Showing papers on "Pentacene published in 2014"
TL;DR: This article reviews the research efforts of developing N-heteropentacenes into organic semiconductors starting from 2003 with emphasis on the work of the author's group since 2009 and highlights the structure-property relationship and design rationale.
Abstract: Introducing N atoms to the pentacene backbone leads to N-heteropentacenes, whose properties can be tuned by changing the number, position and valence state of N atoms in the pentacene backbone. With a rapid development in recent years, N-heteropentacenes and their derivatives have arisen as a new family of organic semiconductors with high performance in organic thin-film transistors (OTFTs). This article reviews the research efforts of developing N-heteropentacenes into organic semiconductors starting from 2003 with emphasis on the work of the author's group since 2009. The structure-property relationship and design rationale are highlighted based on an overview of reported organic semiconductors of N-heteropentacenes.
291 citations
TL;DR: Efficient resonant-energy transfer of molecular spin-triplet excitons from organic semiconductor to inorganic semiconductors is reported, enabling luminescent harvesting of triplet exciton energy in light-emitting structures.
Abstract: The efficient transfer of energy between organic and inorganic semiconductors is a widely sought after property, but has so far been limited to the transfer of spin-singlet excitons. Here we report efficient resonant-energy transfer of molecular spin-triplet excitons from organic semiconductors to inorganic semiconductors. We use ultrafast optical absorption spectroscopy to track the dynamics of triplets, generated in pentacene through singlet exciton fission, at the interface with lead selenide (PbSe) nanocrystals. We show that triplets transfer to PbSe rapidly (<1 ps) and efficiently, with 1.9 triplets transferred for every photon absorbed in pentacene, but only when the bandgap of the nanocrystals is close to resonance (±0.2 eV) with the triplet energy. Following triplet transfer, the excitation can undergo either charge separation, allowing photovoltaic operation, or radiative recombination in the nanocrystal, enabling luminescent harvesting of triplet exciton energy in light-emitting structures.
250 citations
TL;DR: By defining an oscillator strength measure of the coherent population of the multiexcitonic diabat, essential to singlet fission, it is found this population can, in principle, be increased by small compression along a specific crystal direction.
Abstract: We present a detailed study of pentacene monomer and dimer that serves to reconcile extant views of its singlet fission. We obtain the correct ordering of singlet excited- state energy levels in a pentacene molecule (E (S1 )< E (D)) from multireference calculations with an appropriate active orbital space and dynamical correlation being incorporated. In order to understand the mechanism of singlet fission in pentacene, we use a well-developed diabatization scheme to characterize the six low-lying singlet states of a pentacene dimer that approximates the unit cell structure of crystalline pentacene. The local, single-excitonic diabats are not directly coupled with the important multiexcitonic state but rather mix through their mutual couplings with one of the charge-transfer configurations. We analyze the mixing of diabats as a function of monomer separation and pentacene rotation. By defining an oscillator strength measure of the coherent population of the multiexcitonic diabat, essential to singlet fission, we find this population can, in principle, be increased by small compression along a specific crystal direction.
194 citations
TL;DR: Patterns composed of solvent wetting and dewetting regions promote lateral confinement of solution-sheared and lattice-strained TIPS-pentacene crystals, and this lateral confinement causes aligned crystal growth.
Abstract: Patterns composed of solvent wetting and dewetting regions promote lateral confinement of solution-sheared and lattice-strained TIPS-pentacene crystals. This lateral confinement causes aligned crystal growth, and the smallest patterns of 0.5 μm wide solvent wetting regions promotes formation of highly strained, aligned, and single-crystalline TIPS-pentacene regions with mobility as high as 2.7 cm(2) V(-1) s(-1) .
185 citations
TL;DR: It is shown that the SF rate can be increased by more than an order of magnitude through tuning the intermolecular packing, most notably when going from cofacial to the slipped stacked arrangements encountered in some pentacene derivatives.
