Showing papers on "Pentacene published in 2006"
TL;DR: In this article, a chemical design concept of ionic amorphous oxide semiconductor (IAOS) and its unique electron transport properties, and electronic structure, by comparing them with those of conventional ammorphous semiconductors is addressed.
Abstract: Recently we have reported the room temperature fabrication of transparent and flexible thin film transistors on a polyethylene terephthalate (PET) film substrate using an ionic amorphous oxide semiconductor (IAOS) in an In2O3–ZnO–Ga2O3 system. These transistors exhibit a field effect mobility of ∼10 cm2 (V s)−1, which is higher by an order of magnitude than those of hydrogenated amorphous Si and pentacene transistors. This article describes a chemical design concept of IAOS, and its unique electron transport properties, and electronic structure, by comparing them with those of conventional amorphous semiconductors. High potential of IAOS for flexible electronics is addressed.
820 citations
TL;DR: It is shown that the neglect of electronic polarization leads to qualitatively incorrect values and trends for the transfer integrals computed with the energy splitting method, even in simple prototypes such as ethylene or pentacene dimers.
Abstract: Theoretical investigations of charge transport in organic materials are generally based on the "energy splitting in dimer" method and routinely assume that the transport parameters (site energies and transfer integrals) determined from monomer and dimer calculations can be reliably used to describe extended systems. Here, we demonstrate that this transferability can fail even in molecular crystals with weak van der Waals intermolecular interactions, due to the substantial (but often ignored) impact of polarization effects, particularly on the site energies. We show that the neglect of electronic polarization leads to qualitatively incorrect values and trends for the transfer integrals computed with the energy splitting method, even in simple prototypes such as ethylene or pentacene dimers. The polarization effect in these systems is largely electrostatic in nature and can change dramatically upon transition from a dimer to an extended system. For example, the difference in site energy for a prototypical "face-to-edge" one-dimensional stack of pentacene molecules is calculated to be 30% greater than that in the "face-to-edge" dimer, whereas the site energy difference in the pentacene crystal is vanishingly small. Importantly, when computed directly in the framework of localized monomer orbitals, the transfer integral values for dimer and extended systems are very similar.
722 citations
TL;DR: In this article, a pentacene organic thin-film transistor (OTFT) driven active matrix organic light-emitting diode (OLED) displays on flexible polyethylene terephthalete substrates were fabricated.
Abstract: We have fabricated pentacene organic thin-film transistor (OTFT) driven active matrix organic light-emitting diode (OLED) displays on flexible polyethylene terephthalete substrates These displays have 48×48 bottom-emission OLED pixels with two pentacene OTFTs used per pixel Parylene is used to isolate the OTFTs and OLEDs with good OTFT yield and uniformity
577 citations
TL;DR: In this paper, a mixed quantum chemical and molecular dynamic methodology was used to assess the effect of nuclear dynamics on the modulation of the transfer integrals between close molecules in organic crystalline semiconductor molecular components.
Abstract: In organic crystalline semiconductor molecular components are held together by very weak interactions and the transfer integrals between neighboring molecular orbitals are extremely sensitive to small nuclear displacements. We used a mixed quantum chemical and molecular dynamic methodology to assess the effect of nuclear dynamics on the modulation of the transfer integrals between close molecules. We have found that the fluctuations of the transfer integrals are of the same order of magnitude of their average value for pentacene and anthracene. Under these conditions the usual perturbative treatment of the electron-phonon coupling is invalid, the band description of the crystal breaks down and the charge carriers become localized. Organic crystals of pentacene and anthracene, even in the absence of defects, can be regarded as disordered media with respect to their charge transport properties. These results suggest that the dynamic electronic disorder can be the factor limiting the charge mobility in crystalline organic semiconductors.
343 citations
TL;DR: In this article, the effect of hydroxyl groups on the electrical properties of pentacene-based organic thin film transistors (OTFTs) was investigated and it was confirmed that large hysteresis usually observed in OTFT devices was strongly related to the hydroxy bonds existing inside of polymeric dielectrics and could be reduced by substituting with cinnamoyl groups.
