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Metal oxide thin-film transistors are fast becoming a ubiquitous technology for application in driving backplanes of organic light-emitting diode displays. Currently all commercial products rely on metal oxides processed via physical vapor deposition methods. Transition to simpler, higher throughput manufacturing methods such as solution-based processes, are currently been explored as cost-effective alternatives. However, developing printable oxide transistors with high carrier mobility and bias-stable operation has proved challenging. Here we show that hybrid multilayer channels composed of alternating ultra-thin layers ($\leq$4 nm) of indium oxide, zinc oxide nanoparticles, ozone-treated polystyrene and a compact zinc oxide layer, all solution-processed in ambient atmosphere, can be used to create TFTs with remarkably high electron mobility (50 cm$^{2}$/Vs) and record operational stability. Insertion of the ozone-treated polystyrene interlayer is shown to reduce the concentration of electron traps at the metal oxide surfaces and heterointerfaces. The resulting transistors exhibit dramatically enhanced bias stability over 24 h continuous operation and while subjected to large electric field flux density (2.1$\times$10$^{-6}$ C/cm$^{2}$) with no adverse effects on the electron mobility. Density functional theory calculations identify the origin of this enhanced stability as the passivation of the oxygen vacancy-related gap states due to interaction between ozonolyzed styrene moieties and the oxides. Our results sets new design guidelines for bias-stress resilient metal oxide transistors.

Solution-processed organic field-effect transistors (OFETs) have attracted great interest due to their potential as logic devices for bendable and flexible electronics. In relation to n-channel structures, soluble fullerene semiconductors have been widely studied. However, they have not yet met the essential requirements for commercialization, primarily because of low charge carrier mobility, immature large-scale fabrication processes, and insufficient long-term operational stability. Interfacial engineering of the carrier-injecting source/drain (S/D) electrodes has been proposed as an effective approach to improve charge injection, leading also to overall improved device characteristics. Here, it is demonstrated that a non-conjugated neutral dipolar polymer, poly(2-ethyl-2-oxazoline) (PEOz), formed as a nanodot structure on the S/D electrodes, enhances electron mobility in n-channel OFETs using a range of soluble fullerenes. Overall performance is especially notable for (C60 -Ih )[5,6]fullerene (C60 ) and (C70 -D5h(6) )[5,6]fullerene (C70 ) blend films, with an increase from 0.1 to 2.1 cm2 V-1 s-1 . The high relative mobility and eighteen-fold improvement are attributed not only to the anticipated reduction in S/D electrode work function but also to the beneficial effects of PEOz on the formation of a face-centered-cubic C60 :C70 co-crystal structure within the blend films.

Solution-processed organic field-effect transistors (OFETs) have attracted great interest due to their potential as logic devices for bendable and flexible electronics. In relation to n-channel structures, soluble fullerene semiconductors have been widely studied. However, they have not yet met the essential requirements for commercialization, primarily because of low charge carrier mobility, immature large-scale fabrication processes, and insufficient long-term operational stability. Interfacial engineering of the carrier-injecting source/drain (S/D) electrodes has been proposed as an effective approach to improve charge injection, leading also to overall improved device characteristics. Here, it is demonstrated that a non-conjugated neutral dipolar polymer, poly(2-ethyl-2-oxazoline) (PEOz), formed as a nanodot structure on the S/D electrodes, enhances electron mobility in n-channel OFETs using a range of soluble fullerenes. Overall performance is especially notable for (C

Expandability of organic electronics has stimulated ongoing research for the development of a variety of flexible and/or large-area optoelectronic applications. Among these electronic devices, organic non-volatile memories are emerging as suitable components for solid-state data storage because of their low-cost fabrication, large storage capacity, light weight, and conformable mechanical properties. To fully integrate organic memories with wearable and flexible/stretchable electronic systems, it is important to develop a device in which the properties such as threshold voltage and operating regime are controllable. This leads to improvement in the adaptability of the device to peripheral circuitry and encourages the development of multi-functional organic electronic components. Here, we investigate the tunable electrical properties of charge-trap (electret) memory devices based on organic field-effect transistors, obtained by the doping of an ambipolar polymer semiconductor. The electret memory devices using the doped semiconductor showed a remarkable enhancement in the charge-storage capacity, an excellent charge retention time of more than 107 s, and four-fold increase in charge carrier mobility. The improved memory characteristics associated with the controllable molecular doping could pave the way for the development of next-generation memory devices that are compatible with flexible and printed electronic technology.

Three triple bond-conjugated naphthalene diimide (NDI) copolymers, poly{[N,N′-bis(2-R1)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-[(2,5-bis(2-R2)-1,4-phenylene)bis(ethyn-2,1-diyl)]} (PNDIR1-R2), were synthesized via Sonogashira coupling polymerization with varying alkyl side chains at the nitrogen atoms of the imide ring and 2,5-positions of the 1,4-diethynylbenzene moiety. Considering their identical polymer backbone structures, the side chains were found to have a strong influence on the surface morphology/nanostructure, thus playing a critical role in charge-transporting properties of the three NDI-based copolymers. Among the polymers, the one with an octyldodecyl (OD) chain at the nitrogen atoms of imide ring and a hexadecyloxy (HO) chain at the 2,5-positions of 1,4-diethynylbenzene, P(NDIOD-HO), exhibited the highest electron mobility of 0.016 cm2 V–1 s–1, as compared to NDI-based copolymers with an ethylhexyl chain at the 2,5-positions of 1,4-diethynylbenzene. The enhanced charge mobility...

