Interface Engineering in Organic Field-Effect Transistors: Principles, Applications, and Perspectives

Piezophototronic Effect Enhanced Flexible Tunneling Devices by Separating the Photosensitive Layer and the Piezoelectric Modulation Layer

The piezo-phototronic effect uses the piezoelectric potential/piezoelectric charge generated by the piezoelectric semiconductor material to regulate the energy band structure and photogenerated carrier behavior at the interface/junction, thereby modulating the device's performance. The positive/negative piezoelectric charges generated at the interface of piezoelectric semiconductors can reduce the electron/hole barriers and thus enhance the transport of photogenerated carriers. However, electron/hole potential wells are formed when the electron/hole potential barrier caused by positive/negative piezoelectric charges is lowered too much, hindering the transport of photogenerated carriers. It is difficult to balance the relationship between potential barriers and potential wells while introducing the piezo-phototronic effect. In this work, a physical mechanism by separating the photosensitive layer and the piezoelectric modulation layer is proposed to deal with the above-mentioned issue in flexible tunneling devices. The piezoelectric modulation layer is solely used to adjust the electron/hole barriers, while the photosensitive layer is used to absorb photons and generate photogenerated carriers. This avoids the limitation on the transport of photogenerated carriers caused by potential wells in the piezoelectric semiconductor, thereby significantly increasing the adjustable range of the barriers. Experimental results show that the photoresponsivity of the flexible p-Si/Al2O3/n-ZnO tunneling device is optimized from 5.5 A/W to 35.8 A/W by the piezo-phototronic effect after separating the piezoelectric charges and photogenerated carriers. In addition, finite element analysis is used to simulate the influence of piezoelectric charges on the energy bands to corroborate the accuracy of the theoretical mechanism and experimental results. This work not only presents an optoelectronic device with excellent performance but also offers novel guidance for improving the performance of optoelectronic devices using the piezo-phototronic effect.

Mass Production of Carbon Nanotube Transistor Biosensors for Point-of-Care Tests

Low-dimensional semiconductor-based field-effect transistor (FET) biosensors are promising for label-free detection of biotargets while facing challenges in mass fabrication of devices and reliable reading of small signals. Here, we construct a reliable technology for mass production of semiconducting carbon nanotube (CNT) film and FET biosensors. High-uniformity randomly oriented CNT films were prepared through an improved immersion coating technique, and then, CNT FETs were fabricated with coefficient of performance variations within 6% on 4-in. wafers (within 9% interwafer) based on an industrial standard-level process. The CNT FET-based ion sensors demonstrated threshold voltage standard deviations within 5.1 mV at each ion concentration, enabling direct reading of the concentration information based on the drain current. By integrating bioprobes, we achieved detection of biosignals as low as 100 aM through a plug-and-play portable detection system. The reliable technology will contribute to commercial applications of CNT FET biosensors, especially in point-of-care tests.

Leveraging Insulator's Tacticity in Semiconducting Polymer Blends

Blending conjugated polymers with insulating matrices is often utilized for engineering extrinsic properties in organic electronics. Semiconductor/insulator blends are typically processed to form a uniformly distributed network of conductive domains within the insulating matrix, marrying electronic and physical properties from individual components. Understanding of polymer-polymer interactions in such systems is thus crucial for property co-optimization. One of the commonly overlooked parameters is the structural configuration of the insulator on the resulting properties, especially the electronic properties. This study investigated how the tacticity of the matrix polymer, among other relevant parameters in play, impacts solid state crystallization in semiconductor/matrix blends and hence the resulting charge transport properties. We found an intricate dependence of the film morphology, aggregation behavior, electronic charge transport, and mixed ionic-electronic coupling properties on the insulator's tacticity. Our experimentally iterative approach shows that for a given application, when selecting semiconductor/insulator combinations, the tacticity of the matrix can be leveraged to optimize performance and vary solid-state structure.

Insulated π-Conjugated Azido Scaffolds for Stepwise Functionalization via Huisgen Cycloaddition on Metal Oxide Surfaces

In organic-inorganic hybrid devices, fine interfacial controls by organic components directly affect the device performance. However, fabrication of uniformed interfaces using π-conjugated molecules remains challenging due to facile aggregation by their strong π-π interaction. In this report, a π-conjugated scaffold insulated by covalently linked permethylated α-cyclodextrin moiety with an azido group is synthesized for surface Huisgen cycloaddition on metal oxides. Fourier-transformed infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy confirm the successful immobilization of the insulated azido scaffold on ZnO nanowire array surfaces. Owing to the highly independent immobilization, the scaffold allows rapid and complete conversion of the surface azido group in Huisgen cycloaddition reactions with ethynyl-terminated molecules, as confirmed by FT-IR spectroscopy monitoring. Cyclic voltammetry analysis of modified indium tin oxide substrates shows the positive effects of cyclic insulation toward suppression of intermolecular interaction between molecules introduced by the surface Huisgen cycloaddition reactions. The utility of the scaffold for heterogeneous catalysis is demonstrated in electrocatalytic selective O2 reduction to H2O2 with cobalt(II) chlorin modified fluorine doped tin oxide electrode and photocatalytic H2 generation with iridium(III) dye-sensitized Pt-loaded TiO2 nanoparticle. These results highlight the potential of the insulated azido scaffold for a stepwise functionalization process, enabling precise and well-defined hybrid interfaces.

Heterocycle- and Amine-Free Electrochromic and Electrofluorochromic Molecules for Energy-Saving See-Through Smart Windows and Displays

Electrochromic (EC) smart windows are an elegant alternative to dusty curtains, blinds, and traditional dimming devices. The EC energy storage smart windows and displays received remarkable attention in the optoelectronic industry as they hold promise for high energy efficiency, low power consumption, reversibility, and swift response to stimuli. However, achieving these properties remains challenging. Moreover, most EC molecules do not exhibit electrofluorochromism, which is highly essential for smart displays because its EC property can modulate the solar heat entering the building, and its electrofluorochromic (EFC) aspects can create lighting during the night. In this work, a structure-property relationship is utilized to develop new electrochromes that can store the injected charge, and these molecules indeed exhibit electrofluorochromism. The compounds are synthesized from tetrabenzofluorene with two aromatic acceptor units, and avoids the use of widely studied heterocycles and amine derivatives. The electrochromes switches from yellow to dark hue in solution, solid, and gel state. The compounds display exceptional electrochemical stability and reversibility in 1000 cycles and capacity retention of 93-100 % in 300 charging-discharging cycles. The proof-of-concept device fabrication of the self-dimming EC smart window presented here demonstrates that it can furnish visual comfort, modulate transmitted light and glare, and reduce energy usage.

