (DSC) technique showed a uniform distribution and was well mixed in binary polymer systems. This mobility enhancement technique has also been successfully applied to other polymer semiconductor systems, offering a new design strategy for blending-type organic transistor systems. This blending methodology holds great promise for the practical applications of OFETs.

Achieving Ideal and Environmentally Stable n-Type Charge Transport in Polymer Field-Effect Transistors.

Realizing ideal charge transport in field-effect transistors (FETs) of conjugated polymers is crucial for evaluating device performance, such as carrier mobility and practical applications of conjugated polymers. However, the current FETs using conjugated polymers as the active layers generally show certain non-ideal transport characteristics and poor stability. Here, ideal charge transport of n-type polymer FETs is achieved on flexible polyimide substrates by using an organic-inorganic hybrid double-layer dielectric. Deposited conjugated polymer films show highly ordered structures and low disorder, which are supported by grazing-incidence wide-angle X-ray scattering, near-edge X-ray absorption fine structure, and molecular dynamics simulations. Furthermore, the organic-inorganic hybrid double-layer dielectric provides low interfacial defects, leading to excellent charge transport in FETs with high electron mobility (1.49 ± 0.46 cm2 V-1 s-1 ) and ideal reliability factors (102 ± 7%). Fabricated polymer FETs show a self-encapsulation effect, resulting in high stability of the FET charge transport. The polymer FETs still work with high mobility above 1 cm2 V-1 s-1 after storage in air for more than 300 days. Compared with state-of-the-art conjugated polymer FETs, this work simultaneously achieves ideal charge transport and environmental stability in n-type polymer FETs, facilitating rapid device optimization of high-performance polymer electronics.

Recent Progress in Gas Sensors Based on P3HT Polymer Field-Effect Transistors.

In recent decades, the rapid development of the global economy has led to a substantial increase in energy consumption, subsequently resulting in the emission of a significant quantity of toxic gases into the environment. So far, gas sensors based on polymer field-effect transistors (PFETs), a highly practical and cost-efficient strategy, have garnered considerable attention, primarily attributed to their inherent advantages of offering a plethora of material choices, robust flexibility, and cost-effectiveness. Notably, the development of functional organic semiconductors (OSCs), such as poly(3-hexylthiophene-2,5-diyl) (P3HT), has been the subject of extensive scholarly investigation in recent years due to its widespread availability and remarkable sensing characteristics. This paper provides an exhaustive overview encompassing the production, functionalization strategies, and practical applications of gas sensors incorporating P3HT as the OSC layer. The exceptional sensing attributes and wide-ranging utility of P3HT position it as a promising candidate for improving PFET-based gas sensors.

Analyzing Transfer Characteristics of Disordered Polymer Field-Effect Transistors for Intrinsic Device Parameter Extraction

In this study, we present an intrinsic device parameter method based on a single device for disordered polymer field-effect transistors (PFETs). Charges in disordered polymer semiconductors transport through localized states via thermally activated hopping, of which field-effect mobility and contact resistance are gate-bias-dependent. By considering the parameters expressed as gate bias-dependent power laws, dividing drain current with transconductance (Ids/gm method) leads to the current–voltage relation decoupled from the contact effect. Following this derived relationship, the intrinsic field-effect mobility and the contact resistance of the PFETs are extracted and found to be consistent with those using the four-probe method. Thus, we can state that the proposed method offers practical benefits for extracting the intrinsic device parameters of disordered PFETs in terms of using a single transfer characteristic of the devices.

Role of time-dependent foreign molecules bonding in the degradation mechanism of polymer field-effect transistors in ambient conditions.

Long-standing research efforts have enabled the widespread introduction of organic field-effect transistors (OFETs) in next-generation technologies. Concurrently, environmental and operational stability is the major bottleneck in commercializing OFETs. The underpinning mechanism behind these instabilities is still elusive. Here we demonstrate the effect of ambient air on the performance of p-type polymer field-effect transistors. After exposure to ambient air, the device showed significant variations in performance parameters for around 30 days, and then relatively stable behaviour was observed. Two competing mechanisms influencing environmental stability are the diffusion of moisture and oxygen in the metal-organic interface and the active organic layer of the OFET. We measured the time-dependent contact and channel resistances to probe which mechanism is dominant. We found that the dominant role in the degradation of the device stability is the channel resistance rather than the contact resistance. Through time-dependent Fourier transform infrared (FTIR) analysis, we systematically prove that moisture and oxygen cause performance variation in OFETs. FTIR spectra revealed that water and oxygen interact with the polymer chain and perturb its conjugation, thus resulting in degraded performance of the device upon prolonged exposure to ambient air. Our results are important in addressing the environmental instability of organic devices.