We report on the fabrication of an organic thin-film semiconductor formed using a blend solution of soluble ambipolar small molecules and an insulating polymer binder that exhibits vertical phase separation and uniform film formation. The semiconductor thin films are produced in a single step from a mixture containing a small molecular semiconductor, namely, quinoidal biselenophene (QBS), and a binder polymer, namely, poly(2-vinylnaphthalene) (PVN). Organic field-effect transistors (OFETs) based on QBS/PVN blend semiconductor are then assembled using top-gate/bottom-contact device configuration, which achieve almost four times higher mobility than the neat QBS semiconductor. Depth profile via secondary ion mass spectrometry and atomic force microscopy images indicate that the QBS domains in the films made from the blend are evenly distributed with a smooth morphology at the bottom of the PVN layer. Bias stress test and variable-temperature measurements on QBS-based OFETs reveal that the QBS/PVN blend semiconductor remarkably reduces the number of trap sites at the gate dielectric/semiconductor interface and the activation energy in the transistor channel. This work provides a one-step solution processing technique, which makes use of soluble ambipolar small molecules to form a thin-film semiconductor for application in high-performance OFETs.

A specific design for solution-processed doping of active semiconducting materials would be a powerful strategy in order to improve device performance in flexible and/or printed electronics. Tetrabutylammonium fluoride and tetrabutylammonium hydroxide contain Lewis base anions, F− and OH−, respectively, which are considered as organic dopants for efficient and cost-effective n-doping processes both in n-type organic and nanocarbon-based semiconductors, such as poly[[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)] (P(NDI2OD-T2)) and selectively dispersed semiconducting single-walled carbon nanotubes by π-conjugated polymers. The dramatic enhancement of electron transport properties in field-effect transistors is confirmed by the effective electron transfer from the dopants to the semiconductors as well as controllable onset and threshold voltages, convertible charge-transport polarity, and simultaneously showing excellent device stabilities under ambient air and bias stress conditions. This simple solution-processed chemical doping approach could facilitate the understanding of both intrinsic and extrinsic charge transport characteristics in organic semiconductors and nanocarbon-based materials, and is thus widely applicable for developing high-performance organic and printed electronics and optoelectronics devices.

Control of electron and hole transport in conjugated molecules is a challenging but essential task for deeply understanding the intrinsic charge transport behaviors as well as technological benefits for optimizing the performance of various optoelectronic devices. Here we suggest a facile route to controlling ambipolar charge transport in conjugated polymers by precise regulation of the copolymerization ratio between a relatively large electron donor and acceptor building block as a repeating unit. By varying the ratio between poly[2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-(E)-[2,2-bithiophen]-5-yl)-3-(thiophen-2-yl)acrylonitrile] (DPP-CNTVT) as an electron transport unit and DPP-selenophene-vinylene-selenophene (DPP-SVS) as a hole transport unit, mobility (μFET) and onset voltage (Von) in organic field-effect transistors are effectively modulated from p-channel [μFET,h = 6.23 ± 0.4 cm2 V–1 s–1] to n-channel [μFET,e = 6.88 ± 1.01 cm2 V–1 s–1] dominant transport. The same two DPP-based ...

A uniform ultrathin polymer film is deposited over a large area with molecularlevel precision by the simple wire-wound bar-coating method. The bar-coated ultrathin films not only exhibit high transparency of up to 90% in the visible wavelength range but also high charge carrier mobility with a high degree of percolation through the uniformly covered polymer nanofibrils. They are capable of realizing highly sensitive multigas sensors and represent the first successful report of ethylene detection using a sensor based on organic field-effect transistors.

In this report, we investigate a formation mechanism for polymer chains aligned with various semiconductor polymers and a microstructure for directionally aligned film through systematic analysis that includes polarized UV–visible–near infrared (UV–vis–NIR) absorption spectroscopy, atomic force microscopy, polarized charge modulation microscopy (p-CMM), and incident X-ray diffraction (GIXD) measurements. Through this study, we make two important observations: first, the highly aligned organic polymer semiconductor films are achieved by off-center spin coating of the preaggregated conjugated polymer solution. Second, the directionally aligned conjugated polymer films exhibit a larger anisotropy on the top surface compared with bulk film, which allows effective mobility improvement in top-gate/bottom-contact field-effect transistors with high performance uniformity. Finally, we demonstrate high-mobility organic field-effect transistors (OFETs) (7.25 cm2/(V s)) with a mobility large anisotropy (37-fold) usin...

Donor–acceptor (D–A) type conjugated polymers have been developed to absorb longer wavelength light in polymer solar cells (PSCs) and to achieve a high charge carrier mobility in organic field-effect transistors (OFETs). PDTDP, containing dithienothiophene (DTT) as the electron donor and diketopyrrolopyrrole (DPP) as the electron acceptor, was synthesized by stille polycondensation in order to achieve the advantages of D–A type conjugated polymers. The polymer showed optical band gaps of 1.44 and 1.42 eV in solution and in film, respectively, and a HOMO level of 5.09 eV. PDTDP and PC71BM blends with 1,8-diiodooctane (DIO) exhibited improved performance in PSCs with a power conversion efficiency (PCE) of 4.45% under AM 1.5G irradiation. By investigating transmission electron microscopy (TEM), atomic force microscopy (AFM), and the light intensity dependence of JSC and VOC, we conclude that DIO acts as a processing additive that helps to form a nanoscale phase separation between donor and acceptor, resulting in an enhancement of μh and μe, which affects the JSC, EQE, and PCE of PSCs. The charge carrier mobilities of PDTDP in OFETs were also investigated at various annealing temperatures and the polymer exhibited the highest hole and electron mobilities of 2.53 cm2 V−1 s−1 at 250 °C and 0.36 cm2 V−1 s−1 at 310 °C, respectively. XRD and AFM results demonstrated that the thermal annealing temperature had a critical effect on the changes in the crystallinity and morphology of the polymer. The low-voltage device was fabricated using high-k dielectric, P(VDF-TrFE) and P(VDF-TrFE-CTFE), and the carrier mobility of PDTDP was reached 0.1 cm2 V−1 s−1 at Vd = −5 V. PDTDP complementary inverters were fabricated, and the high ambipolar characteristics of the polymer resulted in an output voltage gain of more than 25.

