Spontaneous Phase Separation of Poly(3‐hexylthiophene)s with Different Regioregularity for a Stretchable Semiconducting Film

Highly regioregular (RR) poly(3‐hexylthiophene)s PHTs are known to exhibit excellent electrical properties in comparison to chemically identical but regiorandom (rr) PHTs. In this study, distinct RR (97% and 55%)‐graded PHTs are subjected to solution blending to spontaneously separate the high‐RR PHT chains from the low‐RR PHT media and develop highly conjugated nanodomains in both solution and film. In the spun‐cast blend films, the rr PHT matrix imparts sufficient deformability of the channel layer required for stretchable organic thin‐film transistors (OTFTs), compared to neat RR PHTs and blends with a deformable polymer. OTFTs including RR PHT/rr PHT blend films show excellent hole mobility (µ) values up to 0.13 cm² V^?1 s^?1, surpassing that of the best RR PHT films (0.026 cm² V^?1 s^?1) fabricated by ultrasound solution pretreatment. Furthermore, a 50% stretched RR PHT/rr PHT film maintains ≈55% of its µ value at no strain, while RR PHT films show a sudden decrease in µ even at 10% stretch. The simple blending approach imparts deformability to π‐conjugated polymer films for application in stretchable OTFTs.     

Pyrite‐Based Bi‐Functional Layer for Long‐Term Stability and High‐Performance of Organo‐Lead Halide Perovskite Solar Cells

Organo‐lead halide perovskite solar cells (PSCs) have received great attention because of their optimized optical and electrical properties for solar cell applications. Recently, a dramatic increase in the photovoltaic performance of PSCs with organic hole transport materials (HTMs) has been reported. However, as of now, future commercialization can be hampered because the stability of PSCs with organic HTM has not been guaranteed for long periods under conventional working conditions, including moist conditions. Furthermore, conventional organic HTMs are normally expensive because material synthesis and purification are complicated. It is herein reported, for the first time, octadecylamine‐capped pyrite nanoparticles (ODA‐FeS₂ NPs) as a bi‐functional layer (charge extraction layer and moisture‐proof layer) for organo‐lead halide PSCs. FeS₂ is a promising candidate for the HTM of PSCs because of its high conductivity and suitable energy levels for hole extraction. A bi‐functional layer based on ODA‐FeS₂ NPs shows excellent hole transport ability and moisture‐proof performance. Through this approach, the best‐performing device with ODA‐FeS₂ NPs‐based bi‐functional layer shows a power conversion efficiency of 12.6% and maintains stable photovoltaic performance in 50% relative humidity for 1000 h. As a result, this study has the potential to break through the barriers for the commercialization of PSCs.     

Polymeric Alkoxy PBD [2‐(4‐Biphenylyl)‐5‐Phenyl‐1,3,4‐Oxadiazole] for Light‐Emitting Diodes

The syntheses are reported of the title polymeric alkoxyPBD derivative 5 and the dipyridyl analogue 12 using Suzuki coupling reactions of 1,4‐dialkoxybenzene‐2,5‐diboronic acid with 2,5‐bis(4‐bromophenyl)‐1,3,5‐oxadiazole, and its dipyridyl analogue, respectively. Thermal gravimetric analysis shows that polymers 5 and 12 are stable up to 370 °C and 334 °C, respectively. Films of polymer 5 spun from chloroform solution show an absorption at λ_max = 367 nm, and a weaker band at 312 nm, and strong blue photoluminescence at λ_max = 444 nm. The photoluminescence quantum yield (PLQY) was found to be 27 ± 3 %. For polymer 12 , the absorption spectra reveal bands of equal intensity at λ_max = 374 and 312 nm, with PL at λ_max = 475 nm. Device studies using polymer 12 were hampered by its instability under illumination and/or electrical excitation. Polymer 5 is stable under these conditions and acts as an efficient electron‐transporting/hole‐blocking layer. For devices of configuration ITO/PEDOT/MEH‐PPV/polymer 5 /Al an external quantum efficiency of 0.26 % and brightness of 800 cd/m² was readily achieved: orange emission was observed, identical to the MEH‐PPV electroluminescence.     