Abstract: A novel nonadiabatic molecular dynamics scheme is applied to study the singlet fission (SF) process in pentacene dimers as a function of longitudinal and lateral displacements of the molecular backbones. Detailed two-dimensional mappings of both instantaneous and long-term triplet yields are obtained, characterizing the advantageous and unfavorable stacking arrangements, which can be achieved by chemical substitutions to the bare pentacene molecule. We show that the SF rate can be increased by more than an order of magnitude through tuning the intermolecular packing, most notably when going from cofacial to the slipped stacked arrangements encountered in some pentacene derivatives. The simulations indicate that the SF process is driven by thermal electron–phonon fluctuations at ambient and high temperatures, expected in solar cell applications. Although charge-transfer states are key to construct continuous channels for SF, a large charge-transfer character of the photoexcited state is found to be not ess...
139 citations
TL;DR: An approach that utilizes an organic heterointerface to improve the crystallinity and control the morphology of an organic thin film and opens a new way for the fabrication of nanostructured semiconducting layers towards high-performance organic electronics.
Abstract: High-performance organic electronics require minimal grain boundaries in an organic semiconductor active layer. Here, Kang et al. report the growth of pentacene thin films in a macroporous structure with improved crystallinity, which is guided by a chemically heterogeneous, rubber-like substrate.
132 citations
TL;DR: In this article, a simple three-state model for the dynamics of the singlet fission (SF) process is developed, which facilitates the analysis of the relative significance of different factors, such as electronic energies, couplings, and the entropic contributions.
Abstract: A simple three-state model for the dynamics of the singlet fission (SF) process is developed. The model facilitates the analysis of the relative significance of different factors, such as electronic energies, couplings, and the entropic contributions. The entropic contributions to the rates are important; they drive the SF process in endoergic cases (such as tetracene). The anticipated magnitude of entropic contributions is illustrated by simple calculations. By considering a series of three acenes (tetracene, pentacene, and hexacene), we explained the experimentally observed 3 orders of magnitude difference in the rate of SF in tetracene and pentacene and predicted that the rate in hexacene will be slightly faster than in pentacene. This trend is driven by the increased thermodynamic drive for SF (Gibbs free energy difference of the initial excitonic state and two separated triplets). The model also explains experimentally observed fast SF in 5,12-diphenyltetracene. Consistently with the experimental obs...
120 citations
TL;DR: The results underline that the impact of packing configurations, well established in the case of the charge-transport properties, also extends to the polarization properties of π-conjugated materials.
Abstract: Polarization energy corresponds to the stabilization of the cation or anion state of an atom or molecule when going from the gas phase to the solid state. The decrease in ionization energy and increase in electron affinity in the solid state are related to the (electronic and nuclear) polarization of the surrounding atoms and molecules in the presence of a charged entity. Here, through a combination of molecular mechanics and quantum mechanics calculations, we evaluate the polarization energies in two prototypical organic semiconductors, pentacene and 6,13-bis(2-(tri-isopropylsilyl)ethynyl)pentacene (TIPS-pentacene). Comparison of the results for the two systems reveals the critical role played by the molecular packing configurations in the determination of the polarization energies and provides physical insight into the experimental data reported by Lichtenberger and co-workers (J. Amer. Chem. Soc. 2010, 132, 580; J. Phys. Chem. C 2010, 114, 13838). Our results underline that the impact of packing config...
109 citations
TL;DR: It is found that state-of-the-art pentacene films (grown on SiO2 at elevated temperature) are structurally not homogeneous but exhibit two interpenetrating phases at sub-micrometre scale, documented by a shifted vibrational resonance.
