Showing papers on "Pentacene published in 2019"

Effect of Crystallization Modes in TIPS-pentacene/Insulating Polymer Blends on the Gas Sensing Properties of Organic Field-Effect Transistors

Abstract: Blending organic semiconductors with insulating polymers has been known to be an effective way to overcome the disadvantages of single-component organic semiconductors for high-performance organic field-effect transistors (OFETs). We show that when a solution processable organic semiconductor (6,13-bis(triisopropylsilylethynyl)pentacene, TIPS-pentacene) is blended with an insulating polymer (PS), morphological and structural characteristics of the blend films could be significantly influenced by the processing conditions like the spin coating time. Although vertical phase-separated structures (TIPS-pentacene-top/PS-bottom) were formed on the substrate regardless of the spin coating time, the spin time governed the growth mode of the TIPS-pentacene molecules that phase-separated and crystallized on the insulating polymer. Excess residual solvent in samples spun for a short duration induces a convective flow in the drying droplet, thereby leading to one-dimensional (1D) growth mode of TIPS-pentacene crystals. In contrast, after an appropriate spin-coating time, an optimum amount of the residual solvent in the film led to two-dimensional (2D) growth mode of TIPS-pentacene crystals. The 2D spherulites of TIPS-pentacene are extremely advantageous for improving the field-effect mobility of FETs compared to needle-like 1D structures, because of the high surface coverage of crystals with a unique continuous film structure. In addition, the porous structure observed in the 2D crystalline film allows gas molecules to easily penetrate into the channel region, thereby improving the gas sensing properties.

BN‐Embedded Tetrabenzopentacene: A Pentacene Derivative with Improved Stability

Abstract: Considerable efforts have been devoted to achieving stable acene derivatives for electronic applications; however, the instability is still a major issue for such derivatives. To achieve higher stability with minimum structural change, CC units in the acenes were replaced with isoelectronic BN units to produce a novel BN-embedded tetrabenzopentacene (BNTBP). BNTBP, with a planar structure, is highly stable to air, moisture, light, and heat. Compared with its carbon analogue tetrabenzopentacene (TBP), BN embedment lowered the highest occupied molecular orbital (HOMO) energy level of BNTBP, changed the orbital distribution, and decreased the HOMO orbital coefficients at the central carbon atoms, which stabilize BNTBP molecules upon exposure to oxygen and sunlight. The single-crystal microribbons of BNTBP exhibited good performance in field-effect transistors (FETs). The high stability and good mobility of BNTBP indicates that BN incorporation is an effective approach to afford stable large-sized acenes with desired properties.

Solution-Processed Nonvolatile Organic Transistor Memory Based on Semiconductor Blends.

Abstract: Solution-processed nonvolatile organic transistor memory devices are fabricated by employing semiconductor blends of p-channel 6,13-bis(triisopropylsilylethynyl)pentacene and n-channel poly{[ N, N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]- alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-2T); N2200) on polystyrene-brush as a polymer electret. Electret-based memory characteristics are significantly changed depending on the frontier molecular orbitals of the active semiconductors because the charge-trapping efficiency is mainly determined by the energy barrier to transfer electrons and holes from the active channel to the electret layer. A semiconductor mixture with an optimized blending ratio results in an efficient programming and erasing process. Thus, we obtained a remarkably high ratio of ON/OFF current (memory ratio) about 107 and a large amount of shifts in the threshold voltage (memory window) between the programmed and erased states of 55 V, while single-component N2200 showed only writing-once-read-many (WORM)-type memory. Especially, the programmed data can be stably retained more than 10 years with a sufficient memory ratio of 103. Furthermore, our semiconductor blend system leads to preferable vertical phase separation, which affords good reliability under a sequential memory operation condition as well as stability in ambient air. It is expected that our memory devices can be applied for versatile data storage in printed and flexible electronic applications.

Three-Dimensional Topological Insulator Bi2Te3/Organic Thin Film Heterojunction Photodetector with Fast and Wideband Response from 450 to 3500 Nanometers.

