Triisopropylsilylethynyl Pentacene Research Articles

Solution Processing of Semiconducting Organic Molecules for Tailored Charge Transport Properties

We studied the charge transport characteristics of the organic semiconductor 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-PEN) deposited by dip-coating of a solution in an azeotropic solvent mixture. Arrays of crystalline ribbons were obtained with a morphology controllable by variation of the coating speed U. The charge carrier mobility μ exhibited a systematic and reproducible dependence on the coating speed U and maximum values as high as μ ≈ 1.0 cm2/(V s).

Charge transport in high-performance ink-jet printed single-droplet organic transistors based on a silylethynyl substituted pentacene/insulating polymer blend

We present a systematic study of the influence of material composition and ink-jet processing conditions on the charge transport in bottom-gate field-effect transistors based on blends of 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-PEN) and polystyrene. After careful process optimizations of blending ratio and printing temperature we routinely can make transistors with an average mobility of 1 cm 2/Vs (maximum value 1.5 cm 2/Vs), on/off ratio exceeding 10 7, and sharp turn-on in current (sub-threshold slopes approaching 60 mV/decade). These characteristics are superior to the TIPS-PEN only transistors. Using channel scaling measurements and scanning Kelvin probe microscopy, the sharp turn-on in current in the blends is attributed to a contact resistance that originates from a thin insulating layer between the injecting contacts and the semiconductor channel.

Chemically Cross-Linked Thin Poly(vinylidene fluoride-co-trifluoroethylene)Films for Nonvolatile Ferroelectric Polymer Memory

Both chemically and electrically robust ferroelectric poly(vinylidene fluoride-co-trifluoro ethylene) (PVDF-TrFE) films were developed by spin-coating and subsequent thermal annealing with the thermal cross-linking agent 2,4,4-trimethyl-1,6-hexanediamine (THDA). Well-defined ferroelectric β crystalline domains were developed with THDA up to approximately 50 wt %, with respect to polymer concentration, resulting in characteristic ferroelectric hysteresis polarization-voltage loops in metal/cross-linked ferroelectric layer/metal capacitors with remnant polarization of approximately 4 μC/cm(2). Our chemically networked film allowed for facile stacking of a solution-processable organic semiconductor on top of the film, leading to a bottom-gate ferroelectric field effect transistor (FeFET). A low-voltage operating FeFET was realized with a networked PVDF-TrFE film, which had significantly reduced gate leakage current between the drain and gate electrodes. A solution-processed single crystalline tri-isopropylsilylethynyl pentacene FeFET with a chemically cross-linked PVDF-TrFE film showed reliable I-V hysteresis with source-drain ON/OFF current bistablility of 1 × 10(3) at a sweeping gate voltage of ±20 V. Furthermore, both thermal micro/nanoimprinting and transfer printing techniques were conveniently combined for micro/nanopatterning of chemically resistant cross-linked PVDF-TrFE films.

Nonvolatile Polymer Memory with Nanoconfinement of Ferroelectric Crystals

We demonstrate significantly improved performance of a nonvolatile polymeric ferroelectric field effect transistor (FeFET) memory using nanoscopic confinement of poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) within self-assembled organosilicate (OS) lamellae. Periodic OS lamellae with 30 nm in width and 50 nm in periodicity were templated using block copolymer self-assembly. Confined crystallization of PVDF-TrFE not only significantly reduces gate leakage current but also facilitates ferroelectric polarization switching. These benefits are due to the elimination of structural defects and the development of an effective PVDF-TrFE crystal orientation through nanoconfinement. A bottom gate FeFET fabricated using a single-crystalline triisopropylsilylethynyl pentacene channel and PVDF-TrFE/OS hybrid gate insulator shows characteristic source-drain current hysteresis that is fully saturated at a programming voltage of ±8 V with an ON/OFF current ratio and a data retention time of approximately 10(2) and 2 h, respectively.

