Conjugated Polymers Based on Difluorobenzoxadiazole toward Practical Application of Polymer Solar Cells

To advance polymer solar cells (PSCs) toward real‐world applications, it is crucial to develop materials that are compatible with a low‐cost large‐scale manufacturing technology. In this context, a practically useful polymer should fulfill several critical requirements: the capability to provide high power conversion efficiencies (PCEs) via low‐cost fabrication using environmentally friendly solvents under mild thermal conditions, resulting in an active layer that is thick enough to minimize defects in large‐area films. Here, the development of new photovoltaic polymers is reported through rational molecular design to meet these requirements. Benzodithiophene (BDT)‐difluorobenzoxadiazole (ffBX)‐2‐decyltetradecyl (DT), a wide‐bandgap polymer based on ffBX and BDT emerges as the first example that fulfills the qualifications. When blended with a low‐cost acceptor (C₆₀‐fullerene derivative), BDT‐ffBX‐DT produces a PCE of 9.4% at active layer thickness over 250 nm. BDT‐ffBX‐DT devices can be fabricated from nonhalogenated solvents at low processing temperature. The success of BDT‐ffBX‐DT originates from its appropriate electronic structure and charge transport characteristics, in combination with a favorable face‐on orientation of the polymer backbone in blends, and the ability to form proper phase separation morphology with a fibrillar bicontinuous interpenetrating network in bulk‐heterojunction films. With these characteristics, BDT‐ffBX‐DT represents a meaningful step toward future everyday applications of polymer solar cells.     

Solution‐Processable Conjugated Polymers as Anode Interfacial Layer Materials for Organic Solar Cells

In recent years, solution‐processed conjugated polymers have been extensively used as anode interfacial layer (AIL) materials in organic solar cells (OSCs) due to their excellent film‐forming property and low‐temperature processing advantages. In this review, the authors focus on the recent advances in conjugated polymers as AIL materials in OSCs. Several of the main classes of solution‐processable conjugated polymers, including poly(3,4‐ethylenedioxythiophene):(styrenesulfonate), polyaniline, polythiophene, conjugated polyelectrolytes, sulfonated poly(diphenylamine), and crosslinked polymers as AIL materials are discussed in depth, and the mechanisms of these AIL materials in enhancing OSC performances are also elucidated. The structure–property relationships of various conjugated polymer AIL materials are analyzed, and some important design rules for such materials toward high efficiencies and stable OSCs are presented. In addition, some chemical and physical approaches to optimize the photoelectronic and physic properties of conjugated polymer AIL materials, which improve their performance in modifying OSCs, are also highlighted. Considering the significance of tandem OSCs, the relevant applications of conjugated polymer AIL materials in constructing interconnection layers for tandem OSCs are also mentioned. Finally, a brief summary is presented and some perspectives to help researchers understand the current challenges and opportunities in this area are proposed.     

Design and development of low cost polyurethane biopolymer based on castor oil and glycerol for biomedical applications

In the current study, we present the synthesis of novel low cost bio‐polyurethane compositions with variable mechanical properties based on castor oil and glycerol for biomedical applications. A detailed investigation of the physicochemical properties of the polymer was carried out by using mechanical testing, ATR‐FTIR, and X‐ray photoelectron spectroscopy (XPS). Polymers were also tested in short term in‐vitro cell culture with human mesenchymal stem cells to evaluate their biocompatibility for potential applications as biomaterial. FTIR analysis confirmed the synthesis of castor oil and glycerol based PU polymers. FTIR also showed that the addition of glycerol as co‐polyol increases crosslinking within the polymer backbone hence enhancing the bulk mechanical properties of the polymer. XPS data showed that glycerol incorporation leads to an enrichment of oxidized organic species on the surface of the polymers. Preliminary investigation into in vitro biocompatibility showed that serum protein adsorption can be controlled by varying the glycerol content with polymer backbone. An alamar blue assay looking at the metabolic activity of the cells indicated that castor oil based PU and its variants containing glycerol are non‐toxic to the cells. This study opens an avenue for using low cost bio‐polyurethane based on castor oil and glycerol for biomedical applications.     

