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Ultrastable centimeter-sized atomically flat 2D polymer thin films are produced by interfacial polymerization for flexible electronics.

Low-voltage OFETs with excellent mobility, steep subthreshold swing, and low operating voltage were achieved simultaneously based on a novel solution-processable high-k dielectric.

The identical macrocyclic pair promotes desired packing mode with tight and large-overlapped π–π stacking in phthalocyanine-based cocrystal, which ensures high-performance ambipolar property.

Polycyclic aromatic hydrocarbons (PAHs) as a typical class of organic semiconductors demonstrate unique optical, electrical, magnetic and other interesting properties due to their extended conjugation and diverse structures.

An amorphous carbon film formed by a pyrolysis photoresist as the bottom contact source/drain electrode of OFETs to improve the charge injection as well as the device performance.

The design of two-photon absorption (TPA) materials based on cocrystal engineering is an emerging strategy for constructing nonlinear materials. Here we observe that a prepared BDBT-TCNB cocrystal can retain well the TPA properties from the donor BDBT molecules, but the TPA properties of a BDBT-OFN cocrystal are inhibited upon using the same donor molecule but changing the acceptor molecule of the cocrystal. Via comparing the crystal structures and spectral data of the two cocrystals, we find that BDBT-TCNB cocrystals have obvious intermolecular charge transfer interactions, while the BDBT-OFN cocrystals exhibit totally different intermolecular arene–perfluoroarene interactions. Moreover, strong charge transfer interactions involving the BDBT-TCNB cocrystal also promote an enhancement of the fluorescence intensity and an increase in the lifetime and photoluminescence quantum yield (PLQY) relative to the monomers. Therefore, this example proves that intermolecular interactions involving cocrystals can be controlled via carefully selecting the donor and acceptor molecules, and then the TPA properties of the cocrystals can be selectively adjusted, promoting the development of TPA materials prepared via cocrystal engineering.

Two-dimensional (2D) crystals of conjugated polymers (2DCCPs) have attracted significant attention in the past few decades due to their superior and intriguing optoelectronic properties. With the increase in brain-inspired neuromorphic computing, 2DCCPs have also been employed in the construction of synaptic devices because they offer clear advantages of easy integration, high stability, long–range order and no biological rejection. However, pursuing controllable strategies to obtain high-quality and large-scale 2DCCPs remains a challenge on account of their intrinsic complex structures. Herein, we present a universal methodology to grow centimeter-scale 2DCCPs in a controlled manner within minutes by selecting an appropriate growth-assisting solvent and surfactant. The thickness of the as-produced 2DCCPs was down to two molecular layers. The photonic synaptic transistors based on the as-grown 2DCCPs could perform typical synaptic functions, including short-term plasticity, paired-pulse facilitation, long-term plasticity and spike intensity-dependent plasticity. The transistor was also proven to have potential application as a high-pass filter. This methodology shows great potential to be expanded to many other polymer systems and opens new pathways for large-area integrated wireless communication systems and artificial visual systems.

This review summarizes the development and applications of polymer-based organic photodiodes and organic phototransistors, and provides an outlook on their development prospects and obstacles, aiming to propose new design strategies.

Organic semiconductor single crystals (OSSCs) possess high mobility and ultra-long spin relaxation times in the millisecond or even second range, mainly due to their pure material systems, perfect periodic structures, and inherent weak spin–orbit coupling (SOC). Coupling this with their excellent photoelectric functionality, they have long been considered as perfect materials for organic spintronic applications to obtain both long-distance spin transport and novel multifunctionality at room temperature, attracting wide interest. Currently, spintronic studies based on OSSCs are still at the heuristic stage, and there are many related critical challenges, as well as important opportunities. Herein, this perspective article, relying on developed theory and in-depth investigations of organic semiconductors (OSCs) in electronics and spintronics, provides discussion and future prospects, focusing on several aspects of OSSCs; we aim to inspire progress in this new field and attempt to guide a wide range of research in related fields. Firstly, as the spin relaxation time and charge carrier mobility are the two main factors affecting the spin diffusion length, the effects of the molecular structure and stacking structure regarding these two factors are discussed, covering material design and regulation methods in detail. Then, the current situation and challenges relating to device fabrication technology based on OSSCs are outlined, highlighting what needs to be solved in order to build a foundation for achieving extra-long spin transport in OSSCs and novel multifunctional OSSC-based spintronic devices. Finally, based on various reported multifunctional spintronic devices and OSSCs with excellent photoelectric properties, the exploitation of novel multifunctional spintronic devices is discussed.

An in situ analysis for DNA content detection without DNA separation in samples, which circumvents the influence of the chromophore, fluorophore and other interferents in vivo, based on long-persistent luminescence of organic doped-crystals.

High mobility n-type organic semiconductors with photo-stable and photo-sensitive characteristics.

Recent advances in the controllable growth of bilayer 2D single crystals via the chemical vapor deposition method are comprehensively presented.

