Showing papers on "Pentacene published in 2011"

Tuning charge transport in solution-sheared organic semiconductors using lattice strain

Abstract: A solution-processing method known as solution shearing is used to introduce lattice strain to organic semiconductors, thus improving charge carrier mobility. Solution-processed organic semiconductors show great promise for application in cheap and flexible electronic devices, but generally suffer from greatly reduced electronic performance — most notably charge-carrier mobilities — compared with their inorganic counterparts. Borrowing a trick from the inorganic semiconductor community, Giri et al. show how the introduction of strain into an organic semiconductor, through a simple solution-processing technique, modifies the molecular packing within the material and hence its electronic performance. For one material studied, the preparation of a strained structure is shown to more than double the charge-carrier mobility. Circuits based on organic semiconductors are being actively explored for flexible, transparent and low-cost electronic applications1,2,3,4,5. But to realize such applications, the charge carrier mobilities of solution-processed organic semiconductors must be improved. For inorganic semiconductors, a general method of increasing charge carrier mobility is to introduce strain within the crystal lattice6. Here we describe a solution-processing technique for organic semiconductors in which lattice strain is used to increase charge carrier mobilities by introducing greater electron orbital overlap between the component molecules. For organic semiconductors, the spacing between cofacially stacked, conjugated backbones (the π–π stacking distance) greatly influences electron orbital overlap and therefore mobility7. Using our method to incrementally introduce lattice strain, we alter the π–π stacking distance of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) from 3.33 A to 3.08 A. We believe that 3.08 A is the shortest π–π stacking distance that has been achieved in an organic semiconductor crystal lattice (although a π–π distance of 3.04 A has been achieved through intramolecular bonding8,9,10). The positive charge carrier (hole) mobility in TIPS-pentacene transistors increased from 0.8 cm2 V−1 s−1 for unstrained films to a high mobility of 4.6 cm2 V−1 s−1 for a strained film. Using solution processing to modify molecular packing through lattice strain should aid the development of high-performance, low-cost organic semiconducting devices.

Mechanism for Singlet Fission in Pentacene and Tetracene: From Single Exciton to Two Triplets

Abstract: Singlet fission (SF) could dramatically increase the efficiency of organic solar cells by producing two triplet excitons from each absorbed photon. While this process has been known for decades, most descriptions have assumed the necessity of a charge-transfer intermediate. This ab initio study characterizes the low-lying excited states in acene molecular crystals in order to describe how SF occurs in a realistic crystal environment. Intermolecular interactions are shown to localize the initially delocalized bright state onto a pair of monomers. From this localized state, nonadiabatic coupling mediated by intermolecular motion between the optically allowed exciton and a dark multi-exciton state facilitates SF without the need for a nearby low-lying charge-transfer intermediate. An estimate of the crossing rate shows that this direct quantum mechanical process occurs in well under 1 ps in pentacene. In tetracene, the dark multi-exciton state is uphill from the lowest singlet excited state, resulting in a d...

Surface-Directed Molecular Assembly of Pentacene on Monolayer Graphene for High-Performance Organic Transistors

Abstract: Organic electronic devices that use graphene electrodes have received considerable attention because graphene is regarded as an ideal candidate electrode material. Transfer and lithographic processes during fabrication of patterned graphene electrodes typically leave polymer residues on the graphene surfaces. However, the impact of these residues on the organic semiconductor growth mechanism on graphene surface has not been reported yet. Here, we demonstrate that polymer residues remaining on graphene surfaces induce a stand-up orientation of pentacene, thereby controlling pentacene growth such that the molecular assembly is optimal for charge transport. Thus, pentacene field-effect transistors (FETs) using source/drain monolayer graphene electrodes with polymer residues show a high field-effect mobility of 1.2 cm2/V s. In contrast, epitaxial growth of pentacene having molecular assembly of lying-down structure is facilitated by π−π interaction between pentacene and the clean graphene electrode without po...

The Position of Nitrogen in N‐Heteropentacenes Matters

Abstract: An exploratory study on novel silylethynylated N-heteropentacenes, which have their N atoms on the terminal rings of the pentacene backbone, is reported. This study leads to both p- and n-channel organic thin-film transistors with high field-effect mobility and also reveals that the position of the N atoms plays an important role in tuning the structures and properties of organic semiconductors based on N-heteropentacenes.

Transparent flexible organic transistors based on monolayer graphene electrodes on plastic.