We report the synthesis and optoelectronic properties of novel platinum-based polymers (p-Pt-DPP) incorporating 3,6-di-2-thienyl-2,5-dihydro-2,5-diethylhexylpyrrolo[3,4-c]pyrrole-1,4-dione. The synthesized amorphous metallated polymer exhibited long wavelength absorption in the range of 500–684 nm and a band-gap as low as 1.75 eV. Organic field-effect transistors (OFETs) fabricated from p-Pt-DPP showed hole mobility of 1.6 × 10⁻³ cm² · V⁻¹s⁻¹ and an on/off ratio of 5 × 10⁴. In addition, polymer solar cells (PSCs) based on p-Pt-DPP and PC₇₁BM exhibited a photovoltaic efficiency of 1.22% under AM 1.5 G conditions with an illumination of 100 mW·cm−2 without any annealing process.

This is a non-edited copy of the pre-print version of the paper Adv. Mater. 30 (2018)1705463

Polymer semiconductors have been experiencing a remarkable improvement in electronic and optoelectronic properties, which are largely related to the recent development of a vast library of high-performance, donor-acceptor copolymers showing alternation of chemical moieties with different electronic affinities along their backbones. Such steady improvement is making conjugated polymers even more appealing for large-area and flexible electronic applications, from distributed and portable electronics to healthcare devices, where cost-effective manufacturing, light weight, and ease of integration represent key benefits. Recently, a strong boost to charge carrier mobility in polymer-based field-effect transistors, consistently achieving the range from 1.0 to 10 cm2 V-1 s-1 for both holes and electrons, has been given by uniaxial backbone alignment of polymers in thin films, inducing strong transport anisotropy and favoring enhanced transport properties along the alignment direction. Herein, an overview on this topic is provided with a focus on the processing-structure-property relationships that enable the controlled and uniform alignment of polymer films over large areas with scalable processes. The key aspects are specific molecular structures, such as planarized backbones with a reduced degree of conformational disorder, solution formulation with controlled aggregation, and deposition techniques inducing suitable directional flow.

Facile and efficient fabrication of polyacrylonitrile (PAN)-based conductive graphitic carbon microstructures (GCMs) and their application to the electrodes of organic field-effect transistors (OFETs) is described. The PAN thin films spin-coated on a SiO 2 -deposited Si wafer was irradiated through a pattern mask with 150 keV H + ions at various fluences, and subsequently developed to form PAN microstructures. The resulting PAN microstructures were carbonized at various temperatures to create the GCMs. The analytical results revealed that the optimized fluence and carbonization temperature for well-defined GCMs was 3 × 10 15 ions cm −2 and 100 °C, respectively, and that the resulting GCMs created at the optimized condition exhibited a greatly low surface roughness of 0.36 nm, a good electrical conductivity of about 600 S cm −1 , and a high work function of 5.11 eV. Noticeably, the GCM electrodes-based p-type OFET showed a comparable performance to that of the gold electrode-based one, demonstrating that the practical use of GCMs as cheap electrodes to replace expensive metallic ones for organic electronic devices.

The two small molecules, quinoidal bithiophene (QBT) and quinoidal biselenophene (QBS), are designed based on a quinoid structure, and synthesized via a facile synthetic route. These quinoidal molecules have a reduced band gap and an amphoteric redox behavior, which is caused by an extended delocalization. Due to such properties, organic field-effect transistors based on QBT and QBS have shown balanced ambipolar characteristics. After thermal annealing, the performances of the devices are enhanced by an increase in crystallinity. The field-effect hole and electron mobilities are measured to be 0.031 cm2 V−1 s−1 and 0.005 cm2 V−1 s−1 for QBT, and 0.055 cm2 V−1 s−1 and 0.021 cm2 V−1 s−1 for QBS, respectively. In addition, we investigate the effect of chalcogen atoms (S and Se) on the molecular properties. The optical, electrochemical properties and electronic structures are mainly dominated by the quinoidal structure, whereas molecular properties are scarcely affected by either type of chalcogen atom. The main effect of the chalcogen atoms is ascribed to the difference of crystallinity. Due to a strong intermolecular interaction of the selenophene, QBS exhibits a higher degree of crystallinity, which leads to an enhancement of both hole and electron mobilities. Consequently, these types of quinoidal molecules are found to be promising for use as ambipolar semiconductors.

Organic electronics is regarded as an important branch of future microelectronics especially suited for large-area, flexible, transparent, and green devices, with their low cost being a key benefit. Organic field-effect transistors (OFETs), the primary building blocks of numerous expected applications, have been intensively studied, and considerable progress has recently been made. However, there are still a number of challenges to the realization of high-performance OFETs and integrated circuits (ICs) using printing technologies. Therefore, in this perspective article, we investigate the main issues concerning developing high-performance printed OFETs and ICs and seek strategies for further improvement. Unlike many other studies in the literature that deal with organic semiconductors (OSCs), printing technology, and device physics, our study commences with a detailed examination of OFET performance parameters (e.g., carrier mobility, threshold voltage, and contact resistance) by which the related challenges and potential solutions to performance development are inspected. While keeping this complete understanding of device performance in mind, we check the printed OFETs' components one by one and explore the possibility of performance improvement regarding device physics, material engineering, processing procedure, and printing technology. Finally, we analyze the performance of various organic ICs and discuss ways to optimize OFET characteristics and thus develop high-performance printed ICs for broad practical applications.

