Enhanced photoelectrical response of thermodynamically epitaxial organic crystals at the two-dimensional limit

Recent Advances in Xenes Based FET for Biosensing Applications

In recent years, monoelemental 2D materials (Xenes) such as graphene, graphdiyne, silicene, phosphorene, and tellurene, have gained significant traction in biosensing applications. Owing to their ultra-thin layered structure, exceptionally high specific surface area, unique surface electronic properties, excellent mechanical strength, flexibility, and other distinctive features, Xenes are recognized for their potential as materials with low detection limits, high speed, and exceptional flexibility in biosensing applications. In this review, the unique properties of Xenes, their synthesis, and recent theoretical and experimental advances in applications related to biosensing, including DNA/RNA biosensors, protein biosensors, small molecule biosensors, cell, and ion biosensors are comprehensively summarized. Finally, the challenges and prospects of this emerging field are discussed.

Molecular Sensitizer-Loaded Monolayer Organic Semiconductors for High-Performance H2S Sensors

Monolayer organic semiconductors offer high gas sensitivity due to their exposed active channels and absence of grain boundaries, allowing them to interact directly with the analytes. However, such single-component organic sensors are typically lacking in selective adsorption sites, leading to practical hindrances such as limited chemical selectivity and slow recovery. In this study, we demonstrate a highly crystalline monolayer C10-DNTT semiconductor film sensitized with F4-TCNQ (F4-TCNQ/C10-DNTT), fabricated using a one-step solution-shearing codeposition method, which overcomes the aforementioned challenges to serve as a high-performance chemical gas sensor. Compared to pristine C10-DNTT, the monolayer F4-TCNQ/C10-DNTT films showed an enhanced response to hydrogen sulfide (H2S), an industrial pollutant and an important biomarker for respiratory disorders, as the sensitizer molecules promoted electronic interactions at the gas-organic semiconductor interface. Specifically, this resulted in a 5.3-fold increase in sensitivity to 5 ppm of H2S, with high selectivity and improved recovery compared to pristine C10-DNTT sensors. The precisely defined two-dimensional (2D) structure of the F4-TCNQ/C10-DNTT films enabled the investigation of layer-dependent sensing characteristics, reinforcing the significance of the monolayer configuration for achieving highly sensitive and selective H2S sensing. This research provides an effective strategy for designing high-performance organic sensing devices and highlights the importance of layer precision in sensor response, contributing to the development of more efficient and reliable organic chemical sensors in the future.

Nanoimprint crystalithography for organic semiconductors

Organic semiconductor crystals (OSCs) offer mechanical flexibility, high carrier mobility, and tunable electronic structures, making them promising for optoelectronic and photonic applications. However, traditional lithographic techniques damage OSCs due to high-energy beams or solvents, leading to high defect densities, poor uniformity, and significant device-to-device variation. Existing methods also struggle to eliminate residual layers while forming independent, complex two-dimensional patterns. A chemical-free nanoimprint crystallography (NICL) method is introduced to overcome these challenges by balancing residual-layer-free nanoimprinting with the fabrication of independent, complex 2D patterns. In situ control of crystallization kinetics via temperature gradient adjustment yields OSC nanostructures with low defect densities and good uniformity. Patterning of various OSCs over a range of feature sizes is demonstrated. The patterned OSCs exhibit good lasing performance and low device-to-device variation (as low as 2%), indicating that NICL is a promising approach for fabricating high-performance, uniform OSC-based devices.

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. The commercialization trend of organic optoelectronic devices is driving the development of highly integrated OSSCs. Therefore, timely tracking of material requirements, crystallization demands, and key technologies for high integration, along with exploring their limitations and potential pathways, will provide critical guidance during this pivotal transition period. From the perspective of materials properties, multifunctional materials, such as ambipolar charge transport materials, high mobility emission materials and others, aiming at high integration, deserve our attention, and the material design rules are carefully discussed in the first section. Following this, we delve into the controllable growth of large-scale OSSCs based on crystallization thermodynamics and kinetics. Key technologies for achieving high integration are then discussed, with an emphasis on methods for growing wafer-scale organic single crystals and patterning single crystalline arrays. Subsequently, we outline the cutting-edge optoelectronic applications based on OSSCs, including organic logic circuits, electroluminescent displays, and image sensors. Moreover, explicitly recognizing as yet limitations and prospects on the road to 'lab-to-fab' transitions for OSSCs is crucial. Thus, we conclude by offering an objective assessment of key limitations and potential, encompassing aspects such as uniformity, integration density, stability, and driving capability, providing an instructive projection for future advancements.