Abstract: There has been much interest in graphene-based electronic devices because graphene provides excellent electrical, optical, and mechanical properties. [ 1 ] In this sense, organic electronic devices using graphene electrodes have attracted considerable attention, and several reports have described the use of graphene source/drain electrodes in organic fi eld-effect transistors (OFETs). [ 2 ] One of the ultimate goals in the fabrication of OFETs using graphene electrodes lies in the fabrication of fl exible and transparent organic transistors, assembled on plastics substrates, that maintain their high performance under ambient conditions. However, no reports have described the fabrication of organic transistors assembled on plastic substrates because the synthesis of either graphene or reduced graphene oxide requires high-temperature fabrication processes. Another important goal in the context of fabricating organic electronic devices with graphene electrodes lies in the fabrication of highly transparent graphene electrodes that cover large areas. Graphene transmittance decreases linearly as the number of layers increases in n-layer graphene. [ 3 ] Thus, the use of monolayer graphene is necessary to achieve high transparency in graphene electrodes, provided that the conductivity of the graphene is suffi cient for device electrode applications. Another merit of monolayer graphene is its extremely low thickness (3–4 Å). Source/drain electrodes in staggered bottomcontact FET structures should be thin to ensure step coverage of the active layer during sequential transistor fabrication. [ 4 ] For this reason, one-atom-thick monolayer graphene provides ideal source/drain electrodes for effi cient charge injection. Recently, several groups succeeded in fabricating high-quality/largearea graphene with preferential monolayer thickness using a

Interface Engineering of Semiconductor/Dielectric Heterojunctions toward Functional Organic Thin-Film Transistors

Abstract: Interface modification is an effective and promising route for developing functional organic field-effect transistors (OFETs). In this context, however, researchers have not created a reliable method of functionalizing the interfaces existing in OFETs, although this has been crucial for the technological development of high-performance CMOS circuits. Here, we demonstrate a novel approach that enables us to reversibly photocontrol the carrier density at the interface by using photochromic spiropyran (SP) self-assembled monolayers (SAMs) sandwiched between active semiconductors and gate insulators. Reversible changes in dipole moment of SPs in SAMs triggered by lights with different wavelengths produce two distinct built-in electric fields on the OFET that can modulate the channel conductance and consequently threshold voltage values, thus leading to a low-cost noninvasive memory device. This concept of interface functionalization offers attractive new prospects for the development of organic electronic dev...

A survey of electron-deficient pentacenes as acceptors in polymer bulk heterojunction solar cells

Abstract: We have prepared, characterized and surveyed device performance for a series of electron deficient pentacenes for use as acceptors in polymer bulk heterojunction solar cells, using P3HT as the donor material. All of the materials reported here behaved as acceptors, and variations in the position and nature of the electron-withdrawing group on the pentacene core allowed tuning of device open-circuit voltage. Photocurrent was strongly correlated with the pentacene crystal packing motif; materials with 2D π-stacking interactions performed poorly compared with materials exhibiting 1D π-stacking interactions. The best pentacene acceptors gave repeatable device efficiency in excess of 1.2%, compared with 3.5% exhibited for PCBM-based devices.

Photophysics of pentacene thin films: The role of exciton fission and heating effects

Abstract: There is evidence that the photo-generated singlet exciton in polycrystalline pentacene films undergoes rapid and efficient fission to form two triplet excitons. However, the role of exciton fission in pentacene has been controversial, with previous studies putting forward alternate relaxation pathways for the singlet exciton, such as excimer or charge formation, or internal conversion to a doubly excited exciton. We report temperature- and angular-dependent ultrafast transient optical absorption measurements in a wide spectral and temporal window. Angular-dependent transient spectra identify a common origin to photo-induced absorptions at 530 and 860 nm, which we associate with triplet excitons. These constitute the dominant relaxation channel for singlet excitons. Other features, particularly near 620 nm, previously assigned to excimers or electronic charges, are shown to be caused by thermal modulation from the optical pump.

