Organic Semiconductor Single Crystal Arrays: Preparation and Applications.

The study of organic semiconductor single crystal (OSSC) arrays has recently attracted considerable interest given their potential applications in flexible displays, smart wearable devices, biochemical sensors, etc. Patterning of OSSCs is the prerequisite for the realization of organic integrated circuits. Patterned OSSCs can not only decrease the crosstalk between adjacent organic field-effect transistors (OFETs), but also can be conveniently integrated with other device elements which facilitate circuits application. Tremendous efforts have been devoted in the controllable preparation of OSSC arrays, and great progress has been achieved. In this review, the general strategies for patterning OSSCs are summarized, along with the discussion of the advantages and limitations of different patterning methods. Given the identical thickness of monolayer molecular crystals (MMCs) which is beneficial to achieve super uniformity of OSSC arrays and devices, patterning of MMCs is also emphasized. Then, OFET performance is summarized with comparison of the mobility and coefficient of variation based on the OSSC arrays prepared by different methods. Furthermore, advances of OSSC array-based circuits and flexible devices of different functions are highlighted. Finally, the challenges that need to be tackled in the future are presented.

Photocatalytic hydrogen evolution based on carbon nitride and organic semiconductors.

Photocatalytic hydrogen evolution (PHE) presents a promising way to solve the global energy crisis. Metal-free carbon nitride (CN) and organic semiconductors photocatalysts have drawn intense interests due to their fascinating properties such as tunable molecular structure, electronic states, strong visible-light absorption, low-cost etc. In this paper, the recent progresses of photocatalytic hydrogen production based on organic photocatalysts, including CN, linear polymers, conjugated porous polymers and small molecules, are reviewed, with emphasis on the various strategies to improve PHE efficiency. Finally, the possible future research trends in the organic photocatalysts are prospected.

Organic Small Molecule Activates Transition Metal Foam for Efficient Oxygen Evolution Reaction.

Developing low-cost, highly efficient, and durable electrocatalysts for oxygen evolution reaction (OER) is essential for the practical application of electrochemical water splitting. Herein, it is discovered that organic small molecule (hexabromobenzene, HBB) can activate commercial transition metal (Ni, Fe, and NiFe) foam by directly evolving metal nanomeshes embedded in graphene-like films (M-NM@G) through a facile Br-induced solid-phase migration process. Systematic investigations indicate that HBB can conformally generate graphene-like network on bulk metal foam substrate via the cleavage of CBr bonds and the formation of CC linkage. Simultaneously, the cleaved CBr fragments can efficiently extract metal atoms from bulk substrate, in situ producing transition metal nanomeshes embedded in the graphene-like films. As a result, such functional nanostructure can serve as an efficient OER electrocatalyst with a low overpotential and excellent long-term stability. Specifically, the overpotential at 100 mA cm-2 is only 208 mV for NiFe-NM@G, ranking the top-tier OER electrocatalysts. This work demonstrates an intriguing general strategy for directly transforming bulk transition metals into nanostructured functional electrocatalysts via the interaction with organic small molecules, opening up opportunities for bridging the application of organic small molecules in energy technologies.

Organic Single-Crystal Spintronics: Magnetoresistance Devices with High Magnetic-Field Sensitivity.

Organic spintronics is a new emerging field that deals with the spin-related phenomena of organic materials under the influence of a magnetic field. However, there remain some challenges in organic spintronics including (i) low conductivity and massive disorders of organic thin films blocking the way to controllable spin transport, (ii) relatively low magnetic-field sensitivity of organic magnetoresistance (OMAR) devices with tangled working mechanisms and short of methods for sensitivity improvement. Here, we report the realization of OMAR devices based on organic single crystals. The lesser amount of impurities and defects in crystals guarantees a reduction in spin and charge scatterings, so that the OMAR devices exhibit both a small Lorentz function fitting parameter B0 of 2.3 mT and a non-Lorentz function fitting parameter B1 of 0.86 mT in the strictly limited bipolaron model. Moreover, we demonstrate the effect of aggregation and intrinsic trap states, pointing out a way for the improvement of the sensitivity.

