Highly Crystalline C8-BTBT Thin-Film Transistors by Lateral Homo-Epitaxial Growth on Printed Templates

Exploring the phase behavior of C8-BTBT-C8 at ambient and high temperatures: insights and challenges from molecular dynamics simulations

C8-BTBT-C8 is one promising candidate for the development of high-performance electronic devices based on thin-film technologies. Its monoclinic polymorph has a well-established role in thin-film growth. Yet, quite little information is available about its dynamics on the molecular scale, and the structures of the mesophases which form at high temperature (about 100 K above ambient temperature). The present study is devoted to the analysis of such phases, with the ultimate goal of developing molecular models. Already at ambient temperature, our molecular dynamics simulations reveal a rich conformational behavior of the alkyl side chains, with gauche conformations as leading structural defects. Heating promotes the formation of a stacking faulted mesophase (380 K), and a smectic phase, at 385 K, upon side chain melting. Although more disordered, this phase bears several analogies with the smectic A phase, experimentally observed at 382.5 K. At higher temperatures, the increase in configurational disorder is brought by molecular diffusion and other phenomena, finally leading to an isotropic molten phase. Our in-depth analysis, complemented by hot-stage polarizing microscopy data, provides interesting insights into this material, highlighting the challenges associated with the modeling of soft semiconducting systems.

High Sensitive and Stable UV-Vis Photodetector Based on MoS2/MoO3 vdW Heterojunction

The development of new high-performance photodetectors (PDs) is currently focused on achieving small size, low power consumption, low cost, and large bandwidth. Two-dimensional (2D) materials and heterostructures offer promising approaches for the future development of optoelectronic devices. However, there has been limited research on 2D wide-bandgap semiconductor heterostructures. In this study, we successfully constructed a MoS2/MoO3 vdW heterojunction PD. This PD exhibited excellent response and significant photovoltaic behavior in the ultraviolet (UV) to visible (Vis) range. Under 365 nm UV light and 1 V bias voltage, the PD demonstrated a high responsivity of 645 mA/W, a high specific detectivity of 8.98 × 1010 Jones, and fast response speeds of 55.9/59.6 ms. At 0 V bias voltage, the responsivity reached as high as 157 mA/W. Furthermore, the PD exhibited remarkable stability in its performance. These outstanding characteristics can be attributed to the strong internal electric field created by the type II heterojunction structure and the chemical stability of the materials. This work opens a route for the application of 2D wide-bandgap semiconductor materials in optoelectronic devices.

Breaking Fundamental Limitation of Flow-Induced Anisotropic Growth for Large-Scale and Fast Printing of Organic Single-Crystal Films

Advanced organic electronic technologies have put forward a pressing demand for cost-effective and high-throughput fabrication of organic single-crystal films (OSCFs). However, solution-printed OSCFs are typically plagued by the existence of abundant structural defects, which pose a formidable challenge to achieving large-scale and high-performance organic electronics. Here, it is elucidated that these structural defects are mainly originated from printing flow-induced anisotropic growth, an important factor that is overlooked for too long. In light of this, a surfactant-additive printing method is proposed to effectively overcome the anisotropic growth, enabling the deposition of uniform OSCFs over the wafer scale at a high speed of 1.2 mm s-1 at room temperature. The resulting OSCF exhibits appealing performance with a high average mobility up to 10.7 cm2 V-1 s-1, which is one of the highest values for flexible organic field-effect transistor arrays. Moreover, large-scale OSCF-based flexible logic circuits, which can be bent without degradation to a radius as small as 4.0 mm and over 1000 cycles are realized. The work provides profound insights into breaking the limitation of flow-induced anisotropic growth and opens new avenues for printing large-scale organic single-crystal electronics.

