Showing papers on "Pentacene published in 2013"
TL;DR: An approach--termed fluid-enhanced crystal engineering (FLUENCE)--that allows for a high degree of morphological control of solution-printed thin films and may find use in the fabrication of high-performance, large-area printed electronics.
Abstract: Solution coating of organic semiconductors offers great potential for achieving low-cost manufacturing of large-area and flexible electronics. However, the rapid coating speed needed for industrial-scale production poses challenges to the control of thin-film morphology. Here, we report an approach—termed fluid-enhanced crystal engineering (FLUENCE)—that allows for a high degree of morphological control of solution-printed thin films. We designed a micropillar-patterned printing blade to induce recirculation in the ink for enhancing crystal growth, and engineered the curvature of the ink meniscus to control crystal nucleation. Using FLUENCE, we demonstrate the fast coating and patterning of millimetre-wide, centimetre-long, highly aligned single-crystalline organic semiconductor thin films. In particular, we fabricated thin films of 6,13-bis(triisopropylsilylethynyl) pentacene having non-equilibrium single-crystalline domains and an unprecedented average and maximum mobilities of 8.1±1.2 cm2 V−1 s−1 and 11 cm2 V−1 s−1. FLUENCE of organic semiconductors with non-equilibrium single-crystalline domains may find use in the fabrication of high-performance, large-area printed electronics. Solution printing of organic semiconductors could in principle be scaled to industrial needs, yet attaining aligned single-crystals directly with this method has been challenging. By using a micropillar-patterned printing blade designed to enhance the control of crystal nucleation and growth, thin films of macroscopic, highly aligned single crystals of organic semiconductors can now be fabricated.
876 citations
TL;DR: In this article, the authors demonstrate organic solar cells that exploit singlet exciton fission in pentacene to generate more than one electron per incident photon in a portion of the visible spectrum.
Abstract: Singlet exciton fission transforms a molecular singlet excited state into two triplet states, each with half the energy of the original singlet. In solar cells, it could potentially double the photocurrent from high-energy photons. We demonstrate organic solar cells that exploit singlet exciton fission in pentacene to generate more than one electron per incident photon in a portion of the visible spectrum. Using a fullerene acceptor, a poly(3-hexylthiophene) exciton confinement layer, and a conventional optical trapping scheme, we show a peak external quantum efficiency of (109 ± 1)% at wavelength λ = 670 nanometers for a 15-nanometer-thick pentacene film. The corresponding internal quantum efficiency is (160 ± 10)%. Analysis of the magnetic field effect on photocurrent suggests that the triplet yield approaches 200% for pentacene films thicker than 5 nanometers.
808 citations
TL;DR: Together, these results require that singlets and triplet pairs in tetracene are effectively degenerate in energy, and begin to reconcile the temperature dependence of many macroscopic observables with a fission process which does not require thermal activation.
Abstract: We use transient absorption spectroscopy to demonstrate that the dynamics of singlet exciton fission in tetracene are independent of temperature (10–270 K). Low-intensity, broad-band measurements allow the identification of spectral features while minimizing bimolecular recombination. Hence, by directly observing both species, we find that the time constant for the conversion of singlets to triplet pairs is ∼90 ps. However, in contrast to pentacene, where fission is effectively unidirectional, we confirm that the emissive singlet in tetracene is readily regenerated from spin-correlated “geminate” triplets following fission, leading to equilibrium dynamics. Although free triplets are efficiently generated at room temperature, the interplay of superradiance and frustrated triplet diffusion contributes to a nearly 20-fold increase in the steady-state fluorescence as the sample is cooled. Together, these results require that singlets and triplet pairs in tetracene are effectively degenerate in energy, and beg...
203 citations
TL;DR: In this article, the average electron-hole distance and the degree of charge-transfer character within low-energy optical excitations in solid-state pentacene have been quantified using first-principles calculations based on density functional theory and manybody perturbation theory.