Single-Molecule Electrical Profiling of Peptides and Proteins

In recent decades, there has been a significant increase in the application of single-molecule electrical analysis platforms in studying proteins and peptides. These advanced analysis methods have the potential for deep investigation of enzymatic working mechanisms and accurate monitoring of dynamic changes in protein configurations, which are often challenging to achieve in ensemble measurements. In this work, the prominent research progress in peptide and protein-related studies are surveyed using electronic devices with single-molecule/single-event sensitivity, including single-molecule junctions, single-molecule field-effect transistors, and nanopores. In particular, the successful commercial application of nanopores in DNA sequencing has made it one of the most promising techniques in protein sequencing at the single-molecule level. From single peptides to protein complexes, the correlation between their electrical characteristics, structures, and biological functions is gradually being established. This enables to distinguish different molecular configurations of these biomacromolecules through real-time electrical monitoring of their life activities, significantly improving the understanding of the mechanisms underlying various life processes.

Nanostructured Molecular Packing of Polymer Films Formed on Water Surfaces

In this study, we examined the nanostructured molecular packing and orientations of poly[[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)] (P(NDI2OD-T2)) films formed on water for the application of nanotechnology-based organic electronic devices. First, the nanoscale molecule-substrate interaction between the polymer and water was modulated by controlling the alkyl side chain length in NDI-based copolymers. Increasing alkyl side chain lengths induced a nanomorphological transition from face-on to edge-on orientation, confirmed by molecular dynamics simulations revealing nanostructural behavior. Second, the nanoscale intermolecular interactions of P(NDI2OD-T2) were controlled by varying the volume ratio of the high-boiling-point additive solvent in the binary solvent blends. As the additive solvent ratio increased, the nanostructured molecular orientation of the P(NDI2OD-T2) films on water changed remarkably from edge-on to bimodal with more face-on crystallites, thereby affecting charge transport. Our finding provides essential insights for precise nanoscale morphological control on water substrates, enabling the formation of high-performance polymer films for organic electronic devices.

Arylazopyrazole-modulated stable dual-mode phototransistors

High-performance organic devices with dynamic and stable modulation are essential for building devices adaptable to the environment. However, the existing reported devices incorporating light-activated units exhibit either limited device stability or subpar optoelectronic properties. Here, we synthesize a new optically tunable polymer dielectric functionalized with photochromic arylazopyrazole units with a cis-isomer half-life of as long as 90 days. On this basis, stable dual-mode organic transistors that can be reversibly modulated are successfully fabricated. The trans-state devices exhibit high carrier mobility reaching 7.4 square centimeters per volt per second and excellent optical figures of merit, whereas the cis-state devices demonstrate stable but starkly different optoelectronic performance. Furthermore, optical image sensors are prepared with regulatable nonvolatile memories from 36 hours (cis state) to 108 hours (trans state). The achievement of dynamic light modulation shows remarkable prospects for the intelligent application of organic optoelectronic devices.

Construction of High Accuracy Machine Learning Interatomic Potential for Surface/Interface of Nanomaterials-A Review

The inherent discontinuity and unique dimensional attributes of nanomaterial surfaces and interfaces bestow them with various exceptional properties. These properties, however, also introduce difficulties for both experimental and computational studies. The advent of machine learning interatomic potential (MLIP) addresses some of the limitations associated with empirical force fields, presenting a valuable avenue for accurate simulations of these surfaces/interfaces of nanomaterials. Central to this approach is the idea of capturing the relationship between system configuration and potential energy, leveraging the proficiency of machine learning (ML) to precisely approximate high-dimensional functions. This review offers an in-depth examination of MLIP principles and their execution and elaborates on their applications in the realm of nanomaterial surface and interface systems. The prevailing challenges faced by this potent methodology are also discussed.

Enhancing Sensitivity in Gas Detection: Porous Structures in Organic Field-Effect Transistor-Based Sensors

Gas detection is crucial for detecting environmentally harmful gases. Organic field-effect transistor (OFET)-based gas sensors have attracted attention due to their promising performance and potential for integration into flexible and wearable devices. This review examines the operating mechanisms of OFET-based gas sensors and explores methods for improving sensitivity, with a focus on porous structures. Researchers have achieved significant enhancements in sensor performance by controlling the thickness and free volume of the organic semiconductor layer. Additionally, innovative fabrication techniques like self-assembly and etching have been used to create porous structures, facilitating the diffusion of target gas molecules, and improving sensor response and recovery. These advancements in porous structure fabrication suggest a promising future for OFET-based gas sensors, offering increased sensitivity and selectivity across various applications.

Phosphonic acid anchored tripodal molecular films on indium tin oxide

Whereas monopodal self-assembling monolayers (SAMs) are most frequently used for surface and interface engineering, tripodal SAMs are less popular due to the difficulty in achieving a reliable and homogeneous bonding configuration. In this context, in the present study, the potential of phosphonic acid (PA) decorated triptycene (TripPA) for formation of SAMs on oxide substrates was studied, using indium tin oxide (ITO) as a representative and application-relevant test support. A combination of several complementary experimental techniques was applied and a suitable monopodal reference system, benzylphosphonic acid (PPA), was used. The resulting data consistently show that TripPA forms well-defined, densely packed, and nearly contamination-free tripodal SAMs on ITO, with the similar parameters and properties as the monopodal reference system. Modification of wetting properties and work function of ITO by non-substituted and cyano-decorated TripPA SAMs was demonstrated, showing a potential of this tripodal system for surface engineering of oxide substrates.

Robust Dipolar Layers between Organic Semiconductors and Silver for Energy-Level Alignment

The interface between a metal electrode and an organic semiconductor (OS) layer has a defining role in the properties of the resulting device. To obtain the desired performance, interlayers are introduced to modify the adhesion and growth of OS and enhance the efficiency of charge transport through the interface. However, the employed interlayers face common challenges, including a lack of electric dipoles to tune the mutual position of energy levels, being too thick for efficient electronic transport, or being prone to intermixing with subsequently deposited OS layers. Here, we show that monolayers of 1,3,5-tris(4-carboxyphenyl)benzene (BTB) with fully deprotonated carboxyl groups on silver substrates form a compact layer resistant to intermixing while capable of mediating energy-level alignment and showing a large insensitivity to substrate termination. Employing a combination of surface-sensitive techniques, i.e., low-energy electron microscopy and diffraction, X-ray photoelectron spectroscopy, and scanning tunneling microscopy, we have comprehensively characterized the compact layer and proven its robustness against mixing with the subsequently deposited organic semiconductor layer. Density functional theory calculations show that the robustness arises from a strong interaction of carboxylate groups with the Ag surface, and thus, the BTB in the first layer is energetically favored. Synchrotron radiation photoelectron spectroscopy shows that this layer displays considerable electrical dipoles that can be utilized for work function engineering and electronic alignment of molecular frontier orbitals with respect to the substrate Fermi level. Our work thus provides a widely applicable molecular interlayer and general insights necessary for engineering of charge injection layers for efficient organic electronics.

