Showing papers on "Pentacene published in 2015"
TL;DR: Azaacenes, particularly the symmetrical bis(triisopropylsilylethynyl)-substituted tetraazapentacene, are primarily used in organic field-effect transistors, but smaller azaacene shine in the field as organic light-emitting diode (OLED) emitters.
Abstract: ConspectusThe close structural and chemical relationship of N-heteroacenes to pentacene suggests their broad applicability in organic electronic devices, such as thin-film transistors. The superb materials science properties of azaacenes result from their improved resistance toward oxidation and their potential for electron transport, both of which have been demonstrated recently. The introduction of nitrogen atoms into the aromatic perimeter of acenes stabilizes their frontier molecular orbitals and increases their electron affinity. The HOMO–LUMO gaps in azaacenes in which the nitrogen atoms are symmetrically placed are similar to those of the acenes. The judiciously placed nitrogen atoms induce an “umpolung” of the electronic behavior of these pentacene-like molecules, i.e., instead of hole mobility in thin-film transistors, azaacenes are electron-transporting materials. The fundamental synthetic approaches toward larger azaacenes are described and discussed. Several synthetic methodologies have been e...
386 citations
TL;DR: Two new synthetic techniques have been developed to create stable PAHs that extend conjugation in two dimensions that exhibit good charge-transport properties, comparable to those of traditional linear acenes, while being much more environmentally stable.
Abstract: ConspectusPolycyclic aromatic hydrocarbons (PAHs), consisting of laterally fused benzene rings, are among the most widely studied small-molecule organic semiconductors, with potential applications in organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). Linear acenes, including tetracene, pentacene, and their derivatives, have received particular attention due to the synthetic flexibility in tuning their chemical structure and properties and to their high device performance. Unfortunately, longer acenes, which could exhibit even better performance, are susceptible to oxidation, photodegradation, and, in solar cells which contain fullerenes, Diels–Alder reactions. This Account highlights recent advances in the molecular design of two-dimensional (2-D) PAHs that combine device performance with environmental stability.New synthetic techniques have been developed to create stable PAHs that extend conjugation in two dimensions. The stability of these novel compounds is consistent with Clar...
198 citations
TL;DR: In this article, fast and highly efficient intramolecular singlet exciton fission in a pentacene dimer, consisting of two covalently attached, nearly orthogonal units, was reported.
Abstract: Fast and highly efficient intramolecular singlet exciton fission in a pentacene dimer, consisting of two covalently attached, nearly orthogonal pentacene units is reported. Fission to triplet excitons from this ground state geometry occurs within 1 ps in isolated molecules in solution and dispersed solid matrices. The process exhibits a sensitivity to environmental polarity and competes with geometric relaxation in the singlet state, while subsequent triplet decay is strongly dependent on conformational freedom. The near orthogonal arrangement of the pentacene units is unlike any structure currently proposed for efficient singlet exciton fission and may lead to new molecular design rules.
181 citations
TL;DR: In this paper, a molecular nano-floating gate (NFG) of pentacene-based transistor memory devices is developed using conjugated polymer nanoparticles (CPN) as the discrete trapping sites embedded in an insulating polymer, poly (methacrylic acid) (PMAA).
Abstract: A molecular nano-floating gate (NFG) of pentacene-based transistor memory devices is developed using conjugated polymer nanoparticles (CPN) as the discrete trapping sites embedded in an insulating polymer, poly (methacrylic acid) (PMAA). The nanoparticles of polyfluorene (PF) and poly(fluorene-alt-benzo[2,1,3]thiadiazole (PFBT) with average diameters of around 50–70 nm are used as charge-trapping sites, while hydrophilic PMAA serves as a matrix and a tunneling layer. By inserting PF nanoparticles as the floating gate, the transistor memory device reveals a controllable threshold voltage shift, indicating effectively electron-trapping by the PF CPN. The electron-storage capability can be further improved using the PFBT-based NFG since their lower unoccupied molecular orbital level is beneficial for stabilization of the trapped charges, leading a large memory window (35 V), retention time longer than 104 s with a high ON/OFF ratio of >104. In addition, the memory device performance using conjugated polymer nanoparticle NFG is much higher than that of the corresponding polymer blend thin films of PF/polystyrene. It suggests that the discrete polymer nanoparticles can be effectively covered by the tunneling layer, PMAA, to achieve the superior memory characteristics.
