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Detecting and discriminating chemical vapors are essential for environmental monitoring and medical diagnostics. In this study, highly sensitive chemical vapor sensors fabricated from fluorinated t...

Oligo(ethylene glycol) (OEG) side chains are widely used in donor-acceptor conjugated polymers (D-A CPs) and enable the polymers to dissolve and be processed in environmentally friendly and cost-effective nonchlorinated solvents, such as water. However, the OEG effect on the physical properties of D-A CPs has not been thoroughly studied and sometimes the results are controversial. In this study, two oligothiophene-isoindigo based conjugated polymers, P3TI and P4TI, are selected as model polymers to investigate the OEG effect. PnTI has octyl side chains on the oligothiophene unit and 2-hexyldecyl side chains on the isoindigo unit. The replacement of an alkyl side chain with OEG not only changes the optical and thermal properties but also the molecular arrangements of the polymers such as π-π d-spacing, crystallinity, and packing orientation. The domination of the crystallization behavior changes from the oligothiophene unit to the isoindigo unit when the bulky alkyl group is replaced by the flexible and linear OEG. The packing changes from edge-on to face-on orientation. The results are intriguing and provide new insights into this class of polymers.

The composite electron transporting layer (ETL) of metal oxide with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) prevents perovskite from metal electrode erosion and increases p-i-n perovskite...

The donor–acceptor conjugated polymers (CPs) of terthiophene–thieno[3,4-c]pyrrole-4,6-dione (3T-TPD) are widely used to fabricate low-cost flexible electronics. We present a comprehensive study of the side chain effect on the optical properties, electrochemical properties, thermal properties, and self-assembly behavior of 3T-TPD CPs, including side chain location (outward vs inward), type (tetraethylene glycol (TEG) vs dodecyl), and length (octyl vs hexyl vs butyl). For the side chain location effect, the polymers with outward side chains show better coplanarity of backbone than the polymers with inward side chains, leading to form lamellae structure. However, interestingly, the inward series polymers exhibit novel hexagonal structure. Through replacing dodecyl chains with TEG chains and changing the side chain length, ultrahigh ordered lamellae and hexagonal structure can be obtained. Furthermore, two models are purposed to explain the formation mechanism of lamellae and hexagonal structure. This study c...

Rod-coil block copolymers (BCPs) can self-assemble into nanostructures that are useful for the fabrication of nanodevices. However, BCPs are generally difficult to self-assemble into highly ordered nanostructures due to their low chain mobility and strong rod-rod interaction. A facile approach is developed to achieve rapid self-assembly of rod-coil BCPs by blending them with selective additive and annealing in vacuum. Poly(diethyl hexyl oxy-p-phenylene vinylene)-b-poly(methyl methacrylate) (DEHPPV-b-PMMA or PVM) was used as a model copolymer to validate this approach. By adding 30 wt% of a rod-selective additive, p-phenylene vinylene (PV), into the PVM containing 67% (v/v) PMMA, the copolymer can easily self-assemble into lamellae structure at 150 °C for 1.5hr under 0.05 torr. This is a significant improvement over the 200 °C for 60 h for the sample without additive and vacuum annealing. This energy conservation process should have broad application in the fabrication of highly ordered nanostructure using BCPs.

Metal oxide thin films made from a sol–gel solution process are promising candidates for stable, low cost, and high performance electronic devices. Reducing the thermal budget required for their crystallization process can relax the fabrication limitation and expand their possible applications. We show that with the addition of an adequate amount of tetramethylammonium hydroxide (TMAOH) in the precursor solution, the activation energy of the sol–gel reaction can be reduced by about 50%. Using this strategy, not only can the required thermal treatment time and temperature of the sol–gel reaction be significantly reduced but also the quality of the film can be improved. The enhanced reaction rate can be ascribed to the presence of hydroxyl anions, which facilitate the formation of the metal hydroxide and the subsequent metal oxide. Additionally, the strategy developed here can be applied to multiple kinds of metal oxides. By this method, the processing temperature can be lowered by at least 50 °C and the time can be shortened by half for the fabrication of electronic devices such as thin film transistors and photovoltaics. Our results open up a new paradigm to fabricate highly crystalline metal oxide thin films quickly at an energy saving low temperature using the solution process.