Abstract: The nature of low energy optical excitations, or excitons, in organic solids is of central relevance to many optoelectronic applications, including solar energy conversion. Excitons in solid pentacene, a prototypical organic semiconductor, have been the subject of many experimental and theoretical studies, with differing conclusions as to the degree of their charge-transfer character. Using first-principles calculations based on density functional theory and many-body perturbation theory, we compute the average electron–hole distance and quantify the degree of charge-transfer character within optical excitations in solid-state pentacene. We show that several low-energy singlet excitations are characterized by a weak overlap between electron and hole and an average electron–hole distance greater than 6 A. Additionally, we show that the character of the lowest-lying singlet and triplet excitons is well-described with a simple analytic envelope function of the electron–hole distance.
177 citations
TL;DR: The preparation of nonsubstituted acenes from corresponding precursors is summarized, their physical properties are described, and potential applications including potential usage in organic semiconductor devices are discussed.
Abstract: Acenes are a class of aromatic hydrocarbons composed of linearly fused benzene rings. Noteworthy features of these molecules include their extended flat structure and the narrow gap between the HOMO and LUMO energy levels. However, the preparation of larger acenes, those that are larger than pentacene, has been challenging. These molecules are relatively unstable and have low solubility in typical solvents. Recently researchers have developed a new synthesis route for higher acenes using stable and soluble “precursors,” which generate these structures on demand by either heating or irradiation of light. Using this method, nonsubstituted hexacene, heptacene, octacene, and nonacene were successfully prepared.In this Account, we summarize the preparation of nonsubstituted acenes from corresponding precursors, describe their physical properties, and discuss potential applications including potential usage in organic semiconductor devices. We first introduced the concept of using a precursor in the work with p...
145 citations
TL;DR: Flexible ammonia (NH3) gas sensors based on solution-processable organic thin-film transistors (OTFTs) are fabricated using a TIPS-pentacene active layer/PMMA dielectric layer on glass and plastic substrates.
Abstract: Flexible ammonia (NH3) gas sensors based on solution-processable organic thin-film transistors (OTFTs) are fabricated using a TIPS-pentacene active layer/PMMA dielectric layer on glass and plastic substrates. These OTFT sensors exhibit outstanding NH3 gas response and recovery characteristics under multiple exposure/evacuation cycles at controlled NH3 concentrations.
119 citations
TL;DR: Hopping and band mobilities of holes in organic semiconductors at room temperature were estimated from first principle calculations and it is found that van der Waals interactions play an important role in determining accurate relaxation times.
Abstract: Hopping and band mobilities of holes in organic semiconductors at room temperature were estimated from first principle calculations. Relaxation times of charge carriers were evaluated using the acoustic deformation potential model. It is found that van der Waals interactions play an important role in determining accurate relaxation times. The hopping mobilities of pentacene, rubrene, and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) in bulk single crystalline structures were found to be smaller than 4 cm2/Vs, whereas the band mobilities were estimated between 36 and 58 cm2/Vs, which are close to the maximum reported experimental values. This strongly suggests that band conductivity is dominant in these materials even at room temperature.
117 citations
TL;DR: The results demonstrate that these gap states originate from small imperfections in the Pn packing structure, which are induced by gas penetration into the film through the crystal grain boundaries.
Abstract: We studied gas-exposure effects on pentacene (Pn) films on SiO2 and Au(111) substrates by ultrahigh sensitivity photoelectron spectroscopy, which can detect the density of states of ∼10(16) states eV-1 cm-3 comparable to electrical measurements. The results show the striking effects for Pn/SiO2: exposure to inert gas (N2 and Ar) produces a sharp rise in gap states from ∼10(16) to ∼10(18) states eV-1 cm-3 and pushes the Fermi level closer to the valence band (0.15-0.17 eV), as does exposure to O2 (0.20 eV), while no such gas-exposure effect is observed for Pn/Au(111). The results demonstrate that these gap states originate from small imperfections in the Pn packing structure, which are induced by gas penetration into the film through the crystal grain boundaries.
115 citations
TL;DR: The origins of hysteresis in organic field effect transistors (OFETs) and their applications in organic memory devices are investigated in this article, where it is found that the orientations of the hydroxyl groups in polyvinyl alcohol (PVA) gate dielectrics are correlated with transfer characteristics in pentacene-based OFETs under the forward and backward scan.