Investigation of TDAPBs as hole‐transporting materials for organic light‐emitting devices (OLEDs)

The performance of organic light‐emitting devices (OLEDs) is strongly influenced by the electronic properties of the employed materials. In order to determine the effect of these materials' parameters, several different hole‐transporting 1,3,5‐tris(4‐diphenylaminophenyl)benzenes (TDAPBs) were synthesised. These TDAPBs contained different substituents, different numbers of substituents and different positions of theses substituents. For the evaluation of the electronic properties, cyclic voltammetry was employed in order to determine the HOMO values, and time‐of‐flight (TOF) measurements to obtain the hole mobilities. OLEDs were prepared consisting of the TDAPBs blended in a polymer matrix, and of Alq₃ as electron‐conducting and light‐emitting layer. These devices were investigated regarding their current density/voltage characteristics, efficiencies, onset voltages for electroluminescence, and lifetimes. For hole‐transporting blend systems an exponential relationship between the current density and the HOMO levels of the TDAPBs was found. However, even though the HOMO values cover a range from −5.09 to −5.35 eV, no effects on the performance of the OLEDs were detected for electroluminescent two‐layer systems. In this case the initial voltage seems to be a determining parameter for the behaviour of the devices during operation. Copyright © 1999 John Wiley & Sons, Ltd.     

An Alternative Route Towards Metal–Polymer Hybrid Materials Prepared by Vapor‐Phase Processing

Transition metals incorporated into polymers lead to unusual or improved physical properties that significantly differ from those of purely organic polymers. A simple and practicable incorporation of diverse transition metals into any available polymer would make an important contribution to overcome some of the synthetic difficulties of metal‐polymer hybrid materials. Here, it is demonstrated that atomic layer deposition (ALD) can be a promising means to resolve some of those difficulties. It is found that even polytetrafluoroethylene (PTFE) with its great physical and chemical stability can be easily transformed into a transition metal–PTFE hybrid material simply by applying a metal‐oxide ALD process to PTFE. Upon metal incorporation into the PTFE, the molecular structure as well as mechanical properties (tensile behavior) of PTFE were observed to significantly change. For a better understanding of the changes to the material, experimental investigations using Raman spectroscopy, attenuated‐total‐reflection Fourier‐transform infrared spectroscopy, wide‐angle X‐ray diffraction, and energy‐dispersive X‐ray analysis were performed. In addition, with density functional theory calculations, potential bonding states of the incorporated metal into PTFE were modeled and predicted. The ALD‐based vapor‐phase approach for metal incorporation into a polymer could bring about rapid progress in the research area of metal–polymer hybrid materials.     

Hierarchical Self‐assembly of Microscale Cog‐like Superstructures for Enhanced Performance in Lithium‐Ion Batteries

Assembling complex nanostructures on functional substrates such as electrodes promises new multi‐functional interfaces with synergetic properties capable of integration into larger‐scale devices. Here, we report a microemulsion‐mediated process for the preparation of CuO/Cu electrodes comprising a surface layer of a densely packed array of unusual cog‐shaped CuO microparticles with hierarchical nanofilament‐based superstructure and enhanced electrochemical performance in lithium‐ion batteries. The CuO particles are produced by thermolysis of Cu(OH)₂ micro‐cog precursors that spontaneously assemble on the copper substrate when the metal foil is treated with a reactive oil‐based microemulsion containing nanometer‐scale aqueous droplets. The formation of the hierarchical superstructure improves the coulombic efficiency, specific capacity, and cycling performance compared with anodes based on CuO nanorods or polymer‐blended commercial CuO/C black powders, and the values for the initial discharge capacity (1052 mA h g^?1) and reversible capacity (810 m A h g^?1) are higher than most copper oxide materials used in lithium‐ion batteries. The results indicate that a fabrication strategy based on self‐assembly within confined reaction media, rather than direct synthesis in bulk solution, offers a new approach to the design of electrode surface structures for potential development in a wide range of materials applications.     

