Navigating the transitional window for organic semiconductor single crystals towards practical integration: from materials, crystallization, and technologies to real-world applications.

Organic semiconductor single crystals (OSSCs), which possess the inherent merits of long-range order, low defect density, high mobility, structural tunability and good flexibility, have garnered significant attention in the organic optoelectronic community. Past decades have witnessed the explosive growth of OSSCs. Despite numerous conceptual demonstrations, OSSCs remain in the early stages of implementation for applications that require high integration and multifunctionality.

Organic Nonvolatile 2T Memory Cell Employing a NOT-Gate-Like Architecture Toward Binary Output Level With Enhanced Noise Tolerance.

Organic nonvolatile memory has been considered a low-cost memory technology for flexible electronics and Internet-of-things (IoT). However, a major concern is the nonuniformity of memory units, which is primarily caused by random grain boundaries, interface defects, and charge traps, making it difficult to develop high-density reliable memory arrays. This nonuniformity problem would induce read error, which is directly caused by the narrow distribution margin of memory states and low noise tolerance in conventional organic memory cells.

All-in-One 2D Molecular Crystal Optoelectronic Synapse for Polarization-Sensitive Neuromorphic Visual System.

Neuromorphic visual systems (NVSs) hold the potential to not only preserve but also enhance human visual capabilities. One such augmentation lies in harnessing polarization information from light reflected or scattered off surfaces like bees, which can disclose unique characteristics imperceptible to the human eyes. While creating polarization-sensitive optoelectronic synapses presents an intriguing avenue for equipping NVS with this capability, integrating functions like polarization sensitivity, photodetection, and synaptic operations into a singular device has proven challenging.

Frequency-Dependent Multistep Ferroelectric Polarization Switching Mechanism in P(VDF-TrFE)-Based Capacitors Induced by Polystyrene Electret-like Modulation.

In this work, we investigate multistep ferroelectric polarization switching dynamics of a series of poly(vinylidene fluoride-trifluoroethylene)/polystyrene, P(VDF-TrFE)/PS, as active layers in ferroelectric capacitors with variable P(VDF-TrFE)/PS thickness ratios and a wide range of driving voltage frequencies (1-1000 Hz). The PS electret-like modulation effects on the depolarized field fluctuation are proven to be responsible for this multistep ferroelectric polarization switching process. To be specific, the switching current density peak splits into two peaks in both positive and negative voltage ranges according to the stimulus-response (S-R) data from the metal-ferroelectric-electret-metal capacitor driven by a periodic triangular voltage wave.

Dragon-Boat-Type Heptathienoacenes: Synthesis, Structures, and Their Applications in OFETs.

A novel synthetic strategy for efficient construction of dragon-boat-type heptathienoacenes (s) via the α-β position carbon-carbon cross-coupling between two dithienothiophenes is employed. Their crystal structures are confirmed by X-ray single-crystal analysis. The first thin film FET devices of heptathienoacenes are fabricated using OTS-treated SiO/Si substrates, in which -based devices exhibit an unprecedented highest hole mobility value of 1.

Challenging Bendable Organic Single Crystal and Transistor Arrays with High Mobility and Durability toward Flexible Electronics.

Bendable organic single crystals are promising candidates for flexible electronics owing to their superior charge-transport properties. However, large-area high-quality organic single crystals are rarely available on the polymer substrates generally used in flexible electronics. Here, a surface-assisted assembly strategy based on a polymer modification, poly(amic acid) (PAA), is developed to grow large-area organic singe crystals on polymer substrates using a simple drop-casting method.

Negative Phototransistors with Ultrahigh Sensitivity and Weak-Light Detection Based on 1D/2D Molecular Crystal p-n Heterojunctions and their Application in Light Encoders.

Anomalous negative phototransistors in which the channel current decreases under light illumination hold potential to generate novel and multifunctional optoelectronic applications. Although a variety of design strategies have been developed to construct such devices, NPTs still suffer from far lower device performance compared to well-developed positive phototransistors (PPTs). In this work, a novel 1D/2D molecular crystal p-n heterojunction, in which p-type 1D molecular crystal (1DMC) arrays are embedded into n-type 2D molecular crystals (2DMCs), is developed to produce ultrasensitive NPTs.

Ultra-thin two-dimensional molecular crystals grown on a liquid surface for high-performance phototransistors.

A novel strategy for the growth of molecularly thin two-dimensional molecular crystals (2DMCs) of organic semiconductors with poor solubility was developed. Large-area bilayer 2DMCs were grown on a liquid surface at elevated temperatures, with record mobility and superior photoresponse.