Thin-Film Morphology of Inkjet-Printed Single-Droplet Organic Transistors Using Polarized Raman Spectroscopy: Effect of Blending TIPS-Pentacene with Insulating Polymer

Abstract: We report thin-film morphology studies of inkjet-printed single-droplet organic thin-film transistors (OTFTs) using angle-dependent polarized Raman spectroscopy. We show this to be an effective technique to determine the degree of molecular order as well as to spatially resolve the orientation of the conjugated backbones of the 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pentacene) molecules. The addition of an insulating polymer, polystyrene (PS), does not disrupt the p-p stacking of the TIPS-Pentacene molecules. Blending in fact improves the uniformity of the molecular morphology and the active layer coverage within the device and reduces the variation in molecular orientation between polycrystalline domains. For OTFT performance, blending enhances the saturation mobility from 0.22 ± 0.05 cm2/ (V·s) (TIPS-Pentacene) to 0.72 ± 0.17 cm2/(V·s) (TIPS-Pentacene:PS) in addition to improving the quality of the interface between TIPS-Pentacene and the gate dielectric in the channel, resulting in threshold voltages of ~0 V and steep subthreshold slopes. © 2011 American Chemical Society.

Assembly of iron phthalocyanine and pentacene molecules on a graphene monolayer grown on Ru(0001)

Abstract: Anisotropic triangular graphene monolayers grown on a Ru(0001) surface represent unique two-dimensional templates for creating ordered, large-scale assembly of functional molecules. Using scanning tunneling microscopy and spectroscopy, we demonstrate the selective adsorption and the formation of ordered molecular arrays of iron phthalocyanine and pentacene molecules of different structural symmetries on the graphene/Ru(0001) templates. With in-depth investigations of the molecular adsorption and assembly processes, we reveal the existence of site-specific, lateral electric dipoles (or lateral electric fields) in the epitaxial graphene monolayers and the capability of the dipoles in directing and driving the molecular adsorption and assembly. We show that the lateral dipoles originate from the inhomogeneous distribution of charge due to the epitaxial constraint of graphene on a Ru(0001) surface. The adsorption mechanism is rather general and applicable to similar molecular systems on graphene monolayers formed on other transition metal surfaces.

First-principles calculations of anisotropic charge-carrier mobilities in organic semiconductor crystals

Abstract: The orientational dependence of charge carrier mobilities in organic semiconductor crystals and the correlation with the crystal structure are investigated by means of quantum chemical first principles calculations combined with a model using hopping rates from Marcus theory. A master equation approach is presented which is numerically more efficient than the Monte Carlo method frequently applied in this context. Furthermore, it is shown that the widely used approach to calculate the mobility via the diffusion constant along with rate equations is not appropriate in many important cases. The calculations are compared with experimental data, showing good qualitative agreement for pentacene and rubrene. In addition, charge transport properties of core-fluorinated perylene bisimides are investigated.

Density Functional Theory Study on Electron and Hole Transport Properties of Organic Pentacene Derivatives with Electron-Withdrawing Substituent

Abstract: Attaching electron-withdrawing substituent to organic conjugated molecules is considered as an effective method to produce n-type and ambipolar transport materials. In this work, we use density functional theory calculations to investigate the electron and hole transport properties of pentacene (PENT) derivatives after substituent and simulate the angular resolution anisotropic mobility for both electron and hole transport. Our results show that adding electron-withdrawing substituents can lower the energy level of lowest unoccupied molecular orbital (LUMO) and increase electron affinity, which are beneficial to the electron injection and ambient stability of the material. Also the LUMO electronic couplings for electron transport in these pentacene derivatives can achieve up to a hundred meV which promises good electron transport mobility, although adding electron-withdrawing groups will introduce the increase of electron transfer reorganization energy. The final results of our angular resolution anisotropic mobility simulations show that the electron mobility of these pentacene derivatives can get to several cm(2) V-1 s(-1), but it is important to control the orientation of the organic material relative to the device channel to obtain the highest electron mobility. Our investigation provide detailed information to assist in the design of n-type and ambipolar organic electronic materials with high mobility performance. (C) 2011 Wiley Periodicals, Inc. J Comput Chem 32: 3218-3225, 2011

Solution-deposited organic-inorganic hybrid multilayer gate dielectrics. Design, synthesis, microstructures, and electrical properties with thin-film transistors.

Abstract: We report here on the rational synthesis, processing, and dielectric properties of novel layer-by-layer organic/inorganic hybrid multilayer dielectric films enabled by polarizable π-electron phosphonic acid building blocks and ultrathin ZrO2 layers. These new zirconia-based self-assembled nanodielectric (Zr-SAND) films (5–12 nm thick) are readily fabricated via solution processes under ambient atmosphere. Attractive Zr-SAND properties include amenability to accurate control of film thickness, large-area uniformity, well-defined nanostructure, exceptionally large electrical capacitance (up to 750 nF/cm2), excellent insulating properties (leakage current densities as low as 10–7 A/cm2), and excellent thermal stability. Thin-film transistors (TFTs) fabricated with pentacene and PDIF-CN2 as representative organic semiconductors and zinc–tin–oxide (Zn–Sn–O) as a representative inorganic semiconductor function well at low voltages (<±4.0 V). Furthermore, the TFT performance parameters of representative organic ...