Ambient Layer‐by‐Layer ZnO Assembly for Highly Efficient Polymer Bulk Heterojunction Solar Cells

The use of metal oxide interlayers in polymer solar cells has great potential because metal oxides are abundant, thermally stable, and can be used in flexible devices. Here, a layer‐by‐layer (LbL) protocol is reported as a facile, room‐temperature, solution‐processed method to prepare electron transport layers from commercial ZnO nanoparticles and polyacrylic acid (PAA) with a controlled and tunable porous structure, which provides large interfacial contacts with the active layer. Applying the LbL approach to bulk heterojunction polymer solar cells with an optimized ZnO layer thickness of ≈25 nm yields solar cell power‐conversion efficiencies (PCEs) of ≈6%, exceeding the efficiency of amorphous ZnO interlayers formed by conventional sputtering methods. Interestingly, annealing the ZnO/PAA interlayers in nitrogen and air environments in the range of 60–300 °C reduces the device PCEs by almost 20% to 50%, indicating the importance of conformational changes inherent to the PAA polymer in the LbL‐deposited films to solar cell performance. This protocol suggests a new fabrication method for solution‐processed polymer solar cell devices that does not require postprocessing thermal annealing treatments and that is applicable to flexible devices printed on plastic substrates.     

Colorimetric Logic Gates Based on Poly(2‐alkyl‐2‐oxazoline)‐Coated Gold Nanoparticles

A straightforward end‐capping strategy is applied to synthesize xanthate‐functional poly(2‐alkyl‐2‐oxazoline)s (PAOx) that enable gold nanoparticle functionalization by a direct “grafting to” approach with citrate‐stabilized gold nanoparticles (AuNPs). Owing to the presence of remaining citrate groups, the obtained PAOx@AuNPs exhibit dual stabilization by repulsive electrostatic and steric interactions giving access to water soluble molecular AND logic gates, wherein environmental temperature and ionic strength constitute the input signals, and the solution color the output signal. The temperature input value could be tuned by variation of the PAOx polymer composition, from 22 °C for poly(2‐ⁿpropyl‐2‐oxazoline)@AuNPs to 85 °C for poly(2‐ethyl‐2‐oxazoline)@AuNPs. Besides, advancing the fascinating field of molecular logic gates, the present research offers a facile strategy for the synthesis of PAOx@AuNPs of interest in fields spanning nanotechnology and biomedical sciences. In addition, the functionalization of PAOx with xanthate offers straightforward access to thiol‐functional PAOx of high interest in polymer science.     

Percolation‐Controlled Metal/Polyelectrolyte Complexed Films for All‐Solution‐Processable Electrical Conductors

The use of solution‐processable electrically conducting films is imperative for realizing next‐generation flexible and wearable devices in a large‐scale and economically viable way. However, the conventional approach of simply complexing metallic nanoparticles with a polymeric medium leads to a tradeoff between electrical conductivity and material properties. To address this issue, in this study, a novel strategy is presented for fabricating all‐solution‐processable conducting films by means of metal/polyelectrolyte complexation to achieve controlled electrical percolation; this simultaneously imparts superior electrical conductivity and good mechanical properties. A polymeric matrix comprised of polyelectrolyte multilayers is first formed using layer‐by‐layer assembly, and then Ag nanoparticles are gradually synthesized and gradationally distributed inside the polymeric matrix by means of a subsequent procedure of repeated cationic exchange and reduction. During this process, electrical percolation between Ag nanoparticles and networking of electrical pathways is facilitated in the surface region of the complexed film, providing outstanding electrical conductivity only one order of magnitude less than that of metallic Ag. At the same time, the polymer‐rich underlying region imparts strong, yet compliant, binding characteristics to the upper Ag‐containing conducting region while allowing highly flexible mechanical deformations of bending and folding, which consequently makes the system outperform existing materials.     

Fuel Cell Membrane Electrode Assemblies Fabricated by Layer‐by‐Layer Electrostatic Self‐Assembly Techniques

High activity, carbon supported Pt electrocatalysts were synthesized using a supercritical fluid method and a selective heterogeneous nucleation reaction to disperse Pt onto single walled carbon nanotube and carbon fiber supports. These nanocomposite materials were then incorporated into catalyst and gas diffusion layers consisting of polyelectrolytes, i.e., Nafion, polyaniline, and polyethyleneimine using layer‐by‐layer (LBL) assembly techniques. Due to the ultrathin nature and excellent homogeneity characteristics of LBL materials, the LBL nanocomposite catalyst layers (LNCLs) yielded much higher Pt utilizations, 3,198 mW mg_Pt^?1, than membrane electrode assemblies produced using conventional methods (～800 mW mg_Pt^?1). Thinner membranes (100 bilayers) can further improve the performance of the LNCLs and these layers can function as catalyzed gas diffusion layers for the anode and cathode of a polymer electrolyte membrane fuel cell.     