Abstract: Controlling the domain size and degree of crystallization in organic films is highly important for electronic applications such as organic photovoltaics, but suitable nanoscale mapping is very difficult. Here we apply infrared-spectroscopic nano-imaging to directly determine the local crystallinity of organic thin films with 20-nm resolution. We find that state-of-the-art pentacene films (grown on SiO2 at elevated temperature) are structurally not homogeneous but exhibit two interpenetrating phases at sub-micrometre scale, documented by a shifted vibrational resonance. We observe bulk-phase nucleation of distinct ellipsoidal shape within the dominant pentacene thin-film phase and also further growth during storage. A faint topographical contrast as well as X-ray analysis corroborates our interpretation. As bulk-phase nucleation obstructs carrier percolation paths within the thin-film phase, hitherto uncontrolled structural inhomogeneity might have caused conflicting reports about pentacene carrier mobility. Infrared-spectroscopic nano-imaging of nanoscale polymorphism should have many applications ranging from organic nanocomposites to geologic minerals.
90 citations
TL;DR: In this article, the use of the typical electron-donor (donor) material boron subphthalocyanine chloride (Cl-BsubPc) and a chlorinated derivative (hexachloro BORON SUB-PCNCL, Cl-Cl6BsubPCN) to act as electronaccepting (acceptor) materials and as replacements for C60 was discussed.
Abstract: In this paper, we discuss the use of the typical electron-donor (donor) material boron subphthalocyanine chloride (Cl-BsubPc) and a chlorinated derivative (hexachloro boron subphthalocyanine chloride, Cl–Cl6BsubPc) to act as electron-accepting (acceptor) materials and as replacements for C60, when coupled with tetracene and pentacene as the electron-donor materials in organic photovoltaics (OPVs). A large decrease in photocurrent was observed when C60 was replaced in the pentacene OPVs, although there was evidence of the harvesting of some triplets for the pentacene/Cl–Cl6BsubPc OPV. Large increases in Voc and stability were observed. Photoluminescence quenching, electron mobilities, and photovoltaic device characteristics are also presented and indicate the ambipolar quality of these small molecule organic semiconductors.
66 citations
TL;DR: This study presents a new class of conjugated polycyclic molecules that contain seven-membered rings, detailing their synthesis, crystal structures and semiconductor properties.
Abstract: This study presents a new class of conjugated polycyclic molecules that contain seven-membered rings, detailing their synthesis, crystal structures and semiconductor properties. These molecules have a nearly flat C6-C7-C6-C7-C6 polycyclic framework with a p-quinodimethane core. With field-effect mobilities of up to 0.76 cm2 V−1 s−1 as measured from solution-processed thin-film transistors, these molecules are alternatives to the well-studied pentacene analogues for applications in organic electronic devices.
TL;DR: The effects of the introduction of an sp(2)-hybridized nitrogen atom (═N-) and thiophene ring on the structure geometries, frontier molecular orbital energies, and excited state energies related to singlet fission (SF) were theoretically investigated by quantum chemical methods.
Abstract: The effects of the introduction of an sp2-hybridized nitrogen atom (═N—) and thiophene ring on the structure geometries, frontier molecular orbital energies, and excited state energies related to singlet fission (SF) for some tetracene and pentacene derivatives were theoretically investigated by quantum chemical methods. The introduction of a nitrogen atom significantly decreases the energies of frontier molecular orbitals and hence improves their stabilities in air and light illumination. More importantly, it is helpful for reducing the energy loss of the exothermic singlet fission of pentacene derivatives. For fused benzene-thiophene structures, the (α, β) connection pattern could stabilize the frontier molecular orbitals, while the (β, β) connection pattern can promote the thermodynamic driving force of singlet fission. These facts provide a theoretical ground for rational design of SF materials.
TL;DR: In this paper, the authors demonstrate an effective approach to improve both charge transport and performance consistency in solution-processed organic thin-film transistors (OTFTs) by blending 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene, or TP) with a series of small-molecule additives: 4-butylbenzoic acid (BBA), 4-hexyl benzoic acids (HBA), and 4-octylbenzosic acid(OBA).
TL;DR: After exposure to NH3 gas, the carrier mobility at the monolayer OFET channel decreased down to one-third of its original value, leading to a several orders of magnitude decrease in the drain current, which tremendously enhanced the gas detection sensitivity.