Cocrystal Engineering: A Collaborative Strategy toward Functional Materials.

Cocrystal engineering with a noncovalent assembly feature by simple constituent units has inspired great interest and has emerged as an efficient and versatile route to construct functional materials, especially for the fabrication of novel and multifunctional materials, due to the collaborative strategy in the distinct constituent units. Meanwhile, the precise crystal architectures of organic cocrystals, with long-range order as well as free defects, offer the opportunity to unveil the structure-property and charge-transfer-property relationships, which are beneficial to provide some general rules in rational design and choice of functional materials. In this regard, an overview of organic cocrystals in terms of assembly, containing the intermolecular interactions and growth methods, two functionality-related factors including packing structure and charge-transfer nature, and those advanced and novel functionalities, is presented.

A "Phase Separation" Molecular Design Strategy Towards Large-Area 2D Molecular Crystals.

2D molecular crystals (2DMCs) have attracted considerable attention because of their unique optoelectronic properties and potential applications. Taking advantage of the solution processability of organic semiconductors, solution self-assembly is considered an effective way to grow large-area 2DMCs. However, this route is largely blocked because a precise molecular design towards 2DMCs is missing and little is known about the relationship between 2D solution self-assembly and molecular structure.

A Robust Nonvolatile Resistive Memory Device Based on a Freestanding Ultrathin 2D Imine Polymer Film.

Here, the synthesis of a wafer-scale ultrathin 2D imine polymer (2DP) film with controllable thickness from simple benzene-1,3,5-tricarbaldehyde (BTA) and p-phenylenediamine (PDA) building blocks is reported using a Schiff base polycondensation reaction at the air-water interface. The synthesized freestanding 2DP films are porous, insulating, and more importantly, covalently linked, which is ideally suited for nonvolatile memristors that use a conductive filament mechanism. These devices exhibit excellent switching performance with high reliability and reproducibility, with on/off ratios in the range of 10 to 10 depending on the thickness of the film.

Thermally Activated Delayed Fluorescence in an Organic Cocrystal: Narrowing the Singlet-Triplet Energy Gap via Charge Transfer.

Harvesting non-emissive spin-triplet charge-transfer (CT) excitons of organic semiconductors is fundamentally important for increasing the operation efficiency of future devices. Here we observe thermally activated delayed fluorescence (TADF) in a 1:2 CT cocrystal of trans-1,2-diphenylethylene (TSB) and 1,2,4,5-tetracyanobenzene (TCNB). This cocrystal system is characterized by absorption spectroscopy, variable-temperature steady-state and time-resolved photoluminescence spectroscopy, single-crystal X-ray diffraction, and first-principles calculations.

Scalable Fabrication of Highly Crystalline Organic Semiconductor Thin Film by Channel-Restricted Screen Printing toward the Low-Cost Fabrication of High-Performance Transistor Arrays.

Control over the morphology and crystallinity of small-molecule organic semiconductor (OSC) films is of key importance to enable high-performance organic optoelectronic devices. However, such control remains particularly challenging for solution-processed OSC devices because of the complex crystallization kinetics of small-molecule OSC materials in the dynamic flow of inks. Here, a simple yet effective channel-restricted screen-printing method is reported, which uses small-molecule OSCs/insulating polymer to yield large-grained small-molecule OSC thin-film arrays with good crystallization and preferred orientation.

Organic crystalline materials in flexible electronics.

Flexible electronics have attracted considerable attention recently given their potential to revolutionize human lives. High-performance organic crystalline materials (OCMs) are considered strong candidates for next-generation flexible electronics such as displays, image sensors, and artificial skin. They not only have great advantages in terms of flexibility, molecular diversity, low-cost, solution processability, and inherent compatibility with flexible substrates, but also show less grain boundaries with minimal defects, ensuring excellent and uniform electronic characteristics.

Free-Standing 2D Hexagonal Aluminum Nitride Dielectric Crystals for High-Performance Organic Field-Effect Transistors.

The existence of defects and traps in a transistor plays an adverse role on efficient charge transport. In response to this challenge, extensive research has been conducted on semiconductor crystalline materials in the past decades. However, the development of dielectric crystals for transistors is still in its infancy due to the lack of appropriate dielectric crystalline materials and, most importantly, the crystal morphology required by the gate dielectric layer, which is also crucial for the construction of high-performance transistor as it can greatly improve the interfacial quality of carrier transport path.