140 citations
TL;DR: The scalable synthetic strategy promises to afford access to a structurally diverse class of extended periacenes and related polycyclic aromatic hydrocarbons as advanced materials for electronic, spintronic, optical, and magnetic devices.
Abstract: The thermally induced cyclodehydrogenation reaction of 6,6'-bipentacene precursors on Au(111) yields peripentacene stabilized by surface interactions with the underlying metallic substrate. STM and atomic-resolution non-contact AFM imaging reveal rectangular flakes of nanographene featuring parallel pairs of zig-zag and armchair edges resulting from the lateral fusion of two pentacene subunits. The synthesis of a novel molecular precursor 6,6'-bipentacene, itself a synthetic target of interest for optical and electronic applications, is also reported. The scalable synthetic strategy promises to afford access to a structurally diverse class of extended periacenes and related polycyclic aromatic hydrocarbons as advanced materials for electronic, spintronic, optical, and magnetic devices.
105 citations
TL;DR: In this article, the authors combined density functional theory and many-body perturbation theory calculations, along with polarization-dependent optical absorption spectro-microscopy on ordered domains, to investigate the nature of low-energy excitons within ordered domains of 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-PEN) thin films.
Abstract: Theory and experiment are combined to investigate the nature of low-energy excitons within ordered domains of 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-PEN) polycrystalline thin films. First-principles density functional theory and many-body perturbation theory calculations, along with polarization-dependent optical absorption spectro-microscopy on ordered domains, show multiple low-energy absorption peaks that are composed of excitonic states delocalized over several molecules. While the first absorption peak is composed of a single excitonic transition and retains the polarization-dependent behavior of the molecule, higher energy peaks are composed of multiple transitions with optical properties that can not be described by those of the molecule. The predicted structure-dependence of polarization-dependent absorption reveals the exact inter-grain orientation within the TIPS-PEN film. Additionally, the degree of exciton delocalization can be significantly tuned by modest changes in the solid-state structure and the spatial extent of the excitations along a given direction is correlated with the degree of electronic dispersion along the same direction. These findings pave the way for tailoring the singlet fission efficiency of organic crystals by solid-state structure.
92 citations
TL;DR: The present findings indicate that controlling organic-graphene heterointerface could provide a design strategy of organic solar cell architecture for boosting photon harvesting and show a 5 times increment in the maximum power conversion efficiency than the equivalent devices without a graphene layer.
Abstract: Photon harvesting in organic solar cells is highly dependent on the anisotropic nature of the optoelectronic properties of photoactive materials. Here, we demonstrate an efficient approach to dramatically enhance photon harvesting in planar heterojunction solar cells by using a graphene–organic heterointerface. A large area, residue-free monolayer graphene is inserted at anode interface to serve as an atomically thin epitaxial template for growing highly orientated pentacene crystals with lying-down orientation. This anisotropic orientation enhances the overall optoelectronic properties, including light absorption, charge carrier lifetime, interfacial energetics, and especially the exciton diffusion length. Spectroscopic and crystallographic analysis reveal that the lying-down orientation persists until a thickness of 110 nm, which, along with increased exciton diffusion length up to nearly 100 nm, allows the device optimum thickness to be doubled to yield significantly enhanced light absorption within th...
77 citations
TL;DR: In this paper, a solution processed high-k nanocomposite/low-k polymer bilayer gate dielectric that enables the fabrication of organic field effect transistors (OFETs) that operate effectively at 1 ǫ in high yields is reported.
67 citations
TL;DR: In this paper, a photo-induced cycloaddition process of the 6,13-bis (triisopropylsilylethynyl) (TIPS)-pentacene is used to generate a high-energy emission.