Improving the charge carrier mobility of solution‐processable organic semiconductors is critical for the development of advanced organic thin‐film transistors and their application in the emerging sector of printed electronics. Here, a simple method is reported for enhancing the hole mobility in a wide range of organic semiconductors, including small‐molecules, polymers, and small‐molecule:polymer blends, with the latter systems exhibiting the highest mobility. The method is simple and relies on admixing of the molecular Lewis acid B(C6F5)3 in the semiconductor formulation prior to solution deposition. Two prototypical semiconductors where B(C6F5)3 is shown to have a remarkable impact are the blends of 2,8‐difluoro‐5,11‐bis(triethylsilylethynyl)anthradithiophene:poly(triarylamine) (diF‐TESADT:PTAA) and 2,7‐dioctyl[1]‐benzothieno[3,2‐b][1]benzothiophene:poly(indacenodithiophene‐co‐benzothiadiazole) (C8‐BTBT:C16‐IDTBT), for which hole mobilities of 8 and 11 cm2 V−1 s−1, respectively, are obtained. Doping of the 6,13‐bis(triisopropylsilylethynyl)pentacene:PTAA blend with B(C6F5)3 is also shown to increase the maximum hole mobility to 3.7 cm2 V−1 s−1. Analysis of the single and multicomponent materials reveals that B(C6F5)3 plays a dual role, first acting as an efficient p‐dopant, and secondly as a microstructure modifier. Semiconductors that undergo simultaneous p‐doping and dopant‐induced long‐range crystallization are found to consistently outperform transistors based on the pristine materials. Our work underscores Lewis acid doping as a generic strategy towards high performance printed organic microelectronics.

The selective tuning of the operational mode from ambipolar to unipolar transport in organic field-effect transistors (OFETs) by printing molecular dopants is reported. The field-effect mobility (μFET) and onset voltage (Von) of both for electrons and holes in initially ambipolar methanofullerene [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) OFETs are precisely modulated by incorporating a small amount of cesium fluoride (CsF) n-type dopant or tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) p-type dopant for n-channel or p-channel OFETs either by blending or inkjet printing of the dopant on the pre-deposited semiconductor. Excess carriers introduced by the chemical doping compensate traps by shifting the Fermi level (EF) toward respective transport energy levels and therefore increase the number of mobile charges electrostatically accumulated in channel at the same gate bias voltage. In particular, n-doped OFETs with CsF show gate-voltage independent Ohmic injection. Interestingly, n- or p-doped OFETs show a lower sensitivity to gate-bias stress and an improved ambient stability with respect to pristine devices. Finally, complementary inverters composed of n- and p-type PCBM OFETs are demonstrated by selective doping of the pre-deposited semiconductor via inkjet printing of the dopants.

In this study, we investigated chemically exfoliated two-dimensional (2-D) nanoflakes of molybdenum disulfide (MoS2) as charge-storing elements for use in organic multilevel memory devices (of the printed/flexible non-volatile type) based on organic field-effect transistors (OFETs) containing poly(3-hexylthiophene) (P3HT). The metallic MoS2 nanoflakes were exfoliated in 2-methoxyethanol by the lithium intercalation method and were deposited as nano-floating gates between polystyrene and poly(methyl methacrylate), used as bilayered gate dielectrics, by a simple spin-coating and low temperature (150 °C) process. In the developed OFET memory devices, electrons could be trapped/detrapped in the MoS2 nano-floating gates by modulating the charge carrier density in the active channel through gate bias control. Optimal memory characteristics were achieved by controlling the thickness and concentration of few-layered MoS2 nanoflakes, and the best device showed reliable non-volatile memory properties: a sufficient memory window of ∼23 V, programming-reading-erasing cycling endurance of10(2) times, and most importantly, quasi-permanent charge-storing characteristics, i.e., a very long retention time (longer than the technological requirement of commercial memory devices (10 years)). In addition, we successfully developed multilevel memory cells (2 bits per cell) by controlling the gate bias magnitude.

N-channel organic field-effect transistors (OFETs) have generally shown lower field-effect mobilities (μFET) than their p-type counterparts. One of the reasons is the energetic misalignment between the work function (WF) of commonly used charge injection electrode, i.e. gold (Au), and the lowest unoccupied molecular orbital (LUMO) of n-channel electron-transporting organic semiconductors. Here, we report barium salts as solution-processed interlayers, to improve the electron-injection and/or hole-blocking in top-gate/bottom-contact n-channel OFETs, based on poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-dithiophene)} (P(NDI2OD-T2)) and phenyl-C61-butyric acid methyl ester (PC61BM). Two different barium salts, barium hydroxide (Ba(OH)2) and barium chloride (Ba(Cl)2), are employed as the ultrathin interlayer (∼2 nm); and they effectively tune the WF of Au from 4.9 eV, to as low as 3.5 eV. The resulting n-channel OFETs exhibit significantly improved μFET, approaching 2.6 cm(2)/(V s) and 0.1 cm(2)/(V s) for the best P(NDI2OD-T2) and PC61BM devices, respectively, with Ba(OH)2 as interlayer.

This paper investigates the effects of side chains, which are important structural constituents, on the characteristics of organic resistive memory devices with water-soluble polyfluorene (WPF) derivatives. The WPF derivatives have either an ethylene oxide (EO) or an alkyl side chain the lengths of the EO side chains are 2, 4, or 6 molecules. WPFs exhibit typical bipolar switching behaviors with reliable non-volatile characteristics and good device-to-device uniformity under ambient conditions. WPFs with the EO side chains showed better memory characteristics than those of the alkyl side chains of similar length. In addition, as the EO unit lengthened, the ON/OFF ratio of the memory device gradually increased from 5 × 10 2 to 10 5 , and the threshold voltage ( V th ) progressively decreased from 4 to 3.5 V. The retention times for WPF-hexyl, WPF-2O, WPF-4O, and WPF-6O are 10 4 , 200, 10 4 , and 10 4 s, respectively. The excellent switching properties of WPF-4O and WPF-6O are believed to be mainly attributed to highly localized current pathways and the low trap density.

본 논문에서는 유기전자소자의 반도체 물질로 많이 사용되는 poly(9,9-dioctylflurorene) (PFO), poly(9,9-dioctylfluoreneco-benthiadiazole) (F8BT), (regioregular poly(3-hexylthiophene) (P3HT)를 기반으로 하는 균일한 크기와 특성을 가지는 고분자 나노와이어를 AAO 템플레이트를 이용하여 대량으로 제작하였다. 제작된 나노와이어는 결점이 없이 깨끗한 표면을 보였으며, 약 250~300 nm의 지름과 ~30 μm의 일정한 길이를 가지고 있었다. 나노와이어들은 스프레이 분사 방법을 통하여 유리 기판 위에 균일하게 분사할 수 있었으며, PFO와 F8BT 나노와이어의 경우 UV 빛의 조사하에 각각 나노와이어의 전체에 걸쳐서 왜곡없이 밝은 yellow와 blue luminescence를 보였다.

