“Solvent Annealing” Effect in Polymer Solar Cells Based on Poly(3‐hexylthiophene) and Methanofullerenes

The self‐organization of the polymer in solar cells based on regioregular poly(3‐hexylthiophene) (RR‐P3HT):[6,6]‐phenyl C₆₁‐butyric acid methyl ester (PCBM) is studied systematically as a function of the spin‐coating time t_s (varied from 20–80 s), which controls the solvent annealing time t_a, the time taken by the solvent to dry after the spin‐coating process. These blend films are characterized by photoluminescence spectroscopy, UV‐vis absorption spectroscopy, atomic force microscopy, and grazing incidence X‐ray diffraction (GIXRD) measurements. The results indicate that the π‐conjugated structure of RR‐P3HT in the films is optimally developed when t_a is greater than 1 min (t_s ～ 50 s). For t _s < 50 s, both the short‐circuit current (J_SC) and the power conversion efficiency (PCE) of the corresponding polymer solar cells show a plateau region, whereas for 50 < t_s < 55 s, the J_SC and PCE values are significantly decreased, suggesting that there is a major change in the ordering of the polymer in this time window. The PCE decreases from 3.6 % for a film with a highly ordered π‐conjugated structure of RR‐P3HT to 1.2 % for a less‐ordered film. GIXRD results confirm the change in the ordering of the polymer. In particular, the incident photon‐to‐electron conversion efficiency spectrum of the less‐ordered solar cell shows a clear loss in both the overall magnitude and the long‐wavelength response. The solvent annealing effect is also studied for devices with different concentrations of PCBM (PCBM concentrations ranging from 25 to 67 wt %). Under “solvent annealing” conditions, the polymer is seen to be ordered even at 67 wt % PCBM loading. The open‐circuit voltage (V_OC) is also affected by the ordering of the polymer and the PCBM loading in the active layer.     

Formation of a Ground‐State Charge‐Transfer Complex in Polyfluorene//[6,6]‐Phenyl‐C61 Butyric Acid Methyl Ester (PCBM) Blend Films and Its Role in the Function of Polymer/PCBM Solar Cells

Evidence is presented for the formation of a weak ground‐state charge‐transfer complex in the blend films of poly[9,9‐dioctylfluorene‐co‐N‐(4‐methoxyphenyl)diphenylamine] polymer (TFMO) and [6,6]‐phenyl‐C₆₁ butyric acid methyl ester (PCBM), using photothermal deflection spectroscopy (PDS) and photoluminescence (PL) spectroscopy. Comparison of this polymer blend with other polyfluorene polymer/PCBM blends shows that the appearance of this ground‐state charge‐transfer complex is correlated to the ionization potential of the polymer, but not to the optical gap of the polymer or the surface morphology of the blend film. Moreover, the polymer/PCBM blend films in which this charge‐transfer complex is observed also exhibit efficient photocurrent generation in photovoltaic devices, suggesting that the charge‐transfer complex may be involved in charge separation. Possible mechanisms for this charge‐transfer state formation are discussed as well as the significance of this finding to the understanding and optimization of polymer blend solar cells.     

Conjugated Polymer Nanoparticle–Graphene Oxide Charge‐Transfer Complexes

The game‐changing role of graphene oxide (GO) in tuning the excitonic behavior of conjugated polymer nanoparticles is described for the first time. This is demonstrated by using poly(3‐hexylthiophene) (P3HT) as a benchmark conjugated polymer and employing an in situ reprecipitation approach resulting in P3HT nanoparticles (P3HT_NPs) with sizes of 50–100 nm in intimate contact with GO. During the self‐assembly process, GO changes the crystalline packing of P3HT chains in the forming P3HT_NPs from H to H/J aggregates exhibiting exciton coupling constants as low as 2 meV, indicating favorable charge separation along the P3HT chains. Concomitantly, π–π interface interactions between the P3HT_NPs and GO sheets are established resulting in the creation of P3HT_NPs–GO charge‐transfer complexes whose energy bandgaps are lowered by up to 0.5 eV. Moreover, their optoelectronic properties, preestablished in the liquid phase, are retained when processed into thin films from the stable aqueous dispersions, thus eliminating the critical dependency on external processing parameters. These results can be transferred to other types of conjugated polymers. Combined with the possibility of employing water based “green” processing technologies, charge‐transfer complexes of conjugated polymer nanoparticles and GO open new pathways for the fabrication of improved optoelectronic thin film devices.     