Sol–gel metal oxide films are an important type of functional materials for energy technologies and beyond owing to their versatile properties and ease of processing, but their applications are limited by the typically required high sintering temperatures. This study reports a novel phenomenon where the sintering temperatures of sol–gel metal oxide films were substantially lowered when a metal phase was embedded within the sol–gel precursor films. Morphological and compositional analyses revealed that the reduction in sintering temperatures was enabled by a mechanism similar to the metal-induced crystallization (MIC) process, with a distinction that catalysis of sol–gel reactions occurred alongside the induction of crystallization. We observed this catalytic MIC (c-MIC) mechanism in a variety of sol–gel material systems including NixO with embedded Au or Ag; TiOx with embedded Ni, Au, or Pt; and SnOx with embedded Ni. Based upon this concept, we demonstrated highly efficient flexible and rigid organic/inorganic hybrid perovskite solar cells (PSCs) using a low-temperature-sintered NixO film embedded with Au nanoislands as the hole-transporting layer (HTL). The c-MIC mechanism reduced the sintering temperature of the Au-embedded NixO HTL by 100 °C, making the NixO process compatible with plastic substrates while allowing the NixO HTL to retain more NiOOH surface groups, which enhanced hole collection and improved the quality of the perovskite layer. Thanks to the advantages of the c-MIC NixO film, the flexible and rigid PSCs achieved high power conversion efficiencies of up to 15.9 and 19.0%, respectively, which were sustained for >1200 h at 65 °C and 65% relative humidity. Our findings provide a practical route for low-temperature fabrication of high-quality oxide functional films by solution-based sol–gel processes, which will be valuable to a wide variety of applications in addition to thin film solar cells.

Hybrid lead halide perovskite structured materials have created enormous expectations for low-cost and high-performance optoelectronic devices. The light-harvesting active layer of perovskite solar cell consists of hybrid organic-inorganic lead halide-based material. In this study, we successfully fabricated the perovskite photovoltaics with partial substitution of the lead cation (Pb 2+ ) with calcium ion (Ca 2+ ). The incorporation of Ca 2+ into the original structure was analyzed to observe the doping effect on the crystalline structure and the optical properties. Moreover, UV–vis spectra showed the decreased bandgap with ascending the dopants Ca 2+ amount. 1.0 mol% Ca-doped perovskite film has the lower emission energy, and it shows the low recombination behavior. After optimizing the perovskite solar cells, the V oc is increased from 0.93 to 0.98 V, the J sc is increased from 17.4 to 19.1 mA/cm 2 and the power conversion efficiency is enhanced from 10.7 to 12.9% by using 1.0 mol% Ca-doped perovskite material.

Inorganic–organic hybrid perovskite single crystals are potential materials for the application of high performance optoelectronic devices. The exposed surface of single crystals can dramatically affect the measured properties. Facet-dependent behaviors are also speculated. However, impeded by the lack of facile facet engineering strategy for inorganic–organic hybrid perovskites, the relationship between different facets and respective performance remains elusive. In this work, we present a simple approach of ligand-mediated crystal growth to control the shape and the exposed facets of methylammonium lead iodide single crystals. The addition of oleylamine ligand can trigger the continuous morphological transition from dodecahedral-shaped single crystal enclosed by (100)T and (112)T to cubic-shaped single crystal enclosed by (110)T and (002)T while maintaining the material composition and crystalline phase. We fabricated single crystal based photodetectors and carried out the first unambiguous study on the...

Volatile organic compounds (VOCs) sensors are the imperative technology of modern life for environmental monitoring to detect any harmful elements and to prevent lethal exposure. The sensing material is a fibrous film consisting of poly(3-hexylthiophene)(P3HT)/poly(methyl methacrylate)(PMMA) blend, and it is fabricated on a glass substrate. The P3HT/PMMA fibrous film is made by electrospinning process and shows high specific surface for solvent vapor harvesting. The P3HT/PMMA fibrous films are thus easily designed according to the extinction changes of VOCs. The P3HT/PMMA fibrous film exhibits the detection capability for VOCs. It satisfies the detection limit of acetone, toluene and o-xylene at 500 ppm. The cost of the P3HT/PMMA fibrous film is acceptable to the market in contrast to the commercial sensors toward VOCs.

Organic–inorganic lead halide perovskite solar cells are considered as one of the most promising technologies for future photovoltaics because they show high power conversion efficiency (PCE) and can be fabricated through a simple solution process. Non-toxic alkaline-earth metal cations are suitable candidates to replace toxic lead in perovskite because they maintain the charge balance in perovskite and some of them meet the tolerance factor of Goldschmidt's rule. We investigated four kinds of alkaline-earth metal cations (Mg2+, Ca2+, Sr2+, and Ba2+) to replace lead cations partially. Among these four alkaline-earth metals, the Ba2+ is most suitable for Pb2+ replacement in perovskite films and exhibits the best power conversion efficiency. Furthermore, we systematically studied the crystal structure, absorption behavior and surface morphology of Ba2+-doped perovskite films with different doping levels. The relationship between the charge carrier dynamics and Ba2+ concentration was evaluated by the time-resolved photoluminescence (TRPL) technique. The Ba2+-doped perovskite films that can be processed in the environment containing moisture (1.0% relative humidity) are stable. At the optimal 3.0 mol% Ba2+ replacement, the PCE of the fabricated solar cell is increased from 11.8 to 14.0%, and the PCE of champion devices is as high as 14.9% with increased storage stability.