Space-Confined Strategy toward Large-Area Two-Dimensional Single Crystals of Molecular Materials.

Two-dimensional molecular crystals (2DMCs) are a promising candidate for flexible and large-area electronics. Their large-area production requires both low nuclei density and 2D crystal growth mode. As an emerging type of material, their large-area production remains a case-by-case practice.

Low-Voltage Organic Single-Crystal Field-Effect Transistor with Steep Subthreshold Slope.

Anodization is a promising technique to form high- k dielectrics for low-power organic field-effect transistor (OFET) applications. However, the surface quality of the dielectric, which is mainly inherited from the metal electrode, can be improved further than other fabrication techniques, such as sol-gel. In this study, we applied the template stripping method to fabricate a low-power single-crystalline OFET based on the anodized AlO dielectric.

Molecular cocrystals: design, charge-transfer and optoelectronic functionality.

Organic cocrystals, formed by a combination of electron-rich donors and electron-poor acceptors, play an important role in tailoring the optoelectronic properties of molecular materials. Charge transfer interactions in cocrystals not only endow them with an ordered three-dimensional (3D) supramolecular network in different constituent units, but also render them ideal scaffolds to control the intermolecular interactions in multicomponent solids. In this perspective, we firstly introduce preparation methods, molecular packing modes and charge transfer in organic cocrystals.

2D Organic Materials for Optoelectronic Applications.

The remarkable merits of 2D materials with atomically thin structures and optoelectronic attributes have inspired great interest in integrating 2D materials into electronics and optoelectronics. Moreover, as an emerging field in the 2D-materials family, assembly of organic nanostructures into 2D forms offers the advantages of molecular diversity, intrinsic flexibility, ease of processing, light weight, and so on, providing an exciting prospect for optoelectronic applications. Herein, the applications of organic 2D materials for optoelectronic devices are a main focus.

Intermolecular Charge-Transfer Interactions Facilitate Two-Photon Absorption in Styrylpyridine-Tetracyanobenzene Cocrystals.

Cocrystals of 4-styrylpyridine and 1,2,4,5-tetracyanobenzene were successfully prepared by supramolecular self-assembly. Donor-acceptor interactions between the molecular components are the main driving force for self-assembly and contribute to intermolecular charge transfer. The cocrystals possess two-photon absorption properties that are not observed in the individual components; suggesting that two-photon absorption originates from intermolecular charge-transfer interactions in the donor-acceptor system.

Ternary NiCo P Nanowires as pH-Universal Electrocatalysts for Highly Efficient Hydrogen Evolution Reaction.

A bimetallic-structured ternary phosphide (NiCo P ) as a novel pH-universal electrocatalyst for hydrogen evolution reaction is presented. It exhibits both high activity and long-term stability in all the tested alkaline, neutral, and acidic media. The excellent catalytic performance endows it with a bright future in the large-scale electrochemical water splitting industry.

Mass Production of Nanogap Electrodes toward Robust Resistive Random Access Memory.

Nanogap electrodes arrays are fabricated by combining atomic layer deposition, adhesive tape, and chemical etching. A unipolar nonvolatile resistive-switching behavior is identified in the nanogap electrodes, showing stable, robust performance and the multibit storage ability, demonstrating great potential in ultrahigh-density storage. The formation and dissolution of Si conductive filaments and migration of Au atoms is the mechanism behind the resistive switching.

Unveiling the Switching Riddle of Silver Tetracyanoquinodimethane Towards Novel Planar Single-Crystalline Electrochemical Metallization Memories.

The switching riddle of AgTCNQ is shown to be caused by the solid electrolyte mechanism. Both factors of bulk phase change and contact issue play key roles in the efficient work of the devices. An effective strategy is developed to locate the formation/disruption of Ag conductive filaments using the planar asymmetric configuration of Au/AgTCNQ/AlOx /Al.

Single-displacement controlled spontaneous electrolysis towards CuTCNQ microribbon electrodes in organic single-crystal transistors.

Using single-displacement controlled spontaneous electrolysis solution-prepared CuTCNQ microribbons as the source/drain electrodes, we have fabricated 9,10-bis(2-phenylethynyl)anthracene (BEPA) based organic single crystal top-contact field-effect transistors. The interfacial energetic match between organic semiconductors and CuTCNQ electrodes with the low contact resistance accounts for the compelling improvement in electrical characteristics relative to the copper electrode, even comparable to gold counterparts. Furthermore, we have estimated the contact resistance of single-crystal transistors by the transfer line method (TLM).