Abstract: The origins of hysteresis in organic field-effect transistors (OFETs) and its applications in organic memory devices is investigated. It is found that the orientations of the hydroxyl groups in poly(vinyl alcohol) (PVA) gate dielectrics are correlated with the hysteresis of transfer characteristics in pentacene-based OFETs under the forward and backward scan. The applied gate bias partially aligns the orientations of the hydroxyl groups perpendicular to the substrate as characterized by reflective absorption Fourier transform infrared spectroscopy (RA-FTIR), in which the field-induced surface dipoles at the pentacene/PVA interface trap charges and cause the hysteresis. Treating PVA with an anhydrous solvent eliminates the residual moisture in the dielectrics layer, allowing for more effective control of the induced dipoles by the applied gate bias. OFETs of dehydrated-PVA dielectrics present a pronounced shift of the threshold voltage (ΔVTh) of 35.7 V in transfer characteristics, higher than that of 18.5 V for untreated devices and results in sufficient dynamic response for applications in memory elements. This work highlights the usage of non-ferroelectric gate dielectrics to fabricate OFET memory elements by manipulating the molecular orientations in the dielectrics layer.
110 citations
TL;DR: An N-Type organic thin-film transistor (OTFT) based on doped 6,13-Bis(triisopropylsilylethynyl)pentacene is presented and the highest performing n-channel OTFTs are obtained with 50 mol% dopant.
Abstract: An N-Type organic thin-film transistor (OTFT) based on doped 6,13-Bis(triisopropylsilylethynyl)pentacene is presented. A transition from p-type to n-type occurrs with increasing doping concentrations, and the highest performing n-channel OTFTs are obtained with 50 mol% dopant. X-ray diffraction, scanning Auger microscopy, and secondary ionization mass spectrometry are used to characterize the morphology of the blends. The high performance of the obtained transistors is attributed to the highly crystalline and aligned nature of the doped thin films.
101 citations
TL;DR: To achieve optimal OPV performance, one must be able to understand and ultimately control the morphology of these heterojunctions, as the underlying physical processes at the interface as the relevant electronic states and electrostatic interactions are highly dependent on the molecular packing confi gurations between the donor and acceptor molecules or chain segments.
Abstract: Organic photovoltaics (OPVs) hold promise as a technology for low-cost, large-area power conversion. [ 1–4 ] Though conceptually straightforward, the processes required for effi cient operation of an organic solar cell – photon absorption and exciton (electron-hole pair) formation, dissociation of the exciton into separated charges, and collection of the charges – are inherently complex due to the characteristics of the π -conjugated organic materials, i.e., weak van der Waals intermolecular interactions, low dielectric constants, strong electron-electron interactions, and large electron-vibration couplings. The effective separation of the electron-hole pair requires that the active layer consist of two components, an electron-rich (hole-transport) donor material and an electron-defi cient (electron-transport) acceptor material. [ 5 ] This condition leads to a key bottleneck, both in terms of operation and basic understanding, as there exists a delicate interplay between charge-separation and (geminate and non-geminate) charge-recombination processes at the interface between the donor and acceptor materials. While the importance of the donor–acceptor interface has long been recognized, recent experimental evidence has shone new light on the morphological complexity; this is particularly the case in polymer-fullerene bulk-heterojunction (BHJ) solar cells, [ 6 , 7 ] and more recently in molecule-molecule and polymermolecule bilayers. [ 8 , 9 ] In addition to the possible miscibility of the two components, the deposition protocol (e.g., chemical vapor deposition, solution casting, or spin coating to name a few [ 2 , 10 ] ) and post-processing procedures (e.g., removal of solvent additives or solvent and thermal annealing [ 11 , 12 ] ) can impact the interface morphology. This morphological variability leads to diffi culties, then, in recognizing the underlying physical processes at the interface as the relevant electronic states and electrostatic interactions are highly dependent on the molecular packing confi gurations between the donor and acceptor molecules or chain segments. [ 3 , 13–16 , 17 ] Hence, to achieve optimal OPV performance, one must be able to understand and ultimately control the morphology of these heterojunctions. [ 12 ]
TL;DR: The important relationship between structural and optoelectronic anisotropy in aligned, functionalized-pentacene thin films fabricated using the solution-based zone-casting technique is reported on.