Physicochemically Stable Polymer‐Coupled Oxide Dielectrics for Multipurpose Organic Electronic Applications

Abstract: A chemically coupled polymer layer is introduced onto inorganic oxide dielectrics from a dilute chlorosilane-terminated polystyrene (PS) solution. As a result of this surface modification, hydrophilic-oxide dielectrics gain hydrophobic, physicochemically stable properties. On such PS-coupled SiO2 or AlOx dielectrics, various vacuum- and solution-processable organic semiconductors can develop highly ordered crystalline structures that provide higher field-effect mobilities (μFETs) than other surface-modified systems, and negligible hysteresis in organic field-effect transistors (OFETs). In particular, the use of PS-coupled AlOx nanodielectrics enables a solution-processable triethylsilylethynyl anthradithiophene OFET to operate with μFET ∼ 1.26 cm2 V−1 s−1 at a gate voltage below –1 V. In addition, a complementary metal-oxide semiconductor-like organic inverter with a high voltage gain of approximately 32 was successfully fabricated on a PS-coupled SiO2 dielectric.

Products and mechanism of acene dimerization. A computational study.

Abstract: The high reactivity of acenes can reduce their potential applications in the field of molecular electronics. Although pentacene is an important material for use in organic field-effect transistors because of its high charge mobility, its reactivity is a major disadvantage hindering the development of pentacene applications. In this study, several reaction pathways for the thermal dimerization of acenes were considered computationally. The formation of acene dimers via a central benzene ring and the formation of acene-based polymers were found to be the preferred pathways, depending on the length of the monomer. Interestingly, starting from hexacene, acene dimers are thermodynamically disfavored products, and the reaction pathway is predicted to proceed instead via a double cycloaddition reaction (polymerization) to yield acene-based polymers. A concerted asynchronous reaction mechanism was found for benzene and naphthalene dimerization, while a stepwise biradical mechanism was predicted for the dimerizati...

Capacitive behavior of pentacene-based diodes: Quasistatic dielectric constant and dielectric strength

Abstract: The capacitive behavior of pentacene films was investigated in the metal-semiconductor-metal (MSM) diode structure. Impedance analysis of diodes with a thick pentacene layer up to 1012 nm showed a full depletion of the organic layer. This observation allowed us to regard the MSM diode as a parallel-plate capacitor in the reverse-bias regime without current flow. Under forward-bias, the diode was evaluated through frequency-dependent impedance measurements by using an equivalent circuit composed of a single parallel resistance-capacitance circuit. The analysis of the data in both the reverse and forward bias regime led us to electrical methods for quantifying dielectric properties of pentacene.

Hall-Effect Measurements Probing the Degree of Charge-Carrier Delocalization in Solution-Processed Crystalline Molecular Semiconductors

Abstract: Intramolecular structure and intermolecular packing in crystalline molecular semiconductors should have profound effects on the charge-carrier wave function, but simple drift mobility measurements are not very sensitive to this. Here we show that differences in the Hall resistance of two soluble pentacene derivatives can be explained with different degrees of carrier delocalization being limited by thermal lattice fluctuations. A combination of Hall measurements, optical spectroscopy, and theoretical simulations provides a powerful probe of structure-property relationships at a molecular level.

In situ antibody detection and charge discrimination using aqueous stable pentacene transistor biosensors.

Abstract: Pentacene-based organic thin-film transistors were used to create highly sensitive, real-time electronic sensors for selective antibody detection. Bovine serum albumin was covalently attached to a modified pentacene surface to selectively detect the label free monoclonal antiBSA. These sensors displayed a high affinity constant (K(A)) of (1.1 ± 3) × 10(7) M(-1) at pH 7, which is 1 order of magnitude higher than those obtained with a highly sensitive surface plasmon resonance spectroscopy detection system. Furthermore, a high degree of discrimination in the hybrid antiBSA charges was achieved at different pH values. This demonstration of fast, label-free, real-time detection of nanoscale biomolecules in aqueous buffer solutions using the organic transistor sensing platform will have a significant impact on high-performance microarrays in addition to discriminating the presence of ionizable groups.