Ultrathin, Organic, Semiconductor/Polymer Blends by Scanning Corona‐Discharge Coating for High‐Performance Organic Thin‐Film Transistors

AbstractA new thin‐film coating process, scanning corona‐discharge coating (SCDC), to fabricate ultrathin tri‐isopropylsilylethynyl pentacene (TIPS‐PEN)/amorphous‐polymer blend layers suitable for high‐performance, bottom‐gate, organic thin‐film transistors (OTFTs) is described. The method is based on utilizing the electrodynamic flow of gas molecules that are corona‐discharged at a sharp metallic tip under a high voltage and subsequently directed towards a bottom electrode. With the static movement of the bottom electrode, on which a blend solution of TIPS‐PEN and an amorphous polymer is deposited, SCDC provides an efficient route to produce uniform blend films with thicknesses of less than one hundred nanometers, in which the TIPS‐PEN and the amorphous polymer are vertically phase‐separated into a bilayered structure with a single‐crystalline nature of the TIPS‐PEN. A bottom‐gate field‐effect transistor with a blend layer of TIPS‐PEN/polystyrene (PS) (90/10 wt%) operated at ambient conditions, for example, indeed exhibits a highly reliable device performance with a field‐effect mobility of approximately 0.23 cm2 V−1 s−1: two orders of magnitude greater than that of a spin‐coated blend film. SCDC also turns out to be applicable to other amorphous polymers, such as poly(α‐methyl styrene) and poly(methyl methacrylate) and, readily combined with the conventional transfer‐printing technique, gives rise to micropatterned arrays of TIPS‐PEN/polymer films.

Temperature Dependence of Bis(triisopropylsilylethynyl)-Pentacene Nanofilm Deposited on Octadecyltrichlorosilane Self Assembled Monolayer Surface as a Transistor Channel

Highly pure 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-PEN) nanofilms were deposited on a hydrophobic OTS-SAM surface at two different substrate temperatures (70 degrees C and 90 degrees C) via the vacuum thermal evaporation (VTE) method. X-ray reflectivity measurements over a wide temperature range (30 degrees C-284 degrees C) revealed that out-of-plane crystallinity of the film (approximately 10 nm) remains intact but in-plane crystallinity starts to become poor from approximately 100 degrees C, and to become much more worse from 260 degrees C. Atomic force microscope images showed that TIPS-PEN films (approximately 55 nm) prepared at the substrate temperature of 90 degrees C or above commonly have a number of huge cracks between enormous crystal domains (up to 3 microm) whereas the films didn't form such morphology below T(s) = 90 degrees C. These results clearly suggest that an optimum substrate temperature of TIPS-PEN nanofilms on OTS-SAM surface must be somewhere between 70 degrees C and 90 degrees C, and the process temperature must be kept below 90 degrees C in order to form and maintain a highly crystalline film for an organic thin film transistor device since in-plane crystallinity of a semiconductor channel deeply affects the performance of a transistor.

Organic Thin Film Transistor with Poly(4-vinylbiphenyl) Blended 6,13-Bis(triisopropylsilylethynyl)pentacene on Propyleneglycolmonomethyletheracetate Dielectric Surface

This paper presents the latest results in the use of soluble materials, such as organic semiconductors (OSCs) and gate-dielectrics, for simplified processing of organic thin film transistors (OTFTs). In this work, the fabrication of a solution-processed OTFT, with 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) and TIPS-pentacene mixed with poly(4-vinylbiphenyl) (PVBP) as the OSC, and propyleneglycolmonomethyletheracetate (PGMEA) as the gate-dielectric, is described. From electrical measurements, we observed exemplary I-V characteristics for these TFTs. Device performance characteristics have been obtained, including the charge carrier mobility (micro) of 1.47 x 10(-2) cm2Ns, threshold voltage (V(T)) of -11.36 V, current on/off ratio (I(ON/OFF)) of 1.08 x 10(4), sub-threshold swing (SS) of 2.13 V/decade for an OTFT with PVBP blended TIPS-pentacene and micro of 1.39 x 10(-4) cm2/Vs, V(T) of 0.7 V, I(ON/OFF) of 1.64 x 10(3), SS of 4.21 V/decade for an OTFT without polymer binder, individually.

Roll-Printed Organic Thin-Film Transistor Using Patterned Poly(dimethylsiloxane) (PDMS) Stamp

The roll-printed gate, source, and drain electrodes of organic thin-film transistors (OTFTs) were fabricated by gravure printing or gravure-offset printing using patterned poly(dimethylsiloxane) (PDMS) stamp with various channel lengths and low-resistance silver (Ag) pastes on flexible 150 x 150 mm2 plastic substrates. Bottom-contact roll-printed OTFTs used polyvinylphenol (PVP) as polymeric dielectric and bis(triisopropyl-silylethynyl) pentacene (TIPS-pentacene) as organic semiconductor; they were formed by spin coating or ink-jetting. Depending on the choice of roll-printing method, the printed OTFTs obtained had a field-effect mobility of between 0.08 and 0.1 cm2/Vs, an on/off current ratio of between 10(4) and 10(5), and a subthreshold slope of between 1.96 and 2.32 V/decade. The roll-printing using patterned PDMS stamp and soluble processes made it possible to fabricate a printed OTFT with a channel length of between 12 to 74 microm on a plastic substrate; this was not previously possible using traditional printing techniques. The proposed fabrication process was 20 steps shorted than conventional fabrication techniques.