In this work, through rational monomer design we integrated the conformational change mechanism into a two-dimensional covalent polymer and implemented 3 different low-power memory behaviors on the same device by tuning the compliance current (ICC), including nonvolatile write-once-read-many-times (WORM) memory behaviour, nonvolatile FLASH memory behaviour and volatile dynamic random access memory (DRAM) behaviour. Furthermore, 2DP-based memory devices exhibit excellent flexibility and thermal stability, which is a desirable property for applications in wearable electronics and a high temperature environment. Finally, the conformation-induced conductance switching under an electric field was confirmed by UV-vis spectra. The differences in memory behaviour were attributed to the inherent differences in the degree of regioregularity and ease of the conformational relaxation of the field-induced rearrangement of carbazole groups.

Guest editors Qichun Zhang, Wenping Hu, Thuc-Quyen Nguyen, Qibing Pei and Jia Zhu introduce this Journal of Materials Chemistry C issue in honour of Professor Daoben Zhu on the occasion of his 80th birthday.

Recently organic exciplex materials have captured considerable attention due to the promising luminescent applications in organic optical waveguides, lasers, nonlinear optics, light-emitting diodes and even light-emitting transistors. The emission features together with other optoelectronic properties can be tailored via intermolecular charge-transfer interactions by the judicious selection of various component materials. In this review, first we will discuss the formation mechanism and emission process of exciplex under photoexcitation or electrical excitation, which will shed light on realizing high-efficiency luminescence and generating new optical functions. Next, we will mainly introduce the various organic exciplex materials in terms of donor–acceptor contacting modes (cocrystals, interface, blend, porous coordination, space-limitation) and their potential applications in optoelectronics devices. Finally, we will present the current obstacles and limitations of organic exciplex materials as well as their prospects for future research.

Stretchable electrodes are one of the essential building blocks for stretchable electronics. However, most of the reported stretchable electrodes show a considerable conductivity decrease under large stretchability. Until now, it has still been a big challenge to develop appropriate geometric structures to realize stretchable metal electrodes with a negligible conductivity change under large stretchability. Here, inspired by the armadillo, we develop a novel micro-foldable structure on polydimethylsiloxane (PDMS) using a suspended plasma etching method. This novel structure could endow the obtained stretchable electrodes with excellent properties including high metallic conductivity (>40 000 S cm−1) at released and stretched states, slight resistance change (13%) over a large tensile range (190%), a fully-covered conductive area, excellent cyclic operational stability (over 10 000 times), and a robust interface adhesion strength (>0.28 MPa). These figures of merit are very prominent compared to the reported stretchable gold electrodes, indicating the superiority of this novel micro-foldable structure. Furthermore, these stretchable electrodes show excellent performance in electromyography (EMG) signal detection, stretchable conducting wires and capacitive stretchable sensors. This work provides a novel and efficient avenue for the preparation of stretchable electronics.

Organic long-persistent luminescent materials can be easily quenched in aqueous solutions or air, which limits their wide applications. Here we report novel doped organic crystals to overcome this challenge. The stable LPL performance of this crystalline material is visible for over 8 s and can be maintained for at least three months even in aqueous solution or in air.

Fibriform organic field-effect transistors (OFETs) play a key role in wearable electronic devices due to their unique advantages in optoelectronic and sensing applications. However, most reported devices suffer from poor performance and limited functionality that greatly limit them from being more fully integrated into our daily life. Two-dimensional crystals of organic semiconductors (2DCOS) are promising functional materials attributed to their long-range order, ideal band gaps and few-layered ultrathin structures, which seem to overcome this challenge and open new door for this field. Herein, the first fibriform OFETs and OFET-based functional devices based on ultrathin 2DCOS are demonstrated through a jigsaw puzzle physical chemical method. This method provides a facile way to broaden the practical applications of 2DCOS and construct high-performance electronic components on fibers. Impressively, the results show competitive optoelectronic characteristics, e.g., a high field-effect electron mobility of 1 cm2 V−1 s−1, well-balanced ambipolar characteristic of p–n junction, high voltage gain of inverter up to 12.4 and superior near-infrared (NIR) photo response performance with a photo-responsivity (R) of 1.06 × 104 A W−1 and detectivity of more than 1013 Jones, indicating a great potential of the devices in electronic textile (e-textile) applications.