A Review on the Synthetic Methods towards Benzothienobenzothiophenes

Benzothienobenzothiophenes (BTBTs) are a class of heteroacenes for which two distinct isomers have been identified depending on the locations of the fused benzothiophene motifs. Benzothienobenzothiophenes represent a class of heteroacenes demonstrating remarkable electronic properties that make them prominent in the realm of organic semiconductors. The structure of BTBTs, incorporating two sulfur atoms, contributes to their unique electronic characteristics, including narrow bandgaps and effective charge transport pathways. These compounds have gained attention for their high charge carrier mobility, making them desirable candidates for application in organic field-effect transistors (OFETs) and other electronic devices. Researchers have explored various synthetic strategies to design and tailor the properties of BTBT derivatives, leading to advancements in the development of high-performance organic semiconductors. Various synthetic techniques for benzothienobenzothiophenes have been reported in the literature including multistep synthesis, tandem transformations, electrochemical synthesis, and annulations. This review investigates the generality of each synthetic methodology by highlighting its benefits and drawbacks, and it analyses all synthetic approaches described for the creation of the two isomers. For the advantage of the readers, we have delved upon every mechanism of the reactions that are known. Finally, we have also summarized the synthetic methodologies that are used for making benzothienobenzothiophene analogues for material applications.

Demonstration of p-type stack-channel ternary logic device using scalable DNTT patterning process

A p-type ternary logic device with a stack-channel structure is demonstrated using an organic p-type semiconductor, dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT). A photolithography-based patterning process is developed to fabricate scaled electronic devices with complex organic semiconductor channel structures. Two layers of thin DNTT with a separation layer are fabricated via the low-temperature deposition process, and for the first time, p-type ternary logic switching characteristics exhibiting zero differential conductance in the intermediate current state are demonstrated. The stability of the DNTT stack-channel ternary logic switch device is confirmed by implementing a resistive-load ternary logic inverter circuit.

Exploring the Preparation Dependence of Crystalline 2D-Extended Ultrathin C8-BTBT-C8 Films

Crystalline organic semiconducting thin films from the benchmark molecule C8-BTBT-C8 were obtained using physical vapor deposition and various solution-based methods. Utilizing atomic force microscopy and X-ray spectromicroscopy, we illustrate the influence of the underlying growth mechanism and determine the highly preparation-dependent orientation of the thiophene backbone. We observe a continuous trend for crystalline C8-BTBT-C8 thin film domains to extend into the square millimeter-range under near-equilibrium growth conditions. For such well-defined systems, electron diffraction tomography allows us to precisely determine the unit cell directly after film deposition and to reveal an 8° molecular tilt angle with respect to the surface normal. This finding is in almost perfect accordance with the values derived from near-edge X-ray absorption fine structure linear dichroism. Within this work, we shine a light on both the successes and challenges connected to the realization of potent, thiophene-based semiconducting films, paving the way toward square centimeter-sized ultrathin organic crystals and their application in organic circuitry.

Scalable Growth of Organic Single-Crystal Films via an Orientation Filter Funnel for High-Performance Transistors with Excellent Uniformity

Organic single-crystal films (OSCFs) provide an unprecedented opportunity for the development of new-generation organic single-crystal electronics. However, crystallization of organic films is normally governed by stochastic nucleation and incoherent growth, posing a formidable challenge to grow large-sized OSCFs. Here, an "orientation filter funnel" concept is presented for the scalable growth of OSCFs with well-aligned, singly orientated crystals. By rationally designing solvent wetting/dewetting patterns on the substrate, this approach can produce seed crystals with the same crystallographic orientation and then maintain epitaxial growth of these crystals, enabling the formation of large-area OSCFs. As a result, this unique concept for crystal growth not only enhances the average mobility of organic film by 4.5-fold but also improves its uniformity of electrical properties, with a low mobility variable coefficient of 9.8%, the new lowest record among organic devices. The method offers a general and scalable route to produce OSCFs toward real-word electronic applications.