Simulation of vapor-phase deposition and growth of a pentacene thin film on C60 (001).

Abstract: Current research in organic electronics is clearly evidencing that the strive to produce efficient organic electronic devices requires high performance materials that can only be realized through a rational design [Special11]. Although polymer-based systems are at the moment the most appealing for market applications, mainly because of their solution processability, small molecule-based devices possess potential for commercialization, presenting comparable performances and a better batch-to-batch reproducibility of their properties [Walker11]. The interest in small molecules of well defined crystalline structure arises also from the fine control over final morphologies that can be achieved through vapour-phase growth techniques [Ruiz04, Rolin10], control that allows, with respect to polymer devices, a deeper understanding of the structure-electronic properties relationships. Indeed building an efficient electronic device (e. g. a solar cell) coincides to a large extent with the fine tuning of the electronic properties at the different interfaces, typically metal-organic, inorganic-organic, and organic-organic. In this communication we focus on the latter interface between two of the most studied p-and n-type molecular organic semiconductors, pentacene (A5) and C 60 fullerene. These materials have been recently employed in producing rather efficient thin film bilayer solar cells [Yoo04, Mayer04, Yoo07, Cheyns07, Dissanayake07], ambipolar field effect transistors [Kuwahara04, Yan09, Cosseddu10] and low-voltage-operating organic complementary inverters [Na09]. The relative simplicity and the good performances of C 60 /A5 heterojunctions has stimulated theoretical research on the electronic processes occurring at the interface: density functional theory [Yi09], valence-bond Hartree-Fock [Linares10] and microelectrostatic calculations [Verlaak09] have been employed in studying model interfaces of increasing complexity. These studies coherently underline the importance of relative molecular orientations and positions in determining the interface dipole and electronic couplings, i.e. the key factors governing exciton transport and fission, charge generation and separation [Rao10]. This in turn means that improving computational predictions of the molecular organization at the interface is fundamental to understanding experimental systems of great interest. This task can in principle be tackled by using classical atomistic force fields, but it is definitely not a straightforward one. Indeed, it has been recently recognized that molecular organizations at the interface depend on the preparation process and not just on thermodynamic state of the system, so that imitating the experimental preparation techniques is often necessary to produce realistic morphologies [Liu08, Cheung08, MacKenzie10, Clancy11, Beljonne11]. For this specific system, Clancy and co-workers applied classical simulations at both coarse-grained [Choudhary06] and atomistic detail [Goose07] to study some aspects of the pentacene …

A Promising Approach to Obtain Excellent n-Type Organic Field-Effect Transistors: Introducing Pyrazine Ring

Abstract: The effects of the pyrazine ring on the geometrical and electronic structures, molecular stacking motifs, carrier injection, and transport properties as well as electronic band structures for some typical molecules with pyrazines (such as tetracene, pentacene, and π-extended tetrathiafulvalene derivatives) were theoretically investigated by quantum chemical methods. The introduction of pyrazine does not affect the molecular planarity and in the meantime largely decreases the energies of the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals and hence improves their stability in air and ability of electron injection. More important, it is very helpful for prompting the molecular π-stacking. Small electron reorganization energies and large electronic coupling originated from their dense π-stacking give rise to their excellent electron transport properties, which makes them become a class of promising candidates for excellent n-type organic field-effect transistor (OFET) materia...

Interface Engineering for Organic Electronics; Manufacturing of Hybrid Inorganic-Organic Molecular Crystal Devices

Abstract: Organic semiconductors are at the basis of Organic Electronics. Objective of this dissertation is “to fabricate high-quality organic molecular single-crystal devices”, to explore the intrinsic properties of organic semiconductors. To achieve this, the in situ fabrication of complete field-effect transistors by direct deposition of metal contacts and oxide gate dielectrics on the surface of free-standing pentacene single-crystals at room temperature (with the ‘quasi-dynamic stencil deposition’ technique in pulsed laser deposition) is selected as main approach. First, the structure of vapor-grown pentacene single-crystals is investigated. The observed morphology shows step flow is the dominant crystal growth mechanism. For pentacene, the most common oxidation product and largest impurity present is 6,13-pentacenequinone. It is observed that this quinone is preferentially located as a thin monolayer (partly) covering the crystal surface. In order to remove the quinones selectively, the partly-oxidized crystals are heated in vacuum at a fixed temperature overnight. Next, the direct deposition of various materials through a stencil on the pentacene singlecrystal surface by PLD is investigated. By taking several precautions in the process, lowkinetic energy deposition or ‘soft-landing’ was achieved. Smooth and isolated patterns with a well-defined geometry were successfully deposited, without obvious destruction of the fragile substrate. The terraced structure of the underlying pentacene substrate is often still noticeable on top of the patterned features. A series of gold patterns is deposited on silicon oxide and pentacene single-crystals; the results show that the growth evolution of the surface roughness is similar on both kinds of substrates. Finally, the influence of the deposition parameters applied in the device fabrication and performing a heat treatment on the electrical properties of pentacene single-crystals is investigated, by characterizing space-charge-limited current and field-effect transistor devices fabricated on the surface of pentacene single-crystals.

