Unraveling the Solution‐State Supramolecular Structures of Donor–Acceptor Polymers and their Influence on Solid‐State Morphology and Charge‐Transport Properties

Polymer self‐assembly in solution prior to film fabrication makes solution‐state structures critical for their solid‐state packing and optoelectronic properties. However, unraveling the solution‐state supramolecular structures is challenging, not to mention establishing a clear relationship between the solution‐state structure and the charge‐transport properties in field‐effect transistors. Here, for the first time, it is revealed that the thin‐film morphology of a conjugated polymer inherits the features of its solution‐state supramolecular structures. A “solution‐state supramolecular structure control” strategy is proposed to increase the electron mobility of a benzodifurandione‐based oligo(p‐ phenylene vinylene) (BDOPV)‐based polymer. It is shown that the solution‐state structures of the BDOPV‐based conjugated polymer can be tuned such that it forms a 1D rod‐like structure in good solvent and a 2D lamellar structure in poor solvent. By tuning the solution‐state structure, films with high crystallinity and good interdomain connectivity are obtained. The electron mobility significantly increases from the original value of 1.8 to 3.2 cm² V^?1 s^?1. This work demonstrates that “solution‐state supramolecular structure” control is critical for understanding and optimization of the thin‐film morphology and charge‐transport properties of conjugated polymers.     

High‐Efficiency PbS Quantum‐Dot Solar Cells with Greatly Simplified Fabrication Processing via “Solvent‐Curing”

PbS quantum‐dot (QD) solar cells are promising candidates for low‐cost solution‐processed photovoltaics. However, the device fabrication usually requires ten more times film deposition and rinsing steps, which is not ideal for scalable manufacturing. Here, a greatly simplified deposition processing is demonstrated by replacing methanol with acetonitrile (ACN) as the rinsing solvent. It is discovered that ACN can effectively “cure” the film cracks generated from the volume loss during the solid‐state ligand‐exchange process, which enables the deposition of thick and dense films with much fewer deposition steps. Meanwhile, due to the aprotic nature of ACN, fewer trap states can be introduced during the rinsing process. As a result, with only three deposition steps for the active layer, a CPVT‐certified 11.21% power conversion efficiency is obtained, which is the highest efficiency ever reported for PbS QD solar cells employing a solid‐state ligand‐exchange process. More importantly, the simple film‐deposition processing provides an opportunity for the future application of QDs in low‐cost printing of optoelectronic devices.     

Multilayer Stacked Low‐Temperature‐Reduced Graphene Oxide Films: Preparation,Characterization, and Application in Polymer Memory Devices

Highly reduced graphene oxide (rGO) films are fabricated by combining reduction with smeared hydrazine at low temperature (e.g., 100 °C) and the multilayer stacking technique. The prepared rGO film, which has a lower sheet resistance (≈160–500 Ω sq⁻¹) and higher conductivity (26 S cm⁻¹) as compared to other rGO films obtained by commonly used chemical reduction methods, is fully characterized. The effective reduction can be attributed to the large “effective reduction depth” in the GO films (1.46 µm) and the high C1s/O1s ratio (8.04). By using the above approach, rGO films with a tunable thickness and sheet resistance are achieved. The obtained rGO films are used as electrodes in polymer memory devices, in a configuration of rGO/poly(3‐hexylthiophene) (P3HT):phenyl‐C61‐butyric acid methyl ester (PCBM)/Al, which exhibit an excellent write‐once‐read‐many‐times effect and a high ON/OFF current ratio of 10⁶.     

