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Perovskite solar cells have emerged as a promising next-generation electrical power generating tool. However, imperfections in perovskite films are one of the crucial factors preventing the commercialization of perovskite solar cells. Passivation has proven to be an effective strategy to reduce the density of defect states in perovskite crystals and inhibit ion migration. Although significant work on chloride ion and N,N-dimethylformamide (DMF) has shown that the additives are able to passivate different types of trap defects, systematic studies on the effects of DMF and HCl on perovskite crystallization when used in conjunction with each other are elusive. Here, we systematically investigated the synergistic effect of DMF and hydrochloric acid (HCl) on methylammonium (MA+)-based perovskite films with the two-step spin-coating method. As a Lewis base, DMF coordinates well with Pb2+ to facilitate a decrease in the number of defects, thereby improving the carrier separation and transport, while HCl improves the overall perovskite film morphology. Addition of 20 μL HCl/20 μL DMF to 10 mL of methylammonium iodide/isopropyl alcohol solution afforded ca. 500 nm thick perovskite films with no observable defects within the grains. The process allowed fabrication of devices with an active area of 0.16 cm2, which produced power conversion efficiencies up to 18.37% with minimal hysteresis.

Stimuli-responsive π-conjugated materials present opportunities for chemical sensing, whereby through interaction with an analyte the π-conjugated system undergoes a change in molecular geometry an...

Experimental data from a patent were analyzed to learn about the small molecule additives that were most effective in mitigating the degradation of polyethylene terephthalate. Two sets of molecular...

The rapid rise in single-junction perovskite solar cell (PSC) efficiencies, tunable bandgap, and low-cost solution processability make PSCs an attractive candidate for tandems with Si bottom cells. However, the challenge is to fabricate a high-performance semitransparent perovskite top cell in combination with an appropriate silicon bottom cell with high response to long wavelength photons that are filtered through the perovskite top cell. Currently, semitransparent perovskite cells show much lower performance compared with their opaque counterparts, while high-performance silicon bottom cells, such as heterojunction with intrinsic thin layer and interdigitated back contact, may be too expensive to meet the cost and efficiency targets for commercial viability. Here, we demonstrate a 26.7% perovskite–Si four terminal (4T) tandem cell comprising a highly efficient 17.8% CsFAMAPbIBr semitransparent, 1.63-eV bandgap perovskite top cell, and a ≥22% efficiency n-type Si bottom cell fabricated with a conventional boron diffused emitter on the front and carrier selective n+ poly-Si/SiOx passivated contact on the rear. This is among the highest efficiency perovskite/Si 4T tandems published to date and represents the first report of the use of the high temperature-resistant single side n-tunnel oxide passivated contact Si cell in a 4T configuration.

We fabricate organic field effect transistor (OFET) devices based on highly aligned aggregates of the conjugated polymer, poly[3-(potassium-7-hexanoate)-thiophene-2,5-diyl] (P3PHT), using self-orga...

As editors of a materials chemistry journal, we are thrilled at the awarding of the 2019 Nobel Prize in Chemistry to John B. Goodenough, M. Stanley Whittingham, and Akira Yoshino, for their contributions that have led to the modern lithium ion battery (Figure 1). As the Nobel Prize Committee states succinctly, “They created a rechargeable world.”(1) The commercial and societal rewards of experimental research typically require decades to reach fruition, and lithium ion batteries were no different, with crucial leads dating back to the 1960s, and even earlier.(2) Materials chemistry journals only emerged 30 years ago with the advent of Chemistry of Materials, the Journal of Materials Chemistry, and Advanced Materials in 1989. Much of the earlier work in battery materials appeared beforehand in electrochemistry, physics, and solid state journals. The key fundamental discovery underpinning the lithium ion battery was the understanding and application of ion intercalation, in this case,(3) lithium ions inserted between the layers in graphite, metal sulfides, and, eventually, oxides that were commercialized. This Nobel Prize was evenly split three ways because, as the Nobel committee correctly observed, the contributions of all three inventors were essential to the success of the commercialization of the lithium ion battery.

Discovery of structure–property interrelations in organic electrochemical transistors (OECTs) is limited by the small number of high-performing semiconducting polymer families that are electrochemi...

Rational design and construction of effective silicon (Si) electrode structures to relieve large volumetric changes that occur during the charge/discharge process remain significant challenges for the development of robust lithium-ion batteries (LIBs). Herein, we propose an electrically conductive poly[3-(potassium-4-butanoate)thiophene] (PPBT) capping layer on the Si surface (Si@PPBT) to serve as the active material and be used in conjunction with a common polymer binder as an approach to tackle issues emanating from volumetric changes. The PPBT protective shell layer provides the system with tolerance toward variations in active material volume during cycling, improves the dispersion of Si nanoparticles in the binder, enhances the electrolyte uptake rate, and provides a strong adhesion force between the Si/carbon additives/current collector, thereby helping to maintain electrode integrity during the charge/discharge process. The π-conjugated polythiophene backbone structure also allows the Si core to maintain electrical contact with carbon additives and/or polymer binder, enabling the formation of effective electrical transport bridges and stabilizing solid electrolyte interphase layer growth. The integrated Si@PPBT/carboxymethyl cellulose (CMC) anode exhibited high initial Coulombic efficiency (84.9%), enhanced rate capability performance, and long cycling stability with a reversible capacity of 1793 mA h g-1 after 200 cycles, 3.4 times higher than that of pristine Si anodes with the same CMC binder (528 mA h g-1). The results suggest that the Si@PPBT design presents a promising approach to promote the practical use of Si anodes in LIBs, which could be extended to other anode materials exhibiting large volume changes during lithiation/delithiation.