Abstract: Polymeric dielectrics having different ratios of hydroxyl groups were intentionally synthesized to investigate the effect of hydroxyl groups on the electrical properties of pentacene-based organic thin film transistors (OTFTs). Large hysteresis usually observed in OTFT devices was confirmed to be strongly related to the hydroxyl bonds existing inside of polymeric dielectrics and could be reduced by substituting with cinnamoyl groups. Although the hydroxyl groups deteriorate the capacitance-voltage characteristics and gate leakage current densities, exceptionally high hole mobility (5.5cm2V−1s−1) could be obtained by increasing the number of hydroxyl groups, which was not caused by the improvement of pentacene crystallinity but related to the interface characteristics.
338 citations
TL;DR: A covalent bond between an individual pentacene molecule and a gold atom was formed by means of single-molecule chemistry inside a scanning tunneling microscope junction.
Abstract: A covalent bond between an individual pentacene molecule and a gold atom was formed by means of single-molecule chemistry inside a scanning tunneling microscope junction. The bond formation is reversible, and different structural isomers can be produced. The single-molecule synthesis was done on ultrathin insulating films that electronically isolated the reactants and products from their environment. Direct imaging of the orbital hybridization upon bond formation provides insight into the energetic shifts and occupation of the molecular resonances.
310 citations
TL;DR: The crystal structure of rubrene, C42H28 (5,6,11,12-tetraphenyltetracene), in the temperature interval 100-300 K is reported, and the crystal structure is orthorhombic over the entire temperature range.
Abstract: We report the crystal structure of rubrene, C42H28 (5,6,11,12-tetraphenyltetracene), in the temperature interval 100–300 K. The crystals are grown by physical vapor transport in an open system. The crystal structure is orthorhombic over the entire temperature range.
292 citations
TL;DR: Fan-shaped electrodes were designed on Si∕SiO2 substrate to measure the anisotropic field effect mobility in freestanding single crystal pentacene as mentioned in this paper, and the highest mobility value was estimated to be ∼2.3cm2∕Vs at room temperature.
Abstract: Fan-shaped electrodes were designed on Si∕SiO2 substrate to measure the anisotropic field effect mobility in freestanding single crystal pentacene. Field effect transistor was fabricated by placing single crystal pentacene on the prepatterned electrodes. The contact between the electrodes and single crystal pentacene was enhanced by applying pressure. Angle dependence of field effect mobility in single crystal pentacene showed remarkably anisotropic behavior. The highest mobility value was estimated to be ∼2.3cm2∕Vs at room temperature.
237 citations
TL;DR: In this article, a phosphonate-linked anthracene self-assembled monolayer was used as a buffer between the silicon dioxide gate dielectric and the active pentacene channel region.
Abstract: Pentacene-based organic thin-film transistors have been fabricated using a phosphonate-linked anthracene self-assembled monolayer as a buffer between the silicon dioxide gate dielectric and the active pentacene channel region. Vast improvements in the subthreshold slope and threshold voltage are observed compared to control devices fabricated without the buffer. Both observations are consistent with a greatly reduced density of charge trapping states at the semiconductor-dielectric interface effected by introduction of the self-assembled monolayer.
237 citations
TL;DR: In this article, a two-component layered structure of organic light-emitting transistors (OLETs) with balanced ambipolar transport and mobility as large as 3 × 10 cm V s is presented.