Wood-plastic composites as promising green-composites for automotive industries!

Wood-plastic composite (WPC) is a very promising and sustainable green material to achieve durability without using toxic chemicals. The term WPCs refers to any composites that contain plant fiber and thermosets or thermoplastics. In comparison to other fibrous materials, plant fibers are in general suitable to reinforce plastics due to relative high strength and stiffness, low cost, low density, low CO2 emission, biodegradability and annually renewable. Plant fibers as fillers and reinforcements for polymers are currently the fastest-growing type of polymer additives. Since automakers are aiming to make every part either recyclable or biodegradable, there still seems to be some scope for green-composites based on biodegradable polymers and plant fibers. From a technical point of view, these bio-based composites will enhance mechanical strength and acoustic performance, reduce material weight and fuel consumption, lower production cost, improve passenger safety and shatterproof performance under extreme temperature changes, and improve biodegradability for the auto interior parts.     

Grafted megaporous materials as ion‐exchangers for bioproduct adsorption

Megaporous chromatographic materials were manufactured by a three‐step procedure, including backbone synthesis, chemical grafting, and introduction of ion‐exchange functionality. The backbone of the adsorbent cylindrical bodies was prepared by polymerization of methacrylic acid and poly(ethylene glycol) diacrylate at sub‐zero temperatures. Grafting was performed employing glycidyl methacrylate and a chemical initiator, cerium ammonium nitrate. The degree of grafting was adjusted by modifying the concentration of the initiator in the reaction mixture to a range of values (23, 39, 62, 89, and 105%). Further, the pendant epoxy‐groups generated by the previous step were reacted to cation‐ and anion‐exchanging moieties utilizing known chemical routes. Infrared spectroscopy studies confirmed the incorporation of epoxy and ion‐exchanger groups to the backbone material. Optimized materials were tested for chromatography applications with model proteins; the dynamic binding capacity, as recorded at 10% breakthrough and 2.0 × 10^?4 m/s superficial velocity, were 350 and 58 mg/g for the cation‐exchanger and the anion‐exchanger material, respectively. These results may indicate that long tentacle‐type polymer brushes were formed during grafting therefore increasing the ability of the megaporous body to efficiently capture macromolecules. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29: 386–393, 2013     

Controlled Synthesis and Energy Applications of One‐Dimensional Conducting Polymer Nanostructures: An Overview

The past decade has witnessed increasing attention in the synthesis, properties, and applications of one‐dimensional (1D) conducting polymer nanostructures. This overview first summarizes the synthetic strategies for various 1D nanostructures of conjugated polypyrrole (PPy), polyaniline (PANI), polythiophene (PTh), poly(p‐phenylenevinylene) (PPV) and derivatives thereof. By using template‐directed or template‐free methods, nanoscale rods, wires/fibers, belts/ribbons, tubes, arrays, or composites have been successfully synthesized. With their unique structures and advantageous characteristics (e.g., high conductivity, high carrier mobility, good electrochemical activity, large specific surface area, short and direct path for charge/ion transportation, good mechanical properties), 1D conducting polymer nanostructures are demonstrated to be very useful for energy applications. Next, their applications in solar cells, fuel cells, rechargeable lithium batteries, and electrochemical supercapacitors are highlighted, with a strong emphasis on recent literature examples. Finally, this review ends with a summary and some perspectives on the challenges and opportunities in this emerging area of research.     

3,4‐Dicyanothiophene—a Versatile Building Block for Efficient Nonfullerene Polymer Solar Cells