In present work, we focused on the improvement of short-circuit current density (J sc ) by using zinc-doped TiO 2 (Zn-doped TiO 2 ) as electron transport layer. Various Zn-doped TiO 2 compact layers with different doping concentrations are prepared by sol-gel method followed thermal treatment, and they were then used to fabricate perovskite solar cell. Effects of zinc (Zn) on the power conversion efficiency (PCE), absorption behavior, crystal structure, electrical conductivity, and surface morphology are systemically elucidated. Charge carrier dynamics between perovskite active layer and titanium dioxide (TiO 2 ) compact layer is discussed too. When the dopant concentration is less than 5.0 mol%, the absorption behavior, electrical conductivity and charge separation efficiency increase with Zn doping concentration. In contrast, when the Zn dopant is 7.0 mol%, it results in the decay of these properties mentioned. According to the optimized processing of perovskite solar cells, the J sc is increased from 18.5 to 22.3 mA/cm 2 so as to the PCE is significantly improved from 11.3% to 14.0%.

The auhtors report 3D biomimetic scaffolds using polymer blend of polyurethane and cellulose for cardiac tissue engineering. The biocompatible and biodegradable polyurethane is designed, synthesized and characterized. By incorporating 10 wt% of naturally ordered cellulose into the polyurethane and electrospinning them into 3D scaffold, the scaffold exhibits good biocompatibility and mechanical property to support and accommodate constant cycles of contraction/expansion of cardiac tissue. The biocompatibility is further improved using scaffold fabricated from aligned fibers due to synergistic effects between cells and ordered macromolecules. The anisotropic structured scaffold is mimicked the extracellular matrix and has therapeutic potential in reconstruction of damaged myocardium.

A quick and convenient approach that combines a printing process and chemical vapor deposition is developed for facile construction of nanostructured metal–carbon composite structures. Films of porous RANEY® nickel catalyst particles are deposited on various substrates by stencil printing from dispersions of the catalyst and poly(methyl methacrylate) in 2-(2-butoxyethoxy)ethyl acetate. After removing the organic binders at elevated temperatures, the mesoporous Ni film is applied as a growth template for synthesizing nanostructured carbon materials on the surface. Depending on the synthesis conditions, carbon nanofibers and nanotubes, as well as graphite deposits, are found to form on the substrates, allowing a robust and scalable production of carbon based inert electrodes of high specific surface area. In addition to structural characterization of the composites by means of scanning and transmission electron microscopy, Raman spectroscopy, X-ray diffraction, thermal gravimetric and surface adsorption analyses, the produced carbon/RANEY® nickel composites are also studied as electrodes in electrochemical capacitors (specific capacitance of ∼12 F g−1) and in field emitter devices with a low turn-on field (

The present work demonstrates a biomimetic electrospun scaffold based on polyurethane (PU) and ethyl cellulose (EC), featuring uniform fibrous nanostructures and three dimensional porous networks. The relationship between processing conditions and fibrous nanostructures is established which guides the rational processing with tunable fiber diameters. Additionally, the developed scaffold template reveals biocompatibility in retention and proliferation of cardiac myoblast H9C2 cells. The high mechanical strength of the PU/EC scaffolds enables the processing and handling of an ultrathin patch. Their elastomeric characteristics revealed the compatibility between the patch and contractile tissues. Furthermore, anisotropic PU/EC scaffolds with aligned nanofibers were successfully fabricated, exhibiting higher mechanical strength and essential characteristics for the survival and function of cardiac cells with native anisotropy. This work demonstrates a bioengineered PU/EC fibrous scaffold with uniform nanostructural webs and provides insight into the relationships between processing control, nanostructures and associated properties, with promising potential in cardiac tissue engineering.