Battery electrodes are complex mesoscale systems comprising an active material, conductive agent, current collector, and polymeric binder. Although significant research on composite electrode materials for Li-ion batteries focuses on the design, synthesis, and characterization of the active particles, the binder component has been shown to critically impact stability and ensure electrode integrity during volume changes induced upon cycling. Herein, we explore the ability of water-soluble, carboxylated conjugated polymer binders to aid in electron and ion transport in magnetite-based anodes. Specifically, poly[3-(potassium-4-butanoate)thiophene] (PPBT) and a potassium carboxylate functionalized 3,4-propylenedioxythiophene (ProDOT)-based copolymer (WS-PE2) were investigated and evaluated against the control, potassium salt form of poly(acrylic acid) (PAA-K). When used in conjunction with a polyethylene glycol (PEG) surface coating for the magnetite active material, PPBT provided for overall improved electro...

Elastic, repairable and conductive fibers are desirable in the newly emerging field of soft electronic and wearable devices. Here, we design a multifunctional fiber by incorporation of different components to optimize its performance. The combination of the poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) through hydrogen bonding endows the fiber with high elasticity and repairability. Polydopamine (PDA) significantly increases the stability of the fiber, thus the fiber will not dissolve in alkaline solutions and still keep the repairable ability. The fiber shows a reversible swelling-shrinking property as pH values go up and down. Further, the conductive component, carbon nanotube, is adsorbed at the swelling state and then is fastened with fiber shrinking.

Inducing the self-assembly of π-conjugated polymers into semicrystalline aggregates has been a topic of substantial interest in the field of organic electronics and is typically achieved using energy-intensive solution processing or postfilm deposition methods. Here, we demonstrate the ability of bioderived cellulose nanocrystals (CNCs) to act as structure-directing agents for the conjugated semiconducting polymer, poly(3-hexylthiophene) (P3HT). CNCs were grafted with polystyrene, P3HT or poly(N-isopropylacrylamide), and subsequently blended with P3HT in solution to study the effect on conjugated polymer self-assembly. The presence of polymer-grafted CNCs resulted in an increase in P3HT semicrystalline aggregate formation, the degree of which depended on the surface free energy of the grafted polymer. The time-dependent P3HT aggregation was characterized by UV–vis spectroscopy, and the resulting data was fit to the Avrami crystallization model. The surface energies of each additive were calculated via con...

A new quinoidal acceptor building block (namely IQTT) is designed with directed diradical character to control and narrow the bandgap while good chemical stability is maintained with the assistance...

The development of semiconducting conjugated polymers for organic field effect transistors (OFETs) has been the focus of intense research efforts for their key role in plastic electronics as well a...

Conjugated monomers and polymers containing 2,2′-bithiazole (BTz) and naphthalene diimide (NDI) units in the main chain were prepared. Polymer PNDI2Tz was obtained via palladium-catalyzed Stille polycondensation of a dibromo-substituted NDI derivative with distannyl-2,2′-bithiazole. The optical and electronic properties were investigated using UV–vis absorption spectroscopy and ultraviolet photoelectron spectroscopy. It was found that the polymers show very broad absorption bands in the 540 nm region, and PNDI2Tz has an optical bandgap of 1.87 eV. Computational analysis demonstrates that holes and electrons are mainly localized on the 2,2′-bithiazole and NDI units, respectively. Organic field-effect transistors (OFETs) fabricated with PNDI2Tz exhibit unipolar n-channel characteristics with mobility as high as 0.05 cm2 V–1 s–1.

One major drawback that prevents the large-scale practical implementation of perovskites is their susceptibility to performance degradation in humid environments. Here, we achieved uniform, stable perovskite films within a polyvinylpyrrolidone (PVP) polymer frame via mild solution processing in ambient air with over 60% relative humidity. In addition to facilitating film formation, the hydrophobic PVP served to protect the perovskite grains from atmospheric moisture. Use of PVP, coupled with optimization of the deposition parameters, provided for compact, smooth, pinhole-free perovskite films that when incorporated into a photovoltaic device exhibited highly reproducible efficiencies in the range of up to 17%. In the absence of encapsulation, the devices exhibited stable performance characteristics during exposure to humid ambient air for 600 h. Furthermore, on flexible substrates, the 8 wt % PVP-perovskite samples provided for device efficiencies of ca. 15%. The devices retained ca. 73% of their efficiency after bending 1000 times with a bending radius of 0.5 cm.