Supercapacitively Liquid-Solid Dual-State Optoelectronics

Photo-transduction of solid-state optoelectronics occurs in semiconductors or their interfaces. Considering the confined active area and interfacial capacitance of solid-state materials, solid-state optoelectronics faces inherent limitations in photo-transduction, especially for bionic vision, and the performance is lower than that of living systems. For example, a photoreceptor generates pA-level photocurrent when absorbing a single photon. Here, a liquid-solid dual-state phototransistor is demonstrated, in which photo-transduction and modulation take place at the microporous interface between semiconductors and water, mimicking principles of the photoreceptor. When operating in the water, an orderly stacked photo-harvesting covalent organic framework layer generates supercapacitively photogating modulation of the channel conductivity via a dual-state interface, achieving responsivity of 4.6 × 1010 A W-1 and detectivity of 1.62 × 1016 Jones at room temperature, several orders of magnitude higher than other photodetectors. Such bio-inspired dual-state optoelectronics enables high-contrast scotopic neuromorphic imaging with responsivity greater than photoreceptors, holding promise for constructing optoelectronic systems with performance beyond conventional solid-state optoelectronics.

Epitaxial Growth of Two-Dimensional Organic Crystals with In-Plane Heterostructured Domain Regulation

Complex organic lateral heterostructures (OLHs) with spatial distribution of two or more chemical components are crucial for designing and realizing unique structure-dependent optoelectronic applications. However, the precise design of well-defined OLHs with flexible domain regulation remains a considerable challenge. Herein, we present a stepwise solution self-assembly method to synthesize two-dimensional (2D) OLHs with a central rhombus domain and a lateral region featuring tunable blue and green emission based on the sequential nucleation and growth of 2D crystals. By controlling the initial crystallization time of 2,6-diphenylanthracene, the rhombic length ratio (α) of the multicolor-emissive part of the 2D OLHs is precisely modified. Furthermore, a third lateral layer is constructed on the resulting OLHs, demonstrating scalable lateral regulation. Significantly, these prepared 2D OLHs exhibit great excitation position-dependent waveguide characteristics and enable a 0.06 dB/μm low-loss waveguiding, which are conducive to photon transport and conversion for photonic integrated circuits. This work provides a stepwise strategy for the accurate fabrication of 2D OLHs, fabricating the developments of next-generation optoelectronics devices.

Sensitivity-Enhancing Strategies of Graphene Field-Effect Transistor Biosensors for Biomarker Detection

The ultrasensitive recognition of biomarkers plays a crucial role in the precise diagnosis of diseases. Graphene-based field-effect transistors (GFET) are considered the most promising devices among the next generation of biosensors. GFET biosensors possess distinct advantages, including label-free, ease of integration and operation, and the ability to directly detect biomarkers in liquid environments. This review summarized recent advances in GFET biosensors for biomarker detection, with a focus on interface functionalization. Various sensitivity-enhancing strategies have been overviewed for GFET biosensors, from the perspective of optimizing graphene synthesis and transfer methods, refinement of surface functionalization strategies for the channel layer and gate electrode, design of biorecognition elements and reduction of nonspecific adsorption. Further, this review extensively explores GFET biosensors functionalized with antibodies, aptamers, and enzymes. It delves into sensitivity-enhancing strategies employed in the detection of biomarkers for various diseases (such as cancer, cardiovascular diseases, neurodegenerative disorders, infectious viruses, etc.) along with their application in integrated microfluidic systems. Finally, the issues and challenges in strategies for the modulation of biosensing interfaces are faced by GFET biosensors in detecting biomarkers.

Customizable Organic Charge-Transfer Cocrystals for the Dual-Mode Optoelectronics in the NIR (II) Window

Organic molecules have been regarded as ideal candidates for near-infrared (NIR) optoelectronic active materials due to their customizability and ease of large-scale production. However, constrained by the intricate molecular design and severe energy gap law, the realization of optoelectronic devices in the second near-infrared (NIR (II)) region with required narrow band gaps presents more challenges. Herein, we have originally proposed a cocrystal strategy that utilizes intermolecular charge-transfer interaction to drive the redshift of absorption and emission spectra of a series BFXTQ (X = 0, 1, 2, 4) cocrystals, resulting in the spectra located at NIR (II) window and reducing the optical bandgap to ∼0.98 eV. Significantly, these BFXTQ-based optoelectronic devices can exhibit dual-mode optoelectronic characteristics. An investigation of a series of BFXTQ-based photodetectors exhibits detectivity (D*) surpassing 1013 Jones at 375 to 1064 nm with a maximum of 1.76 × 1014 Jones at 1064 nm. Moreover, the radiative transition of CT excitons within the cocrystals triggers NIR emission over 1000 nm with a photoluminescence quantum yield (PLQY) of ∼4.6% as well as optical waveguide behavior with a low optical-loss coefficient of 0.0097 dB/μm at 950 nm. These results promote the advancement of an emerging cocrystal approach in micro/nanoscale NIR multifunctional optoelectronics.