Cyclohexyl-Substituted Anthracene Derivatives for High Thermal Stability Organic Semiconductors.

A novel p-type organic semiconductor with high thermal stability is developed by simply incorporating cyclohexyl substituted aryl groups into the 2,6-position of anthracene, namely 2,6-di(4-cyclohexylphenyl)anthracene (DcHPA), and a similar compound with linear alkyl chain, 2,6-di(4-n-hexylphenyl)anthracene (DnHPA), is also studied for comparison. DcHPA shows sublimation temperature around 360°C, and thin film field-effect transistors of DcHPA could maintain half of the original mobility value when heated up to 150°C. Corresponding DnHPA has sublimation temperature of 310°C and the performance of its thin film devices decreases by about 50% when heated to 80°C. The impressing thermal stability of the cyclohexyl substitution compounds might provide guidelines for developing organic electronic materials with high thermal stability.

Novel Air Stable Organic Radical Semiconductor of Dimers of Dithienothiophene, Single Crystals, and Field-Effect Transistors.

Singly linked and vinyl-linked dimers of dithienothiophenes exhibit different electronic behaviors. Single crystals of the singly linked dimer show a high conductivity of 0.265 S cm(-1) , five orders of magnitude higher than that of the vinyl-linked dimer. The huge increase in the hole density of singly linked dimers results from the formation of radicals, which can be reversibly tuned by facile thermal de-doping.

High mobility emissive organic semiconductor.

The integration of high charge carrier mobility and high luminescence in an organic semiconductor is challenging. However, there is need of such materials for organic light-emitting transistors and organic electrically pumped lasers. Here we show a novel organic semiconductor, 2,6-diphenylanthracene (DPA), which exhibits not only high emission with single crystal absolute florescence quantum yield of 41.2% but also high charge carrier mobility with single crystal mobility of 34 cm(2) V(-1) s(-1). Organic light-emitting diodes (OLEDs) based on DPA give pure blue emission with brightness up to 6,627 cd m(-2) and turn-on voltage of 2.8 V. 2,6-Diphenylanthracene OLED arrays are successfully driven by DPA field-effect transistor arrays, demonstrating that DPA is a high mobility emissive organic semiconductor with potential in organic optoelectronics.

Thin film field-effect transistors of 2,6-diphenyl anthracene (DPA).

An anthracene derivative, 2,6-diphenyl anthracene (DPA), was successfully synthesized with three simple steps and a high yield. The compound was determined to be a durable high performing semiconductor with thin film device mobility over 10 cm(2) V(-1) s(-1). The efficient synthesis and high performance indicates its great potential in organic electronics.

Tuning the crystal polymorphs of alkyl thienoacene via solution self-assembly toward air-stable and high-performance organic field-effect transistors.

The first example for thienoacene derivatives with selective growth of different crystal polymorphs is simply achieved by solution-phase self-assembly. Compared with platelet-shaped α-phase crystals, organic field-effect transistors (OFETs) based on microribbon-shaped ß-phase crystals show a hole mobility up to 18.9 cm(2) V(-1) s(-1), which is one of the highest values for p-type organic semiconductors measured under ambient conditions.

Porphyrin nanoassemblies via surfactant-assisted assembly and single nanofiber nanoelectronic sensors for high-performance H2O2 vapor sensing.