Abstract: In the pursuit of broadband photodetection materials from visible to mid-IR region, the fresh three-dimensional topological insulators (3D TIs) are theoretically predicted to be a promising candidate due to its Dirac-like stable surface state and high absorption rate. In this work, a self-powered inorganic/organic heterojunction photodetector based on n-type 3D TIs Bi2Te3 combined with p-type pentacene thin film was designed and fabricated. Surprisingly, it was found that the Bi2Te3/pentacene heterojunction photodetector exhibited a fast and wideband response from 450 to 3500 nm. The optimized responsivity of photodetector reached 14.89 A/W, along with the fast response time of 1.89 ms and the ultrahigh external quantum efficiency of 2840%. Moreover, at the mid-IR 3500 nm, our devices demonstrated a responsivity of 1.55 AW–1, which was several orders of magnitude higher than that of previous 3D TIs photodetector. These excellent properties indicate that the inorganic/organic heterojunction, that is, the c...

Sub-ppm and high response organic thin-film transistor NO2 sensor based on nanofibrillar structured TIPS-pentacene

Abstract: We investigated the effect of off-center spin coating process on the characteristics of organic thin-film transistors (OTFTs) based nitrogen dioxide (NO2) sensors. Different nanofibrillar structured directions were obtained through off-center spin coating which significantly improved the sensing property compared to that fabricated by the conventional on-center spin coating process. A remarkable enhancement of gas responsivity from 31.9% to 221.5% under 30 ppm NO2 was achieved by orthogonal off-center spin coating. While, device by parallel off-center spin coating showed an excellent sensitivity of 44.3% under ppb-level NO2 (250 ppb), and the response under 1 ppm also exhibited 35-fold increase. After a comprehensive analysis on the morphology properties of the organic films and electrical properties of devices, it was revealed that the multiform performance improvement was largely related to the nanofibrillar structured organic semiconductor (OSC) films facilitated by off-center spin coating, leading to a well-regulated change of potential barriers at grain boundaries. Compared to the common strategies, this work develops a simple, efficient and reliable access to obtain high performance solution-processed OTFT based gas sensors.

Davydov splitting and singlet fission in excitonically coupled pentacene dimers

Abstract: Singlet fission (SF) allows two charges to be generated from the absorption of a single photon and is, therefore, potentially transformative toward improving solar energy conversion. Key to the present study of SF is the design of pentacene dimers featuring a xanthene linker that strictly places two pentacene chromophores in a rigid arrangement and, in turn, enforces efficient, intramolecular π-overlap that mimics interactions typically found in condensed state (e.g., solids, films, etc.). Inter-chromophore communication ensures Davydov splitting, which plays an unprecedented role toward achieving SF in pentacene dimers. Transient absorption measurements document that intramolecular SF evolves upon excitation into the lower Davydov bands to form a correlated triplet pair at cryogenic temperature. At room temperature, the two spin-correlated triplets, one per pentacene moiety within the dimers, are electronically coupled to an excimer state. The presented results are transferable to a broad range of acene morphologies including aggregates, crystals, and films.

Review Article: Crystal alignment for high performance organic electronics devices

Abstract: Organic electronics devices based on high-performance small-molecule organic semiconductors have gained substantial attention because of their unique advantages such as excellent charge transport, solution processability, and environmental stability. However, the intrinsic crystallization of small-molecule organic semiconductors is anisotropic, resulting in significant device performance variations of organic electronics devices. In this article, the authors review the various approaches and techniques developed to control and align the crystallization of some benchmark solution-processable, high-performance, small-molecule organic semiconductors, such as 6,13-bis(triisopropylsilylethynyl) pentacene, N,N′-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide, and 5,11-bis(triethylgermylethynyl)anthradithiophene. These alignment approaches are studied in the context of capillary force-based techniques, patterning-based techniques, solution-shearing-based techniques, and other miscellaneous techniques, including zone-casting, vertical flowing, air flow navigation, temperature gradient alignment, etc. The organic semiconductors and crystal alignment techniques reviewed in this article shed light on important relationship among crystallization, charge transport, and device performance and can be applied to various high-performance organic electronics devices, such as organic thin film transistors and solar cells.