Ultralow Dispersion Multicomponent Thin‐Film Chalcogenide Glass for Broadband Gradient‐Index Optics

A novel photothermal process to spatially modulate the concentration of sub‐wavelength, high‐index nanocrystals in a multicomponent Ge‐As‐Pb‐Se chalcogenide glass thin film resulting in an optically functional infrared grating is demonstrated. The process results in the formation of an optical nanocomposite possessing ultralow dispersion over unprecedented bandwidth. The spatially tailored index and dispersion modification enables creation of arbitrary refractive index gradients. Sub‐bandgap laser exposure generates a Pb‐rich amorphous phase transforming on heat treatment to high‐index crystal phases. Spatially varying nanocrystal density is controlled by laser dose and is correlated to index change, yielding local index modification to ≈+0.1 in the mid‐infrared.     

A Novel Organic “Polyurea” Thin Film for Ultralong‐Life Lithium‐Metal Anodes via Molecular‐Layer Deposition

Metallic Li is considered as one of the most promising anode materials for next‐generation batteries due to its high theoretical capacity and low electrochemical potential. However, its commercialization has been impeded by the severe safety issues associated with Li‐dendrite growth. Non‐uniform Li‐ion flux on the Li‐metal surface and the formation of unstable solid electrolyte interphase (SEI) during the Li plating/stripping process lead to the growth of dendritic and mossy Li structures that deteriorate the cycling performance and can cause short‐circuits. Herein, an ultrathin polymer film of “polyurea” as an artificial SEI layer for Li‐metal anodes via molecular‐layer deposition (MLD) is reported. Abundant polar groups in polyurea can redistribute the Li‐ion flux and lead to a uniform plating/stripping process. As a result, the dendritic Li growth during cycling is efficiently suppressed and the life span is significantly prolonged (three times longer than bare Li at a current density of 3 mA cm^?2). Moreover, the detailed surface and interfacial chemistry of Li metal are studied comprehensively. This work provides deep insights into the design of artificial SEI coatings for Li metal and progress toward realizing next‐generation Li‐metal batteries.     

“Electro‐Typing” on a Carbon‐Nanoparticles‐Filled Polymeric Film using Conducting Atomic Force Microscopy

Next‐generation electrical nanoimprinting of a polymeric data sheet based on charge trapping phenomena is reported here. Carbon nanoparticles (CNPs) (waste carbon product) are deployed into a polymeric matrix (polyaniline) (PANI) as a charge trapping layer. The data are recorded on the CNPs‐filled polyaniline device layer by “electro‐typing” under a voltage pulse (V_ET, from ±1 to ±7 V), which is applied to the device layer through a localized charge‐injection method. The core idea of this device is to make an electrical image through the charge trapping mechanism, which can be “read” further by the subsequent electrical mapping. The density of stored charges at the carbon–polyaniline layer, near the metal/polymer interface, is found to depend on the voltage amplitude, i.e., the number of injected charge carriers. The relaxation of the stored charges is studied by different probe voltages and for different devices, depending on the percolation of the CNPs into the PANI. The polymeric data sheet retains the recorded data for more than 6 h, which can be refreshed or erased at will. Also, a write–read–erase–read cycle is performed for the smallest “bit” of stored information through a single contact between the probe and the device layer.     

Organic memory using [6,6]-phenyl-C(61) butyric acid methyl ester: morphology, thickness and concentration dependence studies

We report a simple memory device in which the fullerene-derivative [6,6]-phenyl-C(61) butyric acid methyl ester (PCBM) mixed with inert polystyrene (PS) matrix is sandwiched between two aluminum (Al) electrodes. Transmission electron microscopy (TEM) images of PCBM:PS films showed well controlled morphology without forming any aggregates at low weight percentages (<10?wt%) of PCBM in PS. Energy dispersive x-ray spectroscopy (EDX) analysis of the device cross-sections indicated that the thermal evaporation of the Al electrodes did not lead to the inclusion of Al metal nanoparticles into the active PCBM:PS film. Above a threshold voltage of <3?V, independent of thickness, a consistent negative differential resistance (NDR) is observed in devices in the thickness range from 200 to 350?nm made from solutions with 4-10?wt% of PCBM in PS. We found that the threshold voltage (V(th)) for switching from the high-impedance state to the low-impedance state, the voltage at maximum current density (V(max)) and the voltage at minimum current density (V(min)) in the NDR regime are constant within this thickness range. The current density ratio at V(max) and V(min) is more than or equal to 10, increasing with thickness. Furthermore, the current density is exponentially dependent on the longest tunneling jump between two PCBM molecules, suggesting a tunneling mechanism between individual PCBM molecules. This is further supported with temperature independent NDR down to 240?K.     