Carboxylated polythiophenes, such as poly[3-(potassium-4-butanoate) thiophene] (PPBT), play a critical role in securely connecting single-walled carbon nanotube (SWNT) electrical networks onto the surface of carbon-coated silicon monoxide (c-SiOx). These connections are a function of the materials’ surface chemistries and resultant physical/chemical bonding through favorable molecular interactions. Specifically, the PPBT π-conjugated backbone and alkyl side chain carboxylate moieties (COO−), respectively, physically interact with the SWNT and c-SiOx carbon layer π-electron-rich surfaces, and chemically bind to surface hydroxyl (−OH) species of the c-SiOx electroactive materials to form a carboxylate bond. This approach effectively captured pulverized particles that form during battery operation and beneficially suppressed the thickness change that electrodes typically undergo. The resultant electrodes exhibited superior electrochemical performance, which was ascribed to stable SEI layer formation, reduced...

Conjugated polymers possessing polar functionalities were shown to effectively anchor single-walled carbon nanotubes (SWNTs) to the surface of high-capacity anode materials and enable the formation of electrical networks. Specifically, poly[3-(potassium-4-butanoate) thiophene] (PPBT) served as a bridge between SWNT networks and various anode materials, including monodispersed Fe3O4 spheres (sFe3O4) and silicon nanoparticles (Si NPs). The PPBT π-conjugated backbone and carboxylate (COO−) substituted alkyl side chains, respectively, attracted the SWNT π-electron surface and chemically interacted with active material surface hydroxyl (−OH) species to form a carboxylate bond. Beneficially, this architecture effectively captured cracked/pulverized particles that typically form as a result of repeated active material volume changes that occur during charging and discharging. Thus, changes in electrode thickness were suppressed substantially, stable SEI layers were formed, electrode resistance was reduced, and e...

Efficient and earth-abundant electrocatalysts for water oxidation are essential for renewable and sustainable energy conversion technologies. And Ni(Fe)OxHy especially attractive as a state-of-the-art best candidate catalyst for efficient electrochemical oxygen evolution reaction (OER). In previous research, Cr has been reported could benefit the Ni(Fe)OxHy catalysts with conflicting mechanism. Here, a series of ternary (Ni, Fe and Cr) amorphous metal oxide catalysts for OER are synthesized via a simple thermal decomposition method. We show that Ni0.6Fe0.3Cr0.1Ox has a turnover frequency of 0.046 ± 0.004 s−1 at 300 mV overpotential which is ∼31% more active than an analogous Ni0.6Fe0.4Ox film, 0.035 ± 0.007 s−1, in 0.1 M KOH media. Using electrochemical voltammetry and AC impedance analysis, we demonstrate that Cr increases the number of electrochemically available active sites, as a pore forming agent, but does not affect the intrinsic per metal atom activity. We find that the Cr begins to leach immediately upon electrochemical testing, and the Cr is almost completely depleted after a 24 h stability test. Importantly, along with the decreased content of Cr, the catalyst activity is further promoted. Although the Cr itself may not be responsible for the improvement, its dissolution results in an ideal type of pore and/or active sites. We further optimize the deposition of high-surface-area and high-mass-loading Ni0.6Fe0.3Cr0.1Ox on carbon-cloth electrodes and demonstrate an overpotential as low as 251 mV at 10 mA cm−2 in 1 M KOH.

Battery electrodes are complex mesoscale systems comprised of an active material, conductive agent, current collector, and polymeric binder. Previous work showed that introduction of poly [3-(potassium-4-butanoate) thiophene] (PPBT) as a binder component coupled with a polyethylene glycol (PEG) surface coating on magnetite (Fe 3 O 4 ) nanoparticles enhanced electron and ion transport in the high capacity anode system. Here, the impact of Fe 3 O 4 crystallite size (10 nm vs. 20 nm) and surface chemistry were explored to evaluate their effects on interfacial interactions within the composite PEG/PPBT based electrodes and resultant battery performance. The Fe 3 O 4 synthesis methods inevitably lead to differences in surface chemistry. For instance, the Fe 3 O 4 particles synthesized using ammonium hydroxide appeared more dispersed, and afforded improved rate capability performance. Notably, chemical interactions between the active nanoparticles and PPBT binder were only seen with particles synthesized using triethylamine. Capacity retention and cycling performance were unaffected. This study provides fundamental insights into the significant impact of active material synthesis on the design and fabrication of composite battery electrodes.

In this study, for the first time, thermal oxidation, which has only been considered as a degradation pathway for plastics, served as a simple and effective pre-treatment protocol to modulate the chemical structure of linear low density polyethylene (LLDPE) for successful conversion of ‘non-carbonizable’ LLDPE into an ordered carbon. More importantly, LLDPE based carbon could be graphitized into a highly ordered graphitic carbon with exceptional electrical performance exceeding that of Super-P, a pricey reference conductive agent for lithium ion battery fabrication. Upon thermal oxidative pre-treatment, inherently non-carbonizable LLDPE was successfully transformed into an ordered carbon through heat treatment with a high conversion yield reaching 50 %, a yield comparable that obtained from polyacrylonitrile (PAN), a reference polymeric precursor. Systematic interrogation of the chemical structural evolution using X-ray diffraction, Raman, and dynamic scanning calorimetry (DSC) analysis, confirmed that an...