Ruddlesden-Popper-Phase Hybrid Halide Perovskite/Small-Molecule Organic Blend Memory Transistors

Controlling the morphology of metal halide perovskite layers during processing is critical for the manufacturing of optoelectronics. Here, a strategy to control the microstructure of solution-processed layered Ruddlesden-Popper-phase perovskite films based on phenethylammonium lead bromide ((PEA)₂ PbBr₄ ) is reported. The method relies on the addition of the organic semiconductor 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene (C₈ -BTBT) into the perovskite formulation, where it facilitates the formation of large, near-single-crystalline-quality platelet-like (PEA)₂ PbBr₄ domains overlaid by a ≈5-nm-thin C₈ -BTBT layer. Transistors with (PEA)₂ PbBr₄ /C₈ -BTBT channels exhibit an unexpectedly large hysteresis window between forward and return bias sweeps. Material and device analysis combined with theoretical calculations suggest that the C₈ -BTBT-rich phase acts as the hole-transporting channel, while the quantum wells in (PEA)₂ PbBr₄ act as the charge storage element where carriers from the channel are injected, stored, or extracted via tunneling. When tested as a non-volatile memory, the devices exhibit a record memory window (>180 V), a high erase/write channel current ratio (10⁴ ), good data retention, and high endurance (>10⁴ cycles). The results here highlight a new memory device concept for application in large-area electronics, while the growth technique can potentially be exploited for the development of other optoelectronic devices including solar cells, photodetectors, and light-emitting diodes.

Water-Surface Drag Coating: A New Route Toward High-Quality Conjugated Small-Molecule Thin Films with Enhanced Charge Transport Properties

Electronic properties of organic semiconductor (OSC) thin films are largely determined by their morphologies and crystallinities. However, solution-processed conjugated small-molecule OSC thin films usually exhibit abundant grain boundaries and impure grain orientations because of complex fluid dynamics during solution coating. Here, a novel methodology, water-surface drag coating, is demonstrated to fabricate high-quality OSC thin films with greatly enhanced charge transport properties. This method utilizes the water surface to alter the evaporation dynamics of solution to enlarge the grain size, and a unique drag-coating process to achieve the unidirectional growth of organic crystals. Using 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (Dif-TES-ADT) as an example, thin films with millimeter-sized single-crystal domains and pure crystallographic orientations are achieved, revealing a significant enhancement (4.7 times) of carrier mobility. More importantly, the resulting film can be directly transferred onto any desired flexible substrates, and flexible transistors based on the Dif-TES-ADT thin films show a mobility as high as 16.1 cm² V^-1 s^-1 , which represents the highest mobility value for the flexible transistors reported thus far. The method is general for the growth of various high-quality OSC thin films, thus opening up opportunities for high-performance organic flexible electronics.

Cold Crystallization of the Organic n-Type Small Molecule Semiconductor 2-Decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene S,S,S',S'-Tetraoxide

The asymmetric n-type Ph-BTBT-C₁₀ derivative 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene S,S,S',S'-tetraoxide is structurally investigated in the thin film regime. After film preparation by spin coating and physical vapor deposition, a rather disordered structure is observed, with a strong change of its internal degree of order upon heating. At 95 °C, a transition into a layered structure of upright standing molecules without any in-plane order appears, and at 135 °C, crystallization takes place. This phase information is combined with surface morphological studies and charge carrier mobility measurements to describe the structure and thin film transistor applicability of this molecule.

Effectively modulating thermal activated charge transport in organic semiconductors by precise potential barrier engineering

The temperature dependence of charge transport dramatically affects and even determines the properties and applications of organic semiconductors, but is challenging to effectively modulate. Here, we develop a strategy to circumvent this challenge through precisely tuning the effective height of the potential barrier of the grain boundary (i.e., potential barrier engineering). This strategy shows that the charge transport exhibits strong temperature dependence when effective potential barrier height reaches maximum at a grain size near to twice the Debye length, and that larger or smaller grain sizes both reduce effective potential barrier height, rendering devices relatively thermostable. Significantly, through this strategy a traditional thermo-stable organic semiconductor (dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene, DNTT) achieves a high thermo-sensitivity (relative current change) of 155, which is far larger than what is expected from a standard thermally-activated carrier transport. As demonstrations, we show that thermo-sensitive OFETs perform as highly sensitive temperature sensors.