Charge transport in carbon nanotube network transistors strongly depends on the properties of the gate dielectric that is in direct contact with the semiconducting carbon nanotubes. In this work, we investigate the dielectric effects on charge transport in polymer-sorted semiconducting single-walled carbon nanotube field-effect transistors (s-SWNT-FETs) by using three different polymer insulators: A low-permittivity (er) fluoropolymer (CYTOP, er = 1.8), poly(methyl methacrylate) (PMMA, er = 3.3), and a high-er ferroelectric relaxor [P(VDF-TrFE-CTFE), er = 14.2]. The s-SWNT-FETs with polymer dielectrics show typical ambipolar charge transport with high ON/OFF ratios (up to ∼105) and mobilities (hole mobility up to 6.77 cm2 V–1 s–1 for CYTOP). The s-SWNT-FET with the lowest-k dielectric, CYTOP, exhibits the highest mobility owing to formation of a favorable interface for charge transport, which is confirmed by the lowest activation energies, evaluated by the fluctuation-induced tunneling model (FIT) and the...

We report the fabrication of high-performance, printed, n-channel organic field-effect transistors (OFETs) based on an N,N-dialkyl-substituted-(1,71,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide) derivative, PDI-RCN2, optimized by the solvent-vapor annealing (SVA) process. We performed a systematic study on the influence of solubility and the chemical structure of a solvent used for the SVA process on the ordering and orientation of PDI-RCN2 molecules in the thin film. The PDI-RCN2 film showed improved crystallinity under vapor annealing with the aliphatic 1,2-dichloroethane (DCE) as a marginal solvent. The n-type OFETs with DCE-vapor-annealed PDI-RCN2 show highly improved charge-carrier mobility of ~0.5 cm(2) V(-1) s(-1) and higher stability under gate bias stress than the pristine OFETs. This large performance improvement was mainly attributed to increased crystallinity of the semiconductor thin film, enhancing π-π stacking. We also introduced a new method to pattern crystallinity of a certain region in the semiconducting film by selective exposure to the solvent vapor using a shadow mask. The crystal-patterned PDI-RCN2 OFETs exhibit decreased off-currents by ~10× and improved gate bias stability by minimizing crosstalk, reducing leakage current between devices, and reducing the density of charge trap states of the organic semiconductor.

SFA-PQT exhibits self-assembly via a fluorophobic effect in a non-fluorous solvent, which leads to an enhanced electrical performance. Ambipolar transistors and inverters with p- and n- type bilayers are enabled by the unique thermally reversible soluble-insoluble properties of SFA-PQT. More importantly, the hydrophobicity of SFA-PQT facilitates orthogonal hydrophobic patterning and a patterned inverter exhibits low voltage dissipation, a narrow transition zone, a high gain value, and negligible hysteresis.

We report the development of high-performance inkjet-printed organic field-effect transistors (OFETs) and complementary circuits using high- k polymer dielectric blends comprising poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) and poly(methyl methacrylate) (PMMA) for high-speed and low-voltage operation. Inkjet-printed p -type polymer semiconductors containing alkyl-substituted thienylenevinylene (TV) and dodecylthiophene (PC12TV12T) and n -type P(NDI2OD-T2) OFETs showed high field-effect mobilities of 0.1–0.4 cm 2 V −1 s −1 and low threshold voltages down to 5 V. These OFET properties were modified by changing the blend ratio of P(VDF-TrFE) and PMMA. The optimum blend – a 7:3 wt% mixture of P(VDF-TrFE) and PMMA – was successfully used to realize high-performance complementary inverters and ring oscillators (ROs). The complementary ROs operated at a supplied bias ( V DD ) of 5 V and showed an oscillation frequency ( f osc ) as high as ∼80 kHz at V DD = 30 V. Furthermore, the f osc of the complementary ROs was significantly affected by a variety of fundamental parameters such as the electron and hole mobilities, channel width and length, capacitance of the gate dielectrics, V DD , and the overlap capacitance in the circuit configuration.

Solution-processed organic semiconductors are of great potential for large-area, inexpensive, lightweight, and fl exible electronic applications. With respect to these materials, tremendous effort has recently been focused on developing several types of organic electronic and optoelectronic devices, such as organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), organic fi eld-effect transistors (OFETs), and organic memory and sensors, using graphic-art printing methods on fl substrates. [ 1‐5 ] OFETs are a fundamental building block of integrated circuits (ICs) and drivers for active-matrix fl at-panel displays. Accordingly, they are a promising candidate to replace the vacuum-processed amorphous inorganic ICs; this would enable the use of drivers in printed and fl exible radio-frequency identifi cation tags, memories, sensors, and display backplanes. [ 6 , 7 ] To realize high-speed organic printed ICs, the complementary IC geometry, which consists of p- and n-channel transistors, has an advantage over those that comprise unipolar transistors because of reduced transition delays, higher noise immunity, and negligible power consumption in the static state. [ 8 ] In solution-processed devices, p- and n-type active channels have been patterned at resolutions as low as a few micrometers using a variety of printing methods such as inkjet, spray, and gravure printing. [ 9 ] However, these printing processes typically result in device-to-device performance deviations because of diffi culties inherent in controlling the morphology (e.g., roughness and crystallinity) of micrometre-sized deposits. For example, organic semiconductor droplets that are deposited via ink jet onto non-absorbing substrates typically show signifi cant coffee

We report the synthesis and characterization of thienylenevinylene-based donor–acceptor alternating copolymers (PTVPhI-Eh and PTVPhI-C12) as highly efficient ambipolar semiconductors in a thin film transistor. These polymers exhibit significantly improved hole and electron mobilities after thermal annealing. To determine the relationship between ambipolar charge transport and thermal annealing, we investigated these polymers using various analyses such as optical spectroscopy, Raman spectroscopy, computational quantum chemical calculation, X-ray diffraction, atomic force microscopy, and ambipolar charge mobility measurements. In pristine films, the polymer chains exhibited weak intra- and interchain ordering. However, when samples were annealed at sufficiently high temperatures, they exhibited a more ordered intra- and interchain conformation. As a result, we found a strong relationship between intra- and interchain conformational changes of the polymers and corresponding ambipolar charge transport proper...