Synthesis of Unsymmetrical Derivatives of Pentacene for Materials Applications.

Abstract: Pentacene shows unique electronic properties that have long been appreciated and exploited. Over the past 20 years, new synthetic schemes have been developed to address some of the problems encountered with pristine pentacene (e.g., stability and solubility), and pentacene derivatives have become a mainstay in the realm of organic semiconductors in applications such as organic light-emitting diodes, organic field-effect transistors (OFETs), and organic photovoltaics. At the onset of our work, the vast majority of known pentacene derivatives featured a symmetrical structure, often as the result of synthetic protocols that rely on nucleophilic additions to 6,13-pentacenequinone (PQ). The assembly of pentacenes featuring an unsymmetrical framework held great appeal, but the stepwise formation of derivatives, in which a specific function might be incorporated through each individual addition step, did not exist. This Account presents contributions from our lab and others to the synthesis and study of unsymmetrical pentacene derivatives. PQ offers an ideal platform for desymmetrization through the sequential addition of nucleophiles to each of the two ketone groups. Addition can be completed in a one-pot protocol, or through individual steps in which the product of the first addition is isolated and used as a precursor in the divergent synthesis of a series of structurally related molecules. This general approach has been used to assemble pentacene derivatives appended with alkynyl/aryl/alkyl groups, polarized frameworks via substitution with donor and/or acceptor groups, and conjugated oligomers linked by butadiynyl moieties. Stepwise substitution also provides derivatives with remarkable functionality, including pentacene-porphyrin dyads, pendent TEMPO free radicals, cyanoacrylic acid anchor groups (for incorporation into dye-sensitized solar cells), and derivatives with ambipolar behavior for OFET devices. The study of intramolecular singlet fission (iSF) has emerged as one of the most fruitful applications of unsymmetrical pentacene derivatives. SF involves the spontaneous splitting of a photoexcited singlet state (S1) in one chromophore into a pair of triplets (T1) shared with a neighboring chromophore. Pentacene derivatives are particularly well suited for this since E(S1) ≥ 2E(T1) satisfies the thermodynamic requirements for SF, and they have the additional feature that two chromophores can be tethered together by a "spacer" that allows spectroscopic studies of iSF to be done in dilute solution. From a synthetic perspective, the major advantage of the dimeric structure is the ability to modify the spacer, which allows for control over the distance, geometric relationship, and electronic coupling between the two pentacene groups. Dimeric pentacenes are central to providing an in-depth understanding of the molecular mechanism of SF, often providing advances not possible from measurements in the solid state.

Synthesis and Characterization of Oxygen-Embedded Quinoidal Pentacene and Nonacene

Abstract: Extension of oxygen-embedded polycyclic aromatic hydrocarbons (PAHs), in particular with a defined topology, is synthetically challenging primarily because of limited regio-specific methods and poo...

Biodegradable Materials for Organic Field-Effect Transistors on a Paper Substrate

Abstract: Paper-basedpentacene organic thin-film transistors (OTFTs) with spin-coated gelatin (G) stacked gate dielectric layers, the Au/pentacene/G/G matrix-embedded iron (FeG)/Al/paper structure, were fabricated. The proposed composite-stacked bio-dielectric layer can be implemented using solutions with the degradable biomaterials. These materials enable a large-area printing of use-and-throw devices. Control devices (Au/pentacene/G/Al and Au/pentacene/FeG/Al structure) were also fabricated for comparison. High-performance paper-based OTFT constructed from the stacked gate dielectric layer exhibited a carrier mobility of 8 cm2/Vs, an ON/OFF current ratio of approximately 103, a subthreshold swing of 0.6 V/decade, and a threshold voltage of −1.4 V. These results are compatible to those OTFTs fabricated on other substrates. Therefore, the emerging biomaterial-based transistors on paper substrates may help in developing low-cost, environment-friendly devices.

