Dithieno[2,3- d;2'3'- d']benzo[1,2- b;4,5- b']dithiophene forms mixed-stack charge-transfer complexes with fluorinated tetracyanoquinodimethanes (F TCNQs, n = 0, 2, and 4) and dimethyldicyanoquinonediimine (DMDCNQI). The single-crystal transistors of the FTCNQ complexes exhibit electron transport, whereas the DMDCNQI complex shows hole transport as well. The dominance of electron transport is explained by the superexchange mechanism, where transfers corresponding to the acceptor-to-acceptor hopping ( t) are more than 10 times larger than the donor-to-donor hopping ( t). This is because the donor orbital next to the highest occupied molecular orbital makes a large contribution to the electron transport owing to the symmetry matching. Like this, inherently asymmetrical electron and hole transport in alternating stacks is understood by analyzing bridge orbitals other than the transport orbitals.

To investigate charge polarity of transistors based on donor/acceptor cocrystals, charge-transfer complexes of wide donor molecules such as perylene and pyrene are investigated. As-grown single-crystal transistors are deposited from solutions, which attain perfect reproducibility in comparison with the conventional pasted single-crystal transistors. Perylene complexes of dicyanoquinonediimines (DCNQI) with substituents X = CH 3 , Cl, and Br show holedominant ambipolar characteristics. Owing to the large molecular width, the donor/acceptor orbitals are not orthogonal, and ambipolar transport is realized. In contrast, pyrene works similarly to ordinary acenes, and not only the tetracyanoquinodimethane (TCNQ) complexes but also the DCNQI complex show only electron transport. The existence of the short-axis offset in the molecular overlap is the criterion that transforms electron transport to ambipolar transport.

For basic understanding of transistor properties of doped organic semiconductors, 3,3′,5,5′-tetramethylbenzidine charge-transfer complexes are investigated, which change from neutral to ionic by varying the acceptors. When going into the ionic state, the bulk conduction increases more rapidly than the mobility, but sufficiently thin devices exhibit transistor properties. The resulting ambipolar characteristics are analyzed in the linear regions at small drain voltages in analogy with graphene transistors. The model is further extended to include partial overlap of electron and hole transport regions. In the temperature dependence, the activation energy loses gate voltage dependence when the neutral–ionic transition takes place by 0.1–0.2 eV above the equal acceptor and donor levels; the difference comes from the typical trap (polaron) depth or the Madelung energy.

N-Unsubstituted thienoisoindigo and the diphenyl derivative are prepared and these molecules exhibit ambipolar performance in organic thin film transistors.

2D transitional metal dichalcogenide (2D-TMDC) materials, as inorganic graphene analogs (IGAs), have been intensively investigated for their novel chemical and physical properties when the thickness is reduced to a few atomic layers, such as MoS 2 , WS 2 , among others. [1] Tantalum disulfide, TaS 2 , one of the TMDC materials, has attracted growing attention recently. In the bulk state, TaS 2 occupies 2H or 1T structure, which is composed of covalently bonded STaS layers. 1T-TaS 2 with Ta in octahedral coordination with S atoms exhibits semiconducting behavior, and it has a commensurate charge density wave (CCDW) phase under 180 K. Adjusted by pressure, the superconductivity of 1T-TaS 2 develops in the CCDW state and survives to very high pressure. [2][3][4] 2H-TaS 2 with Ta in trigonal prismatic coordination with S atoms exhibits metallic behaviors with CDW phase transition (T CDW = 75 K) and superconductivity (T c = 0.8 K). [5][6][7][8] The electrical conductivity of single-crystal 2H-TaS 2 can reach 6.8 × 10 4 S m −1 at room temperature. [9] When the thickness is reduced to a few layers, interesting phenomena have been found, such as gate-tunable phase transition [10] and enhanced superconductivity, [11] which are promising properties for applications like electrical oscillators, [12] fast memories, [13] hydrogen evolution catalyst. [14] Until now, 2D TaS 2 has been mainly synthesized by the mechanical exfoliation method, [15] which is time consuming and of poor reproductivity and low yield. It has been noticed that the exfoliation of TaS 2 seems rather difficult and the atomically thin layers are unstable in ambient environments due to easy oxidation. [16] Complex encapsulation techniques are therefore required to help preserve the samples in air. [16] The chemical vapor deposition method [17] proves to be swift and effective in fabrication of high-quality 2D materials, but large-area synthesis of full-coverage atomically thin material is still in progress. For device applications, solution-based chemical synthesis is particularly important, as the product can be easily integrated into electronic devices.There is a new solution-based strategy to synthesize 2D materials in the form of inorganic/organic superlattice, in which the inorganic layers may get close to the low-dimensional state due to the spatial separation by the organic molecules. In our previous papers, we synthesized a hybrid superlattice with alternating 2D [TiS 2 ] monolayers and organic cations through an electrochemical reaction process. [18] The isolation of the [TiS 2 ] TaS 2 nanolayers with reduced dimensionality show interesting physics, such as a gate-tunable phase transition and enhanced superconductivity, among others. Here, a solution-based strategy to fabricate a large-area foil of hybrid TaS 2 /organic superlattice, where [TaS 2 ] monolayers and organic molecules alternatively stack in atomic scale, is proposed. The [TaS 2 ] layers are spatially isolated with remarkably weakened interlayer bonding, resulting in lattice vibration ...