Abstract: This work demonstrates a novel proof-of-concept to implement pentacene derivatives as emitters for the third generation of light-emitting electrochemical cells based on small-molecules (SM-LECs). Here, a straightforward procedure is shown to control the chromaticity of pentacene-based lighting devices by means of a photoinduced cycloaddition process of the 6,13-bis(triisopropylsilylethynyl) (TIPS)-pentacene that leads to the formation of anthracene-core dimeric species featuring a high-energy emission. Without using the procedure, SM-LECs featuring deep-red emission with Commission Internationale d'Eclairage (CIE) coordinates of x = 0.69/y = 0.31 and irradiance of 0.4 μW cm−2 are achieved. After a careful optimization of the cycloaddition process, warm white devices with CIE coordinates of x = 0.36/y = 0.38 and luminances of 10 cd m−2 are realized. Here, the mechanism of the device is explained as a host–guest system, in which the dimeric species acts as the high-energy band gap host and the low-energy bandgap TIPS-pentacene is the guest. To the best of the knowledge, this work shows the first warm white SM-LECs. Since this work is based on the archetypal TIPS-pentacene and the photoinduced cycloaddition process is well-knownfor any pentacenes, this proof-of-concept could open a new way to use these compounds for developing white lighting sources.
66 citations
TL;DR: This research provides a promising strategy to access stable higher order acenes with controlled molecular order and exhibited exceptionally high photo-stability in the solution, with a half-life time of 11.2 years.
62 citations
TL;DR: In this article, a pentacene ultrathin film transistor has been integrated into the implement of a gas sensor based on an increase in its mobility and a shift of its threshold voltage.
TL;DR: A new class of stabilized pentacene derivatives with externally fused five-membered rings are prepared by means of a key palladium-catalyzed cyclopentannulation step and Photodegradation studies reveal the new compounds are more photostable than 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacenes).
Abstract: A new class of stabilized pentacene derivatives with externally fused five-membered rings are prepared by means of a key palladium-catalyzed cyclopentannulation step. The target compounds are synthesized by chemical manipulation of a partially saturated 6,13-dibromopentacene precursor that can be fully aromatized in a final step through a DDQ-mediated dehydrogenation reaction (DDQ=2,3-dichloro-5,6-dicyano-1,4-benzoquinone). The new 1,2,8,9-tetraaryldicyclopenta[fg,qr]pentacene derivatives have narrow energy gaps of circa 1.2 eV and behave as strong electron acceptors with lowest unoccupied molecular orbital energies between −3.81 and −3.90 eV. Photodegradation studies reveal the new compounds are more photostable than 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene).
TL;DR: Pentacene (C22H14), a polycyclic aromatic hydrocarbon, was used as both supporting and sacrificing layers for the clean and doping-free graphene transfer and exhibited extremely homogeneous surface potential profiles over a large area.
Abstract: Pentacene (C22H14), a polycyclic aromatic hydrocarbon, was used as both supporting and sacrificing layers for the clean and doping-free graphene transfer. After successful transfer of graphene to a target substrate, the pentacene layer was physically removed from the graphene surface by using intercalating organic solvent. This solvent-mediated removal of pentacene from graphene surface was investigated by both theoretical calculation and experimental studies with various solvents. The uses of pentacene and appropriate intercalation solvent enabled graphene transfer without forming a residue from the supporting layer. Such residues tend to cause charged impurity scattering and unintentional graphene doping effects. As a result, this clean graphene exhibited extremely homogeneous surface potential profiles over a large area. A field-effect transistor fabricated using this graphene displayed a high hole (electron) mobility of 8050 cm2/V·s (9940 cm2/V·s) with a nearly zero Dirac point voltage.
TL;DR: In this paper, the small-molecule organic semiconductor tetraceno[2,3-b]thiophene has been synthesized through an environmentally friendly synthetic route, utilizing NaBH4, rather than Al/HgCl2, for the reduction of the quinone.
Abstract: The small-molecule organic semiconductor tetraceno[2,3-b]thiophene has been synthesized through an environmentally friendly synthetic route, utilizing NaBH4, rather than Al/HgCl2, for the reduction of the quinone. Low-voltage organic thin-film transistors (TFTs) have been fabricated using tetraceno[2,3-b]thiophene and, for comparison, pentacene and anthradithiophene as the semiconductor. The tetraceno[2,3-b]thiophene TFTs have an effective field-effect mobility as large as 0.55 cm2 V–1 s–1 and a subthreshold swing of 0.13 V/decade. In addition, it has been found that the contact resistance of the tetraceno[2,3-b]thiophene TFTs is substantially smaller than that of the anthradithiophene TFTs and similar to that of the pentacene TFTs. The long-term air stability of TFTs based on all three semiconductors has been monitored over a period of 12 months. The initial charge-carrier mobility of the tetraceno[2,3-b]thiophene TFTs is ∼50% smaller than that of the pentacene TFTs, but as a result of the greater ioniza...
