Meniscus-Guided Deposition of Organic Semiconductor Thin Films: Materials, Mechanism, and Application in Organic Field-Effect Transistors

Solution-processable organic semiconductors are one of the promising materials for the next generation of organic electronic products, which call for high-performance materials and mature processing technologies. Among many solution processing methods, meniscus-guided coating (MGC) techniques have the advantages of large-area, low-cost, adjustable film aggregation, and good compatibility with the roll-to-roll process, showing good research results in the preparation of high-performance organic field-effect transistors. In this review, the types of MGC techniques are first listed and the relevant mechanisms (wetting mechanism, fluid mechanism, and deposition mechanism) are introduced. The MGC processes are focused and the effect of the key coating parameters on the thin film morphology and performance with examples is illustrated. Then, the performance of transistors based on small molecule semiconductors and polymer semiconductor thin films prepared by various MGC techniques is summarized. In the third section, various recent thin film morphology control strategies combined with the MGCs are introduced. Finally, the advanced progress of large-area transistor arrays and the challenges for roll-to-roll processes are presented using MGCs. Nowadays, the application of MGCs is still in the exploration stage, its mechanism is still unclear, and the precise control of film deposition still needs experience accumulation.

Strong π-stacking causes unusually large anisotropic thermal expansion and thermochromism

π-stacking in ground-state dimers/trimers/tetramers of N-butoxyphenyl(naphthalene)diimide (BNDI) exceeds 50 kcal ⋅ mol^-1 in strength, drastically surpassing that for the ^*3[pyrene]₂ excimer (∼30 kcal ⋅ mol^-1; formal bond order = 1) and similar to other weak-to-moderate classical covalent bonds. Cooperative π-stacking in triclinic (BNDI-T) and monoclinic (BNDI-M) polymorphs effects unusually large linear thermal expansion coefficients (α _a , α _b , α _c , β) of (452, -16.8, -154, 273) × 10^-6 ⋅ K^-1 and (70.1, -44.7, 163, 177) × 10^-6 ⋅ K^-1, respectively. BNDI-T exhibits highly reversible thermochromism over a 300-K range, manifest by color changes from orange (ambient temperature) toward red (cryogenic temperatures) or yellow (375 K), with repeated thermal cycling sustained for over at least 2 y.

Electron Transport in Naphthalene Diimide Derivatives

Two naphthalene diimides derivatives containing two different (alkyl and alkoxyphenyl) N-substituents were studied, namely, N,N′-bis(sec-butyl)-1,4,5,8-naphthalenetetracarboxylic acid diimide (NDI-s-Bu) and N,N′-bis(4-n-hexyloxyphenyl)-1,4,5,8-naphthalenetetracarboxylic acid diimide (NDI-4-n-OHePh). These compounds are known to exhibit electron transport due to their electron-deficient character evidenced by high electron affinity (EA) values, determined by electrochemical methods and a low-lying lowest unoccupied molecular orbital (LUMO) level, predicted by density functional theory (DFT) calculations. These parameters make the studied organic semiconductors stable in operating conditions and resistant to electron trapping, facilitating, in this manner, electron transport in thin solid layers. Current–voltage characteristics, obtained for the manufactured electron-only devices operating in the low voltage range, yielded mobilities of 4.3 × 10⁻⁴ cm²V⁻¹s⁻¹ and 4.6 × 10⁻⁶ cm²V⁻¹s⁻¹ for (NDI-s-Bu) and (NDI-4-n-OHePh), respectively. Their electron transport characteristics were described using the drift–diffusion model. The studied organic semiconductors can be considered as excellent candidates for the electron transporting layers in organic photovoltaic cells and light-emitting diodes

The thermo-responsive behavior in molecular crystals of naphthalene diimides and their 3D printed thermochromic composites

Alteration of the number of carbon atoms on the alkoxyphenyl substituent in naphthalene diimides results in tunable thermo-salient behavior.

Parylene C as a versatile dielectric material for organic field-effect transistors

An emerging new technology, organic electronics, is approaching the stage of large-scale industrial application. This is due to a remarkable progress in synthesis of a variety of organic semiconductors, allowing one to design and to fabricate, so far on a laboratory scale, different organic electronic devices of satisfactory performance. However, a complete technology requires upgrading of fabrication procedures of all elements of electronic devices and circuits, which not only comprise active layers, but also electrodes, dielectrics, insulators, substrates and protecting/encapsulating coatings. In this review, poly(chloro-para-xylylene) known as Parylene C, which appears to become a versatile supporting material especially suitable for applications in flexible organic electronics, is presented. A synthesis and basic properties of Parylene C are described, followed by several examples of use of parylenes as substrates, dielectrics, insulators, or protecting materials in the construction of organic field-effect transistors.

Thermo-mechanically responsive crystalline organic cantilever

Dynamic molecular crystals lift weights up to ∼100× heavier than themselves powered by a thermally induced single-crystal to single-crystal phase transition.

Synthesis, photophysical properties and application in organic light emitting devices of rhenium(i) carbonyls incorporating functionalized 2,2′:6′,2′′-terpyridines

Photophysics of [ReCl(CO)₃(4′-R-terpy-κ²N)].

Rhenium(i) terpyridine complexes – synthesis, photophysical properties and application in organic light emitting devices

The structural and photophysical characterization of new Re(i) complexes was reported.

Theoretical investigations of charge carrier transport in organic semiconductors of naphthalene bisimides N-substituted with alkoxyphenyl groups

Three novel alkoxyphenyl N-substituted naphthalene bisimide derivatives, N,N′-bis(4-n-butoxyphenyl)-1,8:4,5-naphthalenetetracarboxylic (NBI1), N,N′-bis(4-n-hexyloxyphenyl)-1,8:4,5-naphthalenetetracarboxylic (NBI2), and N,N′-bis(4-n-octyloxyphenyl)-1,8:4,5-naphthalenetetracarboxylic (NBI3) as potential organic semiconductors, have been investigated using density functional theory calculations coupled with the incoherent charge-hopping model at the molecular and crystal levels. The calculated results demonstrate that the low-lying and delocalized LUMOs and larger adiabatic electron affinities of these compounds are beneficial to their stability when acting as n-type organic semiconductors. The reorganization energy and transfer integral can significantly influence the charge carrier mobility. The compounds featured with the small reorganization energy and large transfer integral have relatively high charge mobilities. The electron coupling among the dominant hopping pathways indicates that the charge-transport processes happen in the parallel dimer of neighboring molecules with π–π interaction. The investigation of the angle dependence of charge carrier mobility showed that both NBI1 and NBI3 crystals exhibit remarkable anisotropic charge transporting behaviors. The calculated absorption spectra by the time-dependent density functional theory revealed that the strongest absorption peaks in the visible region are assigned to the π → π* transition and these peaks are regulated by the transitions of HOMO → LUMO. The calculated electron mobilities of NBI1, NBI2, and NBI3 are 0.0365, 0.0312, and 0.0801 cm2 V–1 s–1, respectively, indicating that these compounds are suitable for n-type organic semiconductors.

Theoretical study of the fluorination effect on charge transport properties in fused thiophene derivatives

A strategy for improving electron mobility of fused thiophenes by fluorination.

UV-vis and EPR spectroelectrochemical investigations of triarylamine functionalized arylene bisimides

The ambipolar behavior of groups of N-substituted and core-functionalized triarylamine arylene bisimides were investigated by electrochemical and spectroelectrochemical (UV-vis and EPR spectroelectrochemistry) techniques.