Architecture of Conjugated Donor–Acceptor (D–A)‐Type Polymer Films with Cross‐Linked Structures

A series of new donor–acceptor (D–A)‐type semiconducting conjugated polymers (SCPs), which can form cross‐linked structural and supramolecular assembly films by hydrogen‐bonding, is successfully synthesized. The microstructures of supramolecular assembly films are further investigated by X‐ray diffraction (XRD), high‐ resolution transmission electron microscopy (HRTEM), and variable‐temperature Fourier transform infrared (FT‐IR) absorption spectra. As electronic transmission (ET) materials, the SCPs demonstrate superior properties by means of fabricating electron‐only devices with the configuration of ITO/ET (SCPs)/Ca/Al. According to space‐charge‐limited current (SCLC) measurements, fluorine‐containing SCPs exhibit much smaller threshold voltages and much higher electron mobilities than Alq₃. Meanwhile, a significant enhancement for their luminescence properties is verified by the photoluminescence (PL) and electroluminescent (EL) spectra of cross‐linked‐type SCPs, compared to non‐cross‐linked‐type SCPs. The fabricated polymer light‐emitting diodes (PLEDs) with the configuration of ITO/PEDOT:PSS/EML (SCPs)/BCP/LiF/Al are able to emit the color from green to red with moderately low turn‐on voltages. These results suggested that cross‐linked D–A‐type SCP can become a potential candidate as a kind of multifunctional materials applied in the field of optoelectronic devices.     

A General Electrochemical Strategy for Synthesizing Charge‐Transfer Complex Micro/Nanowires

Universal strategies for synthesizing one‐dimensional organic nanomaterials are of fundamental importance in the development of more flexible, cheaper and lighter electronics. Charge‐transfer (CT) complexes, the major kind of organic conductors, are in the long‐term attractive materials owing to their unique crystal structures and conductive properties. In this article, a general strategy for the synthesis of CT complex micro/nanowires based on the localized nanoelectrochemistry using tiny carbon nanotube (CNT) electrodes is presented. This strategy is successfully demonstrated over 12 typical CT complexes, and a general rule for the preparation of various kinds of CT complex micro/nanowires is summarized. The CT complex micro/nanowires thus synthesized have high aspect ratios and long lengths as compared with traditional macroscopic planar electrodes, originating from the one‐dimensional structural feature with fewer or no defects and the ultrasmall surface area of the CNT. This work provides a more versatile material basis for the fundamental and application studies of low‐dimensional organic conductor materials.     

Solid‐Phase Synthesis of Molecularly Imprinted Polymer Nanoparticles with a Reusable Template–“Plastic Antibodies”

Molecularly imprinted polymers (MIPs) are generic alternatives to antibodies in sensors, diagnostics, and separations. To displace biomolecules without radical changes in infrastructure in device manufacture, MIPs should share their characteristics (solubility, size, specificity and affinity, localized binding domain) whilst maintaining the advantages of MIPs (low‐cost, short development time, and high stability) hence the interest in MIP nanoparticles. Herein, a reusable solid‐phase template approach is reported (fully compatible with automation) for the synthesis of MIP nanoparticles and their precise manufacture using a prototype automated UV photochemical reactor. Batches of nanoparticles (30–400 nm) with narrow size distributions imprinted with: melamine (d = 60 nm, K_d = 6.3 × 10^?8 M ), vancomycin (d = 250 nm, K_d = 3.4 × 10^?9 M ), a peptide (d = 350 nm, K_d = 4.8 × 10^?8 M ) and proteins have been produced. The instrument uses a column packed with glass beads, bearing the template. Process parameters are under computer control, requiring minimal manual intervention. For the first time, the reliable re‐use of molecular templates is demonstrated in the synthesis of MIPs (≥30 batches of nanoMIPs without loss of performance). NanoMIPs are produced template‐free and the solid‐phase acts both as template and affinity separation medium.     