In this contribution, a versatile building block, 3,4‐dicyanothiophene (DCT), which possesses structural simplicity and synthetic accessibility for constructing high‐performance, low‐cost, wide‐bandgap conjugated polymers for use as donors in polymer solar cells (PSCs), is reported. A prototype polymer, PB3TCN‐C66, and its cyano‐free analogue polymer PB3T‐C66, are synthesized to evaluate the potential of using DCT in nonfullerene PSCs. A stronger aggregation property in solution, higher thermal transition temperatures with higher enthalpies, a larger dipole moment, higher relative dielectric constant, and more linear conformation are exhibited by PB3TCN‐C66. Solar cells employing IT‐4F as the electron acceptor offer power conversion efficiencies (PCEs) of 11.2% and 2.3% for PB3TCN‐C66 and PB3T‐C66, respectively. Morphological characterizations reveal that the PB3TCN‐C66:IT‐4F blend exhibits better π–π paracrystallinity, a contracted domain size, and higher phase purity, consistent with its higher molecular interaction parameter, derived from thermodynamic calculations. Moreover, PB3TCN‐C66 offers a higher open‐circuit voltage and reduced energy loss than most state‐of‐the‐art wide‐bandgap polymers, without the need of additional electron‐withdrawing substituents. Two additional polymers derived from DCT also demonstrate promising performance with a higher PCE of 13.4% being achieved. Thus, DCT represents a versatile and promising building block for constructing high‐performance, low‐cost, conjugated polymers for application in PSCs.     

Advances in Cathode Materials for Solid Oxide Fuel Cells: Complex Oxides without Alkaline Earth Metal Elements

Solid oxide fuel cells (SOFCs) represent one of the cleanest and most efficient options for the direct conversion of a wide variety of fuels to electricity. For example, SOFCs powered by natural gas are ideally suited for distributed power generation. However, the commercialization of SOFC technologies hinges on breakthroughs in materials development to dramatically reduce the cost while enhancing performance and durability. One of the critical obstacles to achieving high‐performance SOFC systems is the cathodes for oxygen reduction reaction (ORR), which perform poorly at low temperatures and degrade over time under operating conditions. Here a comprehensive review of the latest advances in the development of SOFC cathodes is presented: complex oxides without alkaline earth metal elements (because these elements could be vulnerable to phase segregation and contaminant poisoning). Various strategies are discussed for enhancing ORR activity while minimizing the effect of contaminant on electrode durability. Furthermore, some of the critical challenges are briefly highlighted and the prospects for future‐generation SOFC cathodes are discussed. A good understanding of the latest advances and remaining challenges in searching for highly active SOFC cathodes with robust tolerance to contaminants may provide useful guidance for the rational design of new materials and structures for commercially viable SOFC technologies.     

In‐situ Crosslinking and n‐Doping of Semiconducting Polymers and Their Application as Efficient Electron‐Transporting Materials in Inverted Polymer Solar Cells

In this study, we demonstrate in‐situ n‐doping and crosslinking of semiconducting polymers as efficient electron‐transporting materials for inverted configuration polymer solar cells. The semiconducting polymers were crosslinked with bis(perfluorophenyl) azide (bis‐PFPA) to form a robust solvent‐resistant film, thereby preventing solvent‐induced erosion during subsequent solution‐based device processing. In addition, chemical n‐doping of semiconducting polymers with (4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol‐2‐yl)phenyl)dimethylamine (N‐DMBI) substantially improved the power conversion efficiency of solar cells from 0.69% to 3.42%. These results open the way for progress on generally applicable polymeric interface materials, providing not only high device performance but also an effective fabrication method for solution‐processed multilayer solar cell devices.     

Nanocarbon Electrocatalysts for Oxygen Reduction in Alkaline Media for Advanced Energy Conversion and Storage

Alkaline oxygen electrocatalysis, targeting anion exchange membrane fuel cells, Zn‐air batteries, and alkaline‐based Li‐air batteries, has become a subject of intensive investigation because of its advantages compared to its acidic counterparts in reaction kinetics and materials stability. However, significant breakthroughs in the design and synthesis of efficient oxygen reduction catalysts from earth‐abundant elements instead of precious metals in alkaline media remain in high demand. Carbon composite materials have been recognized as the most promising because of their reasonable balance between catalytic activity, durability, and cost. In particular, heteroatom (e.g., N, S, B, or P) doping can tune the electronic and geometric properties of carbon, providing more active sites and enhancing the interaction between carbon structure and active sites. Importantly, involvement of transition metals appears to be necessary for achieving high catalytic activity and improved durability by catalyzing carbonization of nitrogen/carbon precursors to form highly graphitized carbon nanostructures with more favorable nitrogen doping. Recently, a synergetic effect was found between the active species in nanocarbon and the loaded oxides/sulfides, resulting in much improved activity. This report focuses on these carbon composite catalysts. Guidance for rational design and synthesis of advanced alkaline ORR catalysts with improved activity and performance durability is also presented.     