Controlling temperature-depending charge transport in organic semiconductors is key to tailoring their electronic properties. Here, the authors report a potential barrier engineering strategy for modulating thermally-activated charge transport in organic semiconductors.

Immobilizing a π-Conjugated Catecholato Framework on Surfaces of SiO2 Insulator Films via a One-Atom Anchor of a Platinum Metal Center to Modulate Organic Transistor Performance

Chemical modification of insulating material surfaces is an important methodology to improve the performance of organic field-effect transistors (OFETs). However, few redox-active self-assembled monolayers (SAMs) have been constructed on gate insulator film surfaces, in contrast to the numerous SAMs formed on many types of conducting electrodes. In this study, we report a new approach to introduce a π-conjugated organic fragment in close proximity to an insulating material surface via a transition metal center acting as a one-atom anchor. On the basis of the reported coordination chemistry of a catecholato complex of Pt(II) in solution, we demonstrate that ligand exchange can occur on an insulating material surface, affording SAMs on the SiO₂ surface derived from a newly synthesized Pt(II) complex containing a benzothienobenzothiophene (BTBT) framework in the catecholato ligand. The resultant SAMs were characterized in detail by water contact angle measurements, X-ray photoelectron spectroscopy, atomic force microscopy, and cyclic voltammetry. The SAMs served as good scaffolds of π-conjugated pillars for forming thin films of a well-known organic semiconductor C8-BTBT (2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene), accompanied by the engagements of the C8-BTBT molecules with the SAMs containing the common BTBT framework at the first layer on SiO₂. OFETs containing the SAMs displayed improved performance in terms of hole mobility and onset voltage, presumably because of the unique interfacial structure between the organic semiconducting and inorganic insulating layers. These findings provide important insight into creating new elaborate interfaces through installing coordination chemistry in solution to solid surfaces, as well as OFET design by considering the compatibility between SAMs and organic semiconductors.

Nanocluster-Based Ultralow-Temperature Driven Oxide Gate Dielectrics for High-Performance Organic Electronic Devices

The development of novel dielectric materials with reliable dielectric properties and low-temperature processibility is crucial to manufacturing flexible and high-performance organic thin-film transistors (OTFTs) for next-generation roll-to-roll organic electronics. Here, we investigate the solution-based fabrication of high-k aluminum oxide (Al₂O₃) thin films for high-performance OTFTs. Nanocluster-based Al₂O₃ films fabricated by highly energetic photochemical activation, which allows low-temperature processing, are compared to the conventional nitrate-based Al₂O₃ films. A wide array of spectroscopic and surface analyses show that ultralow-temperature photochemical activation (<60 °C) induces the decomposition of chemical impurities and causes the densification of the metal-oxide film, resulting in a highly dense high-k Al₂O₃ dielectric layer from Al-13 nanocluster-based solutions. The fabricated nanocluster-based Al₂O₃ films exhibit a low leakage current density (<10⁻⁷ A/cm²) at 2 MV/cm and high dielectric breakdown strength (>6 MV/cm). Using this dielectric layer, precisely aligned microrod-shaped 2,7-dioctyl[1]benzothieno [3,2-b][1] benzothiophene (C8-BTBT) single-crystal OTFTs were fabricated via solvent vapor annealing and photochemical patterning of the sacrificial layer.

van der Waals Epitaxy of Soft Twisted Bilayers: Lattice Relaxation and Mass Density Waves

Interfaces comprising incommensurate or twisted hexagonal lattices are ubiquitous and of great interest, from adsorbed organic/inorganic interfaces in electronic devices, to superlubricants, and more recently to van der Waals bilayer heterostructures (vdWHs) of graphene and other 2D materials that demonstrate a range of properties such as superconductivity and ferromagnetism. Here we show how growth of 2D crystalline domains of soft block copolymers (BCPs) on patterned hard hexagonal lattices provide fundamental insights into van der Waals heteroepitaxy. At moderate registration forces, it is experimentally found that these BCP-hard lattice vdWHs do not adopt a simple moiré superstructure, but instead adopt local structural relaxations known as mass density waves (MDWs). Simulations reveal that MDWs are a primary mechanism of energy minimization and are the origin of the observed preferential twist angle between the lattices.