Abstract: The consideration of anisotropic structural properties and their impact on optoelectronic properties in small-molecule thin films is vital to understand the performance of devices incorporating crystalline organic semiconductors. Here we report on the important relationship between structural and optoelectronic anisotropy in aligned, functionalized-pentacene thin films fabricated using the solution-based zone-casting technique. The microstructure of thin films composed of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) and 6,13-bis(triethylsilylethynyl)pentacene (TES-pentacene) is systematically controlled by varying the casting speed. By controlling the structural alignment, we were able to experimentally decouple, for the first time in these films, an intramolecular absorption transition dipole (at ∼440 nm) oriented close to the pentacene short axis and an intermolecular absorption transition dipole (at ∼695 nm) oriented predominantly along the conjugated pentacene–pentacene core stacking a...
TL;DR: In this paper, the authors investigated the dynamics of triplet excitons resulting from singlet fission in pentacene and their ionization at a C60 heterojunction.
Abstract: Singlet fission sensitized photovoltaics have the potential to surpass the Shockley-Queisser limit for a single-junction structure. We investigate the dynamics of triplet excitons resulting from singlet fission in pentacene and their ionization at a C60 heterojunction. We model the generation and diffusion of excitons to predict the spectral response. We find the triplet diffusion length in polycrystalline pentacene to be 40 nm. Poly(3-hexylthiophene) between the electrode and pentacene works both to confine triplet excitons and also to transfer photogenerated singlet excitons into pentacene with 30% efficiency. The lower bound for the singlet fission quantum efficiency in pentacene is 180 ± 15%.
TL;DR: In this article, the authors proposed a theoretical description of the charge distribution and the contact resistance in coplanar organic field-effect transistors (OFETs), and they derived an analytical formulation for charge distribution inside the organic layer.
Abstract: We propose a theoretical description of the charge distribution and the contact resistance in coplanar organic field-effect transistors (OFETs). Based on the concept that the current in organic semiconductors is only carried by injected carriers from the electrodes, an analytical formulation for the charge distribution inside the organic layer was derived. We found that the contact resistance in coplanar OFETs arises from a sharp low-carrier-density zone at the source/channel edge because the gate-induced channel carrier density is orders of magnitude higher than the source carrier density. This image is totally different from the contact resistance in staggered OFETs, in which the contact resistance mainly originates from the resistance through the semiconductor bulk. The contact resistance was calculated through charge-distribution functions, and the model could explain the effect of the gate voltage and injection barrier on the contact resistance. Experimental data on pentacene OFETs were analyzed using the transmission-line method. We finally noticed that the gate-voltage-dependent mobility is a critical factor for proper understanding of the contact resistance in real devices.
TL;DR: In this article, the phase separation behavior of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene) with amorphous polycarbonate (APC) was investigated.
Abstract: The blending of the crystalline organic semiconductor, 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene), with amorphous polymers exhibits not only excellent solution processability, but also superior performance characteristics in organic thin film transistors (OTFTs). To understand the inkjet-printing behavior of TIPS pentacene/polymer blends, we use amorphous polycarbonate (APC), which is structurally beneficial to the facile phase separation of TIPS pentacene crystals due to the strong segregation strength estimated by the Flory–Huggins interaction parameter. The various inkjet-printing behaviors of TIPS pentacene/APC inks, which depend on the TIPS pentacene/APC compositions, ink viscosities, and different solvent mixtures, are investigated. These behaviors can ultimately determine the phase separation, morphology, shape, and orientation of the TIPS pentacene crystals in OTFT films. Flory–Huggins phase separation theory is applied, and various analytical methods, such as polarized optical microscopy, 3D surface profile, and time-of-flight secondary ion mass spectroscopy (TOF-SIMS), are utilized to explain these relationships. By controlling these inkjet-printing conditions, it is possible to easily regulate the optimal inkjet-printing process for TIPS-pentacene/polymer systems, which can derive the desirable stripe-shaped and vertically phase-separated TIPS pentacene crystals with the proper orientation and enhanced surface morphology. The resultant inkjet-printed films from the TIPS pentacene with APC show excellent device stability and an average mobility of 0.53 cm2 V−1 s−1. Furthermore, the inkjet-printed flexible OTFT array with an average mobility of 0.27 cm2 V−1 s−1 sustains the application of TIPS pentacene/APC in the field of flexible printed electronics.