Electro-Optical Multiclassification Platform for Minimizing Occasional Inaccuracy in Point-of-Care Biomarker Detection

On-site diagnostic tests that accurately identify disease biomarkers lay the foundation for self-healthcare applications. However, these tests routinely rely on single-mode signals and suffer from insufficient accuracy, especially for multiplexed point-of-care tests (POCTs) within a few minutes. Here, this work develops a dual-mode multiclassification diagnostic platform that integrates an electrochemiluminescence sensor and a field-effect transistor sensor in a microfluidic chip. The microfluidic channel guides the testing samples to flow across electro-optical sensor units, which produce dual-mode readouts by detecting infectious biomarkers of tuberculosis (TB), human rhinovirus (HRV), and group B streptococcus (GBS). Then, machine-learning classifiers generate three-dimensional (3D) hyperplanes to diagnose different diseases. Dual-mode readouts derived from distinct mechanisms enhance the anti-interference ability physically, and machine-learning-aided diagnosis in high-dimensional space reduces the occasional inaccuracy mathematically. Clinical validation studies with 501 unprocessed samples indicate that the platform has an accuracy approaching 99%, higher than the 77%-93% accuracy of rapid point-of-care testing technologies at 100% statistical power (>150 clinical tests). Moreover, the diagnosis time is 5 min without a trade-off of accuracy. This work solves the occasional inaccuracy issue of rapid on-site diagnosis, endowing POCT systems with the same accuracy as laboratory tests and holding unique prospects for complicated scenes of personalized healthcare.

Self-Assembled Monolayers for Interfacial Engineering in Solution-Processed Thin-Film Electronic Devices: Design, Fabrication, and Applications

Interfacial engineering has long been a vital means of improving thin-film device performance, especially for organic electronics, perovskites, and hybrid devices. It greatly facilitates the fabrication and performance of solution-processed thin-film devices, including organic field effect transistors (OFETs), organic solar cells (OSCs), perovskite solar cells (PVSCs), and organic light-emitting diodes (OLEDs). However, due to the limitation of traditional interfacial materials, further progress of these thin-film devices is hampered particularly in terms of stability, flexibility, and sensitivity. The deadlock has gradually been broken through the development of self-assembled monolayers (SAMs), which possess distinct benefits in transparency, diversity, stability, sensitivity, selectivity, and surface passivation ability. In this review, we first showed the evolution of SAMs, elucidating their working mechanisms and structure-property relationships by assessing a wide range of SAM materials reported to date. A comprehensive comparison of various SAM growth, fabrication, and characterization methods was presented to help readers interested in applying SAM to their works. Moreover, the recent progress of the SAM design and applications in mainstream thin-film electronic devices, including OFETs, OSCs, PVSCs and OLEDs, was summarized. Finally, an outlook and prospects section summarizes the major challenges for the further development of SAMs used in thin-film devices.

Two-Dimensional Nonbenzenoid Heteroacene Crystals Synthesized via In-Situ Embedding of Ladder Bipyrazinylenes on Au(111)

Precisely introducing topological defects is an important strategy in nanographene crystal engineering because defects can tune π-electronic structures and control molecular assemblies. The synergistic control of the synthesis and assembly of nanographenes by embedding the topological defects to afford two-dimensional (2D) crystals on surfaces is still a great challenge. By in-situ embedding ladder bipyrazinylene (LBPy) into acene, the narrowest nanographene with zigzag edges, we have achieved the precise preparation of 2D nonbenzenoid heteroacene crystals on Au(111). Through intramolecular electrocyclization of o-diisocyanides and Au adatom-directed [2+2] cycloaddition, the nonbenzenoid heteroacene products are produced with high chemoselectivity, and lead to the molecular 2D assembly via LBPy-derived interlocking hydrogen bonds. Using bond-resolved scanning tunneling microscopy, we determined the atomic structures of the nonbenzenoid heteroacene product and diverse organometallic intermediates. The tunneling spectroscopy measurements revealed the electronic structure of the nonbenzenoid heteroacene, which is supported by density functional theory (DFT) calculations. The observed distinct organometallic intermediates during progression annealing combined with DFT calculations demonstrated that LBPy formation proceeds via electrocyclization of o-diisocyanides, trapping of heteroarynes by Au adatoms, and stepwise elimination of Au adatoms.

Intrinsically Stretchable and Healable Polymer Semiconductors

In recent decades, polymer semiconductors, extensively employed as charge transport layers in devices like organic field-effect transistors (OFETs), have undergone thorough investigation due to their capacity for large-area solution processing, making them promising for mass production. Research efforts have been twofold: enhancing the charge mobilities of polymer semiconductors and augmenting their mechanical properties to meet the demands of flexible devices. Significant progress has been made in both realms, propelling the practical application of polymer semiconductors in flexible electronics. However, integrating excellent semiconducting and mechanical properties into a single polymer still remains a significant challenge. This review intends to introduce the design strategies and discuss the properties of high-charge mobility stretchable conjugated polymers. In addition, another key challenge faced in this cutting-edge field is maintaining stable semiconducting performance during long-term mechanical deformations. Therefore, this review also discusses the development of healable polymer semiconductors as a promising avenue to improve the lifetime of stretchable device. In conclusion, challenges and outline future research perspectives in this interdisciplinary field are highlighted.

Contact engineering for 2D Janus MoSSe/metal junctions

The flourish of two-dimensional (2D) materials provides a versatile platform for building high-performance electronic devices in the atomic thickness regime. However, the presence of the high Schottky barrier at the interface between the metal electrode and the 2D semiconductors, which dominates the injection and transport efficiency of carriers, always limits their practical applications. Herein, we show that the Schottky barrier can be controllably lifted in the heterostructure consisting of Janus MoSSe and 2D vdW metals by different means. Based on density functional theory calculations and machine learning modelings, we studied the electrical contact between semiconducting monolayer MoSSe and various metallic 2D materials, where a crossover from Schottky to Ohmic/quasi-Ohmic contact is realized. We demonstrated that the band alignment at the interface of the investigated metal-semiconductor junctions (MSJs) deviates from the ideal Schottky-Mott limit because of the Fermi-level pinning effects induced by the interface dipoles. Besides, the effect of the thickness and applied biaxial strain of MoSSe on the electronic structure of the junctions are explored and found to be powerful tuning knobs for electrical contact engineering. It is highlighted that using the sure-independence-screening-and-sparsifying-operator machine learning method, a general descriptor WM3/exp(Dint) was developed, which enables the prediction of the Schottky barrier height for different MoSSe-based MSJ. These results provide valuable theoretical guidance for realizing ideal Ohmic contacts in electronic devices based on the Janus MoSSe semiconductors.