Evaluation of Digitally Encoded Layer‐by‐layer Coated Microparticles as Cell Carriers

To obtain more biologically relevant data there is a growing interest in the use of living cells for assaying the biological activity of unknown chemical compounds. Density ‘multiplex’ cell‐based assays, where different cell types are mixed in one well and simultaneously investigated upon exposure to a certain compound are beginning to emerge. To be able to identify the cells they should be attached to microscopic carriers that are encoded. This paper investigates how digitally encoded microparticles can be loaded with cells while keeping the digital code in the microcarriers readable. It turns out that coating the surface of the encoded microcarriers with polyelectrolytes using the layer‐by‐layer (LbL) approach provides the microcarriers with a ‘highly functional’ surface. The polyelectrolyte layer allows the growth of the cells, allows the orientation of the cell loaded microcarriers in a magnetic field, and does not hamper the reading of the code. It has further been shown that the cells growing on the polyelectrolyte layer can become transduced by adenoviral particles hosted by the polyelectrolyte layer. It is concluded that the digitally encoded microparticles are promising materials for use in biomedical and pharmaceutical in‐vitro research where cells are used as tools.     

Highly Scalable,Closed‐Loop Synthesis of Drug‐Loaded,Layer‐by‐Layer Nanoparticles

Layer‐by‐layer (LbL) self‐assembly is a versatile technique from which multi­component and stimuli‐responsive nanoscale drug‐carriers can be constructed. Despite the benefits of LbL assembly, the conventional synthetic approach for fabricating LbL nanoparticles requires numerous purification steps that limit scale, yield, efficiency, and potential for clinical translation. In this report, a generalizable method for increasing throughput with LbL assembly is described by using highly scalable, closed‐loop diafiltration to manage intermediate purification steps. This method facilitates highly controlled fabrication of diverse nanoscale LbL formulations smaller than 150 nm composed from solid‐polymer, mesoporous silica, and liposomal vesicles. The technique allows for the deposition of a broad range of polyelectrolytes that included native polysaccharides, linear polypeptides, and synthetic polymers. The cytotoxicity, shelf life, and long‐term storage of LbL nanoparticles produced using this approach are explored. It is found that LbL coated systems can be reliably and rapidly produced: specifically, LbL‐modified liposomes could be lyophilized, stored at room temperature, and reconstituted without compromising drug encapsulation or particle stability, thereby facilitating large scale applications. Overall, this report describes an accessible approach that significantly improves the throughput of nanoscale LbL drug‐carriers that show low toxicity and are amenable to clinically relevant storage conditions.     

Stiff and Transparent Multilayer Thin Films Prepared Through Hydrogen‐Bonding Layer‐by‐Layer Assembly of Graphene and Polymer

Due to their exceptional orientation of 2D nanofillers, layer‐by‐layer (LbL) assembled polymer/graphene oxide thin films exhibit unmatched mechanical performance relative to any conventionally produced counterparts with similar composition. Unprecedented mechanical property improvement, by replacing graphene oxide with pristine graphene, is demonstrated in this work. Polyvinylpyrrolidone‐stabilized graphene platelets are alternately deposited with poly(acrylic acid) using hydrogen bonding assisted LbL assembly. Transmission electron microscopy imaging and the Halpin‐Tsai model are used to demonstrate, for the first time, that intact graphene can be processed from water to generate polymer nanocomposite thin films with simultaneous parallel‐alignment, high packing density, and exfoliation. A multilayer thin film with only 3.9 vol% of highly exfoliated, and structurally intact graphene, increases the elastic modulus (E) of a polymer multilayer thin film by 322% (from 1.41 to 4.81 GPa), while maintaining visible light transmittance of ≈90%. This is one of the greatest improvements in elastic modulus ever reported for a graphene‐filled polymer nanocomposite with a glassy (E > 1 GPa) matrix. The technique described here provides a powerful new tool to improve nanocomposite properties (mechanical, gas transport, etc.) that can be universally applied to a variety of polymer matrices and 2D nanoplatelets.     