Molecular Electronics: From Nanostructure Assembly to Device Integration

Integrated electronics and optoelectronics based on organic semiconductors have attracted considerable interest in displays, photovoltaics, and biosensing owing to their designable electronic properties, solution processability, and flexibility. Miniaturization and integration of devices are growing trends in molecular electronics and optoelectronics for practical applications, which requires large-scale and versatile assembly strategies for patterning organic micro/nano-structures with simultaneously long-range order, pure orientation, and high resolution. Although various integration methods have been developed in past decades, molecular electronics still needs a versatile platform to avoid defects and disorders due to weak intermolecular interactions in organic materials. In this perspective, a roadmap of organic integration technologies in recent three decades is provided to review the history of molecular electronics. First, we highlight the importance of long-range-ordered molecular packing for achieving exotic electronic and photophysical properties. Second, we classify the strategies for large-scale integration of molecular electronics through the control of nucleation and crystallographic orientation, and evaluate them based on factors of resolution, crystallinity, orientation, scalability, and versatility. Third, we discuss the multifunctional devices and integrated circuits based on organic field-effect transistors (OFETs) and photodetectors. Finally, we explore future research directions and outlines the need for further development of molecular electronics, including assembly of doped organic semiconductors and heterostructures, biological interfaces in molecular electronics and integrated organic logics based on complementary FETs.

Recent progress in emerging two-dimensional organic-inorganic van der Waals heterojunctions

Two-dimensional (2D) materials have attracted significant attention in recent decades due to their exceptional optoelectronic properties. Among them, to meet the growing demand for multifunctional applications, 2D organic-inorganic van der Waals (vdW) heterojunctions have become increasingly popular in the development of optoelectronic devices. These heterojunctions demonstrate impressive capability to synergistically combine the favourable characteristics of organic and inorganic materials, thereby offering a wide range of advantages. Also, they enable the creation of innovative device structures and introduce novel functionalities in existing 2D materials, avoiding the need for lattice matching in different material systems. Presently, researchers are actively working on improving the performance of devices based on 2D organic-inorganic vdW heterojunctions by focusing on enhancing the quality of 2D materials, precise stacking methods, energy band regulation, and material selection. Therefore, this review presents a thorough examination of the emerging 2D organic-inorganic vdW heterojunctions, including their classification, fabrication, and corresponding devices. Additionally, this review offers profound and comprehensive insight into the challenges in this field to inspire future research directions. It is expected to propel researchers to harness the extraordinary capabilities of 2D organic-inorganic vdW heterojunctions for a wider range of applications by further advancing the understanding of their fundamental properties, expanding the range of available materials, and exploring novel device architectures. The ongoing research and development in this field hold potential to unlock captivating advancements and foster practical applications across diverse industries.

Monolayer Organic Crystals for Ultrahigh Performance Molecular Diodes

Molecular diodes are of considerable interest for the increasing technical demands of device miniaturization. However, the molecular diode performance remains contact-limited, which represents a major challenge for the advancement of rectification ratio and conductance. Here, it is demonstrated that high-quality ultrathin organic semiconductors can be grown on several classes of metal substrates via solution-shearing epitaxy, with a well-controlled number of layers and monolayer single crystal over 1 mm. The crystals are atomically smooth and pinhole-free, providing a native interface for high-performance monolayer molecular diodes. As a result, the monolayer molecular diodes show record-high rectification ratio up to 5 × 108 , ideality factor close to unity, aggressive unit conductance over 103 S cm-2 , ultrahigh breakdown electric field, excellent electrical stability, and well-defined contact interface. Large-area monolayer molecular diode arrays with 100% yield and excellent uniformity in the diode metrics are further fabricated. These results suggest that monolayer molecular crystals have great potential to build reliable, high-performance molecular diodes and deeply understand their intrinsic electronic behavior.

Lateral epitaxial growth of two-dimensional organic heterostructures

Two-dimensional organic lateral heterostructures (2D OLHs) are attractive for the fabrication of functional materials. However, it is difficult to control the nucleation, growth and orientation of two distinct components. Here we report the combination of two methods-liquid-phase growth and vapour-phase growth-to synthesize 2D OLHs from perylene and a perylenecarboxaldehyde derivative, with a lateral size of ~20 μm and a tunable thickness ranging from 20 to 400 nm. The screw dislocation growth behaviour of the 2D crystals shows the spiral arrangement of atoms within the crystal lattice, which avoids volume expansion and contraction of OLH, thereby minimizing lateral connection defects. Selective control of the nucleation and sequential growth of 2D crystals leads to structural inversion of the 2D OLHs by the vapour-phase growth method. The resulting OLHs show good light-transport capabilities and tunable spatial exciton conversion, useful for photonic applications. This synthetic strategy can be extended to other families of organic polycyclic aromatic hydrocarbons, as demonstrated with other pyrene and perylene derivatives.