Abstract: Today organic materials are routinely employed for the fabrication of light-emitting devices (OLEDs) and thin-film transistors (OTFTs), with the first technological realizations already having reached the market. Moreover, OTFTs with unipolar mobility values comparable to those of amorphous silicon (1 cm V s) have now been demonstrated. Applications impacting display technologies and those sectors where low cost is a key factor and low performance is acceptable include electronic paper and radio-frequency identification (RF-ID) products. In a recent development, OTFTs also exhibiting electroluminescence (EL) have been successfully demonstrated. Organic light-emitting transistors (OLETs) represent a significant technological advance by combining two functionalities, electrical switching and light emission, in a single device, thus significantly increasing the potential applications of organic semiconductors. In particular, if appropriate materials can be introduced, OLETs offer an ideal structure for improving the lifetime and efficiency of organic light-emitting heterostructures due to the intrinsically different driving conditions and charge-carrier balance compared to conventional OLEDs. Potential applications of OLETs include flat-panel display technologies, lighting, and, ultimately, easily fabricated organic lasers. The first OLET prototypes were unipolar transport devices, and recombination was expected to take place in close proximity to the metallic drain electrode where efficiency-depleting exciton quenching is also likely to occur. To avoid this significant device deficiency and to instead generate EL nearer the center of the channel, OLETs with ambipolar charge transport would be highly desirable. Furthermore, balanced ambipolar conduction is crucial for maximizing exciton recombination through efficient electron–hole balancing. Up to now various solutions have been proposed: single ambipolar materials and two-component coevaporated or layered structures. In coevaporated films, two materials are simultaneously sublimed to form bulk heterojunctions. However, carrier transport is unbalanced and the mobility values are below 10 cm V s. Devices employing a polymer film showing intrinsic ambipolar transport have also been reported but with mobility values for both charge carriers around 10 cm V s. In this paper we report OLETs based on two-component layered structures that have balanced ambipolar transport and mobility values as large as 3 × 10 cm V s. These devices are realized by sequentially depositing p-type (a,x-dihexyl-quaterthiophene, DH4T) and n-type films (N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide, PTCDIC13H27, P13). The combination with the highest mobility and most-balanced transport is obtained with DH4T grown in direct contact with the dielectric. For comparison, we have also employed pentacene in place of DH4T as the p-type material and showed that unbalanced ambipolarity is obtained. Morphological analysis of the outermost and buried layers, performed by laser scanning confocal microscopy (LSCM), allows selective imaging of materials with energetically separated photoluminescence (PL) spectra. Importantly, it is shown that ‘growth compatibility’ between the nand p-type materials is essential in forming a continuous interface and thereby controlling the resulting OLET optoelectronic-response properties. Each OLET material was first evaluated in a single layer in a top source–drain contact OTFT. As substrates we employed heavily doped silicon wafers with thermally grown oxides. Surface treatments such as octadecyltrichlorosilane or hexamethyldisilazane did not result in substantial improvement in the device performance. Parameters such as substrate temperature (Tsub) and evaporation rate were varied to optimize electrical characteristics. The optimum growth conditions were found to be: Tsub = 90 °C and rate = 0.1 A s –1 for DH4T, and Tsub = 25 °C and rate = 0.1 A s –1 for P13. In Table 1, the mobility (l) and threshold-voltage (Vth) values obtained are summarized. These are comparable to the highest values reported in the literature. The DH4T devices were stable even C O M M U N IC A TI O N S
220 citations
TL;DR: Two new linear acenes with fused thiophene units have been synthesized that have conjugation lengths between anthracene and pentacene and show growth that greatly resembles pentacenes, while thin-film growth is dendritic.
Abstract: Two new linear acenes with fused thiophene units have been synthesized. These acenes have conjugation lengths between anthracene and pentacene. Thin films of these linear molecules were characterized by ultraviolet spectroscopy, X-ray diffraction, atomic force microscopy (AFM), and field-effect transistor measurements. Submonolayer AFM studies show growth that greatly resembles pentacene, while thin-film growth is dendritic. Mobilites as high as 0.47 cm2 V-1 s-1 have been found for the tetraceno[2,3-b]thiophene and are as high as 0.15 cm2 V-1 s-1 for anthra[2,3-b]thiophene.
TL;DR: This study explores the assembly in the crystalline state of a class of pentacenes that are substituted along their long edges with aromatic rings forming rigid, cruciform molecules, and finds that a planar acene core is the exception rather than the rule.
Abstract: This study explores the assembly in the crystalline state of a class of pentacenes that are substituted along their long edges with aromatic rings forming rigid, cruciform molecules. The crystals were grown from the gas phase, and their structures were compared with DFT-optimized geometries. Both crystallographic and computed structures show that a planar acene core is the exception rather than the rule. In the assembly of these molecules, the phenyl groups block the herringbone motif and further guide the arrangement of the acene core into higher order structures. The packing for the phenyl-substituted derivatives is dictated by close contacts between the C-H's of the pendant aromatic rings and the carbons at the fusions in the acene backbone. Using thiophene substituents instead of phenyls creates cofacially stacked acenes. In thin films, the thiophene-substituted derivative forms devices with good electrical properties: relatively high mobility, high ON/OFF ratios, and low threshold voltage for device activation. An unusual result is obtained for the decaphenyl pentacene when devices are fabricated on its crystalline surface. Although its acene cores are well isolated from each other, this material still exhibits good electrical properties.