TL;DR: In this paper, the morphologies of pentacene and electrical characteristics of the OFETs under various concentrations of ammonia gas sensors are proved to be mainly caused by the diversities of dielectric/pentacene interfacial properties.
TL;DR: In this article, the conjugated polymer additives, used with a slow solution crystallization approach, yield crystal structures that are not accessible by nonconjugated polymer additive and impart excellent long-range order.
Abstract: We use 6,13-bis(triisopropylsilylethynyl)pentacene as a model small molecule organic semiconductor and two conjugated polymer additives to demonstrate conjugated polymer-mediated polymorphism of a small molecule organic semiconductor for the first time. The conjugated polymer additives, used with a slow solution crystallization approach, yield crystal structures that are not accessible by nonconjugated polymer additives and impart excellent long-range order. In both of the small molecule semiconductor/conjugated polymer blends studied here, previously unreported polymorphs of a small molecule semiconductor have been identified which also leads to improved charge transport in the absence of external alignment. These results open up a new exciting avenue to manipulate unit cell structure, long-range order, and charge transport of high performance, solution-processed, small molecule organic semiconductors.
TL;DR: It is hypothesized that for these SAMs, mitigation of molecular scale roughness and subsequent control of surface homogeneity allow for large pentacenes grain growth leading to high performance pentacene OFET devices.
Abstract: A systematic study of six phosphonic acid (PA) self-assembled monolayers (SAMs) with tailored molecular structures is performed to evaluate their effectiveness as dielectric modifying layers in organic field-effect transistors (OFETs) and determine the relationship between SAM structural order, surface homogeneity, and surface energy in dictating device performance. SAM structures and surface properties are examined by near edge X-ray absorption fine structure (NEXAFS) spectroscopy, contact angle goniometry, and atomic force microscopy (AFM). Top-contact pentacene OFET devices are fabricated on SAM modified Si with a thermally grown oxide layer as a dielectric. For less ordered methyl- and phenyl-terminated alkyl ∼(CH2)12 PA SAMs of varying surface energies, pentacene OFETs show high charge carrier mobilities up to 4.1 cm2 V−1 s−1. It is hypothesized that for these SAMs, mitigation of molecular scale roughness and subsequent control of surface homogeneity allow for large pentacene grain growth leading to high performance pentacene OFET devices. PA SAMs that contain bulky terminal groups or are highly crystalline in nature do not allow for a homogenous surface at a molecular level and result in charge carrier mobilities of 1.3 cm2 V−1 s−1 or less. For all molecules used in this study, no causal relationship between SAM surface energy and charge carrier mobility in pentacene FET devices is observed.
TL;DR: In this article, a method is proposed to switch between lateral and vertical phase separations in semiconducting 6,13-bis(triisopropylsilylethynyl) pentacene (TIPSE pentaene)/polymer blend films by simply varying the alkyl length of the polyacrylate polymer component.
Abstract: Lateral and vertical phase separations play critical roles in the performance of the next-generation organic and hybrid electronic devices. A method is demonstrated here to switch between lateral and vertical phase separations in semiconducting 6,13-bis(triisopropylsilylethynyl) pentacene (TIPSE pentacene)/polymer blend films by simply varying the alkyl length of the polyacrylate polymer component. The phase separation modes depend on intermolecular interactions between small molecule TIPSE pentancene and polymer additives. The blend film with a dominant vertical phase separation exhibits a significant enhancement in average mobility and performance consistency of organic thin-film transistors.
TL;DR: It is concluded that none of the oligoacenes investigated become conducting under elevated pressures, assuming that the molecular identity of the system is maintained.
Abstract: Oligoacenes form a fundamental class of polycyclic aromatic hydrocarbons (PAH) which have been extensively explored for use as organic (semi) conductors in the bulk phase and thin films. For this reason it is important to understand their electronic properties in the condensed phase. In this investigation, we use density functional theory with Tkatchenko-Scheffler dispersion correction to explore several crystalline oligoacenes (naphthalene, anthracene, tetracene, and pentacene) under pressures up to 25 GPa in an effort to uncover unique electronic/optical properties. Excellent agreement with experiment is achieved for the pressure dependence of the crystal structure unit cell parameters, densities, and intermolecular close contacts. The pressure dependence of the band gaps is investigated as well as the pressure induced phase transition of tetracene using both generalized gradient approximated and hybrid functionals. It is concluded that none of the oligoacenes investigated become conducting under elevated pressures, assuming that the molecular identity of the system is maintained.