Alternative Face-on Thin Film Structure of Pentacene.

Abstract: Pentacene attracts a great deal of attention as a basic material used in organic thin-film transistors for many years. Pentacene is known to form a highly ordered structure in a thin film, in which the molecular long axis aligns perpendicularly to the substrate surface, i.e., end-on orientation. On the other hand, the face-on oriented thin film, where the molecular plane is parallel to the substrate, has never been found on an inert substrate represented by SiO2. As a result, the face-on orientation has long been believed to be generated only on specific substrates such as a metal single crystal. In the present study, the face-on orientation grown on a SiO2 surface has first been identified by means of visible and infrared p-polarized multiple-angle incidence resolution spectrometry (pMAIRS) together with two-dimensional grazing incidence X-ray diffraction (2D-GIXD). The combination of the multiple techniques readily reveals that the face-on phase is definitely realized as the dominant component. The face-on film is obtained when the film growth is kinetically restricted to be prevented from transforming into the thermodynamically stable structure, i.e., the end-on orientation. This concept is useful for controlling the molecular orientation in general organic semiconductor thin films.

Polymer additive controlled morphology for high performance organic thin film transistors.

Abstract: Solution-crystallizable small-molecule organic semiconductors, such as 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene), 5,11-bis(triethylgermylethynyl)anthradithiophene (diF-TEG-ADT), 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT), and N,N′-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDIF-CN2), demonstrate various practical advantages including high mobility, air stability and solution processibility. In this article, we review various polymer additive based approaches to control the crystal morphology and the resultant charge transport of some bench-mark, high performance, solution crystallizable, small-molecule organic semiconductors. The polymer additives are discussed under the categories of non-conjugated polymers and conjugated polymers. The approaches and structure-performance correlations that we discussed here may be applied far beyond the examples shown in this review and have important implications for high performance organic semiconductors in general.

Spin density encodes intramolecular singlet exciton fission in pentacene dimers.

Abstract: The formation of two triplet excitons at the cost of one photon via singlet exciton fission in organic semiconductors can potentially enhance the photocurrent in photovoltaic devices. However, the role of spin density distribution in driving this photophysical process has been unclear until now. Here we present the significance of electronic spin density distribution in facilitating efficient intramolecular singlet exciton fission (iSEF) in π-bridged pentacene dimers. We synthetically modulate the spin density distribution in a series of pentacene dimers using phenyl-, thienyl- and selenyl- flanked diketopyrrolopyrrole (DPP) derivatives as π-bridges. Using femtosecond transient absorption spectroscopy, we find that efficient iSEF is only observed for the phenyl-derivative in ~2.4 ps while absent in the other two dimers. Electronic structure calculations reveal that phenyl-DPP bridge localizes α- and β-spin densities on distinct terminal pentacenes. Upon photoexcitation, a spin exchange mechanism enables iSEF from a singlet state which has an innate triplet pair character. Singlet exciton fission – the separation of photoexcited singlet states into two triplet states – holds promise for enhancing photocurrents in photovoltaic technologies. Krishnapriya et al. characterize how electron delocalization over the bridges in a series of pentacene dimers controls this process.

Crystallinity and grain boundary control of TIPS-pentacene in organic thin-film transistors for the ultra-high sensitive detection of NO2