A small energy gap between charge transfer (CT) singlet and triplet states enables thermally activated delayed fluorescence (TADF). Nevertheless, the small oscillator strength associated with CT states and their long exciton lifetimes are detrimental to establishing a population inversion for stimulated emission (SE), hindering the application of a TADF material in organic lasers. Here, we demonstrated that a TADF molecule of sulfide-substituted difluoroboron derivatives can achieve stimulated emission in microcrystals by employing a new molecular design, in which an ultrafast reverse intersystem crossing (RISC) process was achieved between a hybrid locally excited CT (HLECT) singlet S1 and a high-lying triplet T2 (3HLECT) state. Femtosecond transient abaorption and time-reolved PL spectra reveal that the two states of S1 and T2 equilibrate within a time of 180 ps. In addition, the energetic spacing of ΔES1–T2 = 0.11 eV enables delayed fluorescence involving the T2 state at room temperature. Besides, the extremely fast exciton lifetime (0.31 μs) that decreases the probability of carrier annihilation, the HLECT singlet provides larger oscillator strength and therefore larger SE cross-section than those of the CT state. A multimode TADF laser was realized based on the good optical feedback (cavity quality factor Q ≈ 2000) provided by Fabry Perot (FP) microcrystal microcavity. Our results not only confirm that the high-lying Tn state plays a key role in the RISC process of TADF, but also provides a design of TADF gain materials.

Three anthracene derivatives, referred to as 2-phenyl anthracene (Ph-Ant), 2-thiazole anthracene (TZ-Ant), and 2-pentafluorophenyl anthracene (F5Ph-Ant), were designed and synthesized to reveal the effects of the electron-withdrawing substituents on the molecular packing structure and photoelectric properties of the anthracene core. As the electron-withdrawing abilities of the substituents increased, the molecular structures of the three semiconductors showed a progressive deterioration in intermolecular interactions and molecular accumulation, and the photoelectric properties became worse. Interestingly, the energy levels of the three semiconductors showed gradually decreasing changes with an enhancement of the electron-withdrawing abilities of the substituents, indicating a possible strategy for fabricating n-type anthracene derivative semiconductor materials.

In recent years, with the increasing demands of high-energy physics, medical diagnosis, radiochemistry, and industrial non-destructive testing, ionizing radiation detectors have received more and more attention. Organic photoelectric materials have been used in ionizing radiation detection for nearly hundred years. Until recently, the novel molecular design, progressive preparation technology and further mechanism exploration have once again greatly expanded their application field, as well as showing a short response time, low limitation of dose rate and high sensitivity, which can be used as candidate materials for next-generation high-energy radiation detectors owing to their low-cost processing techniques, flexible properties and promising low detection limit. Based on a brief description of the detection mechanism, this review investigates the recent research of X-ray and gamma ray detection based on organic thin films, single crystals, polymers and liquid materials. It focuses on the advantages of these materials, bottlenecks encountered, and relatively effective solutions in recent years. This article aims to provide readers with a deeper understanding of the comprehensive approach to design organic materials and improve the conversion efficiency for future ionizing radiation detection.

Single crystalline arrays on the micro-scale are of crucial importance for high performance and high integration level of organic electronics. Here we report an in situ observation of organic single crystal formation via solvent vapor annealing on both bare and Au patterned SiO2 surfaces. The results show that micro-sized organic islands absorb solvent to form droplets, and then the molecules inside the droplet nucleates to form single crystals. The technique gives positional control of the single crystal array fabrication which is confirmed by X-ray diffraction and selective area electron diffraction. In combination with the area selective growth on Au electrodes, organic single crystal device arrays such as a photon-detector can be directly fabricated with improved light absorption and detectability.

Bilayer p–n heterojunctions are promising structures to achieve high-performance ambipolar organic field-effect transistors (aOFETs). However, the performance of aOFETs based on polycrystalline bilayer p–n heterojunctions was substantially reduced compared with that of their unipolar devices due to the unavoidable interlayer mixing in bilayer heterojunctions fabricated by conventional methods such as two-step spin-coating or vacuum-deposition. Herein, the interlayer mixing problem was reduced by 2D molecular crystal (2DMC) templated growth of high-quality bilayer p–n heterojunctions. Due to the excellent wettability of the 2DMC template for organic semiconductors, the grain size of the upper layer was substantially enlarged. Moreover, the atomically flat surface and the long-range order of the 2DMC template reduced the common interlayer mixing problem. As a result, the mobility of copper hexadecafluorophthalocyanine (F16CuPc) increased over one order of magnitude compared with that of their unipolar devices. Actually, the electron mobility of 0.56 cm2 V−1 s−1 was the highest among both ambipolar OFETs and unipolar OFETs adopting F16CuPc as the n-type semiconductor.

Artificial visual memories (AVMs) are crucial to many technologies, including artificial intelligence, humanoid robots, and visual prostheses. Most studies used a thick polycrystalline film as the AVM active layer to achieve a continuous channel for charge collection. However, because of the inherent interlayer shielding effect in thick films, both photogating and electrical gating are inefficient and the photoresponse of these AVMs is extremely low. Herein, the obstacle of the interlayer shielding effect in thick films is overcome by using molecularly thin two-dimensional molecular crystals (2DMCs). Because of the highly efficient photogating and electrical gating effects of 2D channels, the developed AVMs based on few-layered 2DMCs show record-high photoresponse. The AVMs also exhibited multilevel non-volatile memory functionality, with long retention time and excellent write–erase stability, by exploiting the persistent photoconductivity effect.