Organic Solvent Free Synthesis and Processing of Semiconducting Polymers for Field Effect Transistors in Waterborne Dispersions

AbstractConjugated semiconducting polymers are key active materials for printable electronics, sensors and biosensors, organic photovoltaics, organic light emitting devices, and more. The research in the field developed very efficient materials and sound structure property relationships, thus making a case for a transition from laboratory to industrial environment. At this critical juncture, sustainability, and ease of scaling up are at least as important as performances, to the point that efficient materials on a lab scale could become unpractical for the industry. The development of more efficient synthetic protocols and the complete removal of all organic solvents from both the synthesis and the processing of semiconducting polymers can help tremendously to improve sustainability and reduce costs. It is shown that the use of an aqueous dispersion of the food grade surfactant lecithin as the medium, enables the synthesis and processing of the representative semiconducting alternating copolymer poly (9,9‐dioctylfluorene‐alt‐bithiophene) (PF8T2) in high yield and high quality and with transistor performances comparable with those obtained with reference materials synthetized and processed from volatile organic solvents.

Improving Environmental and Operational Stability of Polymer Field-Effect Transistors by Doping with Tetranitrofluorenone.

Operational instability of organic field-effect transistors (OFETs) is one of the key limitations for applications of printed electronics. Environmental species, especially oxygen and water, unintentionally introduced in the OFET channel, can act as either dopants or traps for charge carriers, affecting the electrical characteristics and stability of devices. Here, we report that intentional doping of the benchmark p-type semiconducting polymer (DPP-DTT) with 2,4,5,7-tetranitrofluorenone (TeNF) markedly improves the operational and environmental stability of OFETs. Electrical interrogation of DPP-DTT OFETs in various environments and at variable temperatures shows suppression of electron-induced traps and increase of hole mobility in oxygen-rich environment, while the water molecules act as traps for positive charge carrier, reducing the hole mobility and significantly shifting the threshold voltage. Doping of DPP-DTT with TeNF suppresses both effects, resulting in environmentally independent performance and superior long-term stability of unencapsulated devices for up to 4 months in ambient air. Furthermore, the doped OFETs exhibit dramatically reduced hysteresis and bias-stressed current drop. Such improvement of the environmental and operational stabilities is ascribed to the mitigation of traps induced by the injected minority carrier (electrons) and the reduction of the majority carrier (hole) traps in doped polymer films due to enhanced microstructural order.

Record-High Electron Mobility Exceeding 16 cm2 V- 1 s- 1 in Bisisoindigo-Based Polymer Semiconductor with a Fully Locked Conjugated Backbone.

Polymer semiconductors with mobilities exceeding 10 cm2 V- 1 s- 1 , especially ambipolar and n-type polymer semiconductors, are still rare, although they are of great importance for fabricating polymer field-effect transistors (PFETs) toward commercial high-grade electronics. Herein, two novel donor-acceptor copolymers, PNFFN-DTE and PNFFN-FDTE, are designed and synthesized based on the electron-deficient bisisoindigo (NFFN) and electron-rich dithienylethylenes (DTE or FDTE). The copolymer PNFFN-DTE, containing NFFN and DTE, possesses a partially locked polymeric conjugated backbone, whereas PNFFN-FDTE, containing NFFN and FDTE, has a fully locked one. Fluorine atoms in FDTE not only induce the formation of additional CH∙∙∙F hydrogen bonds, but also lower frontier molecular orbitals for PNFFN-FDTE. Both PNFFN-DTE and PNFFN-FDTE form more ordered molecular packing in thin films prepared from a polymer solution in bicomponent solvent containing 1,2-dichlorobenzene (DCB) and 1-chloronaphthalene (with volume ratio of 99.2/0.8) than pure DCB. The two copolymers-based flexible PFETs exhibit ambipolar charge-transport properties. Notably, the bicomponent solvent-processed PNFFN-FDTE-based PFETs afford a high electron mobility of 16.67 cm2 V-1 s-1 , which is the highest electron-transport mobility for PFETs reported so far. The high electron mobility of PNFFN-FDTE is attributed to its fully locked conjugated backbone, dense molecular packing, and much matched LUMO energy level.