Monodispersed, molecularly imprinted polymers as affinity-based chromatography media

This review article deals with preparation methods for spherical and monodispersed molecularly imprinted polymers (MIPs) in micrometer sizes. Those methods include suspension polymerization in water, liquid perfluorocarbon and mineral oil, seed polymerization and dispersion/precipitation polymerization. The other methods are the use of beaded materials such as a spherical silica or organic polymer for grafting MIP phases onto the surfaces of porous materials or filling the pores of silica with MIPs followed by dissolution of the silica. Furthermore, applications of MIP microspheres as affinity-based chromatography media, HPLC stationary phases and solid-phase extraction media, will be discussed for pharmaceutical, biomedical and environmental analysis.     

Thiophene Rings Improve the Device Performance of Conjugated Polymers in Polymer Solar Cells with Thick Active Layers

Developing novel materials that tolerate thickness variations of the active layer is critical to further enhance the efficiency of polymer solar cells and enable large‐scale manufacturing. Presently, only a few polymers afford high efficiencies at active layer thickness exceeding 200 nm and molecular design guidelines for developing successful materials are lacking. It is thus highly desirable to identify structural factors that determine the performance of semiconducting conjugated polymers in thick‐film polymer solar cells. Here, it is demonstrated that thiophene rings, introduced in the backbone of alternating donor–acceptor type conjugated polymers, enhance the fill factor and overall efficiency for thick (>200 nm) solar cells. For a series of fluorinated semiconducting polymers derived from electron‐rich benzo[1,2‐b:4,5‐b′]dithiophene units and electron‐deficient 5,6‐difluorobenzo[2,1,3]thiazole units a steady increase of the fill factor and power conversion efficiency is found when introducing thiophene rings between the donor and acceptor units. The increased performance is a synergistic result of an enhanced hole mobility and a suppressed bimolecular charge recombination, which is attributed to more favorable polymer chain packing and finer phase separation.     

Tailoring the Membrane‐Electrode Interface in PEM Fuel Cells: A Review and Perspective on Novel Engineering Approaches

The interface between the catalyst layer (CL) and the polymer electrolyte membrane (PEM) in a fuel cell has substantial impact on its electrochemical performance. In consequence, there have been growing research activities to engineer this interface to improve the performance of polymer electrolyte membrane fuel cells (PEMFCs). This review summarizes these novel approaches and compares the various techniques. Based on available fuel cell data in the literature, a quantitative comparison of relative improvements due to a micro‐ and nano‐engineered PEM|CL interface is provided. This allows several conclusions: First, regardless of the applied method, a re‐engineering of the PEM|CL interface leads to an improvement of power‐determining parameters, such as mass transport resistances. The latter has hitherto not been clearly connected to the PEM|CL interface and is an important piece of information for future fuel cell development. Second, for patterned membrane surfaces, feature sizes of about 1–10 µm on the membrane surface seem to result in the most significant power density improvement. Third, an engineered PEMCL interface can contribute to extend the fuel cell durability due to enhanced adhesion and contact between the two layers. With this, novel membrane electrode assemblies (MEAs) can be designed that enable significantly higher power densities compared conventional 2D‐layer MEAs.     

A High‐Crystalline NaV1.25Ti0.75O4 Anode for Wide‐Temperature Sodium‐Ion Battery

Sodium‐ion batteries with abundant and low‐cost sodium resources is a promising alternative to Li‐ion batteries in large‐scale energy applications. While the anode materials, due to their insufficient cycling life and insecure voltage, could not still satisfy the market demands, especially in the wide‐temperature fields, here, a high‐crystallinity anode material with post‐spinel structure, namely NaV_1.25Ti_0.75O₄, which always maintains excellent electrochemical performance at the widely variable temperatures, is reported. The results indicate that this anode delivers a high‐safety and ultrastable room‐temperature performance (i.e., an average output voltage of 0.7 V vs Na⁺/Na and the ultralong cycling life over 10 000 cycles) and good wide‐temperature performance (below 9% capacity variation at 60 and ?20 °C compared to that at 25 °C). These excellent achievements could benefit from the long durability and stability of 1D channels and superfast ion diffusion in a temperature‐dependent range. This finding provides a promising strategy to construct the safe and stable full‐cell prototypes and promotes the wide‐temperature application of sodium‐ion batteries.     