Herein, two new poly(phenylene vinylene)-derivated semiconductors, poly(benzopyrrolone-p-phenylene-vinylene) (PBPPV) and poly(benzopyrrolone-di-p-phenylene-vinylene) (diPBPPV), are designed and synthesized with lactam groups as the electron-deficient and lateral extending units and phenylethylene as the emissive element for achieving integrated optoelectronic properties. Comprehensive characterization demonstrates that both PBPPV and diPBPPV are red-emissive materials with a photoluminescent quantum yield (PLQY) of up to 7% and exhibit well-balanced ambipolar transport properties with the electron and hole mobility approaching 4.5 × 10−4 cm2 V−1 s−1 and 3.0 × 10−4 cm2 V−1 s−1, respectively. This work provides valuable guidelines for further improvement of integrated optoelectronic conjugated polymers by rational molecular design.

By introducing the naphthyl group into the 2,6-positions of anthracene, two different anthracene derivatives, 2,6-di(2-naphthyl)anthracene (2,6-di(2-Na)Ant) and 2,6-di(1-naphthyl)anthracene (2,6-di(1-Na)Ant) were synthesized. The tiny change in the substitution site of the naphthyl group leads to a significant difference in the molecular packing and further exerts a great impact on their optoelectronic properties. Thin film field-effect transistors for 2,6-di(2-Na)Ant show charge transport mobility up to 2.1 cm2 V−1 s−1, while 2,6-di(1-Na)Ant demonstrates no mobility. Moreover, thin film phototransistors of 2,6-di(2-Na)Ant show a photoresponsivity of 6.9 × 103 A W−1, a high photosensitivity of 2.6 × 106 and an excellent detectivity of 3.4 × 1016 Jones, which is one of the highest performances of thin film organic phototransistors reported to date.

Electrohydrodynamic inkjet (E-jet) printing is a promising technology to fabricate high-performance organic electronic devices due to its high resolution, low-cost and drop-on-demand characteristics. Here, we fabricate top-contact OFETs by using E-jet printed source/drain electrodes. The printed resolution could be smaller than 5 μm on an organic semiconductor. A printable Ag ink consisting of the F4-TCNQ additive greatly improves the charge injection of the OFET, and thus the OFETs show comparable performance with thermally evaporated electrodes. The printing and doping of top electrodes can be realized in one step, which is essential to realize fully printed organic devices. The E-jet printing demonstrates its potential in high-resolution, high-performance OFET applications.

Ambulatory electrocardiography (ECG) is used to realize the diagnostics of coronary heart disease. On-skin electrodes are employed for ambulatory ECG sensing through conformable contact with the arbitrarily shaped moving skin. However, the low skin-adhesion of electrodes limits their application in long-term ambulatory ECG sensing. For example, for the current on-skin electrodes, the low shear viscosity of sweat on the skin decreases the skin-adhesion, leading to their slipping and even falling off. Herein, highly adhesive and washable on-skin electrodes were achieved by combining stretchable Au nanofilms with hybrid materials composed of polydopamine and silk fibroin (SF). The strong interaction of polydopamine with water enhanced the adhesion energy of these electrodes by decreasing the Young's modulus of the SF gel and increasing the contact area between electrodes and skin. Additionally, the microcrack structure of Au nanofilms provided good conductivity upon stretching. Remarkably, our electrodes could be easily removed on washing and had low impedance due to the existence of hydrophilic SF and Ca2+. To demonstrate the application of these electrodes for perceiving accurate and reliable signals, they were pasted on the skin to record long-term and high-quality ECG signals for the diagnosis of heart disease.

Nanowire laser arrays for integrated on-chip optical interconnects demand the uniformity of lasing wavelengths from different modules, which, however, is challenging owing to inevitable heterogeneity in subunit fabrication. Herein, we demonstrated a facile method to prepare uniform nanolaser arrays based on a transverse lateral Fabry–Perot (FP) microresonator built within single-crystalline organic microribbons of 1,4-bis((E)-2,4-dimethylstyryl)-2,5-dimethylbenzene (6M-DSB). Theoretically, spectroscopic and crystallographic results together reveal that short-axis brickwork-packing and long-axis uniaxial-alignment of 6M-DSB molecules result in a mixed Hj-type aggregation within microribbons. On the one hand, such a kind of Hj-type aggregation exhibits enhanced radiative decay and therefore 100% photoluminescence quantum yield for minimizing the singlet–triplet annihilation and reabsorption of laser photons owing to triplet absorption. On the other hand, the uniaxial alignment gives rise to a transverse lateral FP microresonator along the width of 6M-DSB microribbons, rather than a longitudinal microresonator in conventional nanowire lasers. By positioning a microribbon onto a PDMS pad with patterned grooves, only the suspended parts support transverse waveguiding and high quality FP resonances. A proof-of-concept 1 × 4 transverse nanolaser array constructed from the same microribbon was demonstrated with almost identical lasing thresholds, wavelengths and FP resonances, providing coupled lasing subunits for integrated organic photonics.