Abstract: We report on the fabrication of an organic field-effect transistor (OFET) of a monolayer pentacene thin film with top-contact electrodes for the aim of ammonia (NH3) gas detection by monitoring changes in its drain current. A top-contact configuration, in which source and drain electrodes on a flexible stamp [poly(dimethylsiloxane)] were directly contacted with the monolayer pentacene film, was applied to maintain pentacene arrangement ordering and enhance the monolayer OFET detection performance. After exposure to NH3 gas, the carrier mobility at the monolayer OFET channel decreased down to one-third of its original value, leading to a several orders of magnitude decrease in the drain current, which tremendously enhanced the gas detection sensitivity. This sensitivity enhancement to a limit of the 10 ppm level was attributed to an increase of charge trapping in the carrier channel, and the amount of trapped states was experimentally evaluated by the threshold voltage shift induced by the absorbed NH3 molecular analyte. In contrast, a conventional device with a 50-nm-thick pentacene layer displayed much higher mobility but lower response to NH3 gas, arising from the impediment of analyte penetrating into the conductive channel, owing to the thick pentacene film.
TL;DR: The comparable characteristics of OTFTs fabricated on widely available, low cost paper and high quality expensive liquid crystal display glass indicate the potential importance of cellulose-based electronic devices.
Abstract: Pentacene-based organic thin-film transistors (OTFTs) were fabricated on several types of flexible substrate: commercial photo paper, ultra-smooth specialty paper and ultra-thin (100 μM) flexible glass The transistors were fabricated entirely through dry-step processing The transconductance and field-effect mobility of OTFTs on photo paper reached values of ∼052 mS m−1 and ∼01 cm2 V −1 s−1, respectively Preliminary results on the lifetime of OTFTs on photo paper yielded stable transconductance and mobility values over a period of more than 250 h The comparable characteristics of OTFTs fabricated on widely available, low cost paper and high quality expensive liquid crystal display glass indicate the potential importance of cellulose-based electronic devices
TL;DR: In this paper, an organic field effect transistor (OFET) using poly(methyl methacrylate) (PMMA) blending with zinc oxide (ZnO) nanoparticles as a gate dielectric layer was fabricated.
Abstract: Ammonia (NH3) gas sensors based on organic field-effect transistor (OFET) using poly(methyl methacrylate) (PMMA) blending with zinc oxide (ZnO) nanoparticles as a gate dielectric layer were fabricated. Compared to those with the pure PMMA dielectric layer, the sensing properties of these devices using ZnO/PMMA hybrid as the gate dielectric layer were significantly improved when the sensors exposed to various concentrations of NH3, and the percentage response was nearly 10 folds higher than that using pure PMMA under 75 ppm NH3. Also, the results showed that there was a remarkable shift in the threshold-voltage as well as a change in field-effect mobility after exposed to NH3 gas. By analyzing the morphologies of the dielectrics and pentacene films and the electrical characteristics of OFET, it was found that ZnO/PMMA hybrid gate dielectric layer was responsible for the enhanced sensing properties. Also, the decreased grain size of pentacene was formed on the ZnO/PMMA hybrid dielectric, facilitating NH3 to diffuse into the conducting channel and then interact with the ZnO nanoparticles. Moreover, the environmental stability of the OFET sensors was measured after storing the sensors under ambient atmosphere for 40 days.
TL;DR: A individually position-addressable large-scale-aligned Cu nanofiber array is fabricated using electro-hydrodynamic nanowire printing and is effectively used as source/drain nanoelectrode in pentacene transistors, which show a 25-fold increased hole mobility than that of a device with Cu thin-film electrodes.
Abstract: A individually position-addressable large-scale-aligned Cu nanofiber (NF) array is fabricated using electro-hydrodynamic nanowire printing. The printed single-stranded Cu NF has a diameter of about 710 nm and resistivity of 14.1 μΩ cm and is effectively used as source/drain nanoelectrode in pentacene transistors, which show a 25-fold increased hole mobility than that of a device with Cu thin-film electrodes.