Tuning phase separation in DPPDTT/PMMA blend to achieve molecular self-assembly in the conducting polymer for organic field effect transistors

The semiconductor/insulator blends for organic field-effect transistors are a potential solution to improve the charge transport in the active layer by inducing phase separation in the blends. However, the technique is less investigated for long-chain conducting polymers such as Poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno [3,2-b]thiophene)] (DPPDTT), and lateral phase separation is generally reported due to the instability during solvent evaporation, which results in degraded device performance. Herein, we report how to tailor the dominant mechanism of phase separation in such blends and the molecular assembly of the polymer. For DPPDTT/PMMA blends, we found that for higher DPPDTT concentrations (more than 75%) where the vertical phase separation mechanism is dominant, PMMA assisted in the self-assembly of DPPDTT to form nanowires and micro-transport channels on top of PMMA. The formation of nanowires yielded 13 times higher mobility as compared to pristine devices. For blend ratios with DPPDTT ≤ 50%, both the competing mechanisms, vertical and lateral phase separation, are taking place. It resulted in somewhat lower charge carrier mobilities. Hence, our results show that by systematic tuning of the blend ratio, PMMA can act as an excellent binding material in long-chain polymers such as DPPDTT and produce vertically stratified and aligned structures to ensure high mobility devices.

Organic Transistors Based on Highly Crystalline Donor-Acceptor π-Conjugated Polymer of Pentathiophene and Diketopyrrolopyrrole

Oligomers and polymers consisting of multiple thiophenes are widely used in organic electronics such as organic transistors and sensors because of their strong electron-donating ability. In this study, a solution to the problem of the poor solubility of polythiophene systems was developed. A novel π-conjugated polymer material, PDPP-5Th, was synthesized by adding the electron acceptor unit, DPP, to the polythiophene system with a long alkyl side chain, which facilitated the solution processing of the material for the preparation of devices. Meanwhile, the presence of the multicarbonyl groups within the DPP molecule facilitated donor-acceptor interactions in the internal chain, which further improved the hole-transport properties of the polythiophene-based material. The weak forces present within the molecules that promoted structural coplanarity were analyzed using theoretical simulations. Furthermore, the grazing incidence wide-angle X-ray scanning (GIWAXS) results indicated that PDPP-5Th features high crystallinity, which is favorable for efficient carrier migration within and between polymer chains. The material showed hole transport properties as high as 0.44 cm2 V-1 s-1 in conductivity testing. Our investigations demonstrate the great potential of this polymer material in the field of optoelectronics.

Recent advances in supramolecular fullerene chemistry

Fullerene chemistry has come a long way since 1990, when the first bulk production of C60 was reported. In the past decade, progress in supramolecular chemistry has opened some remarkable and previously unexpected opportunities regarding the selective (multiple) functionalization of fullerenes and their (self)assembly into larger structures and frameworks. The purpose of this review article is to provide a comprehensive overview of these recent developments. We describe how macrocycles and cages that bind strongly to C60 can be used to block undesired addition patterns and thus allow the selective preparation of single-isomer addition products. We also discuss how the emergence of highly shape-persistent macrocycles has opened opportunities for the study of photoactive fullerene dyads and triads as well as the preparation of mechanically interlocked compounds. The preparation of two- or three-dimensional fullerene materials is another research area that has seen remarkable progress over the past few years. Due to the rapidly decreasing price of C60 and C70, we believe that these achievements will translate into all fields where fullerenes have traditionally (third-generation solar cells) and more recently been applied (catalysis, spintronics).

Fabrication of multi-functional molecular tunnelling junctions by click chemistry

Continuous advancement in molecular electronics demands increasing functionality and diversity of integrated molecular junctions; however, single-functional molecular junctions fail to meet these requirements. In this article, we propose the use of a widely applicable and efficient click reaction on the surface to modify self-assembled monolayers (SAMs) to achieve multifunctional molecular tunnelling junctions, current rectification and memristance, on a single chip. This approach has allowed us to meet the growing demand for versatility and functionality in molecular electronic devices.

Coplanar Conformational Structure of π-Conjugated Polymers for Optoelectronic Applications

Hierarchical structure of conjugated polymers is critical to dominating their optoelectronic properties and applications. Compared to nonplanar conformational segments, coplanar conformational segments of conjugated polymers (CPs) demonstrate favorable properties for applications as a semiconductor. Herein, recent developments in the coplanar conformational structure of CPs for optoelectronic devices are summarized. First, this review comprehensively summarizes the unique properties of planar conformational structures. Second, the characteristics of the coplanar conformation in terms of optoelectrical properties and other polymer physics characteristics are emphasized. Five primary characterization methods for investigating the complanate backbone structures are illustrated, providing a systematical toolbox for studying this specific conformation. Third, internal and external conditions for inducing the coplanar conformational structure are presented, offering guidelines for designing this conformation. Fourth, the optoelectronic applications of this segment, such as light-emitting diodes, solar cells, and field-effect transistors, are briefly summarized. Finally, a conclusion and outlook for the coplanar conformational segment regarding molecular design and applications are provided.

Effect of the Molecular Weight of Polyelectrolyte and Surfactant Chain Length on the Solid-Phase Molecular Self-Assembly

Solid-phase molecular self-assembly (SPMSA) is emerging as an efficient approach, leading to scale-span self-assembled supramolecular films. With SPMSA, freestanding macroscopic supramolecular films can be formed upon mechanically pressing the precipitates formed with polyelectrolytes and oppositely charged surfactants. Herein, we report that the film formation ability and the mechanical strength of the resultant film depend highly on the surfactant chain lengths and the molecular weight of polyelectrolytes. A coarse-grained molecular dynamics study revealed that the longer surfactant chains are beneficial for the ordered assembly of surfactant bilayers in the film, whereas the larger molecular weight of PE favors the enhanced mechanical strength of the film by promoting the long-range order of the surfactant bilayers. The current results disclosed the physical insight of the surfactant chain length and the molecular weight of polyelectrolytes into the film structure and mechanical strength, which is of practical importance in guiding the creation of SPMSA materials.

Ligand-Enhanced Neodymium Doping of Perovskite Quantum Dots for Superior Exciton Confinement

In this study, all-inorganic perovskite quantum dots (QDs) for pure blue emission are explored for full-color displays. We prepared CsPbBr3 and Cs3NdCl6 QDs via hot injection methods and mixed in various ratios at room temperature for color blending. Nd-doped CsPb(Cl/Br)3 QDs showed a blueshift in emission, and the photoluminescence quantum yields (PLQY, ΦPL) were lower in the 460-470 nm range due to surface halogen and Cs vacancies. To address this, we introduced a silane molecule, APTMS, via a ligand exchange process, effectively repairing these vacancies and enhancing Nd doping into the lattice. This modification promotes the PLQY to 94% at 466 nm. Furthermore, combining these QDs with [1]Benzothieno[3,2-b][1]benzothiophene (BTBT), a conjugated small-molecule semiconductor, in a composite film reduced PLQY loss caused by FRET in solid-state QD films. This approach achieved a wide color gamut of 124% National Television System Committee (NTSC), using a UV LED backlight and RGB perovskite QDs in a BTBT-based organic matrix as the color conversion layer. Significantly, the photostability of this composite was enhanced when used as a color conversion layer (CCL) under blue-LED excitation.