The pursuit of intelligent optoelectronics could have profound implications on our future daily life. Simultaneous enhancement of the electrical performance, mechanical stretchability, and optical transparency of semiconducting polymers may significantly broaden the spectrum of realizable applications for these materials in future intelligent optoelectronics, i.e., wearable devices, electronic skin, stretchable displays, and a vast array of biomedical sensors. Here, semiconducting films with significantly improved mechanical elasticity and optical transparency, without affecting the film’s electronic conductivity even under 100% strain, were prepared by blending only a small amount (below 1 wt %) of either p-type or n-type commercial semiconductor polymers. We demonstrate that a self-organized versatile conjugated polymer film displaying an interpenetrating polymer network is formed in the semiconducting films and is crucial for the observed enhancement of elasticity, optical transparency, and charge-carr...

The photovoltaic performance of perovskite solar cells is extremely dependent on the crystallization and morphology of the perovskite film, which are affected by the deposition method. Here, we demonstrate a simple approach to form a microporous PbI 2 film, with subsequent conversion to a compact, highly crystalline perovskite film. The PbI 2 and corresponding perovskite films were further probed by two-dimensional X-ray diffraction. The resultant perovskite exhibited improved photovoltaic performance under ambient conditions with about 50% humidity. The PbI 2 microporous structure was formed by exchanging residual DMSO with DMF vapor in the PbI 2 film, which facilitated contact with the methylammonium iodide (MAI) solution. The process resulted in the formation of compact, smooth, pinhole-free perovskite films having no residual PbI 2 . Solar cells fabricated using this methodology exhibited power conversion efficiencies over 16% with negligible photocurrent hysteresis.

As an effective platform to exploit triplet-triplet-annihilation-based photon upconversion (TTA-UC), microcapsules composed of a fluidic UC core and photonic shell are microfluidically prepared using a triple emulsion as the template. The photonic shell consists of cholesteric liquid crystals (CLCs) with a periodic helical structure, exhibiting a photonic band gap. Combined with planar anchoring at the boundaries, the shell serves as a resonance cavity for TTA-UC emission and enables spectral tuning of the UC under low-power-density excitation. The CLC shell can be stabilized by introducing a polymerizable mesogen in the LC host. Because of the microcapsule spherical symmetry, spontaneous emission of the delayed fluorescence is omnidirectionally amplified at the edge of the stop band. These results demonstrate the range of opportunities provided by TTA-UC systems for the future design of low-threshold photonic devices.

Cellulose nanocrystals (CNCs) are bioderived, rodlike particles that form a chiral nematic liquid crystal (LC) in water. In this work, CNCs were used to induce long-range order in a semiconducting polymer, poly[3-(potassium-4-butanoate) thiophene-2,5-diyl] (PPBT). When mixed with CNCs, it was found that PPBT was incorporated into the liquid crystal "template" to form ordered structures with highly birefringent domains, as observed under polarized light. We show that the π-π interactions between polymer chains, which contribute considerably to the energetics of the semiconducting system, are directly influenced by the presence and packing of the liquid crystal phase. Upon increasing the concentration of CNCs from the isotropic to chiral nematic regime, we observe a bathochromic shift in the UV-vis spectra and the emergence of the 0-0 vibrational peak, suggesting enhanced π-π stacking leading to chain coplanarization. Furthermore, the chiral nature of the PPBT/CNC mixture was evidenced by a negative peak in circular dichroism (CD) spectroscopy, promoting the notion that the polymer chains followed the helicoidal twist of the chiral nematic liquid crystal host. At high temperatures, the peak height ratios and overall intensities of the UV-vis and CD spectra associated with PPBT decreased as the chiral nematic pitch grew larger in size.

Conjugated semiconducting polymers have been the subject of intense study for over two decades with promising advances toward a printable electronics manufacturing ecosystem. These materials will deliver functional electronic devices that are lightweight, flexible, large-area, and cost-effective, with applications ranging from biomedical sensors to solar cells. Synthesis of novel molecules has led to significant improvements in charge carrier mobility, a defining electrical performance metric for many applications. However, the solution processing and thin film deposition of conjugated polymers must also be properly controlled to obtain reproducible device performance. This has led to an abundance of research on the process-structure-property relationships governing the microstructural evolution of the model semicrystalline poly(3-hexylthiophene) (P3HT) as applied to organic field effect transistor (OFET) fabrication. What followed was the production of an expansive body of work on the crystallization, self-assembly, and charge transport behavior of this semiflexible polymer whose strong π-π stacking interactions allow for highly creative methods of structural control, including the modulation of solvent and solution properties, flow-induced crystallization and alignment techniques, structural templating, and solid-state thermal and mechanical processing. This Account relates recent progress in the microstructural control of P3HT thin films through the nucleation, growth, and alignment of P3HT nanofibers. Solution-based nanofiber formation allows one to develop structural order prior to thin film deposition, mitigating the need for intricate deposition processes and enabling the use of batch and continuous chemical processing steps. Fiber growth is framed as a traditional crystallization problem, with the balance between nucleation and growth rates determining the fiber size and ultimately the distribution of grain boundaries in the solid state. Control of nucleation can be accomplished through a sonication-based seeding procedure, while growth can be modulated through supersaturation control via the tuning of solvent quality, the use of UV irradiation or through aging. These principles carry over to the flow-induced growth of P3HT nanofibers in a continuous microfluidic processing system, leading to thin films with significantly enhanced mobility. Further gains can be made by promoting long-range polymer chain alignment, achieved by depositing nanofibers through shear-based coating methods that promote high fiber packing density and alignment. All of these developments in processing were carried out on a standard OFET platform, enabling us to generalize quantitative structure-property relationships from structural data sources such as UV-vis, AFM, and GIWAXS. It is shown that a linear correlation exists between mobility and the in-plane orientational order of nanofibers, as extracted from AFM images using advanced computer vision software developed by our group. Herein, we discuss data-driven approaches to the determination of process-structure-property relationships, as well as the transferability of structural control strategies for P3HT to other conjugated polymer systems and applications.