Porphyrins are recognized as important π-conjugated molecules correlating supramolecular chemistry, nanoscience, and advanced materials science. So far, as their supramolecular nanoassemblies are addressed, most efforts focus on the photo- or opto-related subjects. Beyond these traditional subjects, it is strongly desired to develop advanced porphyrin nanoassemblies in some other new topics of paramount importance. By means of a surfactant-assisted assembly, we herein show that porphyrins of different central metal ions, 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (H2TPyP), zinc 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (ZnTPyP), and oxo-[5,10,15,20-tetra(4-pyridyl)porphyrinato]titanium(IV) (TiOTPyP), could be organized to form irregular aggregates, short nanorods, and long yet straight nanofibers, respectively. Remarkably, in terms of an organic ribbon mask technique, we show that such long yet straight TiOTPyP nanofibers could be integrated into single nanofiber-based two-end nanoelectronics. Such simple nanodevices could serve as high-performance sensors of a satisfactory stability, reproducibility, and selectivity for an expeditious detection of vapor-phase H2O2. This provides a new alternative for a fast sensing of vapor-phase H2O2, which is currently an important issue in the fields of anti-terrorism, industrial healthcare, etc. In contrast to the traditional investigations focusing on the photo- or opto-related topics, our work endows porphyrin nanostructures with new opportunities as advanced nanomaterials in terms of portable yet high-performance nanoelectronic sensors, which is an issue of general concern in modern advanced nanomaterials.

Layer-stacking growth and electrical transport of hierarchical graphene architectures.

Hierarchical graphene architectures (HGAs) that grow by stacking of layers are produced on a liquid copper surface using chemical vapor deposition. The stacking mode--for example hexagonal-hexagonal-hexagonal or hexagonal-snowflake-dendritic--can be simply controlled. Measurements of the electrical properties of HGAs indicate that hierarchical stacking of graphene may be a simple and effective way of tailoring their properties without degrading them.

Thiepin-fused heteroacenes: simple synthesis, unusual structure, and semiconductors with less anisotropic behavior.

The simple one-pot syntheses of sulfur-rich thiepin-fused heteroacences with an alkylidene-fluorene framework, THA1 and THA6 (thiepin-fused heteroacene 1 or 6, in which the thiepin is conjugated at both ortho positions with SCH3 or SC6 H13 , respectively), is reported. Based on electrochemical studies and theoretical calculations, their LUMO energies are relatively low (-3.26 eV), and their HOMO and HOMO-1 orbitals are nearly degenerate. The thiepin ring contributes mainly to HOMO-1 and LUMO orbitals, however, HOMO orbitals dominantly reside on thienoacence rings. Within the crystal of THA1, the molecules adopt a herringbone arrangement and multiple intermolecular interactions lead to the formation of a 2D network. Interestingly, THA6 shows totally different intermolecular arrangements. Organic field-effect transistor (OFET) devices show both compounds exhibiting p-type semiconducting behavior. Thin films or microcrystals of THA1 possess relatively high hole mobility. Moreover, the mobilities of the microcrystal of THA1 along three directions are in the same order, thus the hole-carrier transporting within the hexagonal-plane of microcrystal of THA1 exhibits less anisotropic behavior. In comparison, both thin films and microrods of THA6 show low hole mobilities. This agrees well with the intermolecular arrangements and interactions within crystal of THA6. Further theoretical calculations reveal that significant intermolecular electronic coupling among HOMO-1 orbitals and sulfur atoms play an important role in intermolecular electronic coupling for THA1.

"Double exposure method": a novel photolithographic process to fabricate flexible organic field-effect transistors and circuits.

A novel process called "double exposure method" has for the first time been developed to utilize common organic materials as insulating layers at low annealing temperature in the process of photolithography. In this method, organic dielectric layer will not dissolve in the final lift-off step by using developer to replace traditional acetone. Bottom-gate bottom-contact (BGBC) OFETs are fabricated on the flexible PET substrates with polystyrene (PS) and pentacene as dielectric layer and semiconductor layer, respectively. Transistors with mobility of 0.36 cm2 V(-1) s(-1) and logic inverter with gain of 9 on the plastic substrates have been fabricated, demonstrating the potential appliction of "double exposure method" in flexible organic electronics.