TL;DR: In this article, variable temperature contact resistance measurements on pentacene organic thin-film transistors via a gated four-probe technique are described. But the authors focus on the activation behavior of the source and drain electrodes.
Abstract: We describe variable temperature contact resistance measurements on pentacene organic thin-film transistors via a gated four-probe technique. The transistors consist of Au source and drain electrodes contacting a pentacene film deposited on a dielectric/gate electrode assembly. Additional voltage sensing leads penetrating into the source-drain channel were used to monitor potentials in the pentacene film while passing current between the source and drain electrodes during gate voltage sweeps. Using this device structure, we investigated contact resistance as a function of film thickness (60–3000A), deposition temperature (25 or 80°C), gate voltage, electrode geometry (top or bottom contact), and temperature. Contact resistance values were approximately 2×103–7×106Ωcm, depending on film thickness. In the temperature range of 77–295K, the contact resistance displayed activated behavior with activation energies of 15–160meV. Importantly, it was observed that the activation energies for the source and drain r...
TL;DR: The design, synthesis, optical and electrochemical characterization, crystal packing, modeling and thin film morphology, and organic thin film field effect transistor (OTFT) device data analysis for a novel 2,6-bis[2-(4-pentylphenyl)vinyl]anthracene (DPPVAnt) organic semiconductor ranks among the best performing p-type organic semiconductors reported so far.
Abstract: The development of new organic semiconductors with improved electrical performance and enhanced environmental stability is the focus of considerable research activity. This paper presents the design, synthesis, optical and electrochemical characterization, crystal packing, modeling and thin film morphology, and organic thin film field effect transistor (OTFT) device data analysis for a novel 2,6-bis[2-(4-pentylphenyl)vinyl]anthracene (DPPVAnt) organic semiconductor. We observed a hole mobility of up to 1.28 cm2/V.s and on/off current ratios greater than 107 for OTFTs fabricated using DPPVAnt as an active semiconductor layer. The mobility value is comparable to that of the current best p-type semiconductor pentacene-based device performance. In addition, we found a very interesting relationship between the charge mobility and molecule crystal packing in addition to the thin film orientation and morphology of the semiconductor as determined from single-crystal molecule packing study, thin film X-ray diffraction, and AFM measurements. The high performance of the semiconductor ranks among the best performing p-type organic semiconductors reported so far and will be a very good candidate for applications in organic electronic devices.
TL;DR: In this article, the authors analyzed the pentacene field effect transistor (FET) as a Maxwell-Wagner effect element and showed that the transit time and charging time of injected carriers are key parameters to specify FET characteristics.
Abstract: The pentacene field effect transistor (FET) is analyzed as a Maxwell-Wagner effect element. As a result of the Maxwell-Wagner effect, carriers injected from source electrode are accumulated at the interface between pentacene and SiO2-gate insulator. They are then conveyed along the FET channel by the electric field formed between source and drain electrodes. The drain current Ids shows characteristic behavior depending on the force of the electric field. The transit time and charging time of injected carriers are key parameters to specify FET characteristics ruled by the Maxwell-Wagner effect. Results also show that our pentacene FET characteristics are well explained based on the present theoretical analysis.
TL;DR: In this paper, a printed network of single-walled carbon nanotubes (SWNTs) is integrated with ultrathin layers of the organic semiconductor pentacene to produce bendable, transparent thin-film transistors on plastic substrates.
Abstract: Electrodes based on printed networks of single-walled carbon nanotubes (SWNTs) are integrated with ultrathin layers of the organic semiconductor pentacene to produce bendable, transparent thin-film transistors on plastic substrates The physical and structural properties of the SWNTs lead to the remarkably good electrical contacts with the pentacene Optical transmittances of ∼70%, device mobilities >05cm2V−1s−1, ON/OFF ratios >105 and tensile strains as large as 18% are achieved in devices of this type These characteristics indicate promise for applications in power conserving flexible display systems and other devices
TL;DR: In this article, the authors report the generation of a discrete trap state during negative gate bias stress in pentacene single-crystal field effect transistors with a SiO2 gate dielectric.