For semiconductors, doping is an efficient approach to tune their energy bandgaps, charge transport, and optical properties which could enable the improvement of the corresponding performances and open up the possibility of multifunction integration. Recently, significant advances have been achieved in molecular doped organic semiconductors, especially doped organic semiconductor single crystals (OSSCs) which have features of well-defined packing structures, long-range molecular orders, and low-density defects for fundamental studies and improved properties. In this review, we will give a summary of the exciting progress of molecular doped OSSCs from the aspects of selection criteria of molecular dopants, general growth methods, and resulting optoelectronic properties as well as their applications in optoelectronic devices. Finally, a brief conclusion is given with challenges and perspectives of molecular doped OSSCs and their related promising research directions in this field.

Organic light-emitting transistors (OLETs) are attractive advanced devices but their use is currently limited by multiple challenges, including the absence of ambipolar emissive organic semiconductors and difficulty in achieving balanced ambipolar transport toward high efficiency. Here, we show that efficient ambipolar OLETs can be obtained using a high hole mobility organic semiconductor, 2,6-diphenylanthracene (DPA) via energy-level engineering. Both electron and hole charge injection barriers, Vth,h and Vth,e were significantly reduced leading to a narrower ambipolar regime and high and balanced ambipolar transport. The OLETs exhibited efficient and stable light emission in their conducting channel not in the vicinity of electrodes. Moreover, the excellent consistency of the maximum electroluminescence intensity and minimum source–drain current of the OLETs resulted in high external quantum efficiency at low voltage, providing solid evidence for the efficient charge recombination in these devices under ambipolar conditions. This result suggests the importance of achieving ambipolar charge transport with a narrowed ambipolar regime for high-efficiency OLETs and their related integrated optoelectronic devices/circuits.

While tremendous progress has been made in numerous prototype high-performance field-effect transistors (FETs) during the last several decades, the inauguration of innovative FETs with ultrahigh solvent resistibility and exceptional electrical stability still remains a formidable challenge. In terms of a proof-of-concept of all-covalent FETs with both covalently-rooted source/drain electrodes and semiconductor layers, we herein report that these issues could be feasibly overcome. Taking graphene-based FETs as a paradigm, we demonstrate that the electrical characteristics of the thus-schemed all-covalently-implanted devices display negligible fluctuations even after the whole devices are immersed and ultrasonicated for 100 minutes successively in 10 kinds of common solvents (1000 minutes in total). The shelf life of the as-configured FETs reaches as long as 24 months, wherein negligible degradation could be observed even after the devices are stored for two years under ambient conditions without any protection. In virtue of these characteristics, we additionally demonstrate that our all-covalent FETs could work as high-quality biosensors of outstanding reproducibility and robustness for a label-free diagnosis of liver cancer biomarker. Our new FETs are essentially different from their traditional counterparts in that their all-covalent configuration characteristics afford them with ultrahigh solvent resistibility and exceptional electrical stability. This opens up new perspectives and a bright future for the further functionalization, integration, industrialization and commercialization of FETs, wherein multistep post-productions are inevitably encountered in practice. Beyond graphene-based FETs, our all-covalent concept might be expanded to other types of electronic materials/devices via sophisticated molecular engineering.

As one of the basic units of optoelectronic devices, organic field-effect transistors (OFETs) are not only promising candidates for understanding the intrinsic charge transport mechanism of organic semiconductors (OSCs), but are also attractive for various applications, such as active-matrix displays, logic circuits, photodetectors, sensors and so on. Shrinking the active layer thickness in OFETs to a few molecular layers (MLs) or even down to a monolayer is a very attractive strategy in many aspects: (1) minimize material consumption while maintaining equal or even better charge transport properties, (2) reduce bulk injection resistance for the possible realization of Ohmic contact and short channel devices, (3) enhance phototransistor performance, (4) improve sensing performance, etc. In this review, we first comprehensively summarized the effect of active layer thickness on OFET performances in thin-film and single crystal devices in terms of mobility (μ) and contact resistance (Rc). Then the phototdetector and sensor applications of OFETs toward ultrathin two-dimensional (2D) molecular materials at the monolayer limit are discussed with emphasis on the high performance of monolayer molecular crystal (MMC) based devices. Finally, the challenges and perspectives regarding the controllable preparation of MMCs and corresponding devices applications are discussed.