TL;DR: The combination of a clean graphene surface and a suitable underlying substrate could serve as an atomically thin growth template to engineer the interaction between organic molecules and aromatic graphene network, thereby paving the way for effectively and conveniently tuning the semiconductor layer morphologies in devices prepared using graphene.
Abstract: A two-dimensional epitaxial growth template for organic semiconductors was developed using a new method for transferring clean graphene sheets onto a substrate with controlled surface wettability. The introduction of a sacrificial graphene layer between a patterned polymeric supporting layer and a monolayer graphene sheet enabled the crack-free and residue-free transfer of free-standing monolayer graphene onto arbitrary substrates. The clean graphene template clearly induced the quasi-epitaxial growth of crystalline organic semiconductors with lying-down molecular orientation while maintaining the "wetting transparency", which allowed the transmission of the interaction between organic molecules and the underlying substrate. Consequently, the growth mode and corresponding morphology of the organic semiconductors on graphene templates exhibited distinctive dependence on the substrate hydrophobicity with clear transition from lateral to vertical growth mode on hydrophilic substrates, which originated from the high surface energy of the exposed crystallographic planes of the organic semiconductors on graphene. The optical properties of the pentacene layer, especially the diffusion of the exciton, also showed a strong dependency on the corresponding morphological evolution. Furthermore, the effect of pentacene-substrate interaction was systematically investigated by gradually increasing the number of graphene layers. These results suggested that the combination of a clean graphene surface and a suitable underlying substrate could serve as an atomically thin growth template to engineer the interaction between organic molecules and aromatic graphene network, thereby paving the way for effectively and conveniently tuning the semiconductor layer morphologies in devices prepared using graphene.
TL;DR: In this article, a simple surface treatment method is applied onto an ultrathin (<15 nm) organosilicon-based dielectric layer via the initiated chemical vapor deposition (iCVD) to make it compatible with organic semiconductors without degrading its insulating property.
Abstract: Tailoring the surface of the dielectric layer is of critical importance to form a good interface with the following channel layer for organic thin film transistors (OTFTs) Here, a simple surface treatment method is applied onto an ultrathin (<15 nm) organosilicon-based dielectric layer via the initiated chemical vapor deposition (iCVD) to make it compatible with organic semiconductors without degrading its insulating property A molecular-thin oxide capping layer is formed on a 15 nm thick poly(1,3,5-trimetyl-1,3,5-trivinyl cyclotrisiloxane) (pV3D3) by a brief oxygen plasma treatment The capping layer greatly enhances the thermal stability of the dielectrics, without degrading the original mechanical flexibility and insulating performance of the dielectrics Moreover, the surface silanol functionalities formed by the plasma treatment can also be utilized for the surface modification with silane compounds The surface-modified dielectrics are applied to fabricate low-voltage operating (<5 V) pentacene-based OTFTs The highest field-effect mobility of the device with the surface-treated 15 nm thick pV3D3 is 059 cm2 V−1 s−1, which is improved up to two times compared to the TFT with the pristine pV3D3 It is believed that the simple surface treatment method can widely extend the applicability of the highly robust, ultrathin, and flexible pV3D3 gate dielectrics to design the surface of the dielectrics to match well various kinds of organic semiconductors
TL;DR: It is reported that high-performance insulating films can be generated by judicious control over the microstructure of sol-gel-processed titanium dioxide (TiO2) films, typically known as wide-bandgap semiconductors.