Exfoliation of 2D Metal-Organic Frameworks: toward Advanced Scalable Materials for Optical Sensing

Two-dimensional metal-organic frameworks (MOFs) occupy a special place among the large family of functional 2D materials. Even at a monolayer level, 2D MOFs exhibit unique sensing, separation, catalytic, electronic, and conductive properties due to the combination of porosity and organo-inorganic nature. However, lab-to-fab transfer for 2D MOF layers faces the challenge of their scalability, limited by weak interactions between the organic and inorganic building blocks. Here, comparing three top-down approaches to fabricate 2D MOF layers (sonication, freeze-thaw, and mechanical exfoliation), The technological criteria have established for creation of the layers of the thickness up to 1 nm with a record aspect ratio up to 2*10^4:1. The freezing-thaw and mechanical exfoliation are the most optimal approaches; wherein the rate and manufacturability of the mechanical exfoliation rivaling the greatest scalability of 2D MOF layers obtained by freezing-thaw (21300:1 vs 1330:1 aspect ratio), leaving the sonication approach behind (with a record 900:1 aspect ratio) have discovered. The high quality 2D MOF layers with a record aspect ratio demonstrate unique optical sensitivity to solvents of a varied polarity, which opens the way to fabricate scalable and freestanding 2D MOF-based atomically thin chemo-optical sensors by industry-oriented approach.

A Novel Strategy for the Synthesis of High Stability of Luminescent Zero Dimensional-Two Dimensional CsPbBr3 Quantum Dot/1,4-bis(4-methylstyryl)benzene Nanoplate Heterostructures at an Atmospheric Condition

Perovskite quantum dots (QDs), emerging with excellent bright-green photoluminescence (PL) and a large absorption coefficient, are of great potential for the fabrication of light sources in underwater optical wireless communication systems. However, the instability caused by low formation energy and abundant surface traps is still a major concern for perovskite-based light sources in underwater conditions. Herein, we propose ultra-stable zero dimensional-two dimensional (0D-2D) CsPbBr3 QD/1,4-bis(4-methylstyryl)benzene (p-MSB) nanoplate (NP) heterostructures synthesized via a facile approach at room temperature in air. CsPbBr3 QDs can naturally nucleate on the p-MSB NP toluene solution, and the radiative combination is drastically intensified owing to the electron transfer within the typical type-II heterostructures, leading to a sharply increased PLQY of the heterostructure thin films up to 200% compared with the pristine sample. The passivation of defects within CsPbBr3 QDs can be effectively realized with the existence of p-MSB NPs, and thus the obviously improved PL is steadily witnessed in an ambient atmosphere and thermal environment. Meanwhile, the enhanced humidity stability and a peak EQE of 9.67% suggests a synergetic strategy for concurrently addressing the knotty problems on unsatisfied luminous efficiency and stability of perovskites for high-performance green-emitting optoelectronic devices in underwater applications.

Free-Standing Two-Dimensional Crystals Formed from Self-Assembled Ionic Liquids

The fabrication of two-dimensional crystals (2DCs) has attracted very large interest because it creates materials with various surface structural features and special surface properties. Normally, this is limited to sheets networked together with strong covalent or coordination bonds. Against this understanding, we discovered macroscopic scale free-standing 2DCs in the aqueous dispersions of [C_nmim]X (X = Br, NO₃; n = 14, 16, 18) using simultaneous synchrotron small- and wide-angle X-ray scattering techniques. On the other hand, the 2DCs are also a kind of novel hydrogel holding water content up to 98 wt %. This unusual phenomenon is attributed to the weak interactions between imidazole headgroups and counterions. The observation reported in this work is expected to contribute to theorists in their pursuit of the general principles governing the stability of 2D materials. It may also enlighten experimentalists in designing new free-standing 2DCs for various applications.

Spatially Confined Face-Selective Growth of Large-Area 2D Organic Molecular Crystals in a Supramolecular Gel for Highly Efficient Flexible Photodetection

2D organic molecular crystals (2DOMCs) are promising materials for the fabrication of high-performance optoelectronic devices. However, the growth of organic molecules into 2DOMCs remains a challenge because of the difficulties in controlling their self-assembly with a preferential orientation in solution-process crystallization. Herein, fullerene is chosen as a model molecule to develop a supramolecular gel crystallization approach to grow large-area 2DOMCs by controlling the perfect arrangement on the {220} crystal plane with the assistance of a gelated solvent. In this case, the gel networks provide tuneable confined spaces to control the crystallization kinetics toward the growth of dominant crystal faces by their inhibiting motions of solvent or solute molecules to enable the growth of perfect crystals at appropriate nucleation rates. As a result, a large-area fullerene 2DOMC is produced successfully and its corresponding device on a flexible substrate exhibits excellent bendable properties and ultra-high weak light detection ability (2.9 × 1011 Jones) at a 10 V bias upon irradiation with 450 nm incident light. Moreover, its photoelectric properties remain unchanged after 200 cycles of bending at angles of 45, 90, and 180°. These results can be extended to the growth of other 2DOMCs for potentially fabricating advanced organic (opto)electronics.