The Locus of Free Charge‐Carrier Generation in Solution‐Cast Zn1–xMgxO/Poly(3‐hexylthiophene) Bilayers for Photovoltaic Applications

The photoconductivity of solution‐cast Zn_1–xMg_xO (x=0‐0.4) and poly(3‐hexylthiophene) (P3HT) thin films, and Zn_1‐xMg_xO/P3HT bilayers is investigated using Time‐Resolved Microwave Conductivity (TRMC) with the aim of determining the locus of free charge carrier generation in the bilayer system. The photoconductivity of Zn_1–xMg_xO thin films, under illumination with 300 nm laser pulses, is limited by the formation of stable excitons and by scattering of the carriers at grain boundaries. The electron mobility in Zn_1–xMg_xO films decreases exponentially with Mg concentration, up to x=0.4. In agreement with previous work, free carriers are observed in the P3HT film under illumination with 500 nm pulses in the absence of an acceptor. Under illumination with 500 nm pulses, where only the polymer absorbs, the TRMC signal for the Zn_1–xMg_xO/P3HT bilayers for x≥0.2 is the same as that of pure P3HT, indicating that free carrier generation in these bilayers occurs predominately by exciton dissociation in the polymer bulk, and not at the interface between the polymer and the solution‐cast oxide. At lower Mg concentrations (x<0.2) the TRMC signal increases with decreasing x following the dependence of the electron mobility in the oxide but its light intensity dependence remains consistent with free carrier generation in the polymer bulk. To explain these results and previously published photovoltaic device data (Adv. Funct. Mater. 2007 , 17, 264) we propose that free carrier generation in the bilayers predominantly occurs in the bulk of P3HT, and is followed by electron injection to the oxide to yield photocurrent in photovoltaic cells. The dependence of the TRMC signal of the bilayers on Mg concentration is explained in terms of the yield for free carrier generation in the polymer and the relative contributions of electrons in the oxide and holes in the polymer.     

“Black” Titania Coatings Composed of Sol–Gel Imprinted Mie Resonators Arrays

Optical technologies and devices rely on the controlled manipulation of light propagation through a medium. This is generally governed by the inherent effective refractive index of the material as well as by its structure and dimensionality. Although a precise control over light propagation with sub‐wavelength size objects is a crucial issue for a plethora of applications, the widely used fabrication methods remain cumbersome and expensive. Here, a sol–gel dip‐coating method combined with nanoimprinting lithography on arbitrary glass and silicon substrates is implemented for the fabrication of TiO₂‐based dielectric Mie resonators. The technique allows obtaining sub‐micrometric pillars featuring unprecedented vertical aspect ratios (>1) with relatively high fidelity and precision. Spectroscopic characterization at visible and near‐infrared frequencies demonstrate that the resonant properties of these dielectric pillar arrays allow for a drastic reduction of light transmission (cutting more than 50% on glass) and reduced reflection (reflecting less than 3% on glass and 16% on bulk silicon), accounting for an efficient light trapping. These results provide a guideline for the fabrication of Mie resonators using a fast, versatile, low‐cost, low‐temperature technique for efficient light manipulation at the nanoscale.     