Ferrocene on Insulator: Silane Coupling to a SiO2 Surface and Influence on Electrical Transport at a Buried Interface with an Organic Semiconductor Layer

A silane coupling-based procedure for decoration of an insulator surface containing abundant hydroxy groups by constructing redox-active self-assembled monolayers (SAMs) is described. A newly synthesized ferrocene (Fc) derivative containing a triethoxysilyl group designated FcSi was immobilized on SiO₂/Si by a simple operation that involved immersing the substrate in a toluene solution of the Fc silane coupling reagent and then rinsing the resulting substrate. X-ray photoelectron spectroscopy (XPS) measurements confirmed that the Fc group was immobilized on SiO₂/Si in the Fe(II) state. Cyclic voltammetry measurements showed that the Fc groups were electrically insulated from the Si electrode by the SiO₂ layer. The FcSi on SiO₂/Si structures were found to serve as a good scaffold for formation of organic semiconductor thin films by vacuum thermal evaporation of C8-BTBT (2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene), which is well-known as an organic field-effect transistor (OFET) material. The X-ray diffraction profile indicated that the conventional standing-up conformation of the C8-BTBT molecules perpendicular to the substrates was maintained in the thin films formed on FcSi@SiO₂/Si. Further vacuum thermal evaporation of Au provided an FcSi-based OFET structure with good transfer characteristics. The FcSi-based OFET showed pronounced source-drain current hysteresis between the forward and backward scans. The degree of this hysteresis was varied reversibly via gate bias manipulation, which was presumably accompanied by trapping and detrapping of hole carriers at the Fc-decorated SiO₂ surface. These findings provide new insights into application of redox-active SAMs to nonvolatile OFET memories while also creating new interfaces through junctions with functional thin films, in which the underlying redox-active SAMs play supporting roles.

Regioisomeric control of layered crystallinity in solution-processable organic semiconductors

The construction and control of 2D layered molecular packing motifs with functionally substituted π-electron cores are crucial for developing organic electronic materials and devices. We investigated a regioisomeric structure–property relationship in high-performance and solution-processable layered organic semiconductors based on mono-octyl-substituted benzothieno[3,2-b]naphtho[2,3-b]thiophene (mono-C8-BTNT). We demonstrated that an isomorphous bilayer-type layered herringbone packing motif is obtainable in a series of four positional isomers of mono-C8-BTNTs whose π-electron core is substituted by an octyl chain at one of the four most peripheral positions with roughly keeping the rod-like molecular shape. These regioisomeric compounds exhibited systematic variations in the solvent solubility and liquid-crystalline phase transitions at elevated temperatures. The analysis of intermolecular interaction energies in the crystals based on dispersion-corrected DFT calculations revealed that the crystals of 2- and 8-mono-C8-BTNTs are more stable than those of 3- and 9-mono-C8-BTNTs owing to the higher ordering of alkyl chain layers in the crystals. Such differences of the stability in their crystal formation are closely correlated with TFT performances, where the single-crystal devices of the 2- and 8-mono-C8-BTNTs substituted at the most peripheral positions exhibit high-performance TFT characteristics with a mobility of approximately 10 cm² V⁻¹ s⁻¹.

An isomorphous bilayer-type layered herringbone crystal packing is reported for a series of four positional isomers of mono-C8-BTNTs, where the single-crystal devices with the isomers exhibit high-performance TFT characteristics.

Large-scale patterning of π-conjugated materials by meniscus guided coating methods

Printed organic electronics has attracted considerable interest in recent years as it enables the fabrication of large-scale, low-cost electronic devices, and thus offers significant possibilities in terms of developing new applications in various fields. Easy processing is a prerequisite for the development of low-cost, flexible and printed plastics electronics. Among processing techniques, meniscus guided coating methods are considered simple, efficient, and low-cost methods to fabricate electronic devices in industry. One of the major challenges is the control of thin film morphology, molecular orientations and directional alignment of polymer films during coating processes. Herein, the recent progress of emerging field of meniscus guided printing organic semiconductor materials is discussed. The first part of this report briefly summarizes recent advances in meniscus guided coating techniques. The second part discusses periodic deposits and patterned deposition at moving contact lines, where the mass-transport influences film morphology due to convection at the triple contact line. The last section summarizes our strategy to fabricate large-scale patterning of π-conjugated polymers using meniscus guided method.