Liquid-Film Rupture for Web-like Ag Nanowires toward High-Performance Organic Schottky Barrier Transistors

Organic vertical transistors are promising device with benefits such as high operation speed, high saturation current density, and low-voltage operation owing to their short channel length. However, a short channel length leads to a high off-current, which is undesirable because it affects the on-off ratio and power consumption. This study presents a breakthrough in the development of high-performance organic Schottky barrier transistors (OSBTs) with a low off-current by utilizing a near-ideal source electrode with a web-like Ag nanowire (AgNW) morphology. This is achieved by employing a humidity- and surface-tension-mediated liquid-film rupture technique, which facilitates the formation of well-connected AgNW networks with large pores between them. Therefore, the gate electric field is effectively transmitted to the semiconductor layer. Also, the minimized surface area of the AgNWs causes complete suppression of the off-current and induces ideal saturation of the OSBT output characteristics. p- and n-type OSBTs exhibit off-currents in the picoampere range with on/off ratios exceeding 106 and 105, respectively. Furthermore, complementary inverters are prepared using an aryl azide cross-linker for patterning, with a gain of >16. This study represents a significant milestone in the development of high-performance organic vertical transistors and verifies their applicability in organic electronic circuitry.

Single bacteria identification with second-harmonic generation in MoS2

Transition-metal dichalcogenides exhibit extraordinary optical nonlinearities, making them promising candidates for advanced photonic applications. Here, we present the microbial control over second-harmonic generation (SHG) in monolayer MoS2 and the identification of single-cell bacteria. Bacteria deposited on monolayer MoS2 induce a change in the SHG signal, in the form of anisotropic polarization responses that depend on the relative orientation of the bacteria with respect to the MoS2 crystallographic direction. The anisotropic enhancement is consistent with the presence of a tensile stress along the lateral direction of bacteria axis; SHG imaging is highly effective in monitoring biomaterial strain as low as 0.1%. We also investigate the ultraviolet-induced removal of single bacteria, through the SHG imaging of MoS2. By monitoring the transient SHG signals, we determine the rupture times for bacteria, which varies noticeably for each species. This allows us to distinguish specific bacteria that share habitats; SHG imaging is useful for label free identification of pathogens at the single cell levels such as E. coli and L. casei. This label-free detection and identification of pathogens at the single-cell level can have a profound impact on the development of diagnostic tools for various applications.

Retina-inspired organic neuromorphic vision sensor with polarity modulation for decoding light information

The neuromorphic vision sensor (NeuVS), which is based on organic field-effect transistors (OFETs), uses polar functional groups (PFGs) in polymer dielectrics as interfacial units to control charge carriers. However, the mechanism of modulating charge transport on basis of PFGs in devices is unclear. Here, the carboxyl group is introduced into polymer dielectrics in this study, and it can induce the charge transfer process at the semiconductor/dielectric interfaces for effective carrier transport, giving rise to the best device mobility up to 20 cm2 V-1 s-1 at a low operating voltage of -1 V. Furthermore, the polarity modulation effect could further increase the optical figures of merit in NeuVS devices by at least an order of magnitude more than the devices using carboxyl group-free polymer dielectrics. Additionally, devices containing carboxyl groups improved image sensing for light information decoding with 52 grayscale signals and memory capabilities at an incredibly low power consumption of 1.25 fJ/spike. Our findings provide insight into the production of high-performance polymer dielectrics for NeuVS devices.

The Effect of Alkyl Chain Length in Organic Semiconductor and Surface Polarity of Polymer Dielectrics in Organic Thin-Film Transistors (OTFTs)

The interface between dielectric and organic semiconductor is critically important in determining organic thin-film transistor (OTFT) performance. Surface polarity of the dielectric layer can hinder charge transport characteristics, which has restricted utilization of polymeric dielectric materials containing polar functional groups. Herein, the electrical characteristics of OTFTs are analyzed depending on the alkyl chain length of organic semiconductors and surface polarity of polymer dielectrics. High-performance dibenzothiopheno[6,5-b:6',5'-f]thieno[3,2-b]thiophene (DBTTT) and newly synthesized its alkylated derivatives (C6-DBTTT and C10-DBTTT) are utilized as organic semiconductors. As dielectric layers, non-polar poly(1,3,5-trimethyl-1,3,5-trivinylcyclitrisiloxane) (pV3D3) and poly(2-cyanoethyl acrylate-co-diethylene glycol divinyl ether) [p(CEA-co-DEGDVE)] with polar cyanide functionality are utilized. The fabricated OTFTs with pV3D3 commonly exhibit the excellent charge transport characteristics. In addition, the OTFT performance is improved with lengthening the alkyl chain in organic semiconductors, which can be attributed to the molecular orientation of semiconductors. On the other hand, non-alkylated DBTTT OTFTs with polar p(CEA-co-DEGDVE) show relatively poor electrical characteristics, while their performance is drastically enhanced with the alkylated DBTTTs. The ultraviolet photoelectron spectroscopy (UPS) reveals that surface polarity of the dielectric layer can be abated with alkyl chain in organic semiconductors. It is believed that this study can provide a useful insight to optimize dielectric/semiconductor interface to achieve high-performance OTFTs.

General Spatial Confinement Recrystallization Method for Rapid Preparation of Thickness-Controllable and Uniform Organic Semiconductor Single Crystals

Organic semiconductor single crystals (OSSCs) are ideal materials for studying the intrinsic properties of organic semiconductors (OSCs) and constructing high-performance organic field-effect transistors (OFETs). However, there is no general method to rapidly prepare thickness-controllable and uniform single crystals for various OSCs. Here, inspired by the recrystallization (a spontaneous morphological instability phenomenon) of polycrystalline films, a spatial confinement recrystallization (SCR) method is developed to rapidly (even at several second timescales) grow thickness-controllable and uniform OSSCs in a well-controlled way by applying longitudinal pressure to tailor the growth direction of grains in OSCs polycrystalline films. The relationship between growth parameters including the growth time, temperature, longitudinal pressure, and thickness is comprehensively investigated. Remarkably, this method is applicable for various OSCs including insoluble and soluble small molecules and polymers, and can realize the high-quality crystal array growth. The corresponding 50 dinaphtho[2,3-b:2″,3″-f]thieno[3,2-b]thiophene (DNTT) single crystals coplanar OFETs prepared by the same batch have the mobility of 4.1 ± 0.4 cm2 V-1 s-1 , showing excellent uniformity. The overall performance of the method is superior to the reported methods in term of growth rate, generality, thickness controllability, and uniformity, indicating its broad application prospects in organic electronic and optoelectronic devices.