High‐Performance All‐Polymer Solar Cells Enabled by an n‐Type Polymer Based on a Fluorinated Imide‐Functionalized Arene

A novel imide‐functionalized arene, di(fluorothienyl)thienothiophene diimide (f‐FBTI2), featuring a fused backbone functionalized with electron‐withdrawing F atoms, is designed, and the synthetic challenges associated with highly electron‐deficient fluorinated imide are overcome. The incorporation of f‐FBTI2 into polymer affords a high‐performance n‐type semiconductor f‐FBTI2‐T, which shows a reduced bandgap and lower‐lying lowest unoccupied molecular orbital (LUMO) energy level than the polymer analog without F or with F‐functionalization on the donor moiety. These optoelectronic properties reflect the distinctive advantages of fluorination of electron‐deficient acceptors, yielding “stronger acceptors,” which are desirable for n‐type polymers. When used as a polymer acceptor in all‐polymer solar cells, an excellent power conversion efficiency of 8.1% is achieved without any solvent additive or thermal treatment, which is the highest value reported for all‐polymer solar cells except well‐studied naphthalene diimide and perylene diimide‐based n‐type polymers. In addition, the solar cells show an energy loss of 0.53 eV, the smallest value reported to date for all‐polymer solar cells with efficiency > 8%. These results demonstrate that fluorination of imide‐functionalized arenes offers an effective approach for developing new electron‐deficient building blocks with improved optoelectronic properties, and the emergence of f‐FBTI2 will change the scenario in terms of developing n‐type polymers for high‐performance all‐polymer solar cells.     

Flexible Transparent Films Based on Nanocomposite Networks of Polyaniline and Carbon Nanotubes for High‐Performance Gas Sensing

A flexible, transparent, chemical gas sensor is assembled from a transparent conducting film of carbon nanotube (CNT) networks that are coated with hierarchically nanostructured polyaniline (PANI) nanorods. The nanocomposite film is synthesized by in‐situ, chemical oxidative polymerization of aniline in a functional multiwalled CNT (FMWCNT) suspension and is simultaneously deposited onto a flexible polyethylene terephthalate (PET) substrate. An as‐prepared flexible transparent chemical gas sensor exhibits excellent transparency of 85.0% at 550 nm using the PANI/FMWCNT nanocomposite film prepared over a reaction time of 8 h. The sensor also shows good flexibility, without any obvious decrease in performance after 500 bending/extending cycles, demonstrating high‐performance, portable gas sensing at room temperature. This superior performance could be attributed to the improved electron transport and collection due to the CNTs, resulting in reliable and efficient sensing, as well as the high surface‐to‐volume ratio of the hierarchically nanostructured composites. The excellent transparency, improved sensing performance, and superior flexibility of the device, may enable the integration of this simple, low‐cost, gas sensor into handheld flexible transparent electronic circuitry and optoelectronic devices.     

Two Dimensional Nanoarrays of Individual Protein Molecules

Protein molecules on solid surfaces are essential to a number of applications, such as biosensors, biomaterials, and drug delivery. In most approaches for protein immobilization, inter‐molecular distances on the solid surface are not controlled and this may lead to aggregation and crowding. Here, a simple approach to immobilize individual protein molecules in a well‐ordered 2D array is shown, using nanopatterns obtained from a polystyrene‐block‐poly(2‐hydroxyethyl methacrylate) (PS‐b‐PHEMA) diblock copolymer thin film. This water‐stable and protein‐resistant polymer film contains hexagonally ordered PS cylindrical domains in a PHEMA matrix. The PS domains are activated by incorporating alkyne‐functionalized PS and immobilizing azide‐tagged proteins specifically onto each PS domain using “Click” chemistry. The nanometer size of the PS domain dictates that each domain can accommodate no more than one protein molecule, as verified by atomic force microscopy imaging. Immunoassay shows that the amount of specifically bound antibody scales with the number density of individual protein molecules on the 2D nanoarrays.     