Abstract: In this letter, we report that high-performance insulating films can be generated by judicious control over the microstructure of sol–gel-processed titanium dioxide (TiO2) films, typically known as wide-bandgap semiconductors. The resultant device made of 23 nm-thick TiO2 dielectric layer exhibits a low leakage current density of ∼1 × 10–7 A cm–2 at 2 V and a large areal capacitance of 560 nF cm–2 with the corresponding dielectric constant of 27. Finally, low-voltage flexible organic thin-film transistors were successfully demonstrated by incorporating this versatile solution-processed oxide dielectric material into pentacene transistors on polyimide substrates.
TL;DR: In this paper, copper electrodes fabricated with inkjet-printed nanoparticle inks are photonic sintered on a polymer dielectric layer and their application to source and drain electrodes in organic thin-film transistor (TFT).
TL;DR: It is found that the solid solutions of (1)x(2)1-x function as ambipolar semiconductors, whose hole and electron mobilities are tunable by varying the ratio of 1 and 2 in the solid solution.
Abstract: Here, we report solid solution of p- and n-type organic semiconductors as a new type of p–n blend for solution-processed ambipolar organic thin film transistors (OTFTs). This study compares the solid-solution films of silylethynylated tetraazapentacene 1 (acceptor) and silylethynylated pentacene 2 (donor) with the microphase-separated films of 1 and 3, a heptagon-embedded analogue of 2. It is found that the solid solutions of (1)x(2)1–x function as ambipolar semiconductors, whose hole and electron mobilities are tunable by varying the ratio of 1 and 2 in the solid solution. The OTFTs of (1)0.5(2)0.5 exhibit relatively balanced hole and electron mobilities comparable to the highest values as reported for ambipolar OTFTs of stoichiometric donor–acceptor cocrystals and microphase-separated p-n bulk heterojunctions. The solid solution of (1)0.5(2)0.5 and the microphase-separated blend of 1:3 (0.5:0.5) in OTFTs exhibit different responses to light in terms of absorption and photoeffect of OTFTs because the don...
TL;DR: In this article, the electronic properties and hole mobilities of picene and its isomer pentacene using the density functional theory and classical Marcus charge transfer theory were investigated, and it was shown that picene can exhibit maximum mobility up to 2.629 cm2 V−1 s−1 along the π-π stacking direction, while the highest mobility of pentacidene crystal exhibits along the herringbone stacking direction.
Abstract: We have investigated the electronic properties and hole mobilities of picene and its isomer pentacene using the density functional theory and classical Marcus charge transfer theory. In pristine crystal with herringbone structure, pentacene and picene have drift hole mobilities of 2.147 and 0.644 cm2 V–1 s–1, respectively, which are consistent with recent experimental results. We also show that picene crystal can exhibit maximum mobility up to 2.629 cm2 V–1 s–1 along the π–π stacking direction, while the highest mobility of pentacene crystal exhibits along the herringbone stacking direction. Also the anisotropy of the mobility in the ab plane is 2.4 and 5.6 for picene and pentacene crystals, respectively. Since the air stability of picene is better than pentacene due to lower HOMO levels in picene, we suggest that picene and its homologous phenacenes series are promising candidates toward high mobility organic semiconductor devices with good air stability. This work also sheds light on the favorable or un...
TL;DR: Time-resolved electron paramagnetic resonance experiments confirm that triplet quenching is accompanied by electron spin polarization transfer from the pentacene excited state to the TEMPO doublet state in the weak coupling regime.
Abstract: Understanding the fundamental spin dynamics of photoexcited pentacene derivatives is important in order to maximize their potential for optoelectronic applications. Herein, we report on the synthesis of two pentacene derivatives that are functionalized with the [(2,2,6,6-tetramethylpiperidin-1-yl)oxy] (TEMPO) stable free radical. The presence of TEMPO does not quench the pentacene singlet excited state, but does quench the photoexcited triplet excited state as a function of TEMPO-to-pentacene distance. Time-resolved electron paramagnetic resonance experiments confirm that triplet quenching is accompanied by electron spin polarization transfer from the pentacene excited state to the TEMPO doublet state in the weak coupling regime.
TL;DR: The MOG method, which has potential to be used in batch production and features easy control of crystal growth using non-contact forces, will benefit the development of low-cost, high-performance, organic semiconductor devices.