Formation of Ultimate Thin 2D Crystal of Pt in the Presence of Hexamethylenetetramine

Platinum naturally crystalizes into a three-dimensional crystal due to its highly symmetrical fcc lattice, with a metallic bond which is non-directional and highly isotropic. This inherently means ultimately that 2D crystals of a few atoms thick growth are hardly available in this material. Here, we discovered that a combinative effect of formic acid reductant and hexamethylenetetramine surfactant during the reduction of their metal ions precursor can realize an ultimate thin 2D crystal growth in platinum. High-resolution transmission electron microscopy and filed-emission electron microscopy analysis have also discovered that the 2D crystal of Pt has 111 facets with a lateral dimension that can be up to more than 5 μm × 2 μm. The thickness of the 2D crystal of Pt is 1.55 nm. A mechanism for obtaining ultimate thin 2D crystal of Pt using the present approach is proposed.

Organic ultrathin nanostructure arrays: materials, methods and applications

Organic ultrathin semiconductor nanostructures have attracted continuous attention in recent years owing to their excellent charge transport capability, favorable flexibility, solution-processability and adjustable photoelectric properties, providing opportunities for next-generation optoelectronic applications. For integrated electronics, organic ultrathin nanostructures need to be prepared as large-area patterns with precise alignment and high crystallinity to achieve organic electronic devices with high performance and high throughput. However, the fabrication of organic ultrathin nanostructure arrays still remains challenging due to uncontrollable growth along the height direction in solution processes. In this review, we first introduce the properties, assembly methods and applications of four typical organic ultrathin nanostructures, including small molecules, polymers, and other organic-inorganic hybrid materials. Five categories of representative solution-processing techniques for patterning organic micro- and nanostructures are summarized and discussed. Finally, challenges and perspectives in the controllable preparation of organic ultrathin arrays and potential applications are featured on the basis of their current development.

Two-Dimensional Field-Effect Transistor Sensors: The Road toward Commercialization

The evolutionary success in information technology has been sustained by the rapid growth of sensor technology. Recently, advances in sensor technology have promoted the ambitious requirement to build intelligent systems that can be controlled by external stimuli along with independent operation, adaptivity, and low energy expenditure. Among various sensing techniques, field-effect transistors (FETs) with channels made of two-dimensional (2D) materials attract increasing attention for advantages such as label-free detection, fast response, easy operation, and capability of integration. With atomic thickness, 2D materials restrict the carrier flow within the material surface and expose it directly to the external environment, leading to efficient signal acquisition and conversion. This review summarizes the latest advances of 2D-materials-based FET (2D FET) sensors in a comprehensive manner that contains the material, operating principles, fabrication technologies, proof-of-concept applications, and prototypes. First, a brief description of the background and fundamentals is provided. The subsequent contents summarize physical, chemical, and biological 2D FET sensors and their applications. Then, we highlight the challenges of their commercialization and discuss corresponding solution techniques. The following section presents a systematic survey of recent progress in developing commercial prototypes. Lastly, we summarize the long-standing efforts and prospective future development of 2D FET-based sensing systems toward commercialization.

Thermally Stable Organic Field-Effect Transistors Based on Asymmetric BTBT Derivatives for High Performance Solar-Blind Photodetectors

High-performance solar-blind photodetectors are widely studied due to their unique significance in military and industrial applications. Yet the rational molecular design for materials to possess strong absorption in solar-blind region is rarely addressed. Here, an organic solar-blind photodetector is reported by designing a novel asymmetric molecule integrated strong solar-blind absorption with high charge transport property. Such alkyl substituted [1]benzothieno[3,2-b][1]-benzothiophene (BTBT) derivatives Cn-BTBTN (n = 6, 8, and 10) can be easily assembled into 2D molecular crystals and perform high mobility up to 3.28 cm² V^-1 s^-1 , which is two orders of magnitude higher than the non-substituted core BTBTN. Cn-BTBTNs also exhibit dramatically higher thermal stability than the symmetric alkyl substituted C8-BTBT. Moreover, C10-BTBTN films with the highest mobility and strongest solar-blind absorption among the Cn-BTBTNs are applied for solar-blind photodetectors, which reveal record-high photosensitivity and detectivity up to 1.60 × 10⁷ and 7.70 × 10¹⁴ Jones. Photodetector arrays and flexible devices are also successfully fabricated. The design strategy can provide guidelines for developing materials featuring high thermal stability and stimulating such materials in solar-blind photodetector application.