Hemoglobin‐CdTe‐CaCO3@Polyelectrolytes 3D Architecture: Fabrication,Characterization, and Application in Biosensing

A Hemoglobin‐CdTe‐CaCO₃@polyelectrolyte 3D architecture is synthesized by a stepwise layer‐by‐layer method and is further used to fabricate an electrochemistry biosensor. While the calcium carbonate (CaCO₃) microsphere acts as an effective host for the loading of cadmium telluride (CdTe) quantum dots due to its channel‐like structure, the polyelectrolyte layers further increase the loading amount and help in the formation of a thick and uniform quantum‐dot “shell”, which not only improves the stability of the spheres in water, but also contributes to the fast and effective direct electron transfer between the protein redox center and the macroscopic electrode. The materials are characterized and compared, and the possible mechanism for the direct electrochemistry phenomenon is hypothesized. Our work not only provides a facile and effective route for the preparation of quantum‐dot‐loaded spheres, but also sets an example of how the structure of functional materials can be tuned and related to their applications. In addition, it is one of the few examples of using CaCO₃ microspheres in quantum‐dot loading and biosensing.     

Multi‐Functional Dual‐Layer Polymer Electrolytes for Lithium Metal Polymer Batteries

We prepared a novel multi‐functional dual‐layer polymer electrolyte by impregnating the interconnected pores with an ethylene carbonate (EC)/dimethyl carbonate (DMC)/lithium hexafluorophosphate (LiPF₆) solution. The first layer, based on a microporous polyethylene, is incompatible with a liquid electrolyte, and the second layer, based on poly (vinylidenefluoride‐co‐hexafluoropropylene), is submicroporous and compatible with an electrolyte solution. The maximum ionic conductivity is 7 × 10^?3 S/cm at ambient temperature. A unit cell using the optimum polymer electrolyte showed a reversible capacity of 198 mAh/g at the 500th cycle, which was about 87% of the initial value.     

A Delivery System for Self‐Healing Inorganic Films

Multilayer composites that utilize polymeric and brittle inorganic films are essential components for extending the lifetimes and exploiting the flexibility of many electronic devices. However, crack formation within the brittle inorganic layers that arise from defects as well as the flexing of these multilayer composite materials allows the influx of atmospheric water, a major source of device degradation. Thus, a composite material that can initiate self‐healing upon the influx of environmental water through defects or stress‐induced cracks would find potential applications in multilayer composite materials for permeation barriers. In the present study, the reactive metal oxide precursor TiCl₄ is encapsulated within the pores of a degradable polymer, poly(lactic acid) (PLA). Electrospun PLA fibers are found to be reactive to atmospheric water leading to the hydrolysis of the degradable polymer shell and subsequent release of the reactive metal oxide precursor. Release of the reactive TiCl₄ from the pores results in hydrolysis of the metal oxide precursor, forming solid titanium oxides at the surface of the fibers. The efficacy of this self‐healing delivery system is also demonstrated by the integration of these reactive fibers in the polymer planarization layer, poly(methyl methacrylate), of a multilayer film, upon which an alumina barrier layer is deposited. The introduction of nanocracks in the alumina barrier layer lead to the release of the metal oxide precursor from the pores of the fibers and the formation of titanium dioxide nanoparticles within the crack and upon the thin film surface. In this study the first delivery system that may find utility for the self‐healing of multilayer barrier films through the site‐specific delivery of metal oxide nanoparticles through smart reactive composite fibers is established.     

Self‐Healing Actuating Adhesive Based on Polyelectrolyte Multilayers

Creating actuators capable of mechanical motion in response to external stimuli is a key for design and preparation of smart materials. The lifetime of such materials is limited by their eventual wear. Here, self‐healable and adhesive actuating materials are demonstrated by taking advantage of the solvent responsive of weak polyelectrolyte multilayers consisting of branched poly(ethylenimine)/poly(acrylic acid) (BPEI/PAA). BPEI/PAA multilayers are dehydrated and contract upon contact with organic solvent and become sticky when wetted with water. By constructing an asymmetric heterostructure consisting of a responsive BPEI/PAA multilayer block and a nonresponsive component through either layer‐by‐layer assembly or the paste‐to‐curl process, smart films that actuate upon exposure to alcohol are realized. The curl degree, defined as degrees from horizontal that the actuated material reaches, can be as high as ≈228.9°. With evaporation of the ethanol, the curled film returns to its initial state, and water triggers fast self‐healing extends the actuator's lifetime. Meanwhile, the adhesive nature of the wet material allows it to be attached to various substrates for possible combination with hydrophobic functional surfaces and/or applications in biological environments. This self‐healable adhesive for controlled fast actuation represents a considerable advance in polyelectrolyte multilayers for design and fabrication of robust smart advanced materials.     