Improving OFF-State Bias-Stress Stability in High-Mobility Conjugated Polymer Transistors with an Antisolvent Treatment.

Conjugated polymer field-effect transistors are emerging as an enabling technology for flexible electronics due to their excellent mechanical properties combined with sufficiently high charge-carrier mobilities and compatibility with large-area, low-temperature processing. However, their electrical stability remains a concern. ON-state (accumulation mode) bias-stress instabilities in organic semiconductors have been widely studied, and multiple mitigation strategies have been suggested. In contrast, OFF-state (depletion mode) bias-stress instabilities remain poorly understood despite being crucial for many applications in which the transistors are held in their OFF-state for most of the time. Here, a simple method of using an antisolvent treatment is presented to achieve significant improvements in OFF-state bias-stress and environmental stability as well as general device performance for one of the best performing polymers, solution-processable indacenodithiophene-co-benzothiadiazole (IDT-BT). IDT-BT is weakly crystalline, and the notable improvements to an antisolvent-induced, increased degree of crystallinity, resulting in a lower probability of electron trapping and the removal of charge traps is attributed. The work highlights the importance of the microstructure in weakly crystalline polymer films and offers a simple processing strategy for achieving the reliability required for applications in flexible electronics.

Quantitative Measurement of Interface State Density in Donor-Acceptor Polymer Transistors

Donor-Acceptor (D-A) polymer field-effect transistors (pFETs) are at the cutting edge of organic electronics. However, some fundamental cognition of interface states remains unquantified, particularly at different dynamic scales. In this study, the interface states of D-A polymer transistors are quantified using the dynamic pumping method. The experimental results indicate that the interface state density of the transistor is insensitive to the measurement pulse condition and stays within the range of 1012 1013 cm-2. The experiments described in this paper provide a quantitative analysis of interface states. This analysis can serve as effective guidance for optimizing future devices.

In situ tuning of the performance of polymer field-effect transistors by soft plasma etching

The subthreshold swing, threshold voltage and hysteresis of PCDTPT OFETs can be in situ tuned by soft plasma etching.

Thiazole-Flanked Thiazoloisoindigo as a Monomer for Balanced Ambipolar Polymeric Field-effect Transistors

Thiazole-Flanked Thiazoloisoindigo as a Monomer for Balanced Ambipolar Polymeric Field-effect Transistors

Highly radiation-tolerant polymer field-effect transistors with polystyrene dielectric layer

There is high demand for radiation-tolerant devices for use in electronic applications in extreme irradiation environments, but conventional silicon transistors cannot satisfy the device requirements. In this work, we systematically investigated the total ionizing dose (TID) responses of polymer field-effect transistors (PFETs). By selecting suitable polymer gate dielectric materials (especially PS), it is found that these PFETs show significantly improved tolerances to the TID. Specifically, a PFET fabricated using polystyrene as its gate dielectric layer can maintain more than 95% of its electrical performance even after exposure to a TID of 7.5 Mrad (SiO2). The irradiated device has a long shelf lifetime that exceeds 1000 days. Simple inverter circuits were also fabricated and also demonstrated tolerance to a high TID of 7.5 Mrad. This work provides a possible solution for the development of PFETs for applications in extreme irradiation environments.

Accurate parametrization revealing an extremely low disorder in polymer field-effect transistors

In this paper, a robust self-consistent parameter extraction method is applied to high-performance p-type printed polymer field-effect transistors. Simultaneous extraction of contact resistance and intrinsic channel mobility with their full gate-voltage dependence is achieved through an analytically reinforced transmission-line method. The proposed method yields a minimum width-normalized contact resistance of 12 kΩ cm and a maximum hole mobility of 1.9 cm2 V−1 s−1. Moreover, the gate-voltage-dependent mobility is interpreted in the framework of trap-and-release transport through double-exponential density of states, unveiling a disorder energy near the transport orbital as low as 29 meV.

Stabilization and Specification in Polymer Field-Effect Transistor Semiconductors.