Effect of Strong Intermolecular Interaction in 2D Inorganic Molecular Crystals

Strong intermolecular interactions in 2D organic molecular crystals arising from π-π stacking have been widely explored to achieve high thermal stability, high carrier mobility, and novel physical properties, which have already produced phenomenal progress. However, strong intermolecular interactions in 2D inorganic molecular crystals (2DIMCs) have rarely been investigated, severely limiting both the fundamental research in molecular physics and the potential applications of 2DIMCs for optoelectronics. Here, the effect of strong intermolecular interactions induced by unique short intermolecular Se-Se and P-Se contacts in 2D α-P₄Se₃ nanoflakes is reported. On the basis of theoretical calculations of the charge density distribution and an analysis of the thermal expansion and plastic-crystal transition, the physical picture of strong intermolecular interactions can be elucidated as a higher charge density between adjacent P₄Se₃ molecules, arising from an orderly and close packing of P₄Se₃ molecules. More importantly, encouraged by the strong intermolecular coupling, the in-plane mobility of α-P₄Se₃ nanoflakes is first calculated with a quantum nuclear tunneling model, and a competitive hole mobility of 0.4 cm² V^-1 s^-1 is obtained. Our work sheds new light on the intermolecular interactions in 2D inorganic molecular crystals and is highly significant for promoting the development of molecular physics and optoelectronics.

Organic Single Crystals with High Photoluminescence Quantum Yields Close to 100% and High Mobility for Optoelectronic Devices

Organic single crystals with excellent optical and electrical properties are critical for the development of organic optoelectronics. Herein, two compounds 9,10-bis([N,N-diphenyl]-4'-phenylethynyl)anthracene (TPA-An) and 9,10-bis([1',3'-diphenyl]-5'-phenylethynyl)anthracene (TBA-An) are synthesized by introducing two different luminescent groups, triphenylamine and 1,3-diphenylbenzene, at the 9,10 positions of anthracene via triple bond connection. Single crystals based on TPA-An and TBA-An with a ribbon morphology obtained through the slow solvent-evaporation method exhibit high photoluminescence quantum yields (PLQYs) of 98% and 99% at room temperature, and remarkable hole mobilities of 0.45 and 0.15 cm² V^-1 s^-1 in single-crystal organic field-effect transistors (SC-OFETs). Furthermore, UV phototransistors based on the two single crystals obtain photosensitivities of 1.03 × 10³ and 3.45 × 10⁴ , ultrahigh photoresponsivities of 7.19 × 10⁵ and 1.50 × 10⁵ A W^-1 , and the detectivities exceeding 1.40 × 10¹⁶ and 1.60 × 10¹⁷ Jones.

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.

Organic Semiconductor Micro/Nanocrystals for Laser Applications

Organic semiconductor micro/nanocrystals (OSMCs) have attracted great attention due to their numerous advantages such us free grain boundaries, minimal defects and traps, molecular diversity, low cost, flexibility and solution processability. Due to all these characteristics, they are strong candidates for the next generation of electronic and optoelectronic devices. In this review, we present a comprehensive overview of these OSMCs, discussing molecular packing, the methods to control crystallization and their applications to the area of organic solid-state lasers. Special emphasis is given to OSMC lasers which self-assemble into geometrically defined optical resonators owing to their attractive prospects for tuning/control of light emission properties through geometrical resonator design. The most recent developments together with novel strategies for light emission tuning and effective light extraction are presented.

van der Waals Epitaxy of Soft Twisted Bilayers: Lattice Relaxation and Mass Density Waves

Interfaces comprising incommensurate or twisted hexagonal lattices are ubiquitous and of great interest, from adsorbed organic/inorganic interfaces in electronic devices, to superlubricants, and more recently to van der Waals bilayer heterostructures (vdWHs) of graphene and other 2D materials that demonstrate a range of properties such as superconductivity and ferromagnetism. Here we show how growth of 2D crystalline domains of soft block copolymers (BCPs) on patterned hard hexagonal lattices provide fundamental insights into van der Waals heteroepitaxy. At moderate registration forces, it is experimentally found that these BCP-hard lattice vdWHs do not adopt a simple moiré superstructure, but instead adopt local structural relaxations known as mass density waves (MDWs). Simulations reveal that MDWs are a primary mechanism of energy minimization and are the origin of the observed preferential twist angle between the lattices.