An Amorphous Polythiophene as a Binder Material for Organic Thin-Film Transistor Channel Applications

Blending of crystalline low molecular-weight organic semiconductors, e.g., 6,13-bis (triisopropylsilylethynyl)pentacene (TIPS-Pentacene), and binder polymers has recently been known to be an effective way to achieve high performance organic thin-film transistors (OTFTs). However, only limited number of examples has been reported as binder materials for OTFT applications, e.g., poly(triarylamine), poly(α-methylstyrene), and etc. In this work, an amorphous polythiophene derivative, poly(3-(2-ethylhexyl)thiophene) (P3EHT), was prepared by introducing 2-ethylhexyl group as a side-chain to the polythiophene. The P3EHT was synthesized by Grignard metathesis (GRIM) polymerization to give a molecular weight (Mn) of 4,100 (PDI = 3.4), and it was readily soluble in common organic solvents, such as chloroform, tetrahydrofuran, toluene, and etc. An amorphous nature of the P3EHT was confirmed from differential scanning calorimetry (DSC) and ultraviolet-visible spectroscopy results. A mobility of 2.5 × 10−4 cm2/Vs, an on/off ratio of 0.57 × 103 and a threshold voltage of 1.6 V have been obtained with OTFTs using a P3EHT/TIPS-Pentacene blend.

Organic ferroelectric field-effect transistor with P(VDF-TrFE)/PMMA blend thin films for non-volatile memory applications

Among the many ferroelectrics polymers, poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] has drawn a great attention with its promising memory properties such as large remanent polarization, good fatigue and retention properties. Since the ferroelectric layer plays a critical role in the operation of memory device, it is important to control the structure of ferroelectric thin film. In order to improve the performance of a ferroelectric device, in this contribution we employed P(VDF-TrFE) layers blended with various compositions of an amorphous poly(methyl methacrylate) (PMMA) from 0 wt.% to 20 wt.%. In metal/ferroelectric/metal capacitor structure, we observed the decrease of remanent polarization from 9.13 μC/cm 2 to 4.7 μC/cm 2 and increase of coercive voltage from 9.5 V to 15.2 V with PMMA. Polarization switching time of the ferroelectric blend films estimated from the switched polarization vs. time curves increases with the amount of PMMA. Furthermore, ferroelectric field-effect transistors (FeFETs) based on ferroelectric P(VDF-TrFE) and PMMA blend films with single-crystalline tri-isopropylsilylethynyl pentacene (TIPS-PEN) channels show that both ON and OFF currents of the transistors are maintained with the PMMA contents despite the reduction of remanent polarization of P(VDF-TrFE)/PMMA films.

Azeotropic Binary Solvent Mixtures for Preparation of Organic Single Crystals

AbstractHere, a new approach is introduced to prepare large single crystals of π‐conjugated organic molecules from solution. Utilizing the concept of azeotropism, single crystals of tri‐isopropylsilylethynyl pentacene (TIPS‐PEN) with dimensions up to millimeters are facilely self‐assembled from homogeneous solutions comprising two solvents with opposing polarities and a positive azeotropic point. At solvent compositions close to the azeotropic point, an abrupt transition of morphology from polycrystalline thin‐films to large single crystals is found. How to adjust the initial ratio of the binary solvents so that the change in solvent composition during evaporation favors the specific H‐aggregation and promotes an efficient self‐assembly of TIPS‐PEN is explained. The charge‐carrier (hole) mobilities are substantially enhanced by a factor of 4 from the morphology of thin‐films to large single crystals used as active layer in field‐effect transistors. Additionally, this approach is extended to other π–π stacked organic molecules to elucidate its broad applicability.