All-inorganic perovskite CsPbBr3 microstructures growth via chemical vapor deposition for high-performance photodetectors

Perovskite cesium lead halide (CsPbBr₃) has attracted considerable attention due to its excellent optoelectronic properties and superior stability against moisture, oxygen, light, and heat. In this work, the micro-environment controlled chemical vapor deposition (CVD) method has been adopted to synthesize high-quality single-crystalline CsPbBr₃ microstructures, including microwires, microplates and triangular pyramids. Moreover, the structure-activity relationship between the material microstructures and the device properties is illustrated. The results show that photodetectors based on a single horizontal CsPbBr₃ microwire exhibit a high responsivity (312.2 A W^-1) and a fast response time of 5.8 ms. Photodetectors based on a single CsPbBr₃ microplate exhibit a responsivity of 1.74 A W^-1 and a response of 10 ms. These results indicate that the CsPbBr₃ microwire photodetector is characterized by a higher photodetector performance when compared to the microplate due to its excellent crystallization quality and the Fabry-Pérot cavity effect in the microwire. Furthermore, the flexible CsPbBr₃ microwire photodetector was demonstrated on a mica substrate. The results show that the photocurrent can be maintained at 90% after 3000 cycles at a bending radius of 2.5 mm. This work demonstrates the structure-activity photodetector performance, which is essential to develop a full understanding about high-performance optoelectronic devices based on all-inorganic lead halide perovskite materials.

Field-Effect Transistors Based on 2D Organic Semiconductors Developed by a Hybrid Deposition Method

Solution-processed 2D organic semiconductors (OSCs) have drawn considerable attention because of their novel applications from flexible optoelectronics to biosensors. However, obtaining well-oriented sheets of 2D organic materials with low defect density still poses a challenge. Here, a highly crystallized 2,9-didecyldinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (C10-DNTT) monolayer crystal with large-area uniformity is obtained by an ultraslow shearing (USS) method and its growth pattern shows a kinetic Wulff's construction supported by theoretical calculations of surface energies. The resulting seamless and highly crystalline monolayers are then used as templates for thermally depositing another C10-DNTT ultrathin top-up film. The organic thin films deposited by this hybrid approach show an interesting coherence structure with a copied molecular orientation of the templating crystal. The organic field-effect transistors developed by these hybrid C10-DNTT films exhibit improved carrier mobility of 14.7 cm2 V-1 s-1 as compared with 7.3 cm2 V-1 s-1 achieved by pure thermal evaporation (100% improvement) and 2.8 cm2 V-1 s-1 achieved by solution sheared monolayer C10-DNTT. This work establishes a simple yet effective approach for fabricating high-performance and low-cost electronics on a large scale.

Chasing the "Killer" Phonon Mode for the Rational Design of Low-Disorder, High-Mobility Molecular Semiconductors

Molecular vibrations play a critical role in the charge transport properties of weakly van der Waals bonded organic semiconductors. To understand which specific phonon modes contribute most strongly to the electron-phonon coupling and ensuing thermal energetic disorder in some of the most widely studied high-mobility molecular semiconductors, state-of-the-art quantum mechanical simulations of the vibrational modes and the ensuing electron-phonon coupling constants are combined with experimental measurements of the low-frequency vibrations using inelastic neutron scattering and terahertz time-domain spectroscopy. In this way, the long-axis sliding motion is identified as a "killer" phonon mode, which in some molecules contributes more than 80% to the total thermal disorder. Based on this insight, a way to rationalize mobility trends between different materials and derive important molecular design guidelines for new high-mobility molecular semiconductors is suggested.