TL;DR: In this article, polyimide (PI) materials are introduced into organic field effect transistors (OFETs) and circuits as insulator layers in order to be compatible with the photolithography process.
TL;DR: An effective strategy for significantly increasing the organic transistor mobility with simultaneous reduction of the threshold voltage utilizing discontinuous nano-patches of charge-transfer doping layer is demonstrated.
Abstract: An effective strategy for significantly increasing the organic transistor mobility with simultaneous reduction of the threshold voltage utilizing discontinuous nano-patches of charge-transfer doping layer is demonstrated. By overlaying the nano-patches on top of a given semiconducting film, mobility and threshold voltage of p-type pentacene are remarkably improved to 4.52 cm(2) V(-1) s(-1) and -0.4 V, and those of n-type Hex-4-TFPTA are also improved to 2.57 cm(2) V(-1) s(-1) and 4.1 V.
TL;DR: In this paper, the nonvolatile memory characteristics of pentacene-based organic field-effect transistors (OFETs) using polyimides, namely, PI(6FDA-TPA-CN), PI(DSDA- TPA-CN), and PI(BTDA-CPN), consisting of electron-donating 4,4′-diamino-4′′-cyanotriphenylamine (TPA)-CN) and different electron-accepting dianhydrides as polymer electrets.
Abstract: We report on the nonvolatile memory characteristics of pentacene-based organic field-effect transistors (OFETs) using polyimides, PI(6FDA-TPA-CN), PI(DSDA-TPA-CN), and PI(BTDA-TPA-CN), consisting of electron-donating 4,4′-diamino-4′′-cyanotriphenylamine (TPA-CN) and different electron-accepting dianhydrides as polymer electrets. The dielectric constants of PI(BTDA-TPA-CN), PI(DSDA-TPA-CN), and PI(6FDA-TPA-CN) are 3.44, 3.52, and 3.70, respectively, higher than those (∼3) of common polyimides. Among the polymer electrets, the OFET memory device based on PI(6FDA-TPA-CN) exhibits the highest OFET mobility of 0.5 cm2 V−1 s−1 due to the formation of a pentacene film of large grain size by the hydrophobic surface. The OFET memory devices with the configuration of n+Si/SiO2/PI/pentacene/Au show excellent nonvolatile memory behaviors for bistable switching. The stability for ON and OFF states can be maintained for 104 s with a Ion/Ioff current ratio of 104 for PI(6FDA-TPA-CN). Moreover, the higher dipole moment and larger torsion angle result in the more stable charge transfer complex, accompanied by the largest memory window of 84 V for the fabricated device. The write–read–erase–read (WRER) cycles can be operated over 100 cycles. The present study suggests that the high dielectric constant polyimide electrets with the enhanced capabilities for storing the charges have great potential applications for advanced OFET memory devices.
TL;DR: The electron affinity of pentacene thin films has been evaluated during the last decades, but it is still under controversial due to varieties of film quality and radiation damages of the films introduced during inverse photoemission spectroscopy (IPES) experiment together with insufficient energy resolution of the instruments.
Abstract: The electron affinity of pentacene thin films has been evaluated during the last decades, but it is still under controversial due to varieties of film quality and radiation damages of the films introduced during inverse photoemission spectroscopy (IPES) experiment together with insufficient energy resolution of the instruments. We employed the near-ultraviolet IPES with a better energy resolution 0.27 ∼ 0.32 eV and using lower energy electron beams (0 eV ≤ Ei ≤ 4.9 eV) to study the unoccupied states of pentacene thin film. Due to a large mean-free-path of the electron in this energy region, the threshold electron affinity of the bulk of pentacene film was precisely determined to be 2.70 ± 0.03 eV. Using the threshold ionization energy of 4.90 ± 0.05 eV determined by ultraviolet photoemission spectroscopy, the band-gap energy of the pentacene film is obtained to be 2.20 ± 0.06 eV.
TL;DR: In this article, the gate dielectric of a pentacene organic thin-film transistors (OTFTs) was evaluated in the air-ambient regime with an average field-effect mobility (mFE ) value of ca. 16 cm 2 ǫV −1ǫs −1 in the saturation regime and a low threshold voltage of −1 ǔV.