Two‐Stage Reactive Polymer Network Forming Systems

There are distinct advantages to designing polymer systems that afford two distinct sets of material properties– an intermediate polymer that would enable optimum handling and processing of the material, while maintaining the ability to tune in different, final polymer properties that enable the optimal functioning of the material. In this study, by designing a series of non‐stoichiometric thiol‐acrylate systems, a polymer network is initially formed via a base catalyzed Michael addition reaction that proceeds stoichiometrically via the thiol‐acrylate “click” reaction. This self‐limiting reaction results in a polymer with excess acrylic functional groups within the network. At a later point in time, the photoinitiated, free radical polymerization of the excess acrylic functional groups results in a highly crosslinked, robust material system. These two stage reactive thiol‐acrylate networks that have intermediate stage rubbery moduli and glass transition temperatures that range from 0.5 MPa and ‐10 °C to 22 MPa and 22 °C, respectively, are formulated and characterized. The same polymer networks can then attain glass transition temperatures that range from 5 °C to 195 °C and rubbery moduli of up to 200 MPa after the subsequent photocuring stage. The two stage reactive networks formed by varying the stoichiometric ratios of the thiol and acrylate monomers were shown to perform as substrates for three specific applications: shape memory polymers, impression materials, and as optical materials for writing refractive index patterns.     

Electric‐Field‐Assisted Charge Generation and Separation Process in Transition Metal Oxide‐Based Interconnectors for Tandem Organic Light‐Emitting Diodes

The charge generation and separation process in transition metal oxide (TMO)‐based interconnectors for tandem organic light‐emitting diodes (OLEDs) is explored using data on electrical and spectral emission properties, interface energetics, and capacitance characteristics. The TMO‐based interconnector is composed of MoO₃ and cesium azide (CsN₃)‐doped 4,7‐diphenyl‐1,10‐phenanthroline (BPhen) layers, where CsN₃ is employed to replace the reactive metals as an n‐dopant due to its air stability and low deposition temperature. Experimental evidences identify that spontaneous electron transfer occurs in a vacuum‐deposited MoO₃ layer from various defect states to the conduction band via thermal diffusion. The external electric‐field induces the charge separation through tunneling of generated electrons and holes from MoO₃ into the neighboring CsN₃‐doped BPhen and hole‐transporting layers, respectively. Moreover, the impacts of constituent materials on the functional effectiveness of TMO‐based interconnectors and their influences on carrier recombination processes for light emission have also been addressed.     

Creation of Bifunctional Materials: Improve Electron‐Transporting Ability of Light Emitters Based on AIE‐Active 2,3,4,5‐Tetraphenylsiloles

2,3,4,5‐Tetraphenylsiloles are excellent solid‐state light emitters featured aggregation‐induced emission (AIE) characteristics, but those that can efficiently function as both light‐emitting and electron‐transporting layers in one organic light‐emitting diode (OLED) are much rare. To address this issue, herein, three tailored n‐type light emitters comprised of 2,3,4,5‐tetraphenylsilole and dimesitylboryl functional groups are designed and synthesized. The new siloles are fully characterized by standard spectroscopic and crystallographic methods with satisfactory results. Their thermal stabilities, electronic structures, photophysical properties, electrochemical behaviors and applications in OLEDs are investigated. These new siloles exhibit AIE characteristics with high emission efficiencies in solid films, and possess lower LUMO energy levels than their parents, 2,3,4,5‐tetraphenylsiloles. The double‐layer OLEDs [ITO/NPB (60 nm)/silole (60 nm)/LiF (1 nm)/Al (100 nm)] fabricated by adopting the new siloles as both light emitter and electron transporter afford excellent performances, with high electroluminescence efficiencies up to 13.9 cd A^–1, 4.35% and 11.6 lm W^–1, which are increased greatly relative to those attained from the triple‐layer devices with an additional electron‐transporting layer. These results demonstrate effective access to n‐type solid‐state emissive materials with practical utility.