Abstract: We demonstrate a solution method of Marangoni effect-controlled oriented growth (MOG) to fabricate highly oriented crystals of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene) on the Si/SiO2 substrate. Based on the Marangoni effect induced by mixed solvent systems, large area aligned ribbon crystals can be achieved, covering over 60% on 4 cm × 1 cm Si/SiO2 substrates. We investigated the growth mechanism of the MOG method and found that the correct choice of solvents and appropriate solvent ratios are in favor of aligned crystal growth. With the ribbon crystals of TIPS pentacene, top-contact organic field-effect transistors are fabricated. The optimal device exhibits a field-effect mobility of 0.70 ± 0.22 cm2 V−1 s−1 and an on/off ratio of 105. The MOG method, which has potential to be used in batch production and features easy control of crystal growth using non-contact forces, will benefit the development of low-cost, high-performance, organic semiconductor devices.
TL;DR: The observed strained organic film growth on graphene demonstrates the possibility to tune molecular packing via graphene-molecule interactions and identifies a rare polymorph of pentacene crystal, which shows significant strain along the c-axis.
Abstract: Organic-graphene system has emerged as a new platform for various applications such as flexible organic photovoltaics and organic light emitting diodes. Due to its important implication in charge transport, the study and reliable control of molecular packing structures at the graphene-molecule interface are of great importance for successful incorporation of graphene in related organic devices. Here, an ideal membrane of suspended graphene as a molecular assembly template is utilized to investigate thin-film epitaxial behaviors. Using transmission electron microscopy, two distinct molecular packing structures of pentacene on graphene are found. One observed packing structure is similar to the well-known bulk-phase, which adapts a face-on molecular orientation on graphene substrate. On the other hand, a rare polymorph of pentacene crystal, which shows significant strain along the c-axis, is identified. In particular, the strained film exhibits a specific molecular orientation and a strong azimuthal correlation with underlying graphene. Through ab initio electronic structure calculations, including van der Waals interactions, the unusual polymorph is attributed to the strong graphene-pentacene interaction. The observed strained organic film growth on graphene demonstrates the possibility to tune molecular packing via graphene-molecule interactions.
TL;DR: The graphene/pentacene barristor with ion-gel gate dielectric can offer various flexible device applications with high performances and reveals ambipolar behaviors and related negative differential resistance, which are controlled by external bias.
Abstract: High-quality channel layer is required for next-generation flexible electronic devices. Graphene is a good candidate due to its high carrier mobility and unique ambipolar transport characteristics but typically shows a low on/off ratio caused by gapless band structure. Popularly investigated organic semiconductors, such as pentacene, suffer from poor carrier mobility. Here, we propose a graphene/pentacene channel layer with high-k ion-gel gate dielectric. The graphene/pentacene device shows both high on/off ratio and carrier mobility as well as excellent mechanical flexibility. Most importantly, it reveals ambipolar behaviors and related negative differential resistance, which are controlled by external bias. Therefore, our graphene/pentacene barristor with ion-gel gate dielectric can offer various flexible device applications with high performances.
TL;DR: In this paper, a self-assembled 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-Pentacene) thin films formed by simple spin-coating for the fabrication of high-performance solution-processed organic field effect transistors (OFETs) are reported.
Abstract: Here, a highly crystalline and self-assembled 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-Pentacene) thin films formed by simple spin-coating for the fabrication of high-performance solution-processed organic field-effect transistors (OFETs) are reported. Rather than using semiconducting organic small-molecule–insulating polymer blends for an active layer of an organic transistor, TIPS-Pentacene organic semiconductor is separately self-assembled on partially crosslinked poly-4-vinylphenol:poly(melamine-co-formaldehyde) (PVP:PMF) gate dielectric, which results in a vertically segregated semiconductor-dielectric film with millimeter-sized spherulite-crystalline morphology of TIPS-Pentacene. The structural and electrical properties of TIPS-Pentacene/PVP:PMF films have been studied using a combination of polarized optical microscopy, atomic force microscopy, 2D-grazing incidence wide-angle X-ray scattering, and secondary ion mass spectrometry. It is finally demonstrated a high-performance OFETs with a maximum hole mobility of 3.40 cm2 V−1 s−1 which is, to the best of our knowledge, one of the highest mobility values for TIPS-Pentacene OFETs fabricated using a conventional solution process. It is expected that this new deposition method would be applicable to other small molecular semiconductor–curable polymer gate dielectric systems for high-performance organic electronic applications.
