Keke K. Zhang

High-performance organic single-crystal field-effect transistors of indolo[3,2-b]carbazole and their potential applications in gas controlled organic memory devices.

Organic fi eld-effect transistors (OFETs) have attracted considerable attention because of their potential applications in inverters, display driving circuits, memory cells, sensors, and so on. [ 1 ] High charge-carrier mobility, good environmental stability, and low fabrication cost are the three key factors to realize the goals. Many series of organic semiconductors with rational design have been synthesized to meet these demands. [ 2 ] Linearacene-based OFETs show high mobilities because of the strong extended π – π interaction and enhanced intermolecular overlapping of acene molecules. [ 3–9 ] For instance, pentacene, a representative with fi ve linear acene rings, shows high charge carrier mobilities of above 1 cm 2 V − 1 s − 1 in the form of a single crystal [ 3 ]

Atomically Flat, Large-Sized, Two-Dimensional Organic Nanocrystals

Large-sized, 2D single crystals of perylene are grown by both solution-cast and physical vapor transport methods. The crystals have a atomically flat parallelogram morphology and the aspect ratios of the lateral extension compared to the thickness are up to 10(3) . The atomically flat feature leads to good interface contact, making a single-crystal field-effect transistor with higher mobility. The mobility of atomically flat crystals can be 10(3) -10(4) times higher than rough crystals.

Ultrathin organic single crystals: fabrication, field-effect transistors and thickness dependence of charge carrier mobility

Organic single crystals with thickness ranging from a few monolayers to micrometres were fabricated by an “Organic Crystal Cleavage” method. The mobility slightly increased with decreased thickness and rose sharply when the crystal thickness was below some critical thickness. The gate induced charges in the field-effect transistor (FET) channel and in the vicinity of the metal–semiconductor interface reducing the contact barrier. The values of mobility measured on very thin crystals without the contact barrier precisely reflect the transport properties of organic semiconductors.

Control of Radiative Exciton Recombination by Charge Transfer Induced Surface Dipoles in MoS2 and WS2 Monolayers.

Due to the two dimensional confinement of electrons in a monolayer of 2D materials, the properties of monolayer can be controlled by electrical field formed on the monolayer surface. F4TCNQ was evaporated on MoS2 and WS2 monolayer forming dipoles between strong acceptor, F4TCNQ, and monolayers of MoS2 or WS2. The strong acceptor attracts electrons (charge transfer) and decreases the number of the ionized excitons. Free excitons undergo radiative recombination in both MoS2 and WS2. Moreover, the photoluminescence enhancement is stronger in WS2 where the exciton-phonon coupling is weaker. The theoretical model indicates that the surface dipole controls the radiative exciton recombination and enhances photoluminescence radiation. Deposition of F4TCNQ on the 2D monolayers enables a convenient control of the radiative exciton recombination and leads to the applications of these materials in lasers or LEDs.

Tuning of the degree of charge transfer and the electronic properties in organic binary compounds by crystal engineering: a perspective

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.

From Linear to Angular Isomers: Achieving Tunable Charge Transport in Single‐Crystal Indolocarbazoles Through Delicate Synergetic CH/NH⋅⋅⋅π Interactions

Weak intermolecular interaction in organic semiconducting molecular crystals plays an important role in molecular packing and electronic properties. Here, four five-ring-fused isomers were rationally designed and synthesized to investigate the isomeric influence of linear and angular shapes in affecting their molecular packing and resultant electronic properties. Single-crystal field-effect transistors showed mobility order of 5,7-ICZ (3.61 cm2  V-1  s-1 ) >5,11-ICZ (0.55 cm2  V-1  s-1 ) >11,12-ICZ (ca. 10-5  cm2  V-1  s-1 ) and 5,12-ICZ (ca. 10-6  cm2  V-1  s-1 ). Theoretical calculations based on density functional theory (DFT) and polaron transport model revealed that 5,7-ICZ can reach higher mobilities than the others thanks to relatively higher hole transfer integral that links to stronger intermolecular interaction due to the presence of multiple NH⋅⋅⋅π and CH⋅⋅⋅π(py) interactions with energy close to common NH⋅⋅⋅N hydrogen bonds, as well as overall lower hole-vibrational coupling owing to the absence of coupling of holes to low frequency modes due to better π conjugation.