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Water‐gated organic field‐effect transistors (WGOFETs) are relevant devices for use in the fields of biosensors and biosystems. However, real applications require very stringent performance in terms of electrochemical stability and charge mobility to the organic semiconductor in contact with an aqueous environment. Here, a comparative study of two small‐molecule electron‐transporting perylenediimide semiconductors, which differ only in the N‐substituents named PDIF‐CN2 and PDI8‐CN2 is reported. The two materials present similar solid‐state arrangements but, while the PDI8‐CN2 shows a more 3D growth modality and electron mobility independent of the semiconductor layer thickness (≈10−4 cm2 V−1 s−1), the PDIF‐CN2 has an almost‐2D growth modality and the mobility increases with the semiconductor film thickness, reaching a maximum value of ≈5 × 10−3 cm2 V−1 s−1 at 30 nm. Above this thickness, the PDIF‐CN2 switches to a more 3D growth modality, and the mobility drops by one order of magnitude. XRR analysis indicates that a PDIF‐CN2 film can be modeled as a dense layered structure in which each layer is decoupled from the others due to the presence of fluorocarbon‐chains. The availability of additional pathways for charge transport from buried layers and the 2D versus 3D growth can explain the mobility dependence on the film thickness. [ABSTRACT FROM AUTHOR]

As fabrication and positioning of micro- and nanocrystals grow in importance in a wide range technological applications, there is an increasing requirement for the development of a shared technological platform that is able to process materials from solutions on large areas. Here, the application of lithographically controlled wetting (LCW) for the manipulation and positioning of single crystals directly on devices is reported. In the LCW, a stamp, consisting of a metallic grid, is positioned in contact with a liquid thin film spread on a substrate; under these conditions, the capillary forces pin the solution to the stamp protrusions, thus splitting the continuous film in separated droplets or channels. As the solvent evaporates and the solution reaches the saturation, the solute precipitates onto the substrate within the menisci, giving rise to a structured thin film, in correspondence of the protrusion of the stamp. The possibility to achieve a patterning of crystals of conjugated molecules with a defined shape and with controlled size directly on device is demonstrated and pattern of crystals are investigated using polarized optical microscopy, atomic force microscopy, X-ray diffraction; they are also electrically characterized. [ABSTRACT FROM AUTHOR]

The introduction of side chains in π-conjugated molecules is a design strategy widely exploited to increase molecular solubility thus improving the processability, while directly influencing the self-assembly and consequently the electrical properties of thin films. Here, a multiscale structural analysis performed by X-ray diffraction, X-ray reflectivity, and atomic force microscopy on thin films of dicyanoperylene molecules decorated with either linear or branched side chains is reported. The substitution with asymmetric branched alkyl chains allows obtaining, upon thermal annealing, field-effect transistors with enhanced transport properties with respect to linear alkyl chains. Branched chains induce molecular disorder during the film growth from solution, effectively favouring 2D morphology. Post-deposition thermal annealing leads to a structural transition towards the bulk-phase for molecules with branched chains, still preserving the 2D morphology and allowing efficient charge transport between crystalline domains. Conversely, molecules with linear chains self-assemble into 3D islands exhibiting the bulk-phase structure. Upon thermal annealing, these 3D islands keep their size constant and no major changes are observed in the organic field effect transistor characteristics. These findings demonstrate that the disorder generated by the asymmetric branched chains when the molecule is physisorbed in thin film can be instrumental for enhancing charge transport via thermal annealing. [ABSTRACT FROM AUTHOR]

Many functional properties of organic semiconductors, such as charge transport, are regulated by structural order. The control of crystallinity, orientation, and positioning of crystals—the highest form of order—inside devices presents an extraordinary opportunity to fully exploit their potentialities. On page 2387, M. Cavallini and co‐workers demonstrate direct patterning of crystals of conjugated molecules onto devices, with defined shape and controlled size. [ABSTRACT FROM AUTHOR]

We report on the production of hybrid graphene/semiconducting polymer films in one step procedure by making use of ultrasound-assisted liquid-phase exfoliation of graphite powder in the presence of π-conjugated polymers, i.e. poly(3-hexylthiophene) (P3HT) or poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']dithiophen-2-yl)-alt-[1,2,5]thiadiazolo-[3,4-c]pyridine] (PCDTPT). The polymers were chosen in view of their different propensity to form crystalline structures, their decoration with alkyl chains that are known to possess high affinity for the basal plane of graphene, the energy levels of their frontier orbitals which are extremely similar to the work function of graphene, and their high electrical performance when integrated in field-effect transistors (FETs). The polymers act as a dispersion-stabilizing agent and prevent the re-aggregation of the exfoliated graphene flakes, ultimately enabling the production of homogeneous bi-component dispersions. The electrical characterization of few-layer graphene/PCDTPT hybrids, when integrated as active layer in bottom-contact bottom-gate FETs, revealed an increase of the field-effect mobility compared to the π-conjugated-based pristine devices, a result which can be attributed to the joint effect of the few-layer graphene sheets and semiconducting polymers improving the charge-transport in the channel of the field-effect transistor. In particular, few-layer graphene/PCDTPT films displayed a 30-fold increase of PCDTPT's mobility if compared to pristine polymer samples. Such findings represent a step forward towards the optimization of graphene exfoliation and processing into electronic devices, as well as towards improved electrical performance in organic-based field-effect transistors. [ABSTRACT FROM AUTHOR]

The applications of organic semiconductorsin complex circuitrysuch as printed CMOS-like logic circuits demand miniaturization ofthe active structures to the submicrometric and nanoscale level whileenhancing or at least preserving the charge transport properties uponprocessing. Here, we addressed this issue by using a wet lithographictechnique, which exploits and enhances the molecular order in polymersby spatial confinement, to fabricate ambipolar organic field effecttransistors and inverter circuits based on nanostructured single componentambipolar polymeric semiconductor. In our devices, the current flowsthrough a precisely defined array of nanostripes made of a highlyordered diketopyrrolopyrrole-benzothiadiazole copolymer with highcharge carrier mobility (1.45 cm2V–1s–1for electrons and 0.70 cm2V–1s–1for holes). Finally, we demonstratedthe functionality of the ambipolar nanostripe transistors by assemblingthem into an inverter circuit that exhibits a gain (105) comparableto inverters based on single crystal semiconductors. [ABSTRACT FROM AUTHOR]