Abstract: Herein, ultra-sensitive nitrogen dioxide (NO2) gas sensors based on 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) organic thin-film transistors (OTFTs) are reported. These sensors were fabricated by a simple solvent selection method that enabled crystallinity and grain boundary (GB) control and regulation; superior sensitivity of the sensors could be achieved using appropriate organic solvents to balance the crystallinity and density of the GBs in TIPS-pentacene films. o-Xylene was proved to be the best organic solvent for the optimization of the crystallinity and GB density in TIPS-pentacene films. The sensitivity of the sensors processed using o-xylene towards 10 ppm NO2 was more than 58 times that of the devices processed using the chlorobenzene solvent. Importantly, the limit of detection (LOD) of 1.93 ppb was achieved by our best NO2 sensors. A series of characterizations and tests, including morphology, crystal structure, and surface chemical group measurements, were carried out to illustrate the sensing mechanism. Moreover, the real-time sensing, reproducibility, selectivity, and low gate-voltage tests of these devices were conducted, and the results demonstrated that the selection of an appropriate solvent was essential to achieve high-performance gas sensors.

Spontaneous Generation of a Molecular Thin Hydrophobic Skin Layer on a Sub-20 nm, High-k Polymer Dielectric for Extremely Stable Organic Thin-Film Transistor Operation

Abstract: Polymer dielectric materials with hydroxyl functionalities such as poly(4-vinylphenol) and poly(vinyl alcohol) have been utilized widely in organic thin-film transistors (OTFTs) because of their ex...

A Compact Model and Parameter Extraction Method for a Staggered OFET With Power-Law Contact Resistance and Mobility

Abstract: We present a drain current model and a consistent parameter extraction method for organic field-effect transistors (OFETs) considering the gate voltage-dependent contact resistance and mobility by power-law. The physical origin of the asymptotic power-law dependence of contact resistance is elaborated based on the current crowding model. The parameters of a new model can be completely extracted without ambiguity by the proposed extraction method based on the linear fitting. Pentacene-based OFETs with the Au source/drain contact in a staggered configuration experimentally validate the proposed model and the extraction method, which further reveal the bulk resistivity as the major contribution to contact resistance.

Nonpentacene Polarizing Agents with Improved Air Stability for Triplet Dynamic Nuclear Polarization at Room Temperature.

Abstract: Triplet dynamic nuclear polarization (triplet-DNP), a method to enhance nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) sensitivity using photoexcited triplet electrons, has great potential to hyperpolarize nuclear spins at room temperature. Since the first report of room-temperature triplet-DNP in 1990, pentacene has been the only and best option of triplet polarizing agent. However, the poor air stability of pentacene has severely limited the applicability of triplet-DNP. We report the first example of polarizing agents with significant air stability as well as high polarizing ability comparable to pentacene. The introduction of electron-withdrawing diaza-substitution to pentacene and tetracene reduces the lowest unoccupied molecular orbital level and endows much improved stability under the ambient conditions. Importantly, the diaza-substituted pentacene and tetracene offer similar, or even slightly better, 1H NMR signal enhancement compared with pentacene in the prototypical trip...

Impact of Atomistic Substitution on Thin-Film Structure and Charge Transport in a Germanyl-ethynyl Functionalized Pentacene

Abstract: Functionalization of organic semiconductors through the attachment of bulky side groups to the conjugated core has imparted solution processability to this class of otherwise insoluble materials. A consequence of this functionalization is that the bulky side groups impact the solid-state packing of these materials. To examine the importance of side-group electronic character on accessing the structural phase space of functionalized materials, germanium was substituted for silicon in triisopropylsilylethynylpentacene (TIPS-Pn) to produce triisopropylgermanylethynylpentacene (TIPGe-Pn), with the TIPGe side group comparable in size to TIPS, but higher in electron density. We find TIPGe-Pn single crystals exhibit slip-stack, herringbone, and brickwork packing motifs depending on growth conditions, a stark contrast to TIPS-Pn, which accesses only the brickwork packing motif in both single crystals and thin films. Polycrystalline thin films of TIPGe-Pn exhibit two new, unidentified polymorphs from spin-coating ...