Mechanical Restoration of Damaged Polymer Films by “Repair‐and‐Go”

A microencapsulation and nanoparticle deposition technique, termed “repair‐and‐go,” is employed for inducing mechanical restoration of damaged polymer films. In “repair‐and‐go,” polymer‐stabilized emulsion droplets, containing surface‐functionalized SiO₂ nanoparticles, traverse a substrate and deposit their nanoparticle contents selectively into the damaged regions. Surface‐oxidized poly(dimethylsiloxane) is employed as the substrate, and dynamic mechanical analysis reveals the enhanced mechanical properties of the film following nanoparticle deposition. Healing efficiency is optimal when using thinner test substrates, repeated deposition cycles, and functional SiO₂ nanoparticles that afford access to postdeposition curing.     

Half‐Fused Diketopyrrolopyrrole‐Based Conjugated Donor–Acceptor Polymer for Ambipolar Field‐Effect Transistors

A novel building block, denoted as half‐fused diketopyrrolopyrrole (DPP) (9‐(3‐octadecylhenicosyl)‐8‐(thiophen‐2‐yl)‐7H‐pyrrolo[3,4‐a]thieno[3,2‐g]indolizine‐7,10(9H)‐dione), in which one of the flanking thiophene units is fused to one of the DPP rings via a carbon‐carbon double bond at the N‐position is reported. The half‐fused DPP is successfully utilized as an electron acceptor to prepare the conjugated donor–acceptor polymer PTFDFT , which exhibits ambipolar semiconducting behavior in ambient air. Theoretical calculations and absorption spectral studies show that the backbone of PTFDFT is more planar compared to the reference polymer with conventional DPP units. As a result, PTFDFT shows a narrow bandgap and low lowest unoccupied molecular orbital level. The more planar backbone with fewer side chains favors the dense packing of the polymer chains of PTFDFT with a short π–π stacking distance (3.49 Å). Grazing‐incidence wide‐angle X‐ray scattering data further confirm the predominant edge‐on packing mode of the PTFDFT polymer chains on the substrate. As expected, the PTFDFT thin film shows excellent ambipolar semiconducting properties under ambient conditions, reaching 2.23 and 1.08 cm² V^?1 s^?1 for the n‐ and p‐channels, respectively. In addition, complementary‐like inverter with gain value as high as 141 is successfully constructed using the PTFDFT thin film.     

Open‐Shell Donor–Acceptor Conjugated Polymers with High Electrical Conductivity

Conductive polymers largely derive their electronic functionality from chemical doping, processes by which redox and charge‐transfer reactions form mobile carriers. While decades of research have demonstrated fundamentally new technologies that merge the unique functionality of these materials with the chemical versatility of macromolecules, doping and the resultant material properties are not ideal for many applications. Here, it is demonstrated that open‐shell conjugated polymers comprised of alternating cyclopentadithiophene and thiadiazoloquinoxaline units can achieve high electrical conductivities in their native “undoped” form. Spectroscopic, electrochemical, electron paramagnetic resonance, and magnetic susceptibility measurements demonstrate that this donor–acceptor architecture promotes very narrow bandgaps, strong electronic correlations, high‐spin ground states, and long‐range π‐delocalization. A comparative study of structural variants and processing methodologies demonstrates that the conductivity can be tuned up to 8.18 S cm^?1. This exceeds other neutral narrow bandgap conjugated polymers, many doped polymers, radical conductors, and is comparable to commercial grades of poly(styrene‐sulfonate)‐doped poly(3,4‐ethylenedioxythiophene). X‐ray and morphological studies trace the high conductivity to rigid backbone conformations emanating from strong π‐interactions and long‐range ordered structures formed through self‐organization that lead to a network of delocalized open‐shell sites in electronic communication. The results offer a new platform for the transport of charge in molecular systems.     