TL;DR: It is proved that the casting speed should be large enough to induce a sufficient concentration gradient and the orientation mechanism of TIPS-pentacene was attributed to a synergy of the ordered nuclei and a match between the crystallization velocity and the Casting speed.
Abstract: Uniaxially aligned triisopropylsilylethynyl pentacene (TIPS-pentacene) crystals over a large area were fabricated using zone-casting technique. The array of TIPS-pentacene displayed a high orientation degree with a dichroic ratio (DR) of 0.80. The crystals were arranged with c axis perpendicular to the substrate and the long axis of the ribbon corresponded to the a axis of TIPS-pentacene. The properties of the solutions and the processing parameters were shown to influence the formation of the oriented TIPS-pentacene crystalline array. Solvent with a low boiling point (such as chloroform) favoured the orientation of the ribbon-like crystals. The concentration of the solution should be appropriate, ensuring the crystallization velocity of TIPS-pentacene matching with the receding of the meniscus. Besides, we proved that the casting speed should be large enough to induce a sufficient concentration gradient. The orientation mechanism of TIPS-pentacene was attributed to a synergy of the ordered nuclei and a match between the crystallization velocity and the casting speed. Field effect transistors (FETs) based on the oriented TIPS-pentacene crystalline array showed a mobility of 0.67 cm(2) V(-1) s(-1).
TL;DR: In this article, a facile nonconventional lithographic patterning technique is developed for fabricating banks with microwell structures by inkjet printing solvent droplets onto a polymer layer, thereby locally dissolving the polymer to form microwells.
Abstract: The high-precision deposition of highly crystalline organic semiconductors by inkjet printing is important for the production of printed organic transistors. Herein, a facile nonconventional lithographic patterning technique is developed for fabricating banks with microwell structures by inkjet printing solvent droplets onto a polymer layer, thereby locally dissolving the polymer to form microwells. The semiconductor ink is then inkjet-printed into the microwells. In addition to confining the inkjet-printed organic semiconductor droplets, the microwells provide a platform onto which organic semiconductor molecules crystallize during solvent evaporation. When printed onto the hydrophilic microwells, the inkjet-printed 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS_PEN) molecules undergo self-organization to form highly ordered crystalline structures as a result of contact line pinning at the top corner of the bank and the outward hydrodynamic flow within the drying droplet. By contrast, small crystallites form with relatively poor molecular ordering in the hydrophobic microwells as a result of depinning of the contact line along the walls of the microwells. Because pinning in the hydrophilic microwells occurred at the top corner of the bank, treating the surfaces of the dielectric layer with a hydrophobic organic layer does not disturb the formation of the highly ordered TIPS_PEN crystals. Transistors fabricated on the hydrophilic microwells and the hydrophobic dielectric layer exhibit the best electrical properties, which is explained by the solvent evaporation and crystallization characteristics of the organic semiconductor droplets in the microwell. These results indicate that this technique is suitable for patterning organic semiconductor deposits on large-area flexible substrates for the direct-write fabrication of high-performance organic transistors.
TL;DR: In this paper, the authors carried out an investigation on the origin of enhanced photoelectric characteristics in MoO 3 -doped pentacene films, including charge transport, trap density and conductivity.
TL;DR: The charge trapping mechanism of the fullerene floating gate for both p-type pentacene and n-type copper hexadecafluorophthalocyanine semiconductor in a transistor based flash memory architecture exhibited large memory window, long charge retention time, good endurance property and excellent flexibility.
Abstract: Solution processed fullerene (C60) molecular floating gate layer has been employed in low voltage nonvolatile memory device on flexible substrates. We systematically studied the charge trapping mechanism of the fullerene floating gate for both p-type pentacene and n-type copper hexadecafluorophthalocyanine (F16CuPc) semiconductor in a transistor based flash memory architecture. The devices based on pentacene as semiconductor exhibited both hole and electron trapping ability, whereas devices with F16CuPc trapped electrons alone due to abundant electron density. All the devices exhibited large memory window, long charge retention time, good endurance property and excellent flexibility. The obtained results have great potential for application in large area flexible electronic devices.