TL;DR: In this paper, the authors investigated the effect of a small energy offset at the PEN/C60 heterojunction in tandem organic lighting-emitting diodes (TOLEDs).
TL;DR: In this article, the effects of humidity on the electrical characteristics of pentacene based thin-film transistors (pentacene-TFTs) in the linear and saturation regimes were investigated.
TL;DR: In this article, temperature-dependent transport studies have been carried out from pentacene-based OFETs using the ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) as a gate insulating layer.
Abstract: Ferroelectric dielectrics, permitting access to nearly an order of magnitude range of dielectric constants with temperature as the tuning parameter, offer a great platform to monitor the changes in interfacial transport in organic field-effect transistors (OFETs) as the polarization strength is tuned. Temperature-dependent transport studies have been carried out from pentacene-based OFETs using the ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) as a gate insulating layer. The thickness of the gate dielectric was varied from 20 nm to 500 nm. By fits to an Arrhenius-type dependence of the charge carrier mobility as a function of temperature, the activation energy in the ferroelectric phase is found to increase as the thickness of the PVDF-TrFE layer decreases. The weak temperature-dependence of the charge carrier mobility in the ferroelectric phase of PVDF-TrFE may be attributed to a polarization fluctuation driven transport, which results from a coupling of the charge ca...
TL;DR: Voltage-controlled current traces show a hysteresis characteristic of a bipolar switching behavior of the pentacene analogue anthradithiophene, supported by first-principles calculations.
Abstract: Single molecular switches are basic device elements in organic electronics. The pentacene analogue anthradithiophene (ADT) shows a fully reversible binary switching between different adsorption conformations on a metallic surface accompanied by a charge transfer. These transitions are activated locally in single molecules in a low-temperature scanning tunneling microscope . The switching induces changes between bistable orbital structures and energy level alignment at the interface. The most stable geometry, the "off" state, which all molecules adopt upon evaporation, corresponds to a short adsorption distance at which the electronic interactions of the acene rings bend the central part of the molecule toward the surface accompanied by a significant charge transfer from the metallic surface to the ADT molecules. This leads to a shift of the lowest unoccupied molecular orbital down to the Fermi level (EF). In the "on" state the molecule has a flat geometry at a larger distance from the surface; consequently the interaction is weaker, resulting in a negligible charge transfer with an orbital structure resembling the highest occupied molecular orbital when imaged close to EF. The potential barrier between these two states can be overcome reversibly by injecting charge carriers locally into individual molecules. Voltage-controlled current traces show a hysteresis characteristic of a bipolar switching behavior. The interpretation is supported by first-principles calculations.
TL;DR: In this article, a combined experimental and theoretical study was carried out to investigate the ambipolar charge transport properties of a series of N-heteropentacenes in organic field effect transistors (OFETs).
Abstract: A combined experimental and theoretical study was carried out to investigate the ambipolar charge transport properties of a series of N-heteropentacenes in organic field-effect transistors (OFETs). Introduction of nitrogen atoms in the core and halogen atoms around the periphery of the pentacene framework can efficiently tune the highest occupied molecular orbitals (HOMOs) of the N-heteropentacenes from −5.18 eV to −5.53 eV and the lowest unoccupied molecular orbitals (LUMOs) from −3.08 eV to −3.69 eV. By lowering their HOMO and LUMO energy levels with respect to the Fermi level of the gold electrode, the transistors of these molecules exhibited a transition from hole-dominant bipolar, to balanced ambipolar, and to electron-dominant bipolar transport characteristics. Meanwhile, with the lowering of the frontier molecular orbital energy levels, the transistors also exhibited a decrease of the electron threshold voltage and an increase of the hole threshold voltage. Charge carrier mobility calculations based on Marcus theory and first principle molecular dynamics were conducted to simulate the carrier transport dynamics. The comparison between experimental and theoretical results revealed that for the given device structure, the ratio of electron and hole mobilities of the ambipolar OFETs was strongly affected by the charge injection barrier. This result provides useful guidelines for future molecular design of ambipolar OFETs.