Being a “Good Parent” in Parent–Teacher Conferences

This research advances our understanding of what constitutes a “good parent” in the course of actual social interaction. Examining video‐recorded naturally occurring parent–teacher conferences, this article shows that, while teachers deliver student‐praising utterances, parents may display that they are gaining knowledge; but when teachers' actions adumbrate student‐criticizing utterances, parents systematically display prior knowledge. This article elucidates the details of how teachers and parents tacitly collaborate to enable parents to express student‐troubles first, demonstrating that parents display competence—appropriate involvement with children's schooling—by asserting their prior knowledge of, and/or claiming/describing their efforts to remedy, student‐troubles. People (have to) display competence generically in interaction. By explicating how parents display competence, this article offers insights for several areas of communication research.     

Effect of Donor Molecular Structure and Gate Dielectric on Charge‐Transporting Characteristics for Isoindigo‐Based Donor–Acceptor Conjugated Polymers

This study investigates the effect of the molecular structure of three different donor units, naphthalene (Np), bithiophene (BT), and thiophene–vinylene–thiophene (TVT), in isoindigo (IIG)‐based donor –acceptor conjugated polymers (PIIG‐Np, PIIG‐BT and PIIG‐TVT) on the charge carrier mobility of organic field‐effect transistors (OFETs). The charge transport properties of three different IIG‐based polymers strongly depend on donor units. PIIG–BT OFETs showed 50 times higher hole mobility (0.63 cm² V^?1 s^?1) than PIIG–TVT and PIIG–Np ones of ≈ 0.01 cm² V^?1 s^?1 with CYTOP dielectric though the BT units have less planarity than the TVT and Np units. The reasons for the different mobility in IIG‐based polymers are studied by analyzing the energy structure by absorption spectra, calculating transport levels by density functional theory, investigating the in‐ and out‐of‐plane crystallinity of thin film by grazing‐incidence wide‐angle X‐ray scattering, and extracting key transport parameters via low‐temperature measurements. By combining theoretical, optical, electrical, and structural analyses, this study finds that the large difference in OFET mobility mainly originates from the transport disorders determined by the different microcrystal structure, rather than the intrinsic transport properties in isolated chains for different polymers.     

Multifunctional Visible‐Light Powered Micromotors Based on Semiconducting Sulfur‐ and Nitrogen‐Containing Donor–Acceptor Polymer

Photosensitive micromotors that can be remotely controlled by visible light irradiation demonstrate great potential in biomedical and environmental applications. To date, a vast number of light‐driven micromotors are mainly composed from costly heavy and precious metal‐containing multicomponent systems, that limit the modularity of chemical and physical properties of these materials. Herein, a highly efficient photocatalytic micromotors based exclusively on a purely organic polymer framework—semiconducting sulfur‐ and nitrogen‐containing donor–acceptor polymer, is presented. Thanks to precisely tuned molecular architecture, this material has the ability to absorb visible light due to a conveniently situated energy gap. In addition, the donor‐acceptor dyads within the polymer backbone ensure efficient photoexcited charge separation. Hence, these polymer‐based micromotors can move in aqueous solutions under visible light illumination via a self‐diffusiophoresis mechanism. Moreover, these micromachines can degrade toxic organic pollutants and respond to an increase in acidity of aqueous environments by instantaneous colour change. The combination of autonomous motility and intrinsic fluorescence enables these organic micromotors to be used as colorimetric and optical sensors for monitoring of the environmental aqueous acidity. The current findings open new pathways toward the design of organic polymer‐based micromotors with tuneable band gap architecture for fabrication of self‐propelled microsensors for environmental control and remediation applications.     

Significant Improvement of Dye‐Sensitized Solar Cell Performance by Small Structural Modification in π‐Conjugated Donor–Acceptor Dyes