Poly(3,4‐alkylenedioxypyrroles): The PXDOPs as Versatile Yet Underutilized Electroactive and Conducting Polymers

The poly(3,4‐dioxypyrrole) (PXDOP) family of conducting and electroactive polymers has now been developed to the point that multiple synthetic routes allow many functionalized polymers with controllable optoelectronic and redox properties. These properties, which include high conductivity, multicolor cathodic and anodic electrochromism, and rapid redox switching, allow these materials to be used in a variety of applications that potentially include conducting coatings, electrochromic windows and displays, chemical sensors, bioactive materials, and mechanical actuators. Surprisingly, the scientific literature published on the PXDOP derivatives has been isolated and sparse compared to that of other conducting polymers. This report will highlight the synthesis and materials properties of PXDOPs and show how these powerful materials fit into the frontier of conducting polymers research.     

Transparent,High‐Thermal‐Conductivity Ultradrawn Polyethylene/Graphene Nanocomposite Films

Transparent, ultradrawn, ultrahigh molecular weight polyethylene (UHMWPE)/graphene nanocomposite films with a high thermal conductivity are successfully fabricated by solution‐casting and solid‐state drawing. It is found that the low optical transmittance (<75%) of the ultradrawn UHMWPE/graphene composite films is drastically improved (>90%) by adding 2‐(2H‐benzontriazol‐2‐yl)‐4,6‐ditertpentylphenol (BZT) as a second additive. This high transmission is interpreted in terms of a reduced void content in the composite films and the improved dispersion of graphene both of which decrease light scattering. The high thermal conductivity is attributed to the π–π interaction between BZT and graphene. In addition, a high specific thermal conductivity of ≈75 W m^?1 K^?1 ρ^?1 of the ultradrawn UHMWPE/graphene/BZT composite films is obtained, which is higher than most metals and polymer nanocomposite. These transparent films are potentially excellent candidates for thermal management in various applications due to a combination of low density, ease of processing, and high thermal conductivity.     

Crystal Phase and Architecture Engineering of Lotus‐Thalamus‐Shaped Pt‐Ni Anisotropic Superstructures for Highly Efficient Electrochemical Hydrogen Evolution

The rational design and synthesis of anisotropic 3D nanostructures with specific composition, morphology, surface structure, and crystal phase is of significant importance for their diverse applications. Here, the synthesis of well‐crystalline lotus‐thalamus‐shaped Pt‐Ni anisotropic superstructures (ASs) via a facile one‐pot solvothermal method is reported. The Pt‐Ni ASs with Pt‐rich surface are composed of one Ni‐rich “core” with face‐centered cubic (fcc) phase, Ni‐rich “arms” with hexagonal close‐packed phase protruding from the core, and facet‐selectively grown Pt‐rich “lotus seeds” with fcc phase on the end surfaces of the “arms.” Impressively, these unique Pt‐Ni ASs exhibit superior electrocatalytic activity and stability toward the hydrogen evolution reaction under alkaline conditions compared to commercial Pt/C and previously reported electrocatalysts. The obtained overpotential is as low as 27.7 mV at current density of 10 mA cm^?2, and the turnover frequency reaches 18.63 H₂ s^?1 at the overpotential of 50 mV. This work provides a new strategy for the synthesis of highly anisotropic superstructures with a spatial heterogeneity to boost their promising application in catalytic reactions.     