Abstract: We report on the generation of a discrete trap state during negative gate bias stress in pentacene single-crystal “flip-crystal” field-effect transistors with a SiO2 gate dielectric. Trap densities of up to 2∙1012cm−2 were created in the experiments. Trap formation and trap relaxation are distinctly different above and below ∼280K. In devices in which a self-assembled monolayer on top of the SiO2 provides a hydrophobic insulator surface we do not observe trap formation. These results indicate the microscopic cause of the trap state to be related to molecular layers of water adsorbed on the SiO2 surface.
TL;DR: In this paper, the influence of chemical surface modifications of gold electrodes on the morphology and the electrical properties has been studied for pentacene based thin-film transistors with channel lengths of L⩽4μm.
Abstract: The influence of chemical surface modifications of gold electrodes on the morphology and the electrical properties has been studied for pentacene based thin-film transistors with channel lengths of L⩽4μm. Self-assembled monolayers (SAMs) of various aliphatic and aromatic organothiols have been used to selectively modify the metallic source and drain electrodes and are further compared with reference samples with untreated electrodes. For all SAM-treated devices a reduced roughness of the pentacene film is observed which is accompanied by a reduction of the threshold voltage from about VT=2V for untreated transistors to −0.9V for transistors with SAM modified electrodes. Using aliphatic SAMs a poor on/off ratio of about 102 was obtained which is attributed to their low conductivity. In contrast, the on/off ratio is enhanced by four orders of magnitude if the surface is modified by an aromatic SAM. In this case a subthreshold swing as low as 0.55V/decade is achieved which corresponds to a trap density reduc...
TL;DR: In this paper, a model describing charge transport in disordered unipolar organic field effect transistors is presented, which can be used to calculate all regimes in unipolar as well as ambipolar organic transistors, by applying it to experimental data obtained from amI transistors based on a narrow gap organic molecule.
Abstract: A model describing charge transport in disordered ambipolar organic field-effect transistors is presented. The basis of this model is the variable-range hopping in an exponential density of states developed for disordered unipolar organic transistors. We show that the model can be used to calculate all regimes in unipolar as well as ambipolar organic transistors, by applying it to experimental data obtained from ambipolar organic transistors based on a narrow-gap organic molecule. The threshold voltage was determined independently from metal insulator semiconductor diode measurements. An excellent agreement between theory and experiment is observed over a wide range of biasing regimes and temperatures.
TL;DR: Using deoxyribonucleic acid (DNA)-based biopolymer, derived from salmon milt and roe sac waste by-products, for the gate dielectric region, a bio-organic field effect transistors (BiOFET) was proposed in this paper.
Abstract: Organic-based field-effect transistors (OFETs) utilize organic semiconductor materials with low electron mobilities and organic gate oxide materials with low dielectric constants. These have rendered devices with slow operating speeds and high operating voltages, compared with their inorganic silicon-based counter parts. Using a deoxyribonucleic acid (DNA)-based biopolymer, derived from salmon milt and roe sac waste by-products, for the gate dielectric region, we have fabricated an OFET device that exhibits very promising current-voltage characteristics compared with using other organic-based dielectrics. With minimal optimization, using a thin film of DNA-based biopolymer as the gate insulator and pentacene as the semiconductor, we have demonstrated a bio-organic-FET, or BiOFET, in which the current was modulated over three orders of magnitude using gate voltages less than 10V.
TL;DR: In this article, the electrical reliabilities of poly-4-vinyl phenol (PVP) and SiO2 gate dielectrics for pentacene thin-film transistors were reported.
Abstract: The authors report on the electrical reliabilities of poly-4-vinyl phenol (PVP) and SiO2 gate dielectrics for pentacene thin-film transistors (TFTs). SiO2 films were grown by dry oxidation and PVP films were prepared by spin coating and subsequent cross-linking at 175°C for 15min. The pentacene TFTs with the PVP cured for 15min exhibited a large hysteresis and an abnormal drain-current increase under a gate bias stress over time, while the other TFT with SiO2 displayed a small hysteresis but its drain current decreases with time. The hysteresis behaviors induced by PVP and SiO2 were opposite to each other in the gate bias swing direction, due to the difference in hysteresis mechanism between the two types of TFTs. Comparing their hysteresis behavior, the authors fabricated a far more reliable pentacene TFT with PVP by extending the PVP curing time to 1h. Our improved device with PVP exhibited no hysteresis and persistent toughness to the gate bias stress.