The effects of using a blocking dielectric layer and metal nanoparticles (NPs) as charge-trapping sites on the characteristics of organic nano-floating-gate memory (NFGM) devices are investigated. High-performance NFGM devices are fabricated using the n-type polymer semiconductor, poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)), and various metal NPs. These NPs are embedded within bilayers of various polymer dielectrics (polystyrene (PS)/poly(4-vinyl phenol) (PVP) and PS/poly(methyl methacrylate) (PMMA)). The P(NDI2OD-T2) organic field-effect transistor (OFET)-based NFGM devices exhibit high electron mobilities (0.4–0.5 cm2 V−1 s−1) and reliable non-volatile memory characteristics, which include a wide memory window (≈52 V), a high on/off-current ratio (Ion/Ioff ≈ 105), and a long extrapolated retention time (>107 s), depending on the choice of the blocking dielectric (PVP or PMMA) and the metal (Au, Ag, Cu, or Al) NPs. The best memory characteristics are achieved in the ones fabricated using PMMA and Au or Ag NPs. The NFGM devices with PMMA and spatially well-distributed Cu NPs show quasi-permanent retention characteristics. An inkjet-printed flexible P(NDI2OD-T2) 256-bit transistor memory array (16 × 16 transistors) with Au-NPs on a polyethylene naphthalate substrate is also fabricated. These memory devices in array exhibit a high Ion/Ioff (≈104 ± 0.85), wide memory window (≈43.5 V ± 8.3 V), and a high degree of reliability.

Two conjugated polymers containing stilbene and fumaronitrile moieties were synthesized to investigate their electronic properties by the existence of electron-withdrawing cyano groups on a vinylene backbone. The cyclic voltammetry investigation and time-dependent density functional theory calculations indicated that the cyano substituents lowered the lowest unoccupied molecular orbital (LUMO) energy level by about 0.65 and 0.63 eV, respectively. The lowering of the LUMO energy levels due to the electron-withdrawing properties of the cyano substituents could enhance electron injection capability. Furthermore, bithiophene-fumaronitrile (donor-acceptor) intermolecular interaction facilitates the self-assembly of the polymer chains. Organic field-effect transistors (OFETs) based on PBTSB without the electron-withdrawing group only exhibit hole transport, while OFETs based on PBTFN with cyano substituents exhibit ambipolar characteristics. The growth of PBTFN crystalline fibrils was observed with increasing annealing temperature, which enhanced hole and electron mobility. A complementary-like inverter using PBTFN with ambipolar properties exhibited good symmetry with an inverting voltage nearly half that of the power supply with a gain of 9 at VDD = 100 V. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

This paper reports the controlled growth of atomically sharp In

The threshold voltage and onset voltage for p-channel and n-channel regimes of solution-processed ambipolar organic transistors with top-gate/bottom-contact (TG/BC) geometry were effectively tuned by gate buffer layers in between the gate electrode and the dielectric. The work function of a pristine Al gate electrode (−4.1 eV) was modified by cesium carbonate and vanadium oxide to −2.1 and −5.1 eV, respectively, which could control the flat-band voltage, leading to a remarkable shift of transfer curves in both negative and positive gate voltage directions without any side effects. One important feature is that the mobility of transistors is not very sensitive to the gate buffer layer. This method is simple but useful for electronic devices where the threshold voltage should be precisely controlled, such as ambipolar circuits, memory devices, and light-emitting device applications.

We report here the development of high-performance p- and n-channel organic field-effect transistors (OFETs) and complementary circuits using inkjet-printed semiconducting layers and high-k polymer dielectric blends of poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) and poly(methyl methacrylate) (PMMA). Inkjet-printed p-type polymer semiconductors containing alkyl-substituted thienylenevinylene (TV) and dodecylthiophene (PC12TV12T) and n-type poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-dithiophene)} (P(NDI2OD-T2)) OFETs typically show high field-effect mobilities (μ(FET)) of 0.2-0.5 cm²/(V s), and their operation voltage is effectively reduced to below 5 V by the use of P(VDF-TrFE):PMMA blends. The main interesting result is that the OFET characteristics could be tuned by controlling the mixing ratio of P(VDF-TrFE) to PMMA in the blended dielectric. The μ(FET) of the PC12TV12T OFETs gradually improves, whereas the P(NDI2OD-T2) OFET properties become slightly worse as the P(VDF-TrFE) content increases. When the mixing ratio is optimized, well-balanced hole and electron mobilities of more than 0.2 cm²/(V s) and threshold voltages below ±3 V are obtained at a 7:3 ratio of P(VDF-TrFE) to PMMA. Low-voltage-operated (∼2 V) printed complementary inverters are successfully demonstrated using the blended dielectric and exhibit an ideal inverting voltage of nearly half of the supplied bias, high voltage gains of greater than 25, and excellent noise margins of more than 75% of the ideal values.