Fabrication of Two-Dimensional Crystalline Organic Films by Tilted Spin Coating for High-Performance Organic Field-Effect Transistors

We developed a facile method for fabricating large-area, two-dimensional (2D), organic, highly crystalline films and extended it to organic thin-film transistor arrays. Tilted spinning provided oriented flow at the three-phase contact line, and a 2D crystalline film that consisted of layer-by-layer stacked 2,7-diocty[1]benzothieno[3,2- b]benzothiophene (C₈-BTBT) was obtained facilely for organic thin-film transistors (OTFTs). The extracted field-effect mobility is 4.6 cm² V^-1 s^-1, but with nonideal features. By applying this method to microdroplet arrays, an oriented crystal was fabricated, and the channel region for OTFTs was covered by adjusting the spinning speed. By tuning the tilt angle (θ) of the revolving substrate, we fabricated high-performance OTFT arrays with average and maximum mobilities of 7.5 and 10.1 cm² V^-1 s^-1, respectively, which exhibited high reliability factors of over 90% and were close to that of ideal transistors. These results suggest that high-quality crystalline films can be obtained via a facile tilted-spinning method.

Exploration of SMM behavior of Ln2 complexes derived from thianaphthene-2-carboxylic acid

Observations were made of field-induced SMM property of a dysprosium-based dinuclear complex derived from thianaphthene-2-carboxylic acid ligand.

Inch-Scale Grain Boundary Free Organic Crystals Developed by Nucleation Seed-Controlled Shearing Method

Crystals of organic semiconductors are excellent candidates for flexible and array-based electronics. Large-scale synthesis of organic crystals in a controllable way while maintaining homogeneous single-crystal property has been a great challenge. The existence of grain boundaries and small crystal domains, however, restrict the device performance and limit the access to commercially viable organic electronics in the industry. Herein, we report the inch-scale synthesis of highly oriented 2,7-dioctyl[1]benzothieno[3,2- b][1]benzothiophene (C₈-BTBT) organic single crystal by nucleation seed-controlled shearing method. The organic field-effect transistors developed from such single crystal have excellent carrier mobility as high as 14.9 cm² V^-1 s^-1 and uniformity (standard deviation is 1.3 cm² V^-1 s^-1) of 225 devices. We also found that the rotation of the principal axis in the crystal is governed by the orientations of seeds and the possible mechanism behind this phenomenon is proposed based on the density functional theory calculations. We anticipate that this proposed approach will have great potential to be developed as a platform for the growth of organic crystals with high crystallinity on a large scale.

Experimental and theoretical evidence of a supercritical-like transition in an organic semiconductor presenting colossal uniaxial negative thermal expansion

Thermal expansion coefficients of most materials are usually small, typically up to 50 parts per million per kelvin, and positive, i.e. materials expand when heated. Some materials show an atypical shrinking behavior in one or more crystallographic directions when heated. Here we show that a high mobility thiophene-based organic semiconductor, BHH-BTBT, has an exceptionally large negative expansion between 95 and 295 K (-216 < α2 = αb < -333 MK-1), being compensated by an even larger positive expansion in the perpendicular direction (287 < α1 < 634 MK-1). It is shown that these anomalous expansivities are completely absent in C8-BTBT, a much studied organic semiconductor with a closely related molecular formula and 3D crystallographic structure. Complete theoretical characterization of BHH-BTBT using ab initio molecular dynamics shows that below ∼200 K two different α and β domains exist of which one is dominant but which dynamically exchange around and above 210 K. A supercritical-like transition from an α dominated phase to a β dominated phase is observed using DSC measurements, UV-VIS spectroscopy, and X-ray diffraction. The origin of the extreme negative and positive thermal expansion is related to steric hindrance between adjacent tilted thiophene units and strongly enhanced by attractive S···S and S···C interactions within the highly anharmonic mixed-domain phase. This material could trigger the tailoring of optoelectronic devices highly sensitive to strain and temperature.

Two-dimensional light-emitting materials: preparation, properties and applications

We review the recent development in two-dimensional (2D) light-emitting materials and describe their preparation methods, optical/optoelectronic properties and applications.