We report on single crystal high mobility organic field-effect transistors (OFETs) prepared on prefabricated substrates using a "flip-crystal" approach. This method minimizes crystal handling and avoids direct processing of the crystal that may degrade the FET electrical characteristics. A chemical treatment process for the substrate ensures a reproducible device quality. With limited purification of the starting materials, hole mobilities of 10.7, 1.3, and 1.4 cm^2/Vs have been measured on rubrene, tetracene, and pentacene single crystals, respectively. Four-terminal measurements allow for the extraction of the "intrinsic" transistor channel resistance and the parasitic series contact resistances. The technique employed in this study shows potential as a general method for studying charge transport in field-accumulated carrier channels near the surface of organic single crystals.

https://arxiv.org/pdf/cond-mat/0403210.pdf

Hole mobility in organic single crystals measured by a "flip-crystal" field-effect technique

Small‐Molecule‐Based Organic Field‐Effect Transistor for Nonvolatile Memory and Artificial Synapse

The continued growth in the demand of data storage and processing has spurred the development of high-performance storage technologies and brain-inspired neuromorphic hardware. Semiconductor quantum dots (QDs) offer an appealing option for these applications since they combine excellent electronic/optical properties and structural stability and can address the requirements of low-cost, large-area, and solution-based manufactured technologies. Here, we focus on the development of nonvolatile memories and neuromorphic computing systems based on QD thin-film solids. We introduce recent advances of QDs and highlight their unique electrical and optical features for designing future electronic devices. We also discuss the advantageous traits of QDs for novel and optimized memory techniques in both conventional flash memories and emerging memristors. Then, we review recent advances in QD-based neuromorphic devices from artificial synapses to light-sensory synaptic platforms. Finally, we highlight major challenges for commercial translation and consider future directions for the postsilicon era.

Semiconductor Quantum Dots for Memories and Neuromorphic Computing Systems

Functional emulation of biological synapses using electronic devices is regarded as the first step toward neuromorphic engineering and artificial neural networks (ANNs). Electrolyte-gated transistors (EGTs) are mixed ionic–electronic conductivity devices capable of efficient gate-channel capacitance coupling, biocompatibility, and flexible architectures. Electrolyte gating offers significant advantages for the realization of neuromorphic devices/architectures, including ultralow-voltage operation and the ability to form parallel-interconnected networks with minimal hardwired connectivity. In this review, the most recent developments in EGT-based electronics are introduced with their synaptic behaviors and detailed mechanisms, including short-/long-term plasticity, global regulation phenomena, lateral coupling between device terminals, and spatiotemporal correlated functions. Analog memory phenomena allow for the implementation of perceptron-based ANNs. Due to their mixed-conductivity phenomena, neuromorphic circuits based on EGTs allow for facile interfacing with biological environments. We also discuss the future challenges in implementing low power, high speed, and reliable neuromorphic computing for large-scale ANNs with these neuromorphic devices. The advancement of neuromorphic devices that rely on EGTs highlights the importance of this field for neuromorphic computing and for novel healthcare technologies in the form of adaptable or trainable biointerfacing.

Electrolyte-gated transistors for synaptic electronics, neuromorphic computing, and adaptable biointerfacing

Organic tribophosphorescence materials are rarely reported and the introduction of Br atoms may be a practical way to design such materials. Here four bromine-substituted fluorene-based derivatives are presented and BrFlu-CBr, having fluorescence-phosphorescence dual-emission induced not only by UV light but also by mechanical stimulus, manifests the highest phosphorescence efficiency of 4.56 % upon photoirradiation. During the grinding process, three different triboluminescent spectra were identified. Upon introduction of a mechanical stimulus, the triboluminescence emission is cyan, whereas after an extended period it changed to blue. After removing the mechanical stimulus, green-white phosphorescent emission was observed. Careful research on single-crystal structures and theoretical calculations demonstrate that strong Br⋅⋅⋅Br interactions are vital to facilitate spin-orbit coupling and promote intersystem crossing, thus generating the unique properties.