TL;DR: In this article, a materials-general technique for the fabrication of single-crystal field effect transistors with the use of a spin-coated elastomer gate dielectric was presented.
Abstract: Organic single crystals have emerged as powerful tools for the exploration of the intrinsic charge transport properties of organic materials. To date, however, the limited number of fabrication techniques has forced a steep compromise between performance, reproducibility, range of feature sizes, gentle treatment of the single crystal, and facility of construction. Here the authors present a materials-general technique for the fabrication of single-crystal field-effect transistors with the use of a spin-coated elastomer gate dielectric and photolithographically defined source and drain electrodes. This allows the production of feature sizes and patterns previously impossible with reported elastomeric techniques yet yields devices with performance far superior to those fabricated on nonconformal dielectrics. The authors measure saturation-regime mobilities of 19.0 and 1.9cm2∕Vs for the semiconductors rubrene and pentacene, comparable to the best published values, and 2.4cm2∕Vs for tetracene, nearly double t...
TL;DR: In this article, the authors used an unconventional mode of lateral force microscopy to generate high-contrast images of the grain-boundary (GB) network in the first pentacene monolayer.
Abstract: The properties of organic-semiconductor/insulator (O/I) interfaces are critically important to the operation of organic thin-film transistors (OTFTs) currently being developed for printed flexible electronics. Here we report striking observations of structural defects and correlated electrostatic-potential variations at the interface between the benchmark organic semiconductor pentacene and a common insulator, silicon dioxide. Using an unconventional mode of lateral force microscopy, we generate high-contrast images of the grain-boundary (GB) network in the first pentacene monolayer. Concurrent imaging by Kelvin probe force microscopy reveals localized surface-potential wells at the GBs, indicating that GBs will serve as charge-carrier (hole) traps. Scanning probe microscopy and chemical etching also demonstrate that slightly thicker pentacene films have domains with high line-dislocation densities. These domains produce significant changes in surface potential across the film. The correlation of structural and electrostatic complexity at O/I interfaces has important implications for understanding electrical transport in OTFTs and for defining strategies to improve device performance.
TL;DR: In this paper, the authors used the transfer line method to estimate the gate-voltage dependent mobility of OFTs with bottom-gate, top-contact architecture on alumina substrates.
TL;DR: In this article, the electrical characteristics of bottom contact organic field effect transistors fabricated with the air-stable n-type semiconductor N,N′-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis (dicarboximide) (PDI-8CN2) are described.
Abstract: The electrical characteristics of bottom-contact organic field-effect transistors fabricated with the air-stable n-type semiconductor N,N′-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN2) are described. The mobility, threshold voltage, subthreshold swing, and Ion∕Ioff ratio(VDS=40V, VG=0∼40V) are 0.14cm2∕Vs, 1.6V, 2.0V/decade, and 1.2×103, respectively. The effect of electrode/dielectric surface treatment on these devices is also examined, with a combination of 1-octadecanethiol and hexamethyldisilazane. Organic complementary five-stage ring oscillators were fabricated using pentacene and PDI-8CN2, and operated at an oscillation frequency of 34kHz and a propagation delay per stage of 3μs.
TL;DR: In this paper, an organic field effect transistors (OFET) for lowvoltage operation has been realized with conventional polymer gate dielectrics such as polyimides and cross-linked poly-4-vinyl phenols (PVPs) by fabricating ultrathin films.
Abstract: Organic field-effect transistors (OFETs) for low-voltage operation have been realized with conventional polymer gate dielectrics such as polyimides and cross-linked poly-4-vinyl phenols (PVPs) by fabricating ultrathin films. These ultrathin polymers (thickness ∼10nm) have shown good insulating properties, including high breakdown fields (>2.5MV∕cm). With ultrathin dielectrics, high capacitances (>250nF∕cm2) have been achieved, allowing operation of OFETs within −3V. Pentacene OFETs with ultrathin PVP dielectrics exhibit a mobility of 0.5cm2∕Vs, an on-off ratio of 105, and a small subthreshold swing of 174mV∕decade when devices are operated at −3V.