High-performance top-gated organic fi eld-effect transistor (OFET) memory devices using electrets and their applications to flprinted organic NAND fl ash are reported. The OFETs based on an inkjet-printed p-type polymer semiconductor with effi ciently chargeable dielectric poly(2-vinylnaphthalene) (PVN) and high-k blocking gate dielectric poly(vinylidenefl trifl uoroethylene) (P(VDF-TrFE)) shows excellent non-volatile memory characteristics. The superior memory characteristics originate mainly from reversible charge trapping and detrapping in the PVN electret layer effi ciently in low-k/high-k bilayered dielectrics. A strategy is devised for the successful development of monolithically inkjet-printed fl exible organic NAND fl ash memory through the proper selection of the polymer electrets (PVN or PS), where PVN/- and PS/P(VDF-TrFE) devices are used as non-volatile memory cells and ground- and bit-line select transistors, respectively. Electrical simulations reveal that the fl exible printed organic NAND fl ash can be possible to program, read, and erase all memory cells in the memory array repeatedly without affecting the non-selected memory cells.

Herein is a description of the mass production of poly(9, 9-dioctylfluorene-co-benthiadiazole) (F8BT) and poly(9, 9-dioctylfluorene) (PFO) nanowires (NWs) using a melt-assisted wetting method with an anodic alumina membrane. The conjugated polymer NWs had a uniform shape (D = 250-300 nm/L = 10-30 microm) and a defect-free smooth surface. Optical properties were investigated by UV-vis, photoluminescent spectroscope, and fluorescent optical microscope. Individual F8BT and PFO NWs had a bright yellow (lambda = 541 nm) andblue (lambda = 442 nm) luminescence, respectively, under UV light irradiation.

We investigated the effects of a gate dielectric and its solvent on the characteristics of top-gated organic fieldeffect transistors (OFETs). Despite the rough top surface of the inkjet-printed active features, the charge transport in an OFET is still favorable, with no significant degradation in performance. Moreover, the characteristics of the OFETs showed a strong dependency on the gate dielectrics used and its orthogonal solvents. Poly(3hexylthiophene) OFETs with a poly(methyl methacrylate) dielectric showed typical p-type OFET characteristics. The selection of gate dielectric and solvent is very important to achieve high-performance organic electronic circuits.

Ambipolar π-conjugated polymers may provide inexpensive large-area manufacturing of complementary integrated circuits (CICs) without requiring micro-patterning of the individual p- and n-channel semiconductors. However, current-generation ambipolar semiconductor-based CICs suffer from higher static power consumption, low operation frequencies, and degraded noise margins compared to complementary logics based on unipolar p- and n-channel organic field-effect transistors (OFETs). Here, we demonstrate a simple methodology to control charge injection and transport in ambipolar OFETs via engineering of the electrical contacts. Solution-processed caesium (Cs) salts, as electron-injection and hole-blocking layers at the interface between semiconductors and charge injection electrodes, significantly decrease the gold (Au) work function (∼4.1 eV) compared to that of a pristine Au electrode (∼4.7 eV). By controlling the electrode surface chemistry, excellent p-channel (hole mobility ∼0.1-0.6 cm(2)/(Vs)) and n-channel (electron mobility ∼0.1-0.3 cm(2)/(Vs)) OFET characteristics with the same semiconductor are demonstrated. Most importantly, in these OFETs the counterpart charge carrier currents are highly suppressed for depletion mode operation (I(off)70 nA when I(on)0.1-0.2 mA). Thus, high-performance, truly complementary inverters (high gain50 and high noise margin75% of ideal value) and ring oscillators (oscillation frequency ∼12 kHz) based on a solution-processed ambipolar polymer are demonstrated.

A novel donor-acceptor-type polymer with a low band-gap that alternates electron-rich thienylenevinylene groups with electron-deficient diketopyrrolopyrrole (DPP) units (PETVTDPP) has been synthesized by Pd-catalyzed Stille cross-coupling polymerization. The polymer shows a broad absorption band of wavelengths that range from 330 to 900 nm, and a low band-gap value of 1.43 eV. The field-effect mobility of an organic thin-film transistor based on this polymer is 0.05 cm(2 ) · Vs(-1) . Bulk-heterojunction solar cells using a mixture of PETVTDPP and PC[71] BM for the active layer show a power conversion efficiency (PCE) of 1.94% under simulated AM 1.5 G solar irradiation at 100 mW · cm(-2) .

We present a new concept of functionalizing solid surfaces using polymeric self-assembled monolayers (PSAM) that are obtained by grafting onto solid surfaces an asymmetric block copolymer composed of a long rodlike block and a short surface-reactive block. Poly(n-hexylisocyanate)-b-poly[3-(trimethoxysilyl)propyl methacrylate] (PHIC-b-PTMSM) is synthesized via a living anionic polymerization and an atom transfer radical polymerization. The new rod–coil block copolymer forms a polymeric self-assembled monolayer (PSAM) through covalent bonding of the sticky PTMSM block and planar adsorption of PHIC rodlike chains onto the substrate surface. The uniform PSAM with a thickness identical to the diameter of the rodlike chain is produced by the immersion coating method in a range of immersion solution concentrations and coating times. The PSAMs present unique properties thanks to the freedom of rotation of the end-grafted rodlike chains. The PSAMs exhibit nematic liquid crystalline ordering when the monolayer is f...

In the present study, we demonstrate inkjet-printed n-type organic field-effect transistors (OFETs) and their complementary inverters with high performance uniformity, using soluble N,N′-bis(n-octyl)-(1,7&1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI8-CN2). The device performance and uniformity were improved by ink-jet printing a PDI8-CN2 solution onto a heated substrate (60 °C). The printed features, which were discontinuous crystalline films at RT, were uniform films when the substrate temperature was increased to 60 °C. Optimized n-channel PDI8-CN2 FETs showed a high field-effect mobility of 0.05–0.06 cm2/Vs, a high on/off ratio of ∼106, and a high uniformity that was within 10% with a bottom-gate/bottom-contact device configuration. Inkjet-printed organic complementary inverters were constructed by direct inkjet-printing of n-channel (PDI8-CN2) and p-channel (6,13-bis(triisopropyl-silylethynyl)-pentacene or poly(3-hexylthiophene)) organic semiconductors onto silicon dioxide gate dielectrics. The inkjet-printed organic complementary inverters exhibited a high voltage gain of more than 15 and small standard deviation of inverting voltage and gain of ±0.95 V and ±0.56, respectively, for measuring 12 samples from four difference batches.