To reveal the influence of synergistic effect of non-covalent forces on the FET performance, two highly symmetrical “H”-shaped heteroarene derivatives anthra[2,1-b:3,4-b′:6,5-b′′:7,8-b′′′]tetra(benzothiophene) (ATBT) and anthra[2,1-b:3,4-b′:6,5-b′′:7,8-b′′′]tetra(benzofuran) (ATBF) as novel two-dimensional (2D) organic semiconductor materials were synthesized. The thermal, optical and electrochemical properties of ATBT and ATBF were investigated and high stability was confirmed. Single crystal XRD of ATBT confirmed the close π–π stacking due to the “wider” π-conjugation framework and four S atoms sited on both sides of each molecule could produce eight S⋯S contacts with neighbouring molecules. Mobility of up to 15.6 cm2 V−1 s−1 could be achieved for the single-crystalline field effect transistor, which was fabricated by the ‘two-dimensional organic-ribbon mask’ technique based on the individual ATBT microribbon. The strong anisotropy along different crystal axes is consistent with the molecular arrangement, which was evidenced by XRD, TEM and corresponding selected-area electron diffraction pattern. Moreover, the analogue ATBF shows lower FET performance due to lack of S⋯S contacts in comparison to that of ATBT, which reflects that the synergistic effect of non-covalent forces has an important influence on the molecular aggregation and electrical properties.

Enhancing charge injection from electrodes to the conducting channel and reducing the contact resistance (Rc) are valid strategies not only to improve the performance of organic field-effect transistors (OFETs), but also to enable low-voltage operating devices with a short channel. In order to improve the charge injection efficiency, many efforts have been made to reduce the interfacial injection resistance (Rc,int) in the past few decades, such as by adjusting the metal work function, inserting a buffer layer and so on. However, the method of decreasing the bulk injection resistance (Rc,bulk) in the vertical direction of the semiconductor layer is rarely studied. In this paper, two-dimensional (2D) monolayer and multilayer single-crystal devices of 1,4-bis((5′-hexyl-2,2′-bithiophen-5-yl)ethynyl)benzene (HTEB) were fabricated to study the dependence of the contact resistance of OFETs on crystal thickness. Devices based on monolayer molecular crystals (MMCs), and 4-layer and 15-layer single-crystal devices were found to have Rc of 1.77 kΩ cm, 26.9 kΩ cm and 5.15 MΩ cm, respectively. Thanks to the lower Rc, the MMC devices possess more steady linear mobility at a varied VDS, and a smaller deviation of the linear and saturation mobility. Finally, a low-voltage operating (−2 V) HTEB MMC device was fabricated on a 30 nm HfO2 insulating layer with an ultra-low Rc of 540 Ω cm.

Organic semiconductors combining high mobility and efficient solid fluorescence are in high demand for developing organic light-emitting transistors and electrically driven organic lasers. But, achieving such dual functional molecules is extremely challenging. In this manuscript, we report 2-phenylbenzo[g]furo[2,3-b]quinoxaline derivatives (3a–3c) and develop a new synthesis method for the furo[2,3-b]quinoxaline core. It was found that 3a exhibited favorable aggregation induced emissive enhancement behavior and reasonable hole mobility. The absolute photoluminescence quantum yield of 3a is determined to be 22.1% in solid powders and can reach a maximum of 19.7% in 50% water in THF, twice that in CH2Cl2 solution (9.2%) and dispersed in PS film (9.3%). The single crystal and thin film organic field-effect transistor of 3a show a hole mobility of 2.58 × 10−2 cm2 V−1 s−1 and 5.7 × 10−3 cm2 V−1 s−1, respectively. Our results demonstrated that the 2-phenyl-benzo[g]furo[2,3-b]quinoxaline skeleton is a promising candidate for building multifunctional organic optoelectronics.

Simultaneously modulating the optical and electrical properties of organic semiconductors is crucial for advancing their desired applications in integrated optoelectronic devices. Here, we realize a goal of optimizing the light emission and field-effect properties of an anthracene derivative, 1,4-di(anthracen-9-yl)buta-1,3-diyne (DABD) by tuning its crystal polymorphs. Two phase crystals, that is α-phase rhombic-sheet crystals and β-phase ribbon-shape crystals of DABD are controllably obtained. Compared with the α-phase crystals, the β-phase DABD crystals exhibit better integrated optoelectronic performances with charge carrier mobility of 0.25 cm2 V−1 s−1 and strong fluorescent emission. This work suggests that polymorph engineering would be a promising avenue to realize simultaneous modulation of the multifunctional properties of organic semiconductors towards appropriate applications in organic optoelectronics.

Unidirectional and crystalline organic microwire arrays hold great potential for transistors, logic circuits and optoelectronic devices. A fundamental step towards a practical implementation is their effective production. However, unidirectional alignment and high crystallinity of the organic microwire arrays are challenging to achieve by most of the current methods, either because of the complex procedures or the incapability of unidirectional alignment. Herein, we reported a simple yet efficient method, i.e., the polymer assisted solvent vapor annealing (PASVA) approach, for the production of unidirectional and crystalline organic semiconductor microwire arrays. A tilted substrate and a PMMA assisting layer were introduced to guide the growth direction of the microwire arrays and to increase the fluidity of the organic semiconductor molecules during the PASVA process. The charge carrier mobility was increased three times as compared with microwires produced by the traditional SVA method without the assisting polymer layer.