A “Phase Separation” Molecular Design Strategy Towards Large‐Area 2D Molecular Crystals

2D molecular crystals (2DMCs) have attracted considerable attention because of their unique optoelectronic properties and potential applications. Taking advantage of the solution processability of organic semiconductors, solution self‐assembly is considered an effective way to grow large‐area 2DMCs. However, this route is largely blocked because a precise molecular design towards 2DMCs is missing and little is known about the relationship between 2D solution self‐assembly and molecular structure. A “phase separation” molecular design strategy towards 2DMCs is proposed and layer‐by‐layer growth of millimeter‐sized monolayer or few‐layer 2DMCs is realized. High‐performance organic phototransistors are constructed based on the 2DMCs with unprecedented photosensitivity (2.58 × 10⁷), high responsivity (1.91 × 10⁴ A W^?1), and high detectivity (4.93 × 10¹⁵ Jones). This “phase separation” molecular design strategy provides a guide for the design and synthesis of novel organic semiconductors that self‐assemble into large‐area 2DMCs for advanced organic (opto)electronics.     

Progress Report on Phase Separation in Polymer Solutions

Polymeric porous media (PPM) are widely used as advanced materials, such as sound dampening foams, lithium‐ion batteries, stretchable sensors, and biofilters. The functionality, reliability, and durability of these materials have a strong dependence on the microstructural patterns of PPM. One underlying mechanism for the formation of porosity in PPM is phase separation, which engenders polymer‐rich and polymer‐poor (pore) phases. Herein, the phase separation in polymer solutions is discussed from two different aspects: diffusion and hydrodynamic effects. For phase separation governed by diffusion, two novel morphological transitions are reviewed: “cluster‐to‐percolation” and “percolation‐to‐droplets,” which are attributed to an effect that the polymer‐rich and the solvent‐rich phases reach the equilibrium states asynchronously. In the case dictated by hydrodynamics, a deterministic nature for the microstructural evolution during phase separation is scrutinized. The deterministic nature is caused by an interfacial‐tension‐gradient (solutal Marangoni force), which can lead to directional movement of droplets as well as hydrodynamic instabilities during phase separation.     

Enhanced Dielectric Performance in Polymer Composite Films with Carbon Nanotube‐Reduced Graphene Oxide Hybrid Filler

The electrical conductivity and the specific surface area of conductive fillers in conductor‐insulator composite films can drastically improve the dielectric performance of those films through changing their polarization density by interfacial polarization. We have made a polymer composite film with a hybrid conductive filler material made of carbon nanotubes grown onto reduced graphene oxide platelets (rG‐O/CNT). We report the effect of the rG‐O/CNT hybrid filler on the dielectric performance of the composite film. The composite film had a dielectric constant of 32 with a dielectric loss of 0.051 at 0.062 wt% rG‐O/CNT filler and 100 Hz, while the neat polymer film gave a dielectric constant of 15 with a dielectric loss of 0.036. This is attributed to the increased electrical conductivity and specific surface area of the rG‐O/CNT hybrid filler, which results in an increase in interfacial polarization density between the hybrid filler and the polymer.     

Thin-film phases of organic charge-transfer complexes formed by chemical vapor deposition

Thin films of organic charge-transfer salts, (TTF)(TCNQ) and (TTF)(DMDCNQI), are prepared by the chemical vapor deposition method, where TTF is tetrathiafulvalene, TCNQ is tetracyanoquinodimethane, and DMDCNQI is dimethyldicyanoquinonediimine. Depending on the substrate temperatures, we have obtained randomly oriented polycrystalline phases composed of relatively large crystals and microcrystalline thin-film phases, which sometimes contain well-grown nanowires. The latter shows much different conducting properties from the bulk crystals, and particularly the (TTF)(DMDCNQI) film is nearly as conductive as the (TTF)(TCNQ) film in spite of the bulk insulating property coming from the mixed-stack crystal structure.     