Non-Conjugated Poly(Diphenylene Phthalide)-New Electroactive Material

In organic electronics, conjugated conductive polymers are most widely used. The scope of their application is currently very wide. Non-conjugated polymers are used much less in electronics and are usually used as insulation materials or materials for capacitors. However, the potential of non-conjugated polymers is much wider, due to the fact that new electronic materials with unique electronic properties can be created on the basis of non-conjugated polymers, as well as other inorganic dielectrics. This article demonstrates the possibilities of creating electrically conductive materials with unique electronic parameters based on non-conjugated polymers. The results of the study of the sensory properties of humidity are given as examples of the practical application of the structure. The abnormal electronic properties are realized along the interface of two polymer dielectrics with functional polar groups. The submicron films of polydiphenylenephthalide were used as a dielectric. It is shown that a quasi-two-dimensional electronic structure with abnormally large values of conductivity and mobility of charge carriers occurs along the interface. These structures are often called quasi-two-dimensional electron gas (Q2DEG). This article describes the manufacturing processes of multielectrode devices. Polymer films are deposited via the spin-coating method with polymer solutions in cyclohexanone. The metal electrodes were manufactured through thermal deposition in a vacuum. Three types of metal electrodes made of aluminum, copper and chromium were used. The influence of the electron work function of contacting metals on the electronic parameters of the structure was studied. It was established that the work function decrease leads to an increase in the conductivity and mobility of charge carriers. The charge carrier parameters were estimated based on the analysis of the current-voltage characteristics within the space-charge-limited current technique. The Richardson-Schottky thermionic emission model was used to evaluate values a potential barrier at metal/organic interfaces. It was established that the change in ambient humidity strongly affects the electronic transport properties along the polymer/polymer interface. It is demonstrated that the increase in conductivity with an increase in humidity occurs due to an increase in the mobility of charge carriers and a decrease in the height of the potential barrier at the three-dimensional metal contact with two-dimensional polymer interface. The potential barrier between the electrode and the bulk of the polymer film is significantly higher than between the electrode and the quasi-two-dimensional polymer structure.

Investigating the function and design of molecular materials through terahertz vibrational spectroscopy

Terahertz spectroscopy has proved to be an essential tool for the study of condensed phase materials. Terahertz spectroscopy probes the low-frequency vibrational dynamics of atoms and molecules, usually in the condensed phase. These nuclear dynamics, which typically involve displacements of entire molecules, have been linked to bulk phenomena ranging from phase transformations to semiconducting efficiency. The terahertz region of the electromagnetic spectrum has historically been referred to as the 'terahertz gap', but this is a misnomer, as there exist a multitude of methods for accessing terahertz frequencies, and now there are cost-effective instruments that have made terahertz studies much more user-friendly. This Review highlights some of the most exciting applications of terahertz vibrational spectroscopy so far, and provides an in-depth overview of the methods of this technique and its utility to the study of the chemical sciences.

An Anthracene-Based Bis-Stilbene Derivative as Luminescent Materials for Organic Light Emitting Diodes

In this work, a new luminescent material of a small-molecule stilbene derivative (BABCz) containing anthracene was designed and synthesized by three simple reactions. The material was characterized by ¹H-NMR, FTMS, and X-ray and tested using TGA, DSC, UV/Vis, fluorescence spectroscopy, and atomic force microscopy. The results demonstrate that BABCz has luminescence properties with good thermal stability and can be doped with 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) to prepare highly uniform films, which allows the fabrication of OLED devices with ITO/Cs₂CO₃:BABCz/CBP:BABCz/MoO₃/Al configuration. This simplest device in the sandwich structure emits green light at 6.6-12 V and has a brightness of 2300 cd/m², indicating the potential of this material in OLED manufacturing.

Control of the resistive switching voltage and reduction of the high-resistive-state current of zinc oxide by self-assembled monolayers

We investigated the effect of self-assembled monolayer (SAM) modification of ZnO on the resistive switching behaviour by fabricating electrode-sandwiched devices (ITO/ZnO-SAM/Al). The resistive switching voltages of SAM-modified ZnO films were shifted from that of bare ZnO depending on the surface dipole induced by the SAMs. In particular, methylaminopropyl-substituted SAM-modified ZnO showed lower switching voltage (1.6 V) than bare ZnO (2.9 V). Moreover, the on/off ratio was also improved by SAM modification (from 10² to 10⁴).

Guiding Metal Organic Framework Morphology via Monolayer Artificial Defect-Induced Preferential Facet Selection

Guiding metal organic framework (MOF) morphology, especially without the need for chemical additives, still remains a challenge. For the first time, we report a unique surface guiding approach in controlling the crystal morphology formation of zeolitic imidazole framework-8 (ZIF-8) and HKUST-1 MOFs on disrupted alkanethiol self-assembled monolayer (SAM)-covered Au substrates. Selective molecule removal is applied to generate diverse SAM matrices rich in artificial molecular defects in a monolayer to direct the dynamic crystal growth process. When a 11-mercaptoundecanol alkanethiol monolayer is ruptured, the hydroxyl tail groups of surface residue molecules act as nucleating sites by coordination with precursor metal ions. Meanwhile, the exposed alkane chain backbones stabilize a particular facet of MOF nuclei in the dynamic growth by slowing down their crystal growth rates along a specific direction. The competitive formation between the [110] and [100] planes of ZIF-8 ultimately regulates the crystal shapes from rhombic dodecahedron, truncated rhombic dodecahedron, and truncated cube to cube. Similarly, changeable morphologies of HKUST-1 crystals are also achieved from cube and tetrakaidekahedron to octahedron, originating from the competitive selection between the [100] and [111] planes. In addition to the artificial matrix preferred orientation of initial nucleation, parameters such as temperature also play a crucial role in the resulting crystal morphology. Standing on the additive-free MOF crystal morphology growth control, porous architectures prepared in this approach can act as templates for ligand-free metal (Au, Ag, and Cu) nanocluster synthesis. The nanocluster-embedded MOF structures represent distinct crystal morphology-dependent optical properties, and interestingly, their fluorescence emission can be highly enhanced by facet-induced nanocluster packing alignments. These findings not only provide a unique thought on MOF crystal morphology guidance but also pave a new route for the accompanied property investigation and further application.

Organic thin-film transistors and related devices in life and health monitoring

The early determination of disease-related biomarkers can significantly improve the survival rate of patients. Thus, a series of explorations for new diagnosis technologies, such as optical and electrochemical methods, have been devoted to life and health monitoring. Organic thin-film transistor (OTFT), as a state-of-the-art nano-sensing technology, has attracted significant attention from construction to application owing to the merits of being label-free, low-cost, facial, and rapid detection with multi-parameter responses. Nevertheless, interference from non-specific adsorption is inevitable in complex biological samples such as body liquid and exhaled gas, so the reliability and accuracy of the biosensor need to be further improved while ensuring sensitivity, selectivity, and stability. Herein, we overviewed the composition, mechanism, and construction strategies of OTFTs for the practical determination of disease-related biomarkers in both body fluids and exhaled gas. The results show that the realization of bio-inspired applications will come true with the rapid development of high-effective OTFTs and related devices.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at 10.1007/s12274-023-5606-1.