Two donor‐π‐acceptor (D‐π‐A) dyes are synthesized for application in dye‐sensitized solar cells (DSSC). These D‐π‐A sensitizers use triphenylamine as donor, oligothiophene as both donor and π‐bridge, and benzothiadiazole (BTDA)/cyanoacrylic acid as acceptor that can be anchored to the TiO₂ surface. Tuning of the optical and electrochemical properties is observed by the insertion of a phenyl ring between the BTDA and cyanoacrylic acid acceptor units. Density functional theory (DFT) calculations of these sensitizers provide further insight into the molecular geometry and the impact of the additional phenyl group on the photophysical and photovoltaic performance. These dyes are investigated as sensitizers in liquid‐electrolyte‐based dye‐sensitized solar cells. The insertion of an additional phenyl ring shows significant influence on the solar cells' performance leading to an over 6.5 times higher efficiency (η = 8.21%) in DSSCs compared to the sensitizer without phenyl unit (η = 1.24%). Photophysical investigations reveal that the insertion of the phenyl ring blocks the back electron transfer of the charge separated state, thus slowing down recombination processes by over 5 times, while maintaining efficient electron injection from the excited dye into the TiO₂‐photoanode.     

Original Fuel‐Cell Membranes from Crosslinked Terpolymers via a “Sol–gel” Strategy

Hybrid organic/inorganic membranes that include a functionalized (‐SO₃H), interconnected silica network, a non‐porogenic organic matrix, and a ‐SO₃H‐functionalized terpolymer are synthesized through a sol–gel‐based strategy. The use of a novel crosslinkable poly(vinylidene fluoride‐ter‐perfluoro(4‐methyl‐3,6‐dioxaoct‐7‐ene sulfonyl fluoride)‐ter‐vinyltriethoxysilane) (poly(VDF‐ter‐PFSVE‐ter‐VTEOS)) terpolymer allows a multiple tuning of the different interfaces to produce original hybrid membranes with improved properties. The synthesized terpolymer and the composite membranes are characterized, and the proton conductivity of a hybrid membrane in the absence of the terpolymer is promising, since 8 mS cm^?1 is reached at room temperature, immersed in water, with an experimental ion‐exchange‐capacity (IEC_exp) value of 0.4 meq g^?1. Furthermore, when the composite membranes contain the interfaced terpolymer, they exhibit both a higher proton conductivity (43 mS cm^?1 at 65 °C under 100% relative humidity) and better stability than the standard hybrid membrane, arising from the occurrence of a better interface between the inorganic silica and the poly[(vinylidene fluoride)‐co‐hexafluoropropylene] (poly(VDF‐co‐HFP)) copolymer network. Accordingly, the hybrid SiO₂‐SO₃H/terpolymer/poly(VDF‐co‐HFP) copolymer membrane has potential use as an electrolyte in a polymer‐electrolyte‐membrane fuel cell operating at intermediate temperatures.     

Lanthanide “Chameleon” Multistage Anti‐Counterfeit Materials

Hybrid materials displaying multistage security behavior, where a single material shows both wavelength‐ and temperature‐dependent luminescence properties, are reported. The materials consist of mixed‐lanthanide β‐diketonate complexes grafted into the pores of a nanosized 2,2′‐bipyridine‐5,5′‐dicarboxylate‐acid MOF. A very specific choice of lanthanides and their ratios, as well as β‐diketonate ligand, is crucial for obtaining the desired properties. The wavelength‐dependent luminescence properties of the materials are very well matched with the excitation wavelengths of a standard UV lamp, and a clearly visible change in luminescence is observed in a narrow temperature range (slightly below and above room temperature), proving them to be excellent materials for use in anti‐counterfeit technologies, which would be almost impossible to mimic.     

Polymer Photovoltaic Devices Employing a Chemically Fixed p–i–n Junction

Polymer photovoltaic devices commonly suffer from low power conversion efficiencies despite the potential for much higher performance. Here we apply a recently reported system for creating a chemically fixed polymer p‐i‐n junction to polymer photovoltaic devices. Both single‐component and blended donor/acceptor devices are fabricated and tested. We study the devices during charging and find that the changes in light and dark current characteristics are consistent with the formation of a p‐i‐n junction in the active material. While the overall performance of these systems need improvement, the devices show promising open circuit voltages, suggesting the possibility for improving the state‐of‐the‐art in polymer photovoltaic techno logies with continued materials development.