TL;DR: The authors' observations of a solid-state phase transition in TIPS pentacene crystals upon heating or cooling reveal that the transition is associated with a conformational reorganization of the TIPS side groups, accompanied by a slight decrease in the acene-to-acene spacing and a shift of the overlap between the neighboring pentacenes.
Abstract: Bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) is a functionalized pentacene derivative designed to enhance both the solution solubility and solid-state packing of pentacene. In this paper, we report our observations of a solid-state phase transition in TIPS pentacene crystals upon heating or cooling. Evidence from differential scanning calorimetry (DSC), hot-stage optical microscopy, as well as high-temperature X-ray and electron diffraction are presented. A reasonable match with experimental data is obtained with molecular modeling. Our results reveal that the transition is associated with a conformational reorganization of the TIPS side groups, accompanied by a slight decrease in the acene-to-acene spacing and a shift of the overlap between the neighboring pentacene units. The observed cracking should be avoided or minimized in TIPS pentacene-based thin film transistors to maintain their relatively high charge carrier mobility.
TL;DR: The pentacene transistors with low-cost Ag-TCNQ-modified Ag bottom-contact electrodes exhibit outstanding electrical properties, which are comparable with that of the Au top-contact devices.
Abstract: The characteristics of organic field-effect transistors (OFETs) were dramatically improved by chemically modifying the surface of the bottom-contact Ag or Cu source−drain (D−S) electrodes with a simple solution method. The contact resistance and energetic mismatch typically observed with Ag D−S electrodes in pentacene bottom-contact OFETs can be properly eliminated when modified by the Ag-TCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane). The pentacene transistors with low-cost Ag-TCNQ-modified Ag bottom-contact electrodes exhibit outstanding electrical properties, which are comparable with that of the Au top-contact devices. It thus provides a novel way toward high-performance low-cost bottom-contact OFETs.
TL;DR: In this article, an organic heterojunction with an interpenetrating network is obtained as the active layer for the OFETs, which displays significant ambipolar charge transport with symmetric electron and hole mobilities of the order of 10−4 cm(2) V-1 s−1 in air.
Abstract: Ambipolar organic field-effect transistors (OFETs) are produced, based on organic heterojunctions fabricated by a two-step vacuum-deposition process. Copper phthalocyanine (CuPc) deposited at a high temperature (250 degrees C) acts as the first (p-type component) layer, and hexadecafluorophthalocyaninatocopper (F16CuPc) deposited at room temperature (25 degrees C) acts as the second (n-type component) layer. A heterojunction with an interpenetrating network is obtained as the active layer for the OFETs. These heterojunction devices display significant ambipolar charge transport with symmetric electron and hole mobilities of the order of 10(-4) cm(2) V-1 s(-1) in air. Conductive channels are at the interface between the F16CuPc and CuPc domains in the interpenetrating networks. Electrons are transported in the F16CuPc regions, and holes in the CuPc regions. The molecular arrangement in the heterojunction is well ordered, resulting in a balance of the two carrier densities responsible for the ambipolar electrical characteristics. The thin-film morphology of the organic heterojunction with its interpenetrating network structure can be controlled well by the vacuum-deposition process.
TL;DR: The surface free energy of a dielectric has a strong influence on the performance of pentacene thin-film transistors and has been shown to enhance the field effect mobility of transistors as discussed by the authors.
Abstract: The surface free energy of a dielectric has a strong influence on the performance of pentacene thin-film transistors. Research shows that by matching surface free energy in the interface of the dielectric and the orthorhombic thin-film phase of pentacene film, the field-effect mobility of transistors is enhanced reaching above 2.0cm2∕Vs. The authors suggested that a more complete first monolayer of pentacene was formed upon the gate dielectric surface with almost identical surface free energy, benefiting carrier transportation. The research also discusses the mechanism of surface free energy effects on the crystalline size and structural disorder in pentacene film.