Fabrication of Organic Thin-Film Transistors with Roll-Printed Electrodes Using Patterned Polymer Stamp

The roll-printed electrodes of organic thin-film transistors (OTFTs) were fabricated by gravure or flexography printing using patterned poly(dimethylsiloxane) (PDMS) stamp with various channel lengths and low-resistance silver (Ag) paste on plastic substrates. The roll-printed OTFTs used poly(vinyl)(phenol) polymeric dielectrics and bis(triisopropyl-silylethynyl) pentacene organic semiconductors. The roll-printed OTFTs obtained had a field-effect mobility 0.08 (±0.02) cm2/Vs, an on/off current ratio of 104 and a subthreshold slope of 2.53 V/decade. The roll printing using patterned PDMS stamp for Ag paste transferring made it possible to fabricate a printed OTFT with a channel length as small as to 12 μm on plastic substrate.

Solvent Effect on the Electrical Properties of Triisopropylsilylethynyl (TIPS) Pentacene Organic Thin-Film Transistors

We investigated the electrical properties of triisopropylsilylethynyl (TIPS) pentacene organic thin-film transistor (OTFT) depending on solvent type. TIPS pentacene was spin coated by using chlorobenzene, p-xylene, chloroform, and toluene as solvents. A broad spectrum of electrical properties was affected by the solvent choice. Fabricated OTFT with chlorobenzene shows field-effect mobility of 1.0 × 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0-2</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V · s, on/off ratio of 4.3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , and threshold voltage of 5.5 V. In contrast, with chloroform, the mobility is 5.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V · s, on/off ratio of 1.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and threshold voltage of 1.7 V. Further investigation by measurement of the grain size of TIPS thin films by atomic force microscopy (AFM) and X-ray diffraction spectroscopy showed that solvents with higher boiling points resulted in larger grain sizes and improved crystallinity. The higher performance electrical characteristics are explained by large grain size and high crystallinity of the TIPS pentacene layer in films spin coated with higher boiling point such as chlorobenzene.

Non‐volatile Ferroelectric Poly(vinylidene fluoride‐co‐trifluoroethylene) Memory Based on a Single‐Crystalline Tri‐isopropylsilylethynyl Pentacene Field‐Effect Transistor

AbstractA new type of nonvolatile ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)) memory based on an organic thin‐film transistor (OTFT) with a single crystal of tri‐isopropylsilylethynyl pentacene (TIPS‐PEN) as the active layer is developed. A bottom‐gate OTFT is fabricated with a thin P(VDF‐TrFE) film gate insulator on which a one‐dimensional ribbon‐type TIPS‐PEN single crystal, grown via a solvent‐exchange method, is positioned between the Au source and drain electrodes. Post‐thermal treatment optimizes the interface between the flat, single‐crystalline ab plane of TIPS‐PEN and the polycrystalline P(VDF‐TrFE) surface with characteristic needle‐like crystalline lamellae. As a consequence, the memory device exhibits a substantially stable source–drain current modulation with an ON/OFF ratio hysteresis greater than 103, which is superior to a ferroelectric P(VDF‐TrFE) OTFT that has a vacuum‐evaporated pentacene layer. Data retention longer than 5 × 104 s is additionally achieved in ambient conditions by incorporating an interlayer between the gate electrode and P(VDF‐TrFE) thin film. The device is environmentally stable for more than 40 days without additional passivation. The deposition of a seed solution of TIPS‐PEN on the chemically micropatterned surface allows fabrication arrays of TIPS‐PEN single crystals that can be potentially useful for integrated arrays of ferroelectric polymeric TFT memory.

π-σ-Phosphonic acid organic monolayer–amorphous sol–gel hafnium oxide hybrid dielectric for low-voltage organic transistors on plastic

A vacuum-free solution processed hybrid dielectric composed of an anthryl-alkyl-phosphonic acid (π-σ-PA) self-assembled monolayer on an amorphous sol–gel processed hafnium oxide (HfOx) is demonstrated for low-voltage organic thin film transistors (OTFTs) on plastic substrates. The π-σ-PA/HfOx hybrid dielectric provides high capacitance (0.54 µF cm−2) and low leakage current (2 × 10−8 A cm−2), and has a chemically and electrically compatible dielectric interface for evaporated and solution processed acene semiconductors. The utility of this dielectric is demonstrated by fabricating pentacene and 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-PEN) based OTFTs with operating voltages under 2 V, subthreshold slopes as low as 100 mV dec−1, and average mobilities of 0.32 cm2 V−1 s−1 and 0.38 cm2 V−1 s−1, for pentacene and TIPS-PEN, respectively.