Light-modulated vertical heterojunction phototransistors with distinct logical photocurrents

The intriguing carrier dynamics in graphene heterojunctions have stimulated great interest in modulating the optoelectronic features to realize high-performance photodetectors. However, for most phototransistors, the photoresponse characteristics are modulated with an electrical gate or a static field. In this paper, we demonstrate a graphene/C60/pentacene vertical phototransistor to tune both the photoresponse time and photocurrent based on light modulation. By exploiting the power-dependent multiple states of the photocurrent, remarkable logical photocurrent switching under infrared light modulation occurs in a thick C60 layer (11 nm) device, which implies competition of the photogenerated carriers between graphene/C60 and C60/pentacene. Meanwhile, we observe a complete positive-negative alternating process under continuous 405 nm irradiation. Furthermore, infrared light modulation of a thin C60 (5 nm) device results in a photoresponsivity improvement from 3425 A/W up to 7673 A/W, and we clearly probe the primary reason for the distinct modulation results between the 5 and 11 nm C60 devices. In addition, the tuneable bandwidth of the infrared response from 10 to 3 × 103 Hz under visible light modulation is explored. Such distinct types of optical modulation phenomena and logical photocurrent inversion characteristics pave the way for future tuneable logical photocurrent switching devices and high-performance phototransistors with vertical graphene heterojunction structures.

Graphene-Quantum-Dots-Induced Centimeter-Sized Growth of Monolayer Organic Crystals for High-Performance Transistors

Monolayer organic crystals have attracted considerable attention due to their extraordinary optoelectronic properties. Solution self-assembly on the surface of water is an effective approach to fabricate monolayer organic crystals. However, due to the difficulties in controlling the spreading of organic solution on the water surface and the weak intermolecular interaction between the organic molecules, large-area growth of monolayer organic crystals remains a great challenge. Here, a graphene quantum dots (GQDs)-induced self-assembly method for centimeter-sized growth of monolayer organic crystals on a GQDs solution surface is reported. The spreading area of the organic solution can be readily controlled by tuning the pH value of the GQDs solution. Meanwhile, the π-π stacking interaction between the GQDs and the organic molecules can effectively reduce the nucleation energy of the organic molecules and afford a cohesive force to bond the crystals, enabling large-area growth of monolayer organic crystals. Using 2,7-didecyl benzothienobenzothiopene (C₁₀-BTBT) as an examples, centimeter-sized monolayer C₁₀-BTBT crystal with uniform molecular packing and crystal orientation is attained. Organic field-effect transistors based on the monolayer C₁₀-BTBT crystals exhibit a high mobility up to 2.6 cm² V^-1 s^-1, representing the highest mobility value for solution-assembled monolayer organic crystals. This work provides a feasible route for large-scale fabrication of monolayer organic crystals toward high-performance organic devices.

2D Inorganic Bimolecular Crystals with Strong In-Plane Anisotropy for Second-Order Nonlinear Optics

2D inorganic bimolecular crystals, consisting of two different inorganic molecules, are expected to possess novel physical and chemical properties due to the synergistic effect of the individual components. However, 2D inorganic bimolecular crystals remain unexploited because of the difficulties in preparation arising from non-typical layered structures and intricate intermolecular interactions. Here, the synthesis of 2D inorganic bimolecular crystal SbI₃ ·3S₈ nanobelts via a facile vertical microspacing sublimation strategy is reported. The as-synthesized SbI₃ ·3S₈ nanobelts exhibit strong in-plane anisotropy of phonon vibrations and intramolecular vibrations as well as show anisotropic light absorption with a high dichroism ratio of 3.9. Furthermore, it is revealed that the second harmonic generation intensity of SbI₃ ·3S₈ nanobelts is highly dependent on the excitation wavelength and crystallographic orientation. This work can inspire the growth of more 2D inorganic bimolecular crystals and excite potential applications for bimolecular optoelectronic devices.

Solution-Processed, Large-Area, Two-Dimensional Crystals of Organic Semiconductors for Field-Effect Transistors and Phototransistors

Organic electronics with π-conjugated organic semiconductors are promising candidates for the next electronics revolution. For the conductive channel, the large-area two-dimensional (2D) crystals of organic semiconductors (2DCOS) serve as useful scaffolds for modern organic electronics, benefiting not only from long-range order and low defect density nature but also from unique charge transport characteristic and photoelectrical properties. Meanwhile, the solution process with advantages of cost-effectiveness and room temperature compatibility is the foundation of high-throughput print electrical devices. Herein, we will give an insightful overview to witness the huge advances in 2DCOS over the past decade. First, the typical influencing factors and state-of-the-art assembly strategies of the solution-process for large-area 2DCOS over sub-millimeter even to wafer size are discussed accompanying rational evaluation. Then, the charge transport characteristics and contact resistance of 2DCOS-based transistors are explored. Following this, beyond single transistors, the p-n junction devices and planar integrated circuits based on 2DCOS are also emphasized. Furthermore, the burgeoning phototransistors (OPTs) based on crystals in the 2D limits are elaborated. Next, we emphasized the unique and enhanced photoelectrical properties based on a hybrid system with other 2D van der Waals solids. Finally, frontier insights and opportunities are proposed, promoting further research in this field.