Bromine‐Substituted Fluorene: Molecular Structure, Br–Br Interactions, Room‐Temperature Phosphorescence, and Tricolor Triboluminescence

Three diazafluorene derivatives triphenylamine (TPA)(PDAF) n (n = 1, 2, 3) serving as small molecular elements are designed and synthesized via concentrated sulfuric acid mediated Friedel-Crafts reaction With highly nonplanar topological configuration, TPA(PDAF)3 shows weaker intermolecular interaction in the solid states and thus exhibits single nanomolecular behavior, which is crucial for charge stored and retained in an organic field-effect transistor (OFET) memory device Furthermore, diazafluorene derivatives possess a completely separate highest occupied molecular orbital/lowest unoccupied molecular orbital, which offers ideal hole and electron trapping sites As charge storage elements, triphenylamine groups provide the hole trapping sites, while diazafluorene units provide the electron trapping sites and act as a hole blocking group to restrain the leakage of stored holes trapped in triphenylamine The pentacene-based OFET memory device with solution-processing TPA(PDAF)3 shows a good hole-trapping ability, high hole trapping density (455 × 1012 cm-2), fast trapping speed ( 104 s), and reliable endurance properties This study suggests that diazafluorene based donor-acceptor small molecular elements have great promise for high-performance OFET memory

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201800747

4,5-Diazafluorene-Based Donor–Acceptor Small Molecules as Charge Trapping Elements for Tunable Nonvolatile Organic Transistor Memory

Molecular bulks are favorable for the thermal and morphological stability in organic wide-bandgap semiconducting polymers with potential applications in both information and energy electronics. In this review, we present our progress in the design of fluorene-based bulky semiconductors with a fractal four-element pattern. Firstly, we established one-pot methods to spirofluorenes, especially spiro[fluorene-9,9′-xanthene] (SFX) serving as the next-generation spiro-based semiconductors. Secondly, we observed the supramolecular forces at the bulky groups and discovered the supramolecular steric hindrance (SSH) effect on polymorphisms, nanocrystals as well as device performance. Thus, a synergistically molecular attractor-repulsor theory (SMART) was proposed for the control of nanocrystal morphology, thin film phase and morphology. Thirdly, the third possible type of defects has been identified to generate green band (g-band) emission in wide-bandgap semiconductors by the introduction of molecular strain design of cyclofluorene. Finally, the first bulky polydiarylfluorene with highly crystalline and β conformation was achieved by an attractor-repulsor design of tadpole-shape monomer, which offered an effective platform to fabricate stable wide-bandgap semiconducting devices. All the discoveries offer the solid basis to break through bottlenecks of organic/polymer wide-bandgap semiconductors by the improvements of overall performances.

Progress in fluorene-based wide-bandgap steric semiconductors

A series of donor–acceptor “”-shaped gridarenes were synthesized with BT units as the crossbeam and thiophene units as the π-bridge. The donor–acceptor gridization functional effects on optoelectro...

Synthesis of Donor–Acceptor Gridarenes with Tunable Electronic Structures for Synaptic Learning Memristor

The invention relates to a nanometer grid, a nanometer polymer grid material and their preparation method and use method and belongs to the field of a photoelectric high and new technology. The nanometer polymer grid material is a homopolymer or copolymer utilizing the nanometer grid as a monomer and has a general structural formula shown in the following description. The nanometer polymer grid material has the characteristics that 1, the nanometer grid monomer has hole and semiconductor photoelectric characteristics, 2, raw materials are cheap and easily available, reaction conditions are mild and operation is easy, 3, the nanometer polymer grid material has excellent mechanical characteristics, 4, the nanometer polymer grid material has good solubility and is convenient for nanometer film or fibration processing, and 5, a rigid skeleton has the advantages of high glass-transition temperature, high heat, electrochemical stability and spectrum stability. The nanometer polymer grid material can be used as a novel nanometer polymer photoelectric material and has a good application prospect in the fields of organic electrons, spinning electrons, photoelectrons, mechano-electronic and nano-biology.

Bian Linyi

Papers

Small‐Molecule‐Based Organic Field‐Effect Transistor for Nonvolatile Memory and Artificial Synapse

4,5-Diazafluorene-Based Donor–Acceptor Small Molecules as Charge Trapping Elements for Tunable Nonvolatile Organic Transistor Memory

Progress in fluorene-based wide-bandgap steric semiconductors

Synthesis of Donor–Acceptor Gridarenes with Tunable Electronic Structures for Synaptic Learning Memristor

Nanometer grid, nanometer polymer grid material and their preparation method and use method