Record-High Electron Mobility Exceeding 16 cm2 V- 1 s- 1 in Bisisoindigo-Based Polymer Semiconductor with a Fully Locked Conjugated Backbone

Polymer semiconductors with mobilities exceeding 10 cm² V^{- 1} s^{- 1} , especially ambipolar and n-type polymer semiconductors, are still rare, although they are of great importance for fabricating polymer field-effect transistors (PFETs) toward commercial high-grade electronics. Herein, two novel donor-acceptor copolymers, PNFFN-DTE and PNFFN-FDTE, are designed and synthesized based on the electron-deficient bisisoindigo (NFFN) and electron-rich dithienylethylenes (DTE or FDTE). The copolymer PNFFN-DTE, containing NFFN and DTE, possesses a partially locked polymeric conjugated backbone, whereas PNFFN-FDTE, containing NFFN and FDTE, has a fully locked one. Fluorine atoms in FDTE not only induce the formation of additional CH∙∙∙F hydrogen bonds, but also lower frontier molecular orbitals for PNFFN-FDTE. Both PNFFN-DTE and PNFFN-FDTE form more ordered molecular packing in thin films prepared from a polymer solution in bicomponent solvent containing 1,2-dichlorobenzene (DCB) and 1-chloronaphthalene (with volume ratio of 99.2/0.8) than pure DCB. The two copolymers-based flexible PFETs exhibit ambipolar charge-transport properties. Notably, the bicomponent solvent-processed PNFFN-FDTE-based PFETs afford a high electron mobility of 16.67 cm² V^-1 s^-1 , which is the highest electron-transport mobility for PFETs reported so far. The high electron mobility of PNFFN-FDTE is attributed to its fully locked conjugated backbone, dense molecular packing, and much matched LUMO energy level.

Flexible organic field-effect transistors-based biosensors: progress and perspectives

Organic field-effect transistors (OFETs) have been proposed beyond three decades while becoming a research hotspot again in recent years because of the fast development of flexible electronics. Many novel flexible OFETs-based devices have been reported in these years. Among these devices, flexible OFETs-based sensors made great strides because of the extraordinary sensing capability of FET. Most of these flexible OFETs-based sensors were designed for biological applications due to the advantages of flexibility, reduced complexity, and lightweight. This paper reviews the materials, fabrications, and applications of flexible OFETs-based biosensors. Besides, the challenges and opportunities of the flexible OFETs-based biosensors are also discussed.

Combination of Polymer Gate Dielectric and Two-Dimensional Semiconductor for Emerging Field-Effect Transistors

Two-dimensional (2D) materials are considered attractive semiconducting layers for emerging field-effect transistors owing to their unique electronic and optoelectronic properties. Polymers have been utilized in combination with 2D semiconductors as gate dielectric layers in field-effect transistors (FETs). Despite their distinctive advantages, the applicability of polymer gate dielectric materials for 2D semiconductor FETs has rarely been discussed in a comprehensive manner. Therefore, this paper reviews recent progress relating to 2D semiconductor FETs based on a wide range of polymeric gate dielectric materials, including (1) solution-based polymer dielectrics, (2) vacuum-deposited polymer dielectrics, (3) ferroelectric polymers, and (4) ion gels. Exploiting appropriate materials and corresponding processes, polymer gate dielectrics have enhanced the performance of 2D semiconductor FETs and enabled the development of versatile device structures in energy-efficient ways. Furthermore, FET-based functional electronic devices, such as flash memory devices, photodetectors, ferroelectric memory devices, and flexible electronics, are highlighted in this review. This paper also outlines challenges and opportunities in order to help develop high-performance FETs based on 2D semiconductors and polymer gate dielectrics and realize their practical applications.

Flexible Electronics Based on Organic Semiconductors: from Patterned Assembly to Integrated Applications

Organic flexible electronic devices are at the forefront of the electronics as they possess the potential to bring about a major lifestyle revolution owing to outstanding properties of organic semiconductors, including solution processability, lightweight and flexibility. For the integration of organic flexible electronics, the precise patterning and ordered assembly of organic semiconductors have attracted wide attention and gained rapid developments, which not only reduces the charge crosstalk between adjacent devices, but also enhances device uniformity and reproducibility. This review focuses on recent advances in the design, patterned assembly of organic semiconductors, and flexible electronic devices, especially for flexible organic field-effect transistors (FOFETs) and their multifunctional applications. First, typical organic semiconductor materials and material design methods are introduced. Based on these organic materials with not only superior mechanical properties but also high carrier mobility, patterned assembly strategies on flexible substrates, including one-step and two-step approaches are discussed. Advanced applications of flexible electronic devices based on organic semiconductor patterns are then highlighted. Finally, future challenges and possible directions in the field to motivate the development of the next generation of flexible electronics are proposed.

Non-enzymatic detection of glucose levels in human blood plasma by a graphene oxide-modified organic transistor sensor

We herein report an organic transistor functionalized with a phenylboronic acid derivative and graphene oxide for the quantification of plasma glucose levels, which has been achieved by the minimization of interferent effects derived from physical protein adsorption on the detection electrode.

PEDOT-Polyamine-Based Organic Electrochemical Transistors for Monitoring Protein Binding

The fabrication of efficient organic electrochemical transistors (OECTs)-based biosensors requires the design of biocompatible interfaces for the immobilization of biorecognition elements, as well as the development of robust channel materials to enable the transduction of the biochemical event into a reliable electrical signal. In this work, PEDOT-polyamine blends are shown as versatile organic films that can act as both highly conducting channels of the transistors and non-denaturing platforms for the construction of the biomolecular architectures that operate as sensing surfaces. To achieve this goal, we synthesized and characterized films of PEDOT and polyallylamine hydrochloride (PAH) and employed them as conducting channels in the construction of OECTs. Next, we studied the response of the obtained devices to protein adsorption, using glucose oxidase (GOx) as a model system, through two different strategies: The direct electrostatic adsorption of GOx on the PEDOT-PAH film and the specific recognition of the protein by a lectin attached to the surface. Firstly, we used surface plasmon resonance to monitor the adsorption of the proteins and the stability of the assemblies on PEDOT-PAH films. Then, we monitored the same processes with the OECT showing the capability of the device to perform the detection of the protein binding process in real time. In addition, the sensing mechanisms enabling the monitoring of the adsorption process with the OECTs for the two strategies are discussed.

π-Extended Pyrrole-Fused Heteropine: Synthesis, Properties, and Application in Organic Field-Effect Transistors

Sulfur-embedded polycyclic aromatic compounds have been used as building blocks for numerous organic semiconductors over the past few decades. While the success is based on thiophene-containing compounds, aromatic compounds that contain thiepine, a sulfur-containing seven-membered-ring arene, has been less well investigated. Here we report the synthesis and properties of π-extended pyrrole-fused heteropine compounds such as thiepine and oxepine. A π-extended pyrrole-fused thiepine exhibited a "pitched π-stacking" structure in the crystal, and exhibited a high charge carrier mobility of up to 1.0 cm²  V^-1  s^-1 in single-crystal field-effect transistors.