While the focus of research related to the design of robust, high-performance Li-ion batteries relates primarily to the synthesis of active particles, the binder plays a crucial role in stability and ensures electrode integrity during volume changes that occur with cycling. Conventional polymeric binders such as poly(vinylidene difluoride) generally do not interact with active particle surfaces and fail to accommodate large changes in particle spacing during cycling. Thus, attention is now turning toward the exploration of interfacial interactions between composite electrode constituents as a key element in ensuring electrode stability. Recently, a poly[3-(potassium-4-butanoate)thiophene] (PPBT) binder component, coupled with a polyethylene glycol (PEG) surface coating for the active material was demonstrated to enhance both electron and ion transport in magnetite-based anodes, and it was established that the PEG/PPBT approach aids in overall battery electrode performance. Herein, the PEG/PPBT system is used as a model polymeric binder for understanding cation effects in anode systems. As such, the potassium ion was replaced with sodium, lithium, hydrogen, and ammonium through ion exchange. The potassium salt exhibited the most stable electrochemical performance, which is attributed to the cation size and resultant electrode morphology that facilitates ion transport. The lithium analogue demonstrated an initial increase in capacity but was unable to maintain this performance over 100 cycles; while the sodium-based system exhibited initially lower capacity as a result of slow reaction kinetics, which increased as cycling progressed. The parent carboxylic acid polymer and its ammonium salt were notably inferior. The results exploring the effect of ion exchange creates a framework for understanding how cations associated directly with the polymer impact electrochemical performance and aid in the overall design of binders for composite Li-ion battery anodes.

This chapter focuses on poly(3-alkylthiophenes) (P3AT) with linear side chains ranging from 4 (butyl-) to 14 (tetradecyl-) carbons as a class of materials that exhibit important correlations between the structure and electronic properties. It draws on comparative studies investigating how the structure of poly(3-alkylthiophene)s varies with side chain length and its impact on charge carrier mobility. The chapter presents a case study using poly(3-hexylthiophene) to document advances in processing methods that can manipulate the microstructure and charge transport properties. It discusses advances in controlled deposition techniques and explains advances in P3AT processing methods to enable stretchable and flexible electronic devices. Understanding of the role of thermal treatment on P3AT crystallization can provide supporting information regarding the packing behavior of these conjugated polymers. The conformational arrangement of individual polymer chains in solution has profound impacts on the self-assembly process to form ordered domains.

The resolution of inkjet printing technology is determined by wetting and evaporation processes after the jet drop contacts the substrate. Here, the wetting of different picoliter solubilized polymer droplets jetting onto one-end-closed porous alumina was investigated. The selected polymers are commonly used in inkjet ink. The synergistic effects of the hierarchical structure and substrate surface modification were used to control the behavior of polymer-based ink drops. A model that invokes the effect of surface tension was applied to calculate the amount of polymer solution penetrating into the pores. The calculation corroborates experimental observations and shows that the volume of polymer solution in the pores increases with an increase in pore radius and depth, resulting in less solution remaining on the substrate surface. The structure of the porous substrate coupled with intrinsic polymer properties and surface modifications all contribute to the resolution that can be achieved via inkjet printing.

The deposition of conjugated polymers is typically subject to chain-entanglement effects, which can severely hinder chain unfolding, alignment, and π–π stacking during rapid solution-coating processes. Here, long-range ordering and highly aligned poly(3-hexylthiophene) (P3HT) thin films were demonstrated by preprocessing the polymer solution with ultraviolet (UV) irradiation/solution aging and then depositing via the blade-coating method, which is compatible with roll-to-roll printing processes. The surface morphologies and optical anisotropy of deposited films revealed that the degree of chain alignment was greatly improved with increased levels of polymer assembly that can be precisely controlled by solution-aging time. The correlations between oriented nanofibrillar structures and their charge-transport anisotropy were further systematically investigated by blade coating pretreated solutions parallel and perpendicular to the direction of the source and drain electrodes. Interestingly, charge transport ...