In this paper, a novel fullerene-naphthalenediimide derivative (abbreviated as C60-NDI) was synthesized and used as an interlayer in pentacene transistors. We found that a significant improvement was achieved with C60-NDI as an interlayer between the pentacene active layer and the gate dielectric. The highest field-effect mobility and on/off current ratio approached 1.76 cm2 V−1 s−1 and 108, respectively, which is even higher than those of devices under the same experimental conditions fabricated on conventional SAMs (such as octadecylsilanes (OTS) and hexamethylene disilazane (HMDS)) treated substrates. Further investigations carried out by contact angle tests, atomic force microscopy, X-ray diffraction, and Raman spectroscopy demonstrated that the formation of large grain sizes, high crystallinity, and good grain interconnectivity for pentacene thin films on a C60-NDI surface leads to high device performance, suggesting its application as a new interface engineering species for modifying the gate dielectric to improve device performance.

Increasing the length of azaacene derivatives through quinone bridges is very important because these materials could have deep LUMO energy levels and larger overlapping in the solid state, which would have great applications in organic semiconducting devices. Here, two fully characterized large quinone-fused azaacenes Hex-CO and Hept-CO prepared through a novel palladium-catalyzed coupling reaction are reported. Our research clearly proved that the quinone unit can be employed as a bridge to extend the molecular conjugation length, increase the molecular overlapping, and engineer the molecular stacking mode. Hex-CO shows lamellar 2-D π-stacking modes, while Hept-CO shows 1-D π-stacking and adopts a 3-D interlocked stacking mode with the adjacent molecular layers vertical to each other. With the deep LUMO energy levels (∼−4.27 eV), Hex-CO and Hept-CO were both demonstrated to be electron-transport layers. Their charge transport properties were investigated through OFETs and theoretical calculations. Due to the different stacking modes, Hex-CO shows a higher electron mobility of 0.22 cm2 V−1 s−1 than Hept-CO (7.5 × 10−3 cm2 V−1 s−1) in a single-crystal-based OFET. Our results provide a new route for structure engineering through extending the azaacene derivatives by quinone bridges, which can be of profound significance in organic electronics. MOE (Min. of Education, S’pore)

The fabrication of large-scale unidirectionally aligned organic crystalline ribbons is a great challenge. Here, we developed a limited solvent vapor-assisted crystallization (LSVC) method. By adopting an up-side-down funnel, single crystalline microribbons of C8-BTBT with uniform alignment were easily prepared on different substrates, indicating the feasibility of the LSVC method.

Two new anthracene derivatives were designed and synthesized. Ant-Th-Ph and Ant-ThPh show high single crystal mobilities of 1.1 cm2 V−1 s−1 and 4.7 cm2 V−1 s−1. Moreover, strong solid state emission was determined to be 36.52% and 33.32% for Ant-Th-Ph and Ant-ThPh respectively.

Organic charge-transfer compounds have received significant attention because of their tunable electronic properties, ranging from insulators to superconductors. It has been demonstrated that these compounds can be applied to both organic semiconducting active materials and organic conductors by appropriate molecular design. 7,7,8,8-Tetracyanoquinodimethane (TCNQ) and FxTCNQ (x = 1, 2, 4) as acceptors and aromatic hydrocarbons form a variety of compounds in which the degree of charge transfer (DCT) is adjustable. The donor, acceptor, and stoichiometry of organic charge-transfer compounds are the main factors for tuning the DCT. Tuning of the DCT by crystal engineering allows control of the delocalized electrons and thus the physical properties of materials in a range that is not available in one-component organic solids. MOE (Min. of Education, S’pore)

A new compound, 2-(2,2-diphenylethenyl) anthracene (DPEA), was designed and synthesized, which showed a hole carrier mobility of 0.66 cm2 V−1 s−1 and typical aggregated induced emission (AIE) behaviour with a ratio of 15 times, which is among the best performance of recently reported semiconducting AIE materials. This work not only enriches the AIE electronic material systems, but also initiates a new direction for developing high performance integrated optoelectronic organic semiconductors for potential multifunctional applications.

Traditional conjugated polymers (CPs) that are chain-like macromolecules with quasi-one-dimensional (1D) charge transport along conjugated backbones have received considerable attention in various optoelectronic devices. Extending π-conjugation in CPs from 1D to 2D can not only give significantly enhanced charge transport but may also induce other favorable properties, such as excellent mechanicality, flexibility, isotropic properties, etc. Currently, various approaches, including chemical synthesis, interfacial reaction, topochemical and electrochemical polymerization (EP) and so on, have been developed to create 2D conjugated polymers that have their own advantages and disadvantages. In this article, we focus on the current progress of the EP method for assembling CP materials. A brief comparison of the properties of 1D and 2D CPs is given in the beginning of the article. This is followed by a special focus on the EP method and its applications for preparing 1D and 2D CPs. Current challenges in this field and future research directions are discussed.