Hysteresis Effects by Source/Drain Interdigitated-Finger Geometry in 6,13-Bis(triisopropylsilylethynyl)pentacene Thin-Film Transistors

This work reports on the fabrication of organic thin-film transistors (OTFTs) with a solution-based 6,13-bis(triisopropylsilylethynyl)pentacene by a drop-casting method, and the determination of the electrical properties of OTFTs having different source/drain interdigitated-finger electrodes. The results show that the hysteresis in transfer characteristics of the OTFTs depends on the variation of contact fingers. These hystereses lead to changes in threshold voltage, which originates from charge trapping/detrapping at or near the organic semiconductor/dielectric interface. These related phenomena also influence the device parameters such as the field-effect mobility, the on/off current ratio, and the gate current.

Solution-processed organic field-effect transistors composed of poly(4-styrene sulfonate) wrapped multiwalled carbon nanotube source/drain electrodes

Multiwalled carbon nanotubes (MWNTs) were solubilized in water by wrapping them noncovalently with poly(4-styrene sulfonate) (PSS). The PSS-wrapped MWNTs exhibited a high conductivity (2.0 × 10 2 S/cm) when compared to other solution-processed electrodes. Ultraviolet photoelectron spectroscopy results show the PSS-wrapped nanotubes have a work function of 4.83 eV, which is 0.36 eV higher than that of untreated MWNTs. We fabricated triisopropylsilylethynyl pentacene field-effect transistors (FETs) using the PSS-wrapped MWNTs as source/drain electrodes and found that the field-effect mobility of the thus obtained devices was 0.043 cm 2 V −1 s −2. This mobility is four times higher than that of similar FETs containing gold electrodes (0.011 cm 2 V −1 s −2).

High Performance Organic Thin Film Transistors Made Simple Through Molecular Design and Processing

We report on a simple a method of inducing self-isolation of the thin film transistors via manipulation of the chemical interactions between the organic molecules and the surfaces where they are deposited. We use pentafluorobenzenethiol (PFBT) treatment of the contacts and investigate the thin film formation of different types of chemical compounds. In particular, three similar organic molecules: triisopropyl-silylethynyl pentacene (TIPS pentacene), triisopropyl-silylethynyl peri-fluoro-pentacene (TIPS PFP) and triisopropyl-silylethynyl cata-fluoro-pentacene (TIPS CFP), were studied and compared to better understand how the molecular, crystal structure and thin film formation influence the electrical behavior of devices fabricated with them. The molecules exhibit significantly different interactions with the chemically treated substrates. The field-effect mobilities of these devices are directly related to their thin film microstructure.

High-performance solution-processed triisopropylsilylethynyl pentacene transistors and inverters fabricated by using the selective self-organization technique

To obtain selectively self-organized active layers of organic field-effect transistors (OFETs) and inverters from a solution-phased triisopropylsilylethynyl pentacene (TIPS-PEN) semiconductor, we locally patterned an oxide dielectric, covered with a hydrophobic fluoropolymer, using O2 plasma etching. Drop-cast TIPS-PEN molecules were selectively crystallized on the O2-plasma-etched area, where a hydrophilic oxide surface was produced. Modification of the patterned oxide dielectrics with hexamethyldisilazane led to a field-effect mobility of the TIPS-PEN OFETs of 0.185 cm2 V−1 s−1, a substhreshold swing of 0.738 V/decade and an on/off ratio of 107. Moreover, an inverter composed of two of these OFETs showed good device operation and inverter gain of 5.6.

Tuning of Ag work functions by self-assembled monolayers of aromatic thiols for an efficient hole injection for solution processed triisopropylsilylethynyl pentacene organic thin film transistors

We demonstrate tuning of hole injection barriers in bottom contact triisopropylsilylethynyl pentacene (TIPS-pentacene) organic thin film transistors (OTFTs) by forming the self-assembled monolayers (SAMs) of thiophenol, 4-fluorothiophenol, or pentafluorothiophenol on the pristine Ag electrode. The work functions of SAM-treated Ag electrodes are measured by Kelvin probe method. The TIPS-pentacene OTFT devices were fabricated by a drop-cast method with a micropipette like an inkjet printing. The OTFTs with pentafluorothiophenol-Ag electrodes as source and drain exhibit carrier mobility of 0.17cm2∕Vs and on/off current ratio of 105 because of almost no hole injection barrier to TIPS pentacenes. The SAM-treated Ag electrodes are robust over repeated electrical scans of 100cycles.