Magnetite (Fe3O4) was used as a model high capacity metal oxide active material to demonstrate advantages derived from consideration of both electron and ion transport in the design of composite battery electrodes. The conjugated polymer, poly[3-(potassium-4-butanoate) thiophene] (PPBT), was introduced as a binder component, while polyethylene glycol (PEG) was coated onto the surface of Fe3O4 nanoparticles. The introduction of PEG reduced aggregate size, enabled effective dispersion of the active materials and facilitated ionic conduction. As a binder for the composite electrode, PPBT underwent electrochemical doping which enabled the formation of effective electrical bridges between the carbon and Fe3O4 components, allowing for more efficient electron transport. Additionally, the PPBT carboxylic moieties effect a porous structure, and stable electrode performance. The methodical consideration of both enhanced electron and ion transport by introducing a carboxylated PPBT binder and PEG surface treatment l...

Nanofibers are a ubiquitous structural motif in a variety of functional materials. In the field of organic electronics, π–π-stacking of conjugated polymers leads to fibrillar morphologies with a wide array of fiber packing behavior. Fiber orientation and alignment are known to influence the charge transport properties of devices such as organic field effect transistors. The solution processing methods used to create these devices give rise to large variations in these structural parameters—however, they are only observable with imaging techniques such as atomic force microscopy (AFM). To bring more rigorous quantification of orientation and alignment to these materials, a comprehensive image analysis tool is introduced to quantify the two-dimensional orientation and alignment of nanofibers from AFM images. It has been developed in MATLAB and packaged as a stand-alone application, so that researchers with no computational expertise can produce publication-ready figures directly from their images. AFM frequ...

An inverse relationship between mechanical ductility and mobility/molecular ordering in conjugated polymer systems was determined definitively through systematic interrogation of poly(3-hexylthiophene) (P3HT) films with varied degrees of molecular ordering and associated charge transport performance. The dilemma, whereby molecular ordering required for efficient charge transport conclusively undermines the applicability of these materials for stretchable, flexible device applications, was resolved using a polymer blend approach. Specifically, the molecular interactions between dissimilar polymer materials advantageously induced semiconducting polymer ordering into efficient π–π stacked fibrillar networks. Changes in the molecular environment surrounding the conjugated polymer during the elastomer curing process further facilitated development of high mobility networked semiconductor pathways. A processed P3HT: poly(dimethylsiloxane) (PDMS) composite afforded a semiconducting film that exhibits superior du...

Over the past decade, conversion-type anodes have been viewed as an attractive frontrunner for use in the next-generation of high-capacity battery materials. However, many technological limitations exist in the stability and long-term reliability of these anodes for the commercialization of these electrodes. This perspective studies how interfacial interactions between different components of the electrode can help elucidate the key physical and chemical properties needed for the development of high-capacity materials for battery applications.

Understanding the role of the distribution of polymer chain lengths on process–structure–property relationships in semiconducting organic electronics has remained elusive due to challenges in synthesizing targeted molecular weights (Mw) and polydispersity indices. Here, a facile blending approach of various poly(3-hexylthiophene) (P3HT) molecular weights is used to investigate the impact of the distribution of polymer chain lengths on self-assembly into aggregates and associated charge transport properties. Low and high Mw samples were blended to form a highly polydisperse sample which was compared to a similar, medium Mw control. Self-assembly was induced by preprocessing the polymer solution with UV irradiation and subsequent solution aging before deposition via blade-coating. Superior charge carrier (hole) mobilities were observed for the blend and control samples. Furthermore, their solution lifetimes exceeded 14 days. UV–vis spectral analysis suggests that low Mw P3HT lacks the mesoscale crystallinit...

A thermally “switchable” liquid-crystalline (LC) phase is observed in aqueous suspensions of cellulose nanocrystals (CNCs) featuring patchy grafts of the thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM). “Patchy” polymer decoration of the CNCs is achieved by preferential attachment of an atom transfer radical polymerization (ATRP) initiator to the ends of the rods and subsequent surface-initiated ATRP. The patchy PNIPAM-grafted CNCs display a higher colloidal stability above the lower critical solution temperature (LCST) of PNIPAM than CNCs decorated with PNIPAM in a brush-like manner. A 10 wt% suspension of the “patchy” PNIPAM-modified CNCs displays birefringence at room temperature, indicating the presence of an LC phase. When heated above the LCST of PNIPAM, the birefringence disappears, indicating the transition to an isotropic phase. This switching is reversible and appears to be driven by the collapse of the PNIPAM chains above the LCST, causing a reduction of the rods' packing density and an increase in translational and rotational freedom. Suspensions of the “brush” PNIPAM-modified CNCs display a different behavior. Heating above the LCST causes phase separation, likely because the chain collapse renders the particles more hydrophobic. The thermal switching observed for the “patchy” PNIPAM-modified CNCs is unprecedented and possibly useful for sensing and smart packaging applications.

A carbon nanotube (CNT) web electrode comprising magnetite spheres and few-walled carbon nanotubes (FWNTs) linked by the carboxylated conjugated polymer, poly[3-(potassium-4-butanoate) thiophene] (PPBT), was designed to demonstrate benefits derived from the rational consideration of electron/ion transport coupled with the surface chemistry of the electrode materials components. To maximize transport properties, the approach introduces monodispersed spherical Fe3O4 (sFe3O4) for uniform Li+ diffusion and a FWNT web electrode frame that affords characteristics of long-ranged electronic pathways and porous networks. The sFe3O4 particles were used as a model high-capacity energy active material, owing to their well-defined chemistry with surface hydroxyl (−OH) functionalities that provide for facile detection of molecular interactions. PPBT, having a π-conjugated backbone and alkyl side chains substituted with carboxylate moieties, interacted with the FWNT π-electron-rich and hydroxylated sFe3O4 surfaces, whic...