TL;DR: In this article, the role of self-assembled monolayer (SAM) of dipolar molecules on the threshold voltage and charge carrier mobility of organic field effect transistor (OFET) made of both amorphous and polycrystalline organic semiconductors was investigated.
TL;DR: The highly fluorinated polyimide dielectric showed negligible hysteresis and a notable gate bias stability under both a N2 environment and ambient air, and a better crystalline morphology in the semiconductor film grown over their surfaces.
Abstract: Organic field-effect transistors (OFETs) that operated with good electrical stability were prepared by synthesizing fluorinated polyimide (PI) gate dielectrics based on 6FDA-PDA-PDA PI and 6FDA-CF3Bz-PDA PI. 6FDA-PDA-PDA PI and 6FDA-CF3Bz-PDA PI contain 6 and 18 fluorine atoms per repeat unit, respectively. These fluorinated polymers provided smooth surface topographies and surface energies that decreased as the number of fluorine atoms in the polymer backbone increased. These properties led to a better crystalline morphology in the semiconductor film grown over their surfaces. The number of fluorine atoms in the PI backbone increased, the field-effect mobility improved, and the threshold voltage shifted toward positive values (from -0.38 to +2.21 V) in the OFETs with pentacene and triethylsilylethynyl anthradithiophene. In addition, the highly fluorinated polyimide dielectric showed negligible hysteresis and a notable gate bias stability under both a N2 environment and ambient air.
TL;DR: Two 7,14-disubstituted-5,12-dithiapentacenes (1 and 2) with quinoidal conjugation were synthesized and showed very different electronic and optical properties from those of the corresponding pentacene derivatives with diene conjugations, and their stability was significantly improved.
TL;DR: The excited-state dynamics of pentacene derivatives with stable radical substituents were evaluated in detail and showed ultrafast formation of triplet excited state(s) in the pentacenes moiety from a photoexcited singlet state through the contributions of enhanced intersystem crossing and singlet fission.
Abstract: The excited-state dynamics of pentacene derivatives with stable radical substituents were evaluated in detail through transient absorption measurements. The derivatives showed ultrafast formation of triplet excited state(s) in the pentacene moiety from a photoexcited singlet state through the contributions of enhanced intersystem crossing and singlet fission. Detailed kinetic analyses for the transient absorption data were conducted to quantify the excited-state characteristics of the derivatives.
TL;DR: In this paper, a pentacene-based organic field effect transistor nonvolatile memory, in which polystyrene covered Au nanoparticles act as the nano-floating-gate, is probed under different illumination conditions.
TL;DR: In this article, the impact of structural anisotropy on the charge transport in 6,13-bis (triisopropylsilylethynyl) (TIPS) and 6, 13-bis(triethylsily lethylyl), (TES) pentacene field effect transistors, in which microstructure is controlled by solution processing conditions is investigated.
Abstract: To understand and optimize the performance of thin-film electronic devices incorporating crystalline organic semiconductors, it is important to consider the impact of their structural anisotropy on the charge transport. Here we report on the charge mobility anisotropy in 6,13-bis(triisopropylsilylethynyl) (TIPS) and 6,13-bis(triethylsilylethynyl) (TES) pentacene field effect transistors, in which microstructure is controlled by solution processing conditions. Thin-film structures that range from millimetre size, crystalline domains to macroscopic, high-aspect-ratio (∼1 μm wide and >1 cm long) needles are systematically produced by controlling the substrate displacement rate during zone-cast deposition. Through precise control of the microstructure we experimentally explore the differences in charge transport anisotropy between TIPS- and TES-pentacene molecules. Aligned needles of TIPS- pentacene result in a mobility anisotropy (μ∥/μ⊥) of ∼20 (mobility of ∼0.7 cm2 V−1 s−1) whereas TES-pentacene produce an order of magnitude lower mobility (∼0.06 cm2 V−1 s−1) but much higher mobility anisotropy (>45). Such significant changes in absolute mobility and mobility anisotropy are attributed to their different packing structures, which permit 2D charge transport in TIPS-pentacene and 1D transport in TES-pentacene. Bulky TIPS- side groups (diameter ∼7.5 A) force a brick-wall type packing structure, whereas TES- side groups (diameter ∼6.6 A) pack in a 1D slipped-stack. Furthermore, through precise control of the molecular alignment, the impact of crystal orientation on charge transport is investigated. TIPS-pentacene achieves the highest mobility when the angle between the needle long-axis and charge transport directions is ∼35°, whereas in TES-pentacene it is much closer to 0°. These results are supported by theoretical simulations.