Enhanced Performance Consistency in Nanoparticle/TIPS Pentacene-Based Organic Thin Film Transistors

Abstract: In this study, inorganic silica nanoparticles are used to manipulate the morphology of 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS pentacene) thin films and the performance of solution-processed organic thin-film transistors (OTFTs). This approach is taken to control crystal anisotropy, which is the origin of poor consistency in TIPS pentacene based OTFT devices. Thin film active layers are produced by drop-casting mixtures of SiO{sub 2} nanoparticles and TIPS pentacene. The resultant drop-cast films yield improved morphological uniformity at {approx}10% SiO{sub 2} loading, which also leads to a 3-fold increase in average mobility and nearly 4 times reduction in the ratio of measured mobility standard deviation ({mu}{sub Stdev}) to average mobility ({mu}{sub Avg}). Grazing-incidence X-ray diffraction, scanning and transmission electron microscopy as well as polarized optical microscopy are used to investigate the nanoparticle-mediated TIPS pentacene crystallization. The experimental results suggest that the SiO{sub 2} nanoparticles mostly aggregate at TIPS pentacene grain boundaries, and 10% nanoparticle concentration effectively reduces the undesirable crystal misorientation without considerably compromising TIPS pentacene crystallinity.

Simultaneous Modification of Bottom-Contact Electrode and Dielectric Surfaces for Organic Thin-Film Transistors Through Single-Component Spin-Cast Monolayers

Abstract: An efficient process is developed by spin-coating a single-component, self-assembled monolayer (SAM) to simultaneously modify the bottom-contact electrode and dielectric surfaces of organic thin-film transistors (OTFTs). This efficient interface modification is achieved using n-alkyl phosphonic acid based SAMs to prime silver bottom-contacts and hafnium oxide (HfO{sub 2}) dielectrics in low-voltage OTFTs. Surface characterization using near edge X-ray absorption fine structure (NEXAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry suggest this process yields structurally well-defined phosphonate SAMs on both metal and oxide surfaces. Rational selection of the alkyl length of the SAM leads to greatly enhanced performance for both n-channel (C60) and p-channel (pentacene) based OTFTs. Specifically, SAMs of n-octylphos-phonic acid (OPA) provide both low-contact resistance at the bottom-contact electrodes and excellent interfacial properties for compact semiconductor grain growth with high carrier mobilities. OTFTs based on OPA modifi ed silver electrode/HfO{sub 2} dielectric bottom-contact structures can be operated using < 3V with low contact resistance (down to 700 Ohm-cm), low subthreshold swing (as low as 75 mV dec{sup -1}), high on/off current ratios of 107, and charge carrier mobilities as high as 4.6 and 0.8 cm{sup 2} V{supmore » -1} s{sup -1}, for C60 and pentacene, respectively. These results demonstrate that this is a simple and efficient process for improving the performance of bottom-contact OTFTs.« less

High-Mobility Pentacene-Based Thin-Film Transistors With a Solution-Processed Barium Titanate Insulator

Abstract: Pentacene-based organic thin-film transistors (OTFTs) with solution-processed barium titanate (Ba1.2Ti0.8O3) as a gate insulator are demonstrated. The electrical properties of pentacene-based TFTs show a high field-effect mobility of 8.85 cm2 · V-1 · s-1, a low threshold voltage of -1.89 V, and a low subthreshold slope swing of 310 mV/decade. The chemical composition and binding energy of solution-processed barium titanate thin films are analyzed through X-ray photoelectron spectroscopy. The matching surface energy on the surface of the barium titanate thin film is 43.12 mJ · m-2, which leads to Stranski-Krastanov mode growth, and thus, high mobility is exhibited in pentacene-based TFTs.