Three new alternating copolymers containing 3,3′-dicyano-2,2′-bithiophene (BT2CN), i.e., DPPTh-BT2CN, DPPPy-BT2CN and 2FIID-BT2CN based on diketopyrrolopyrrole (DPP) and isoindigo (IID) derivatives, were synthesized. The properties of these three polymers were compared with those of the reference polymer without a cyano (CN) group, DPPTh-BT. The introduction of CN groups dramatically lowered both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of the polymers. DPPTh-BT2CN exhibited HOMO and LUMO energy levels of −5.41 and −3.67 eV, respectively, which are much lower than those of the analogue polymer DPPTh-BT comprising a biothiophene (BT) segment. DPPPy-BT2CN and 2FIID-BT2CN showed even lower HOMO and LUMO levels, which are −5.83 and −3.75 eV for DPPPy-BT2CN and −6.15 and −3.92 eV for 2FIID-BT2CN. Organic thin-film transistors (OTFTs) were fabricated to evaluate the semiconducting properties of the polymers. DPPTh-BT2CN-based OTFTs exhibited electron-dominant transport characteristics, similar to the devices based on the benchmark n-type conjugated polymer N2200. By contrast, DPPPy-BT2CN and 2FIID-BT2CN-based devices displayed pure n-channel characteristics due to their lower HOMO and LUMO levels. All three polymers displayed an electron mobility (μe) of ca. 0.3 cm2 V−1 s−1, which is comparable to that of N2200 when the same device structure and measurement conditions were adopted.

Optimization of molecular interactions between filler materials and a polymer matrix is one of the key methods to improve the dielectric properties of composite films. In films composed of two-dimensional fluorographene (FG) and fluorinated polyimide (f-PI), the repulsion between the C–F bonds hinders the dispersion of the filler in the matrix. In this work, we describe a low dielectric constant FG/f-PI nanocomposite film obtained by the preparation of f-PI on exfoliated FG grafted with 2,2′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-diamine (t-FG). The strong interfacial interaction between f-PI and t-FG promotes the dispersion of t-FG in the f-PI matrix. The effects of the addition of t-FG on the optical, mechanical, and dielectric properties of the composite film are investigated by incorporating different amounts of t-FG. When the t-FG content reaches 0.75 wt%, we obtain a transparent, strong, and flexible t-FG/f-PI composite film, which exhibits a low dielectric constant (2.09) and a high tensile strength (300.1 MPa). An organic thin-film transistor fabricated using this film as a dielectric layer exhibits good transistor mobility and ON/OFF ratio. t-FG/f-PI dielectric films are therefore suitable for application in transparent flexible displays.

Specific electrostatic interactions are highly efficient for fluorescent bioassays but they are difficult to achieve. In this work, smartly designed aggregation-induced emission (AIE) triazoliums with donor–acceptor structures were developed via click conjugating a triazole heterocycle onto a tetraphenylethylene (TPE) fluorophore followed by a cationization reaction. The strongly electron-deficient nature of the triazolium coupled with intermolecular electrostatic repulsions resulted in the decrease of TPE's AIE character when it was in solution. However, specific “electrostatic locking” was found to take place between the triazolium and multiple sulfonates and this unique targeting combination attenuated triazolium's electrophilicity and electrostatic repulsion resulting in the recovery of the AIE. Cryo-electron microscopy (Cryo-EM) was used to reveal the in situ aggregation state of the probe. The triazolium probes exhibited a highly specific turn-on fluorescence response toward sulfonic biomacromolecules such as heparin, chondroitin and sulfonate cyclodextrin, demonstrating that the AIE-triazoliums have great potential for bioassay applications.

The development of optical and electrical organic semiconductors is crucial for the construction of integrated optoelectronic devices. Herein, a new anthracene derivative, 2,6-diphenyl-9,10-bis(phenylethynyl)anthracene (DP-BPEA), was designed and synthesized by enlarging the π-conjugation of 9,10-bis(phenylethynyl)anthracene (BPEA) via 2,6-diphenyl substitution. Compared with the parent BPEA molecule, an improved field-effect mobility of 1.37 cm2 V−1 s−1 with a comparable solid fluorescence efficiency of 32% is obtained for DP-BPEA, suggesting its potential applications in integrated optoelectronic devices.

A convenient and controlled organic semiconductor alignment strategy, superhydrophobic micropillar flow-coating (SMFC), is presented. Patterned, large-area (>1 cm2) 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) single-crystalline arrays which show hole mobilities up to 6.8 cm2 V−1 s−1 were obtained via this method. Crucially, the polymorphism of TIPS-pentacene was regulated by tuning the flow rate, solvent and the substrate hydrophobicity. These results indicate that this technique is reliable for creating uniform and homogenous organic single-crystalline arrays with controlled crystal packing, thickness, and position.