Roll‐to‐Roll Printed Large‐Area All‐Polymer Solar Cells with 5% Efficiency Based on a Low Crystallinity Conjugated Polymer Blend

The challenge of continuous printing in high‐efficiency large‐area organic solar cells is a key limiting factor for their widespread adoption. A materials design concept for achieving large‐area, solution‐coated all‐polymer bulk heterojunction solar cells with stable phase separation morphology between the donor and acceptor is presented. The key concept lies in inhibiting strong crystallization of donor and acceptor polymers, thus forming intermixed, low crystallinity, and mostly amorphous blends. Based on experiments using donors and acceptors with different degree of crystallinity, the results show that microphase separated donor and acceptor domain sizes are inversely proportional to the crystallinity of the conjugated polymers. This methodology of using low crystallinity donors and acceptors has the added benefit of forming a consistent and robust morphology that is insensitive to different processing conditions, allowing one to easily scale up the printing process from a small‐scale solution shearing coater to a large‐scale continuous roll‐to‐roll (R2R) printer. Large‐area all‐polymer solar cells are continuously roll‐to‐roll slot die printed with power conversion efficiencies of 5%, with combined cell area up to 10 cm². This is among the highest efficiencies realized with R2R‐coated active layer organic materials on flexible substrate.     

Recent Advances and Emerging Trends in Photo‐Electrochemical Solar Energy Conversion

Photo‐electrochemical (PEC) solar energy conversion offers the promise of low‐cost renewable fuel generation from abundant sunlight and water. In this Review, recent developments in photo‐electrochemical water splitting are discussed with respect to this promise. State‐of‐the‐art photo‐electrochemical device performance is put in context with the current understanding of the necessary requirements for cost‐effective solar hydrogen generation (in terms of solar‐to‐hydrogen conversion efficiency and system durability, in particular). Several important studies of photo‐electrochemical hydrogen generation at p‐type photocathodes are highlighted, mostly with protection layers (for enhanced durability), but also a few recent examples where protective layers are not needed. Recent work with the widely studied n‐type BiVO₄ photoanode is detailed, which highlights the needs and necessities for the next big photoanode material yet to be discovered. The emerging new research direction of photo‐electrocatalytic upgrading of biomass substrates toward value‐added chemicals is then discussed, before closing with a commentary on how research on PEC materials remains a worthwhile endeavor.     

Incorporation of Indium Tin Oxide Nanoparticles in PEMFC Electrodes

Carbon materials suffer from corrosion at the cathode of polymer electrolyte membrane fuel cells (PEMFCs). In the presence of water, carbon support materials are oxidized to carbon dioxide even at low potentials. Hence, nowadays it is very fashionable to look for alternative support materials, like oxides or conductive polymers. To gain the maximum performance for a new material one should also consider an appropriate electrode structure. This study shows the results for the incorporation of nanosized alternative support materials into advanced electrode architectures. Commercially available indium tin oxide (ITO) nanoparticles (<50 nm) are used as support for Pt nanoparticles in combination with Nafion‐coated multi‐walled carbon nanotubes (MWCNTs) on the cathode side of a PEMFC. The MWCNTs promote a high electronic conductivity and help to form a porous network, which could accommodate the Pt/ITO nanoparticles. The microscopic investigations show a homogeneous electrode structure composed of Pt/ITO and MWCNT/Nafion multilayer. Single cell measurements show a maximum power density of 73 mW cm^?2 and a Pt utilization of 1468 mW mg_Pt^?1 for the cathode. The performance data and the Pt utilization are comparable to a standard Pt/carbon black electrode possessing the same Pt loading in the electrode. Beside this, it is shown for the first time that ITO serves as support material under real fuel cell conditions.     