UV-sensing organic phototransistor memory devices with a doped organic polymer electret composed of triphenylamine-based aggregation-induced emission luminogens

Abstract: This paper reports a UV-sensing organic field-effect phototransistor with a stacked pentacene channel and a doped aggregation-enhanced emission (AIE)-fluorescent electret for potential applications, such as photomemory storage and photodetectors. It is found that the emission of the photoirradiated doped electret (PA-SMX and PI-SMX) layer can be manipulated at various doping levels, which can be further absorbed by the photoactive pentacene channel. These photogenerated excitons can be separated, and the electrons can be trapped into the electret layer in the presence of gate voltage bias. Therefore, the photoinduced programming and electric field-driven erasing effects of the designed memory device based on doped electrets exhibit optimal photomemory performance with a memory window (MW) of 37.2 V and a reliable retention time over 10 000 s with good cyclic endurance. The photodetection can also be modulated by the illumination power intensity, which reflects a photosensitivity (S) of 1.92 × 106 and a photoresponsivity (R) of 45 A W−1 for organic phototransistors with the PI-SM5 doped electret at a photoexcitation intensity of 720 μW cm−2 at 365 nm. The photoresponse following the change in the threshold voltage and photocurrent correlate well with the spectroscopic results and provide further understanding and optimization of organic phototransistor memory devices.

Self-assembly crystal microribbons with nucleation additive for high-performance organic thin film transistors

Abstract: We demonstrate fabrication of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) crystal microribbon based organic thin film transistors (OTFTs) with a solvent exchange method and the addition of a nucleation agent. TIPS pentacene crystals were formed via self-assembly as a result of solubility difference between the double solvents. At the same time, 4-hexylbenzoic acid (HBA) was added as a nucleation agent and formed an interfacial layer on the silicon dioxide gate dielectrics, which dispersed the aggregated crystals and enhanced its morphology uniformity. TIPS pentacene crystal microribbon based OTFTs with HBA nucleation additive showed a hole mobility of up to 0.36 cm2 V−1 s−1, and particularly, a 9-fold enhancement in average mobilities, as compared to pristine crystal based OTFTs. The remarkable enhancement in device performance can be attributed to the improved crystallinity, reduced defects and charge trap centers located at the grain boundaries, and controlled crystallization and dispersion effect due to the addition of the HBA nucleation agent.

Controlling the Efficiency of Singlet Fission in TIPS-Pentacene/Polymer Composite Nanoparticles

Abstract: Singlet fission (SF) is a process with the potential to increase the efficiency of solar cells by reducing losses from thermal relaxation of hot carriers. By generating two triplet excitons from one singlet exciton, the process effectively splits the energy of high-energy photons into two, providing a means to circumvent the Shockley–Queisser limit. Although the applications of SF are promising, questions remain about the mechanistic details and practicalities of implementation in photovoltaic devices that must be resolved to exploit its full potential. In this study, we present a way to investigate the effect of average intermolecular distance on SF by embedding 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pn) in an amorphous polymer matrix in the form of aqueous nanoparticle dispersions. By controlling the mass ratio of TIPS-Pn to the host polymer, we systematically tune the concentration of TIPS-Pn molecules in a nanoparticle and in turn, the average intermolecular separation, leading to a range o...

Singlet exciton fission via an intermolecular charge transfer state in coevaporated pentacene-perfluoropentacene thin films

Abstract: Singlet exciton fission is a spin-allowed process in organic semiconductors by which one absorbed photon generates two triplet excitons. Theory predicts that singlet fission is mediated by intermolecular charge-transfer states in solid-state materials with appropriate singlet-triplet energy spacing, but direct evidence for the involvement of such states in the process has not been provided yet. Here, we report on the observation of subpicosecond singlet fission in mixed films of pentacene and perfluoropentacene. By combining transient spectroscopy measurements to nonadiabatic quantum-dynamics simulations, we show that direct excitation in the charge-transfer absorption band of the mixed films leads to the formation of triplet excitons, unambiguously proving that they act as intermediate states in the fission process.

Photoinduced Carrier Dynamics at the Interface of Pentacene and Molybdenum Disulfide.

Abstract: Understanding of photoinduced interfacial carrier dynamics in organic-transition metal dichalcogenides heterostructures is very important for the enhancement of their potential photoelectronic conv...