TL;DR: In this article, a non-classical organic strain gauge as a voltage signal sensor is reported, using an inverter-type thin-film transistor (TFT) circuit, which is able to sensitively measure a large quantity of elastic strain (up to ≈ 2.48%).
Abstract: A non-classical organic strain gauge as a voltage signal sensor is reported, using an inverter-type thin-film transistor (TFT) circuit, which is able to sensitively measure a large quantity of elastic strain (up to ≈2.48%), which approaches an almost folding state. Novel heptazole-based organic TFTs are chosen to be incorporated in this gauge circuit; organic solid heptazole has small domain size in general. While large crystal domain-pentacene TFTs seldom show sufficient current variation upon mechanical bending for tensile strain, these heptazole TFTs demonstrate a significant variation for the same strain condition as applied to pentacene devices. In addition, the pentacene channel does not recover to its original electric state after bending but heptazole channels are very elastic and reversible, even after going through serious bending. More interesting is that the heptazole TFTs show only a little variation of signal current under horizontal direction strain, while they make a significant amount of current decrease under vertical direction strain. Utilizing the anisotropic response to the tensile bending strain, an ultrasensitive voltage output strain gauge composed of a horizontally and vertically oriented TFT couple is demonstrated.
TL;DR: Hydrophobic organo-compatible but low-capacitance dielectrics (10.5 nFcm(-2) ), polystyrene-grafted SiO2 could induce surface-mediated large crystal grains of face-to-face stacked triethylsilylethynyl anthradithiophene (TES-ADT), producing more efficient charge-carrier transport, in comparison to μm-sized pentacene crystals containing a face- ToE packing.
Abstract: Hydrophobic organo-compatible but low-capacitance dielectrics (10.5 nFcm(-2) ), polystyrene-grafted SiO2 could induce surface-mediated large crystal grains of face-to-face stacked triethylsilylethynyl anthradithiophene (TES-ADT), producing more efficient charge-carrier transport, in comparison to μm-sized pentacene crystals containing a face-to-edge packing. Low-voltage operating TES-ADT OFETs showed good device performance (μFET ≈ 1.3 cm(2) V(-1) s(-1) , Vth ≈ 0.5 V, SS ≈ 0.2 V), as well as excellent device reliability.
TL;DR: In this paper, the effect of molecular doping on the bias stress behavior is explained in terms of the shift of Fermi Level and thus, exponentially reduced proton generation at the pentacene/oxide interface.
Abstract: The key active devices of future organic electronic circuits are organic thin film transistors (OTFTs). Reliability of OTFTs remains one of the most challenging obstacles to be overcome for broad commercial applications. In particular, bias stress was identified as the key instability under operation for numerous OTFT devices and interfaces. Despite a multitude of experimental observations, a comprehensive mechanism describing this behavior is still missing. Furthermore, controlled methods to overcome these instabilities are so far lacking. Here, we present the approach to control and significantly alleviate the bias stress effect by using molecular doping at low concentrations. For pentacene and silicon oxide as gate oxide, we are able to reduce the time constant of degradation by three orders of magnitude. The effect of molecular doping on the bias stress behavior is explained in terms of the shift of Fermi Level and, thus, exponentially reduced proton generation at the pentacene/oxide interface.