Enhanced emission in organic nanocrystals via asymmetrical design of spirocyclic aromatic hydrocarbons

Two spirocyclic aromatic hydrocarbon derivatives were prepared to clarify the molecular geometry effects on the regulation of the crystalline morphologies and photophysical behaviors of organic nanocrystals. Due to the different structural symmetry of a spiro-center, distinguishing nanocrystal morphologies with unique crystallization-enhanced/quenched emission was achieved.

Omnidirectional Photodetectors Based on Spatial Resonance Asymmetric Facade via a 3D Self-Standing Strategy

Integration of photovoltaic materials directly into 3D light-matter resonance architectures can extend their functionality beyond traditional optoelectronics. Semiconductor structures at subwavelength scale naturally possess optical resonances, which provides the possibility to manipulate light-matter interactions. In this work, a structure and function integrated printing method to remodel 2D film to 3D self-standing facade between predesigned gold electrodes, realizing the advancement of structure and function from 2D to 3D, is demonstrated. Due to the enlarged cross section in the 3D asymmetric rectangular structure, the facade photodetectors possess sensitive light-matter interaction. The single 3D facade photodetectors can measure the incident angle of light in 3D space with a 10° angular resolution. The resonance interaction of the incident light at different illumination angles and the 3D subwavelength photosensitive facade is analyzed by the simulated light flow in the facade. The 3D facade structure enhances the manipulation of the light-matter interaction and extends metasurface nanophotonics to a wider range of materials. The monitoring of dynamic variation is achieved in a single facade photodetector. Together with the flexibility of structure and function integrated printing strategy, three and four branched photodetectors extend the angle detection to omnidirectional ranges, which will be significant for the development of 3D angle-sensing devices.

Strain-Sensitive Fluorescence from Two-Dimensional Organic Crystal

Strain-sensitive fluorescence materials have great potential in sensing applications owing to their low cost, intuitive signal, and user friendliness. Organic crystals are one of the most developed fluorescence materials. However, modulation of the fluorescence by strain is still a challenge. Here, for the first time, we investigate the strain-sensitive fluorescence of the two-dimensional (2D) organic crystal. Without interlayer interactions, the molecular arrangement in a 2D crystal can be easily tuned, which results in photoluminescence transformation between monomer emission and excimer emission. The 2D organic crystal has higher sensitivity under strain, compared with bulk organic crystals, showing great potential in practical applications such as tactile monitors, chameleon bionic skin, and visible leakage alarms.

Highly luminescent crystals of a novel linear π-conjugated thiophene-phenylene co-oligomer with a benzothiadiazole fragment

The synthesis, growth from solutions and structure of crystals of a new linear thiophene-phenylene co-oligomer with a central benzothiadiazole fragment with a conjugated core, (TMS-2T-Ph)₂-BTD, are presented. Single-crystal samples in the form of needles with a length of up to 7 mm were grown and their crystal structure was determined at 85 K and 293 K using single-crystal X-ray diffraction. The conformational differences between the crystal structures are insignificant. The parameters of melting and liquid crystalline phase transitions of (TMS-2T-Ph)₂-BTD were established using differential scanning calorimetry and the thermal stability of the crystals was investigated using thermogravimetric analysis. The optical absorption and photoluminescence spectra of the solutions and crystals of (TMS-2T-Ph)₂-BTD were obtained, and the kinetics of their photodegradation under the action of UV radiation were studied.

Unconventional Nanofabrication for Supramolecular Electronics

The scientific effort toward achieving a full control over the correlation between structure and function in organic and polymer electronics has prompted the use of supramolecular interactions to drive the formation of highly ordered functional assemblies, which have been integrated into real devices. In the resulting field of supramolecular electronics, self-assembly of organic semiconducting materials constitutes a powerful tool to generate low-dimensional and crystalline functional architectures. These include 1D nanostructures (nanoribbons, nanotubes, and nanowires) and 2D molecular crystals with tuneable and unique optical, electronic, and mechanical properties. Optimizing the (opto)electronic properties of organic semiconducting materials is imperative to harness such supramolecular structures as active components for supramolecular electronics. However, their integration in real devices currently represents a significant challenge to the advancement of (opto)electronics. Here, an overview of the unconventional nanofabrication techniques and device configurations to enable supramolecular electronics to become a real technology is provided. A particular focus is put on how single and multiple supramolecular fibers and gels as well as supramolecularly engineered 2D materials can be integrated into novel vertical or horizontal junctions to realize flexible and high-density multifunctional transistors, photodetectors, and memristors, exhibiting a set of new properties and excelling in their performances.

Nanoscale thermal mapping of few-layer organic crystals

Combining a scanning thermal microscope with a finite element simulation, the conductivity of an organic thin-film can be quantitatively detected.