The strong and varied chemical interactions between polymer semiconductors and small molecules, and the electronic consequences of these interactions, make polymer organic field-effect transistors (OFETs) attractive as vapor sensing elements. Two hindrances to their wider acceptance and use are their environmental drift and the poor specificity of individual OFETs. Approaches to addressing these two present drawbacks are presented in this Spotlight on Applications. They include the use of semiconducting polymers with greater inherent stability, circuits that add further stability, and arrays that generate patterns that are much more specific to analyte vapors of interest than the individual responses.

Semiconducting Polymer Nanowires with Highly Aligned Molecules for Polymer Field Effect Transistors

Conjugated polymers have emerged as promising materials for next-generation electronics. However, in spite of having several advantages, such as a low cost, large area processability and flexibility, polymer-based electronics have their own limitations concerning low electrical performance. To achieve high-performance polymer electronic devices, various strategies have been suggested, including aligning polymer backbones in the desired orientation. In the present paper, we report a simple patterning technique using a polydimethylsiloxane (PDMS) mold that can fabricate highly aligned nanowires of a diketopyrrolopyrrole (DPP)-based donor–acceptor-type copolymer (poly (diketopyrrolopyrrole-alt-thieno [3,2-b] thiophene), DPP-DTT) for high-performance field effect transistors. The morphology of the patterns was controlled by changing the concentration of the DPP-based copolymer solution (1, 3, 5 mg mL−1). The molecular alignment properties of three different patterns were observed with a polarized optical microscope, polarized UV-vis spectroscopy and an X-ray diffractometer. DPP-DTT nanowires made with 1 mg mL−1 solution are highly aligned and the polymer field-effect transistors based on nanowires exhibit more than a five times higher charge carrier mobility as compared to spin-coated film-based devices.

Effect of fluorine–fluorine repulsive coupling on charge transport in cyclopentadithiophene-based donor–acceptor-type conjugated copolymer films

This study elucidates the effect of fluorine–fluorine interactions on the charge transport properties of semiconductor channels in polymer-based field effect transistors (PFETs) in which both a donor–acceptor (D–A)-type conjugated polymer and a polymer dielectric material contain fluorinated units. The fluorinated units on the benzothiadiazole (BTZ) block of cyclopentadithiophene- alt -benzothiadiazole (CDT-BTZ) allow conformation locking via F⋯S nonbonding interactions, which increases the planarity of cyclopentadithiophene- alt -fluoro-2,1,3-benzothiadiazole (CDT-FBTZ). Thus, the CDT-FBTZ copolymer films are highly crystalline and adopt the edge-on orientation, resulting in an eight-fold increase in the field-effect mobility for CDT-FBTZ-based PFETs coated with a poly(methyl methacrylate) (PMMA) dielectric layer compared with PMMA-coated CDT-BTZ-based PFETs. Meanwhile, the field-effect mobility of CDT-BTZ-based PFETs containing a fluorinated dielectric polymer (CYTOP) is double that of PMMA-coated CDT-BTZ-based PFETs. These enhanced electrical properties are attributed to surface polarization doping at the interface between the conjugated polymer and the fluorinated polymer dielectric. However, despite the effect of surface polarization doping, the electrical properties of CDT-FBTZ-based PFETs deteriorate when combined with the fluorinated CYTOP dielectric. Charge transport analyses based on the Gaussian disorder model reveal that, for CDT-based D–A-type conjugated copolymer PFETs, very few localized states in the semiconducting channel of PFET devices in which fluorine–fluorine interaction effects occur at the interface switch to delocalized states as the gate-bias increases. In contrast, the localized charge states in PFET channels without fluorine–fluorine interactions depend strongly on the applied gate-bias and become delocalized upon applying a gate-bias. Thus, it is inferred that the fluorine–fluorine repulsive coupling in D–A-type conjugated copolymers containing fluorinated functional moieties that interface with fluorinated polymer dielectric layers hinders the delocalization of charges induced by the gate-bias, thereby degrading the device performance. • Effect of fluorine–fluorine interactions on charge transport in polymer transistors investigated. • High-performance polymer field effect transistor obtained using fluorinated polymer. • Temperature-variable current-voltage analyses of the devices conducted. • Electrical degradation of polymer transistor caused by the fluorine–fluorine interactions.

Visualizing transport in thiazole flanked isoindigo-based donor–acceptor polymer field-effect transistors

Replacing S with Se in fluorinated isoindigo (IID) copolymers enhances charge transport properties in field-effect transistors (FET). Nonlinear optical imaging from IID FETs helps visualize transport.