The electronic properties of interfaces between two different solids can differ strikingly from those of the constituent materials. For instance, metallic conductivity-and even superconductivity-have recently been discovered at interfaces formed by insulating transition-metal oxides. Here, we investigate interfaces between crystals of conjugated organic molecules, which are large-gap undoped semiconductors, that is, essentially insulators. We find that highly conducting interfaces can be realized with resistivity ranging from 1 to 30 kohms per square, and that, for the best samples, the temperature dependence of the conductivity is metallic. The observed electrical conduction originates from a large transfer of charge between the two crystals that takes place at the interface, on a molecular scale. As the interface assembly process is simple and can be applied to crystals of virtually any conjugated molecule, the conducting interfaces described here represent the first examples of a new class of electronic systems.

Single-crystal field-effect transistors (FETs) based on a fluorocarbon-substituted dicyanoperylene-3,4:9,10-bis(dicarboximide) [PDIF-CN(2)] were fabricated by lamination of the semiconductor crystal on Si-SiO(2)/PMMA-Au gate-dielectric-contact substrates. These devices were characterized both in vacuum and in the air, and they exhibit electron mobilities of ca. 6-3 and ca. 3-1 cm(2) V(-1) s(-1), respectively, I(on):I(off) > 10(3), and near-zero threshold voltage.

Organic semiconductors have unique optical, mechanical and electronic properties that can be combined with customized chemical functionality. In the crystalline form, determinant features for electronic applications, such as molecular purity, the charge mobility or the exciton diffusion length, reveal a superior improved performance when compared with materials in a more disordered form. However, the use of organic single crystals in devices is still limited to a few applications, such as field-effect transistors. Here we report the first example of photoconductive behaviour of single-crystal charge-transfer interfaces. The system composed of rubrene and 7,7,8,8-tetracyanoquinodimethane presents a responsivity reaching 1 A W À 1 , corresponding to an external quantum efficiency of nearly 100%. This result opens the possibility of using organic single-crystal interfaces in photonic applications.

Transparent and flexible electrodes are widely used on a variety of substrates such as plastics and glass. Yet, to date, transparent electrodes on a textile substrate have not been explored. The exceptional electrical, mechanical and optical properties of monolayer graphene make it highly attractive as a transparent electrode for applications in wearable electronics. Here, we report the transfer of monolayer graphene, grown by chemical vapor deposition on copper foil, to fibers commonly used by the textile industry. The graphene-coated fibers have a sheet resistance as low as ~1 kΩ per square, an equivalent value to the one obtained by the same transfer process onto a Si substrate, with a reduction of only 2.3 per cent in optical transparency while keeping high stability under mechanical stress. With this approach, we successfully achieved the first example of a textile electrode, flexible and truly embedded in a yarn.

Atomically thin materials such as graphene are uniquely responsive to charge transfer from adjacent materials, making them ideal charge-transport layers in phototransistor devices. Effective implementation of organic semiconductors as a photoactive layer would open up a multitude of applications in biomimetic circuitry and ultra-broadband imaging but polycrystalline and amorphous thin films have shown inferior performance compared to inorganic semiconductors. Here, the long-range order in rubrene single crystals is utilized to engineer organic-semiconductor-graphene phototransistors surpassing previously reported photogating efficiencies by one order of magnitude. Phototransistors based upon these interfaces are spectrally selective to visible wavelengths and, through photoconductive gain mechanisms, achieve responsivity as large as 10 A W and a detectivity of 9 × 10 Jones at room temperature. These findings point toward implementing low-cost, flexible materials for amplified imaging at ultralow light levels.

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We perform a combined experimental and theoretical study of tetramethyltetraselenafulvalene ͑TMTSF͒ single-crystal field-effect transistors, whose electrical characteristics exhibit clear signatures of the intrinsic transport properties of the material. We present a simple, well-defined model based on physical parameters and we successfully reproduce quantitatively the device properties as a function of temperature and carrier density. The analysis allows its internal consistency to be checked, and enables the reliable extraction of the density and characteristic energy of shallow and deep traps in the material. Our findings provide indications as to the origin of shallow traps in TMTSF transistors.

Starting from the first organic spin ladder reported, a dithiophene‐tetrathiafulvalene salt ((DT‐TTF)2[Au(mnt)2]) (mnt = maleonitriledithiolate), two different approaches to enlarge the family of organic spin‐ladder systems are described. The first approach consists of a molecular variation of the donor; to that purpose, the new TTF derivative ethylenethiothiophene‐tetrathiafulvalene (ETT‐TTF, 3), is synthesized and structurally characterized. From this donor a new ladder‐like structure compound, (ETT‐TTF)2[Au(mnt)2] (4), isostructural with (DT‐TTF)2[Au(mnt)2], is obtained. However, the magnetic properties of 4 do not follow the known spin‐ladder behavior owing to orientational disorder exhibited by the ETT‐TTF molecules in the crystal structure. In the second approach, the acceptor complex is changed, either in the nature of the ligand or in the metal. With the [Au(i‐mnt)2]– salt (i‐mnt = iso‐maleonitriledithiolate), the new ladder‐like compound (DT‐TTF)2[Au(i‐mnt)2] (5), isostructural with 4, is obtained, but only as a minority product. Two other compounds with a different anion generated in situ, bearing a Au(I) dimeric core, were also isolated; (DT‐TTF)9[Au2(i‐mnt)2]2 (6) as the most abundant phase and (DT‐TTF)2[Au2(i‐mnt)2] (7) as another minority phase. Salt 7 is characterized by X‐ray crystallography as a chiral compound, due to the torsion of the ligands around the central Au–Au bond. The magnetic properties of (DT‐TTF)2[Au(i‐mnt)2] (5) indicate that it follows a spin‐ladder behavior and the electron paramagnetic resonance (EPR) data is fitted to the Troyer and Barnes and Riera equations with the parameters Δ/kB = 71 K, J∥/kB = 86 K, and J⟂/kB = 142 K, indicating a J⟂/J∥ ratio of 1.65. The change of the gold complex [Au(mnt)2] for its copper analogue, [Cu(mnt)2] also leads to a ladder‐like structure, (DT‐TTF)2[Cu(mnt)2] (8), which is isostructural with the gold analogue and with salts 4 and 5. The fully ionic salt (DT‐TTF)[Cu(mnt)2] (9) is also obtained. The magnetic properties demonstrated that compound 8 is the third organic spin‐ladder system of this family, and the values found by a fitting to the ladder equations were Δ/kB = 123 K, J∥/kB = 121 K, and J⟂/kB = 218 K, corresponding to a J⟂/J∥ ratio of 1.75, similar to that of 5 and close to that of an ideal spin ladder.