Conjugated semiconducting polymers present a new paradigm in electronics manufacturing. Examination of structure-property relationships in poly(3-hexylthiophene) (P3HT), a workhorse semiconducting polymer, has indicated that highly ordered crystals with long range interconnectivity exhibit the highest charge carrier mobility. Here we demonstrated the utility of using structural characterization to probe for tie chains, chains that tie together crystalline domains. P3HT nucleated via UV-irradiation was mixed with non-nucleated P3HT in a continuous flow system in which the flow rate and recollection tube length were varied. The setting with the lowest flow rate and shear rate (LL:LF) displayed the highest charge carrier mobility. This was associated with a trade-off between the quantity of fibril bundles formed and the interconnectivity. Comparable batch studies with solution aging exhibited higher mobilities than the flow system. The lack of correlations between the orientational order parameter and fiber packing density to charge mobility demonstrated that the structural design space is multidimensional and requires numerous structural metrics.

In an aqueous suspension process, protein dispersions facilitated improved alignment and organization of poly(3-hexylthiophene) (P3HT) chains into highly ordered crystalline structures. A solution of P3HT in 1,2,4-trichlorobenzene (TCB) was added to an aqueous dispersion of the hydrophobin, Cerato ulmin (CU). Upon gentle agitation, the semiconductor solution was readily confined within CU membrane-stabilized microstructures, often with extended shapes. UV–vis and polarized micro-Raman spectroscopy suggested complex, enhanced molecular alignment due to a transition from isotropic to liquid crystalline fluid to polycrystalline states. Grazing-incidence X-ray diffraction corroborates this interpretation. On aging, the initial CU:P3HT/TCB structures develop dendritic architectures that slowly release polymer-containing capsules. The counterintuitive evolution from large structures to smaller ones suggests the initial structures were nonequilibrium, and it opens the door to latex-like processing of semiconduct...

Semiconducting conjugated polymers have drawn a great deal of attention over the past decade due to their solution processability and potential use in roll to roll fabrication of organic solar cells. Here, we report the effect of solvent vapor pressure on poly(3-hexylthiophene):[6,6]-phenyl C 61 -butyric acid methyl ester (P3HT:PCBM) blade coated inverted solar cells using ZnO as the electron transporting layer and MoO 3 as the hole transporting layer. The resultant morphology and device performance are investigated for devices processed from solvents with varied vapor pressure and a mixed solvent. We report that the use of a mixed solvent system is advantageous for controlling the initial vapor pressure of the processing solution, thereby controlling the phase separated morphology between P3HT and PCBM which impacts ultimate solar cell performance.

Very few studies have reported oriented crystallization of conjugated polymers directly in solution. Here, solution crystallization of conjugated polymers in a microfluidic system is found to produce tightly π-stacked fibers with commensurate improved charge transport characteristics. For poly(3-hexylthiophene) (P3HT) films, processing under flow caused exciton bandwidth to decrease from 140 to 25 meV, π-π stacking distance to decrease from 3.93 to 3.72 Å and hole mobility to increase from an average of 0.013 to 0.16 cm(2) V(-1) s(-1), vs films spin-coated from pristine, untreated solutions. Variation of the flow rate affected thin-film structure and properties, with an intermediate flow rate of 0.25 m s(-1) yielding the optimal π-π stacking distance and mobility. The flow process included sequential cooling followed by low-dose ultraviolet irradiation that promoted growth of conjugated polymer fibers. Image analysis coupled with mechanistic interpretation supports the supposition that "tie chains" provide for charge transport pathways between nanoaggregated structures. The "microfluidic flow enhanced semiconducting polymer crystal engineering" was also successfully applied to a representative electron transport polymer and a nonhalogenated solvent. The process can be applied as a general strategy and is expected to facilitate the fabrication of high-performance electrically active polymer devices.

Low-dose UV irradiation of poly(3-hexylthiophene) (P3HT)-insulating polymer (polystyrene (PS) or polyisobutylene (PIB)) blend solutions led to the formation of highly ordered P3HT nanofibrillar structures in solidified thin films. The P3HT nanofibers were effectively interconnected through P3HT islands phase-separated from insulating polymer regions in blend films comprising a relatively low fraction of P3HT. Films prepared with a P3HT content as low as 5 wt % exhibited excellent macroscopic charge transport characteristics. The impact of PS on P3HT intramolecular and intermolecular interactions was systematically investigated. The presence of PS chains appeared to assist in the UV irradiation process of the blend solutions to facilitate molecular interactions of the semiconductor component, and to enhance P3HT chain interactions during spin coating because of relatively unfavorable P3HT-PS chain interactions. However, P3HT lamellar packing was hindered in the presence of PS chains, because of favorable hydrophobic interactions between the P3HT hexyl substituents and the PS chains. As a result, the lamellar packing d-spacing increased, and the coherence length corresponding to the lamellar packing decreased, as the amount of PS in the blend films increased.