Coexisting Charge States in a Unary Organic Monolayer Film on a Metal.

Abstract: The electronic and geometric structures of tetracene films on Ag(110) and Cu(110) have been studied with photoemission tomography and compared to that of pentacene. Despite similar energy level alignment of the two oligoacenes on these surfaces revealed by conventional ultraviolet photoelectron spectroscopy, the momentum-space resolved photoemission tomography reveals a significant difference in both structural and electronic properties of tetracene and pentacene films. Particularly, the saturated monolayer of tetracene on Ag(110) is found to consist of two molecular species that, despite having the same orientation, are electronically very different-while one molecule remains neutral, another is charged because of electron donation from the substrate.

Long-range crystal alignment with polymer additive for organic thin film transistors

Abstract: In this work, we study for the first time the effect of a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer to control the crystal growth of solution-processed, small-molecule organic semiconductors and to improve the device performance of organic thin film transistors (OTFTs). A benchmark semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was employed to blend with the polymer additive. The TIPS pentacene blend film with 5% PVDF-HFP by weight ratio exhibited a significant morphology enhancement with crystals strictly aligned in long-range order. In particular, it showed an average grain width of 69.98 μm and a misorientation angle of 6.6°, which is a 3.5-fold increase and a 7-fold reduction as compared to the pristine TIPS pentacene film. The bottom-gate, top-contact TIPS pentacene OTFTs with PVDF-HFP polymer additive were fabricated. Electrical characterization showed a hole mobility of up to 0.1 cm2/Vs with 5% PVDF-HFP. The performance improvement of TIPS pentacene/PVDF-HFP based OTFTs can be attributed to the reduced amount of charge trap centers at the enlarged grain width, alleviated crystal misorientation and increased areal coverage. This facile approach to blend PVDF-HFP additive to align crystals and improve orientation in long-range order as demonstrated in this work can be useful for controlling the crystallization and charge transport of other small-molecule organic semiconductors for application in organic electronics on large-scale flexible substrate.

Tailored Plasmons in Pentacene/Graphene Heterostructures with Interlayer Electron Transfer.

Abstract: van der Waals (vdW) heterostructures, which are produced by the precise assemblies of varieties of two-dimensional (2D) materials, have demonstrated many novel properties and functionalities. Here ...

A Pentacene-based Nanotube Displaying Enriched Electrochemical and Photochemical Activities.

Abstract: Unlike previously well-studied, acyclic pentacene oligomers, the first synthesis of a cyclic pentacene trimer with a fixed tubular conformation is reported. A short-step synthesis starting from common pentacenequinone yielded the target molecule with a 1.5 nanometer length and a subnanometer pore. Steady-state spectroscopic analyses revealed that the close proximity of the non-conjugated, three pentacene chromophores allows the nanotube to display stepwise electrochemical/chemical oxidation characteristics. Furthermore, time-resolved transient absorption measurements elucidated the generation of an excited triplet state of the nanotube, with high quantum yield reaching about 180 % through intramolecular singlet fission and a very long triplet lifetime.

Small-molecule additives for organic thin film transistors

Abstract: Although much research progress has recently been achieved in solution-soluble, small-molecule, organic semiconductors, their randomly oriented crystals still remain as an issue that leads to nonuniform charge transport and severely degrades performance consistency of organic thin film transistors (OTFTs). In the paper, we reviewed the various small-molecule additives that have been reported to blend with these semiconductors in order to reduce their crystal misorientation and mobility variations of OTFTs. By mainly studying the examples of a representative small-molecule organic semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene, we intend to disclose the important effects of the various additives on controlling the semiconductor crystallization, film morphology, and charge transport. This work can be facilely employed to align the crystal orientation and tweak the electrical performance of newly discovered small-molecule organic semiconductors, and will provide an in-depth understanding of the important application in high-performance, solution-based, large-area organic electronics devices.