Isomer‐Pure Bis‐PCBM‐Assisted Crystal Engineering of Perovskite Solar Cells Showing Excellent Efficiency and Stability

A fullerene derivative (α‐bis‐PCBM) is purified from an as‐produced bis‐phenyl‐C₆₁‐butyric acid methyl ester (bis‐[60]PCBM) isomer mixture by preparative peak‐recycling, high‐performance liquid chromatography, and is employed as a templating agent for solution processing of metal halide perovskite films via an antisolvent method. The resulting α‐bis‐PCBM‐containing perovskite solar cells achieve better stability, efficiency, and reproducibility when compared with analogous cells containing PCBM. α‐bis‐PCBM fills the vacancies and grain boundaries of the perovskite film, enhancing the crystallization of perovskites and addressing the issue of slow electron extraction. In addition, α‐bis‐PCBM resists the ingression of moisture and passivates voids or pinholes generated in the hole‐transporting layer. As a result, a power conversion efficiency (PCE) of 20.8% is obtained, compared with 19.9% by PCBM, and is accompanied by excellent stability under heat and simulated sunlight. The PCE of unsealed devices dropped by less than 10% in ambient air (40% RH) after 44 d at 65 °C, and by 4% after 600 h under continuous full‐sun illumination and maximum power point tracking, respectively.     

Mechanically Flexible Conductors for Stretchable and Wearable E‐Skin and E‐Textile Devices

Considerable progress in materials development and device integration for mechanically bendable and stretchable optoelectronics will broaden the application of “Internet‐of‐Things” concepts to a myriad of new applications. When addressing the needs associated with the human body, such as the detection of mechanical functions, monitoring of health parameters, and integration with human tissues, optoelectronic devices, interconnects/circuits enabling their functions, and the core passive components from which the whole system is built must sustain different degrees of mechanical stresses. Herein, the basic characteristics and performance of several of these devices are reported, particularly focusing on the conducting element constituting them. Among these devices, strain sensors of different types, energy storage elements, and power/energy storage and generators are included. Specifically, the advances during the past 3 years are reported, wherein mechanically flexible conducting elements are fabricated from (0D, 1D, and 2D) conducting nanomaterials from metals (e.g., Au nanoparticles, Ag flakes, Cu nanowires), carbon nanotubes/nanofibers, 2D conductors (e.g., graphene, MoS₂), metal oxides (e.g., Zn nanorods), and conducting polymers (e.g., poly(3,4‐ethylenedioxythiophene):poly(4‐styrene sulfonate), polyaniline) in combination with passive fibrotic and elastomeric materials enabling, after integration, the so‐called electronic skins and electronic textiles.     

Effect of hinokitiol impregnated sheets on shelf life and quality of “KEK‐1” tomatoes during storage

Hinokitiol (β‐thujaplicin, volatile oil extracted from the wood of Hiba arborvitae [Thujopsis dolabrata var. hondae], cypress family) is a natural preservative, antimicrobial, and chelating agent, used to prevent decay and extend the shelf life of fruits and vegetables. In the present study, we used nonwoven rayon sheets impregnated with hinokitiol to conduct packaging studies. Mature green tomatoes var. “KEK‐1” were packaged under three packaging conditions, ie, modified atmosphere packaging (MAP), MAP + hinokitiol (MH), and perforated film package (as control), and their quality attributes were compared during storage. The packaging materials used were low‐density polyethylene (LDPE) film (40 μm) and fresh sheets of nonwoven rayon impregnated with hinokitiol. O₂ in the MAP packaged tomatoes were retained throughout the storage period (3% to 5% O₂). Results showed that MH had slightly improved quality attributes throughout the storage period when compared with MAP alone. Expression levels of LeACS, LeADH, and LeTBG4 genes were higher in 5 and 9 days of control when compared with MAP and MH. “KEK‐1” tomatoes had longer shelf life under MAP and MH packaging and maintained the quality at 15°C. Hence, the effect of the MAP with bioactive packaging treatments could be effective in the future application for the extension of shelf life and quality of fruits and vegetables.