The electron deficiency and trans-planar conformation of bithiazole is potentially beneficial for the electron-transport performance of organic semiconductors. However, the incorporation of bithiazole into polymers through a facile synthetic strategy remains a challenge. Herein, 2,2′-bithiazole was synthesized in one step and copolymerized with dithienyldiketopyrrolopyrrole to afford poly(dithienyldiketopyrrolopyrrole-bithiazole), PDBTz. PDBTz exhibited electron mobility reaching 0.3 cm2 V–1 s–1 in organic field-effect transistor (OFET) configuration; this contrasts with a recently discussed isoelectronic conjugated polymer comprising an electron-rich bithiophene and dithienyldiketopyrrolopyrrole, which displays merely hole-transport characteristics. This inversion of charge-carrier transport characteristics confirms the significant potential for bithiazole in the development of electron-transport semiconducting materials. Branched 5-decylheptacyl side chains were incorporated into PDBTz to enhance polyme...

Concurrent in situ Raman spectroscopic studies and drain current measurements were performed during drop-cast poly(3-hexylthiophene) (P3HT) film formation. Together, these techniques allow interrogation and elucidation of the evolution of P3HT structural changes and associated electrical characteristics as the solvent evaporates. Two observations are especially significant: i) solvent continued to be present in the developing thin-film at the point where the drain current exhibited a sharp increase and ii) continued to be observed after crystallization of the polymer. The in situ studies provide vital insights into the polymer organization and chain alignment processes at the molecular and macroscopic scales. The results suggest that final conjugated polymer thin-film morphology can be tailored for enhanced performance and desired electronic properties through quenching of the active polymer layer at a specified time during the solidification process.

High-throughput discovery of process-structure-property relationships in materials through an informatics-enabled empirical approach is an increasingly utilized technique in materials research due to the rapidly expanding availability of data. Here, process-structure-property relationships are extracted for the nucleation, growth, and deposition of semiconducting poly(3-hexylthiophene) (P3HT) nanofibers used in organic field effect transistors, via high-throughput image analysis. This study is performed using an automated image analysis pipeline combining existing open-source software and new algorithms, enabling the rapid evaluation of structural metrics for images of fibrillar materials, including local orientational order, fiber length density, and fiber length distributions. We observe that microfluidic processing leads to fibers that pack with unusually high density, while sonication yields fibers that pack sparsely with low alignment. This is attributed to differences in their crystallization mechanisms. P3HT nanofiber packing during thin film deposition exhibits behavior suggesting that fibers are confined to packing in two-dimensional layers. We find that fiber alignment, a feature correlated with charge carrier mobility, is driven by increasing fiber length, and that shorter fibers tend to segregate to the buried dielectric interface during deposition, creating potentially performance-limiting defects in alignment. Another barrier to perfect alignment is the curvature of P3HT fibers; we propose a mechanistic simulation of fiber growth that reconciles both this curvature and the log-normal distribution of fiber lengths inherent to the fiber populations under consideration.

We demonstrate that homopolypeptides covalently tethered to anisotropically shaped silica particles induce crystalline ordering of representative semiconducting polymers. Films drop-cast from chloroform dispersions of poly(γ-stearyl-l-glutamate) (PSLG) composite particles and poly(3-hexythiophene) (P3HT) led to highly ordered crystalline structures of P3HT. Hydrophobic-hydrophobic interactions between the alkyl side chains of P3HT and PSLG were the main driving force for P3HT chain ordering into the crystalline assemblies. It was found that the orientation of rigid P3HT fibrils on the substrate adopted the directionality of the evaporating front. Regardless of the PSLG-coated particle dimensions used, the drop-cast films displayed patterns that were shaped by the coffee ring and Marangoni effects. PSLG-coated particles of high axial ratio (4.2) were more efficient in enhancing the electronic performance of P3HT than low axial ratio (2.6) homologues. Devices fabricated from the ordered assemblies displayed improved charge-carrier transport performance when compared to devices fabricated from P3HT alone. These results suggest that PSLG can favorably mediate the organization of semiconducting polymers.

Self-assembly of conjugated organic semiconductors into ordered, larger scale entities is a critical process to achieve efficient charge transport at the nano- through macro-scales, and various methodologies aimed at enhancing molecular ordering have been introduced. However, mechanistic understanding is limited. Here, a mechanistic elucidation of poly(3-hexylthiophene) (P3HT) molecular self-assembly is proposed based on experimental demonstration of controlled, solution-based P3HT self-assembly into rod-like polycrystalline nanostructures. The synergistic combination of nonsolvent addition and ultrasonication facilitates rod-like P3HT nanostructure formation in solution. Importantly, through sequential application of both treatments, nanostructure length can be easily modulated, and the assembly process is shown to follow a simple 2-step crystallization model, which depends upon nucleation followed by growth. Through arrays of experimental results, the validity of 2-step crystallization is confirmed and is proposed as a comprehensive platform to understand self-assembly processes of conjugated polymers into larger, ordered mesoscale entities.