TL;DR: The results indicate that the laterally stacked ambipolar crystal wire for high-mobility organic field-effect transistors (OFETs) are potentially useful for miniaturized organic electronic devices.
Abstract: We report the formation of laterally stacked ambipolar crystal wire for high-mobility organic field-effect transistors (OFETs), along with a simple logic circuit through a solution process. A soluble pentacene derivative, 6,13-bis(triisopropylsilylethynyl)pentacene (Tips-pentacene), and N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) were used as p-type and n-type organic semiconductors, respectively. The laterally stacked ambipolar crystal wire is made up of Tips-pentacene and PTCDI-C8 crystals in a structure of Tips-pentacene/PTCDI-C8/Tips-pentacene (TPT). The inner part of the crystal is made up of PTCDI-C8, and Tips-pentacene is present on both sides. These TPT crystals exhibit typical ambipolar charge transport behavior in organic electronic devices, which show very balanced hole and electron mobility as high as 0.23 cm2/V·s and 0.13 cm2/V·s, respectively. Static and dynamic operational stability of the device is investigated by measuring the device performance as a function of storage time an...
TL;DR: Bias stress studies show that FF-MNS-based pentacene FETs are more resistant to degradation than pentacenes FETS using FF thin film (without any nanostructures) as the dielectric layer when both are subjected to sustained electric fields.
Abstract: Peptide-based nanostructures derived from natural amino acids are superior building blocks for biocompatible devices as they can be used in a bottom-up process without the need for expensive lithography. A dense nanostructured network of l,l-diphenylalanine (FF) was synthesized using the solid–vapor-phase technique. Formation of the nanostructures and structure–phase relationship were investigated by electron microscopy and Raman scattering. Thin films of l,l-diphenylalanine micro/nanostructures (FF-MNSs) were used as the dielectric layer in pentacene-based field-effect transistors (FETs) and metal–insulator–semiconductor diodes both in bottom-gate and in top-gate structures. Bias stress studies show that FF-MNS-based pentacene FETs are more resistant to degradation than pentacene FETs using FF thin film (without any nanostructures) as the dielectric layer when both are subjected to sustained electric fields. Furthermore, it is demonstrated that the FF-MNSs can be functionalized for detection of enzyme–an...
TL;DR: In this paper, a photostable organic layer is reported, heptazole (C26H16N2), which has almost the same HOMO level as that of pentacene but with a higher HOMOMO-LUMO gap (≈2.95 eV).
Abstract: Small molecule pentacene layer has been a representative among many organic thin-film transistor (OTFT) channels with decent p-type mobilities, but it is certainly light-sensitive due to its relatively small highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap (1.85 eV). Although a few other small molecule-based layers have been reported later, their photo-stabilities or related device applications have hardly been addressed. Here, a new photostable organic layer is reported, heptazole (C26H16N2), which has almost the same HOMO level as that of pentacene but with a higher HOMO-LUMO gap (≈2.95 eV). This heptazole OTFT displays a decent mobility comparable to that of conventional amorphous Si TFTs, showing good photostability unlike pentacene OTFTs. An image pixel driving the photostable heptazole OTFT connected to a pentacene/Al Schottky photodiode is demonstrated. This heptazole OTFT also conveniently forms a logic inverter coupled with a pentacene OTFT, sharing Au for source/drain.
TL;DR: The results highlight the coverage-dependent impact of the SAM on the density of semiconductor states and enable the rationalization and the control of the OTFT characteristics.
Abstract: This study sheds light on the microscopic mechanisms by which self-assembled monolayers (SAMs) determine the onset voltage in organic thin-film transistors (OTFTs). Experiments and modeling are combined to investigate the self-assembly and electrostatic interaction processes in prototypical OTFT structures (SiO2/SAM/pentacene), where alkylated and fluoroalkylated silane SAMs are compared. The results highlight the coverage-dependent impact of the SAM on the density of semiconductor states and enable the rationalization and the control of the OTFT characteristics.