A Solution‐Processable Liquid‐Crystalline Semiconductor for Low‐Temperature‐Annealed Air‐Stable N‐Channel Field‐Effect Transistors

Abstract

A new solution-processable and air-stable liquid-crystalline n-channel organic semiconductor (2,2'-(2,8-bis(5-(2-octyldodecyl)thiophen-2-yl)indeno[1,2-b]fluorene-6,12-diylidene)dimalononitrile, α,ω-2OD-TIFDMT) with donor-acceptor-donor (D-A-D) π conjugation has been designed, synthesized, and fully characterized. The new semiconductor exhibits a low LUMO energy (-4.19 eV) and a narrow optical bandgap (1.35 eV). The typical pseudo-focal-conic fan-shaped texture of a hexagonal columnar liquid-crystalline (LC) phase was observed over a wide temperature range. The spin-coated semiconductor thin films show the formation of large (≈0.5-1 μm) and highly crystalline platelike grains with edge-on molecular orientations. Low-temperature-annealed (50 °C) top-contact/bottom-gate OFETs have provided good electron mobility values as high as 0.11 cm (V s) and high I /I ratios of 10 to 10 with excellent ambient stability. This indicates an enhancement of two orders of magnitude (100×) when compared with the β-substituted parent semiconductor, β-DD-TIFDMT (2,2'-(2,8-bis(3-dodecylthiophen-2-yl)indeno[1,2-b]fluorene-6,12-diylidene)dimalononitrile). The current rational alkyl-chain engineering route offers great advantages for D-A-D π-core coplanarity in addition to maintaining good solubility in organic solvents, and leads to favorable optoelectronic/physicochemical characteristics. These remarkable findings demonstrate that α,ω-2OD-TIFDMT is a promising semiconductor material for the development of n-channel OFETs on flexible plastic substrates and LC-state annealing of the columnar liquid crystals can lower the electron mobility for transistor-type charge transport.

Trends in molecular design strategies for ambient stable n-channel organic field effect transistors

“…Usta and co-workers have varied the position of two terminal alkyl chains in compound 4p from b-to a,o positions to develop a new air stable molecular semiconductor 4q which shows liquid crystalline (LC) properties. 204 But, interestingly, at higher temperature the charge transport characteristics diminish as compared to those of devices annealed at 50 1C. This might be due to poorer thin film microstructure at the semiconductor/dielectric interface while cooling from the LC phase for the annealed samples.…”

A Solution‐Processable meso‐Phenyl‐BODIPY‐Based n‐Channel Semiconductor with Enhanced Fluorescence Emission

“…Owing to its highly π‐electron deficient electronic structure resulting in an energetically stabilized frontier orbitals, BODIPY is one of the unique π‐acceptor building blocks that could be synthesized and functionalized in a few steps. Thanks to its excellent structural properties including high π‐core planarity, large dipole moment (μ∼3–4 D), good π‐delocalization, and high solubility, BODIPY is an ideal building block to form solution‐processable donor‐acceptor (D‐A) type n ‐channel semiconductor architectures . In addition to these structural features, the electronic properties of BODIPY‐based semiconductors are unique because the majority charge carrier is highly dependent on its π‐architecture.…”

“…Thanks to its excellent structural properties including high π-core planarity, large dipole moment (μ~3-4 D), good π-delocalization, and high solubility, BODIPY is an ideal building block to form solutionprocessable donor-acceptor (D-A) type n-channel semiconductor architectures. [25][26][27][28] In addition to these structural features, the electronic properties of BODIPY-based semiconductors are unique because the majority charge carrier is highly dependent on its π-architecture. While aromatic substitution on BODIPY's meso-position yields n-channel (electron-transporting) semiconductivity, [29] π-extension through 2,6-positions leads to hole-transport (p-channel) characteristics.…”

An A‐D‐A′‐D‐A Conjugated Molecule Entailing Diazapentalene Unit for an n‐Type Organic Semiconductor

“…[16,[34][35][36] Various conjugated molecules with electron-withdrawing groups or/andq uinoidal structures have been investigated for n-types emiconductors. [37][38][39][40][41] Gao, Zhu and co-workers developed core-expanded naphthalene diimides fused with 2-(1,3dithiol-2-ylidene)malonitrile groups as n-type semiconductors, which exhibited high electron mobilities up to 0.51 cm 2 V À1 s À1 . [17] Zhu, Heeneya nd co-workerss eparately reportedc onjugated molecules in which the DPP moieties were transformed into the quinoidal structure to promote planarity and lower LUMO level, leading to electron mobilitiesu pt o 0.5 cm 2 V À1 s À1 .…”