Connecting the dots for fundamental understanding of structure-photophysics-property relationships of COFs, MOFs, and perovskites using a Multiparticle Holstein Formalism

Photoactive organic and hybrid organic-inorganic materials such as conjugated polymers, covalent organic frameworks (COFs), metal-organic frameworks (MOFs), and layered perovskites, display intriguing photophysical signatures upon interaction with light. Elucidating structure-photophysics-property relationships across a broad range of functional materials is nontrivial and requires our fundamental understanding of the intricate interplay among excitons (electron-hole pair), polarons (charges), bipolarons, phonons (vibrations), inter-layer stacking interactions, and different forms of structural and conformational defects. In parallel with electronic structure modeling and data-driven science that are actively pursued to successfully accelerate materials discovery, an accurate, computationally inexpensive, and physically-motivated theoretical model, which consistently makes quantitative connections with conceptually complicated experimental observations, is equally important. Within this context, the first part of this perspective highlights a unified theoretical framework in which the electronic coupling as well as the local coupling between the electronic and nuclear degrees of freedom can be efficiently described for a broad range of quasiparticles with similarly structured Holstein-style vibronic Hamiltonians. The second part of this perspective discusses excitonic and polaronic photophysical signatures in polymers, COFs, MOFs, and perovskites, and attempts to bridge the gap between different research fields using a common theoretical construct - the Multiparticle Holstein Formalism. We envision that the synergistic integration of state-of-the-art computational approaches with the Multiparticle Holstein Formalism will help identify and establish new, transformative design strategies that will guide the synthesis and characterization of next-generation energy materials optimized for a broad range of optoelectronic, spintronic, and photonic applications.

Enhancement of electronic effects at a biomolecule-inorganic interface by multivalent interactions

The binding of peptides and proteins through multiple weak interactions is ubiquitous in nature. Biopanning has been used to "hijack" this multivalent binding for the functionalization of surfaces. For practical applications it is important to understand how multivalency influences the binding interactions and the resulting behaviour of the surface. Considering the importance of optimization of the electronic properties of surfaces in diverse electronic and optoelectronic applications, we study here the relation between the multivalency effect and the resulting modulation of the surface work function. We use 12-mer peptides, which were found to strongly bind to oxide surfaces, to functionalize indium tin oxide (ITO) surfaces. We show that the affinity of the peptides for the ITO surface, and concurrently the effect on the ITO work function, are linearly affected by the number of basic residues in the sequence. The multivalent binding interactions lead to a peptide crowding effect, and a stronger modulation of the work function for adodecapeptide than for a single basic amino acid functionalization. The bioderived molecular platform presented herein can pave the way to a novel approach to improve the performance of optoelectronic devices in an eco-friendly manner.

Enhanced Organic Thin-Film Transistor Stability by Preventing MoO3 Diffusion with Metal/MoO3/Organic Multilayered Interface Source-Drain Contact

The source-drain electrode with a MoO₃ interfacial modification layer (IML) is considered the most promising method to solve electrical contact issues impeding organic thin-film transistors (OTFTs) from commercialization. However, this method raises many concerns because MoO₃ might diffuse into organic materials, which causes device instability. In this work, we observed a significant device stability degradation by damaging on/off switching performance caused by MoO₃ diffusion. To prevent the MoO₃ diffusion, a source-drain electrode with a multilayered interface contact (MIC) consisting of a top-down stack of metal, MoO₃ IML, and organic buffer layer (OBL) is proposed. In the MIC device, the MoO₃ IML serves well for its intended functions of reducing contact resistance and suppressing minority carrier injection to the OTFT channel. The inclusion of OBL to the MIC helps block MoO₃ diffusion and thereby leads to better device stability and an increased on/off ratio. Through combinations with several organic compounds as a buffer layer, the MoO₃ diffusion related electrical behaviors of OTFTs are systematically studied. Key parameters related to MoO₃ diffusion such as the Fick coefficient and bias-stress stability such as carrier trapping time are extracted from numerical device analysis. Finally, we summarize a general rule of material selection for making robust source-drain contact.

Solution-Processed Isoindigo- and Thienoisoindigo-Based Donor-Acceptor-Donor π-Conjugated Small Molecules: Synthesis, Morphology, Molecular Packing, and Field-Effect Transistor Characterization

Molecular design and precise control of thin-film morphology and crystallinity of solution-processed small molecules are important for enhancing charge transport mobility of organic field-effect transistors and gaining more insight into the structure-property relationship. Here, two donor-acceptor-donor (D-A-D) architecture small molecules TRA-IID-TRA and TRA-TIID-TRA comprising an electron-donating triarylamine (TRA) and two different electron-withdrawing cores, isoindigo (IID) and thienoisoindigo (TIID), respectively, were synthesized and characterized. Replacing the phenylene rings of central IID A with thiophene gives a TIID core, which reduces the optical band gap and upshifts the energy levels of frontier molecular orbitals. The single-crystal structures and grazing-incidence wide-angle X-ray scattering (GIWAXS) analysis revealed that TRA-TIID-TRA exhibits the relatively tighter π-π stacking packing with preferential edge-on orientation, larger coherence length, and higher crystallinity due to the noncovalent S···O/S···π intermolecular interactions. The distinctly oriented and connected ribbon-like TRA-TIID-TRA crystalline film by the solution-shearing process achieved a superior hole mobility of 0.89 cm² V^-1 s^-1 in the organic field-effect transistor (OFET) device, which is at least five times higher than that (0.17 cm² V^-1 s^-1) of TRA-IID-TRA with clear cracks. Eventually, rational modulation of fused core in the π-conjugated D-A-D small molecule provides a new understanding of structural design for enhancing the performance of solution-processed organic semiconductors.

Electrospun Conducting Polymers: Approaches and Applications

Inherently conductive polymers (CPs) can generally be switched between two or more stable oxidation states, giving rise to changes in properties including conductivity, color, and volume. The ability to prepare CP nanofibers could lead to applications including water purification, sensors, separations, nerve regeneration, wound healing, wearable electronic devices, and flexible energy storage. Electrospinning is a relatively inexpensive, simple process that is used to produce polymer nanofibers from solution. The nanofibers have many desirable qualities including high surface area per unit mass, high porosity, and low weight. Unfortunately, the low molecular weight and rigid rod nature of most CPs cannot yield enough chain entanglement for electrospinning, instead yielding polymer nanoparticles via an electrospraying process. Common workarounds include co-extruding with an insulating carrier polymer, coaxial electrospinning, and coating insulating electrospun polymer nanofibers with CPs. This review explores the benefits and drawbacks of these methods, as well as the use of these materials in sensing, biomedical, electronic, separation, purification, and energy conversion and storage applications.