Intrinsically Stretchable Fuel Cell Based on Enokitake‐Like Standing Gold Nanowires

Conventional fuel cells are based on rigid electrodes, limiting their applications in wearable and implantable electronics. Here, it is demonstrated that enokitake‐like vertically‐aligned standing gold nanowires (v‐AuNWs) can also serve as powerful platform for stretchable fuel cells by using ethanol as model system. Unlike traditional fuel cell electrodes, the v‐AuNWs have “Janus Morphology” on both sides of the film and also are highly stretchable. The comparative studies demonstrate that tail side exposed v‐AuNWs based stretchable electrodes outperform the head‐side exposed v‐AuNWs toward the electro‐oxidation of ethanol due to the direct exposure of high‐surface‐area nanowires to the fuels. Therefore, a stretchable fuel cell is fabricated utilizing tail side based interdigitated electrodes, where v‐AuNWs and Pt black modified v‐AuNWs serve as the anode and cathode, respectively. The as‐prepared stretchable fuel cell exhibits good overall performance, including high power density, current density, open‐circuit voltage, stretchability, and durability. Most importantly, a wearable fuel cell is also achieved by integrating tattoo‐like interdigitated electrodes with a thin layer of sponge as a fuel container, exhibiting good performance under various deformations (compression, stretching, and twisting). Such attractive performance in conjunction with skin‐like in‐plane design indicates its great potential to power the next‐generation of wearable and implantable devices.     

Emerging Conductive Atomic Force Microscopy for Metal Halide Perovskite Materials and Solar Cells

Metal halide perovskite materials, benefiting from a combination of outstanding optoelectronic properties and low‐cost solution‐preparation processes, show tremendous potential for optoelectronics and photovoltaics. However, the nanoscale inhomogeneities of the electronic properties of perovskite materials cause a number of difficulties, such as recombination, stability, and hysteresis, all of which seriously restrict device performance. Scanning probe microscopy, as a high‐resolution imaging technique, has been widely used to connect local properties and micro‐area morphologies to overall device performance. Conductive atomic force microscopy (C‐AFM) can realize a real‐space visualization of topography coupled with optoelectronic properties on a microscopic scale and thereby is uniquely suited to probe the local effects of perovskite materials and devices. The fundamental principles, alternative operation modes, and development of C‐AFM are comprehensively reviewed, and applications in perovskite solar cells (PSCs) for electronic transport behavior, ion migration and hysteresis, ferroelectric polarization, and facet orientation investigation are discussed. A comprehensive understanding and summary of up‐to‐date applications in PSCs is beneficial to further fully exploit the potential of such an emerging technique, so as to provide a novel and effective approach for perovskite materials analysis.     

Conductive,Solution‐Processed Dioxythiophene Copolymers for Thermoelectric and Transparent Electrode Applications

Conjugated polymers with high electrical conductivities are attractive for applications in capacitors, biosensors, organic thermoelectrics, and transparent electrodes. Here, a series of solution processable dioxythiophene copolymers based on 3,4‐propylenedioxythiophene (ProDOT) and 3,4‐ethylenedioxythiophene (EDOT) is investigated as thermoelectric and transparent electrode materials. Through structural manipulation of the polymer repeat unit, the conductivity of the polymers upon oxidative solution doping is tuned from 1 × 10^?3 to 3 S cm^?1, with a polymer consisting of a solubilizing alkylated ProDOT unit and an electron‐rich biEDOT unit (referred to as PE₂) showing the highest electrical conductivity. Optimization of the film casting method and screening of dopants result in AgPF₆‐doped PE₂ achieving a high electrical conductivity of over 250 S cm^?1 and a thermoelectric power factor of 7 μW m^?1 K^?2. Oxidized spray cast films of PE₂ are also assessed as a transparent electrode material for use with another electrochromic polymer. This bilayer shows reversible electrochemical switching from a colored charge‐neutral state to a highly transmissive color‐neutral, oxidized state. These results demonstrate that dioxythiophene‐based copolymers are a promising class of materials, with ProDOT–biEDOT serving as a soluble analog to the well‐studied PEDOT as a p‐type thermoelectric and electrode material.