A new thienylenevinylene–benzothiadiazole copolymer, poly{1,2-(E)-bis[2-(5-bromo-3-dodecyl-2-thienyl)-5-thienyl]ethene-2,1,3-benzothiadiazole} (PETVTBT), was synthesized and characterized for potential use in solar cells. The polymer had broad absorption over the entire visible region and a low band gap of 1.57 eV. In addition, the polymer had a relatively low HOMO level of about 5.1 eV. Although PETVTBT was a donor–acceptor-type copolymer, the hole mobility reached 0.025 cm2/V s using field-effect transistors. Bulk-heterojunction solar cells that used a PETVTBT:PC[71]BM blend as the active layer showed a power conversion efficiency of 1.0% under a simulated AM 1.5 G solar irradiation at 100 mW/cm2.

Inkjet-printed high speed polymeric complementary circuits are fabricated using an n-type ([poly{[N,N'-bis(2-octyldo-decyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-dithiophene)} [P(NDI2OD-T2), Polyera Activlnk N2200] and two p-type polymers [poly(3-hexylthiophene) (P3HT) and a dithiophene-based polymer (Polyera ActivInk P2100)]. The top-gate/bottom-contact (TG/BC) organic field-effect transistors (OFETs) exhibit well-balanced and very-high hole and electron mobilities (μ FET ) of 0.2-0.5 cm 2 /Vs, which were enabled by optimization of the inkjet-printed active features, small contact resistance both of electron and hole injections, and effective control over gate dielectrics and its orthogonal solvent effect (selection of poly(methyl methacrylate) and 2-ethoxyethanol). Our first demonstrated inkjet-printed polymeric complementary devices have been integrated to high-performance complementary inverters (gain >30) and ring oscillators (oscillation frequency ~50 kHz). We believe that the operating frequency of printable organic circuits can be further improved more than 10 MHz by fine-tuning of the device architecture and optimization of the p- and n-channel semiconductor processing.

Highly efficient and cost-effective polymer solar cells (PSCs) based poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) have been fabricated by inkjet-printing with various additives. All solution-processed layers in the solar cells—a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer and a photoactive layer based on P3HT and PCBM with additives—were inkjet-printed. The device performance is strongly influenced by the addition of high boiling point additives in the photoactive ink with chlorobenzene (CB) solvent. The morphology, optoelectronic properties, and overall solar cell performance of the devices were dramatically affected by additives, such as 1,8 octanedithiol (ODT), o-dichlorobenzene (ODCB) and chloronaphthalene (Cl-naph). A device fabricated from ink formulated with ODT exhibited the best overall performance with power conversion efficiency (PCE) of 3.71%.

We report high-performance top-gated organic field-effect transistors (OFETs) with regio-regular poly(3-hexylthiophene) (rr-P3HT). The high charge carrier mobility in rr-P3HT FETs (0.4 cm2/Vs) was achieved due to the relatively low contact resistance and high crystallinity of rr-P3HT films. The contact resistance was controlled mainly through the use of high work-function platinum (Pt) (5.6 eV) for the charge injection electrode and a top-gate, bottom-contact geometry that enabled an enhanced current injection via current crowding in the staggered device structure. Moreover, the top-gate configuration provided improved device stability in air ambient conditions via the presence of a gate dielectric and gate electrode on top of the organic semiconductor.

The work reported here was supported by the King Abdullah University of Science and Technology (KAUST).

In this paper, we report a simple and effective method to simultaneously achieve a high charge-carrier mobility and low off current in conjugated polymer-wrapped semiconducting single-walled carbon nanotube (s-SWNT) transistors by applying a SWNT bilayer. To achieve the high mobility and low off current, highly purified and less purified s-SWNTs are successively coated to form the semiconducting layer consisting of poly (3-dodecylthiophene-2,5-diyl) (P3DDT)-wrapped high-pressure carbon mono oxide (HiPCO) SWNT (P3DDT-HiPCO) and poly (9, 9-di-n-dodecylfluorene) (PFDD)-wrapped plasma discharge (PD) SWNT (PFDD-PD). The SWNT transistors with bilayer SWNT networked film showed highly improved hole field-effect mobility (6.18 ± 0.85 cm2V−1s−1 average), on/off current ratio (107), and off current (~1 pA). Thus, the combination of less purified PFDD-PD (98%–99%) charge-injection layer and highly purified s-P3DDT-HiPCO (>99%) charge-transport layer as the bi-layered semiconducting film achieved high mobility and low off current simultaneously.

Efficient charge injection is critical for flexible organic electronic devices such as organic light-emitting diodes (OLEDs) and field-effect transistors (OFETs). Here, we investigated conjugated polymer-wrapped semiconducting single-walled carbon nanotubes (s-SWNTs) as solution-processable charge-injection layers in ambipolar organic field-effect transistors with poly(thienylenevinylene-co-phthalimide)s. The interlayers were prepared using poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) or poly(9,9-dioctylfluorene) (PFO) to wrap s-SWNTs. In the contact-limited ambipolar OFETs, the interlayer led to significantly lower contact resistance (Rc) and increased mobilities for both holes and electrons. The resulting PTVPhI-Eh OFETs with PFO-wrapped s-SWNT interlayers showed very well-balanced ambipolar transport properties with a hole mobility of 0.5 cm2V-1S-1 and an electron mobility of 0.5 cm2V-1S-1 in linear regime. In addition, the chirality of s-SWNTs and kind of wrapping of conjugated polymers are not critical to improving charge-injection properties. We found that the improvements caused by the interlayer were due to the better charge injection at the metal/organic semiconductor contact interface and the increase in the charge concentration through a detailed examination of charge transport with low-temperature measurements. Finally, we successfully demonstrated complementary ambipolar inverters incorporating the interlayers without excessive patterning.