In this work, we demonstrate the solution processing of optical and electrochemical dye sensors based on 4-(dioctylamino)-4′-(trifluoroacetyl)azobenzene and its application in sensing different amine compounds. Distinct optical response of the sensors exposed to ammonia, tetramethylammonium hydroxide, ethylamine, cadaverine and putrescine (typical compounds upon the decomposition of proteins) is observed. Incorporation of inkjet deposited thin films of the dye as sensors in food packages of ground meat and salmon is found as a feasible route to detect the appearance of biogenic amines produced by the degrading food products. Furthermore, we demonstrate an electrochemical amine sensor based on (trifluoroacetyl)azobenzene dye added in carbon nanotube–Nafion® composites. The electrochemical sensor exploits the reaction between the dye and amines to detect amines in electrolytes, while the carbon nanotubes provide large surface for adsorption and also provide a percolating electrical network for allowing efficient charge transfer at the electrode electrolyte interface.

High performance p-type thin-film transistor (p-TFT) was realized by a simple process of reactive sputtering from a tin (Sn) target under oxygen ambient, where remarkably high field-effect mobility (μ FE ) of 7.6 cm2/Vs, 140 mV/dec subthreshold slope, and 3 × 104 on-current/off-current were measured. In sharp contrast, the SnO formed by direct sputtering from a SnO target showed much degraded μ FE , because of the limited low process temperature of SnO and sputtering damage. From the first principle quantum-mechanical calculation, the high hole μ FE of SnO p-TFT is due to its considerably unique merit of the small effective mass and single hole band without the heavy hole band. The high performance p-TFTs are the enabling technology for future ultra-low-power complementary-logic circuits on display and three-dimensional brain-mimicking integrated circuits.

Hydrogenated titanium dioxide has attracted intensive research interests in pollutant removal applications due to its high photocatalytic activity. Herein, we demonstrate hydrogenated TiO2 nanofibers (H:TiO2 NFs) with a core-shell structure prepared by the hydrothermal synthesis and subsequent heat treatment in hydrogen flow. H:TiO2 NFs has excellent solar light absorption and photogenerated charge formation behavior as confirmed by optical absorbance, photo-Kelvin force probe microscopy and photoinduced charge carrier dynamics analyses. Photodegradation of various organic dyes such as methyl orange, rhodamine 6G and brilliant green is shown to take place with significantly higher rates on our novel catalyst than on pristine TiO2 nanofibers and commercial nanoparticle based photocatalytic materials, which is attributed to surface defects (oxygen vacancy and Ti3+ interstitial defect) on the hydrogen treated surface. We propose three properties/mechanisms responsible for the enhanced photocatalytic activity, which are: (1) improved absorbance allowing for increased exciton generation, (2) highly crystalline anatase TiO2 that promotes fast charge transport rate, and (3) decreased charge recombination caused by the nanoscopic Schottky junctions at the interface of pristine core and hydrogenated shell thus promoting long-life surface charges. The developed H:TiO2 NFs can be helpful for future high performance photocatalysts in environmental applications.

Bulk heterojunction (BHJ) organic photovoltaic (OPV) promise low cost solar energy and have caused an explosive increase in investigations during the last decade. Control over the 3D morphology of BHJ blend films in various length scales is one of the pillars accounting for the significant advance of OPV performance recently. In this contribution, we focus on the strategy of incorporating an additive into BHJ blend films as a morphological control agent, i.e., ternary blend system. This strategy has shown to be effective in tailoring the morphology of BHJ through different inter- and intra-molecular interactions. We systematically review the morphological observations and associated mechanisms with respect to various kinds of additives, i.e., polymers, small molecules and inorganic nanoparticles. We organize the effects of morphological control (compatibilization, stabilization, etc.) and provide general guidelines for rational molecular design for additives toward high efficiency and high stability organic solar cells.

A series of isoindigo-based low-band-gap copolymers (PnTI) containing an extended thiophene unit in the donor segment of the polymer were synthesized. The results show that the extended thiophene unit with centrosymmetric conformation simultaneously broadens the polymer absorption and enhances the crystallinity and, thus, hole mobility. Consequently, with additional improved solubility, the polymer P6TI exhibits the highest PCE of 7.25% (and a high Jsc of 16.24 mA cm−2) among isoindigo-based low-band-gap copolymers. This work demonstrates that by simply adjusting the donor segment and with relatively simple synthetic schemes, a material for high-performance and scalable PSCs will become available.

We have demonstrated BiFeO3 (BFO) as a potential bilayer electrolyte for 650 °C low temperature solid oxide fuel cell application. The stoichiometric perovskite BFO is synthesized by wet chemistry, calcined at 500 °C and sintered at 850 °C. The crystalline structure is confirmed by X-ray diffraction spectroscopy, the atomic ratios (Bi : Fe) of 1.02 and 1.00 are determined by X-ray energy dispersive spectroscopy and inductively coupled plasma-mass spectroscopy, respectively. The X-ray photoelectron spectroscopy analysis indicates the presence of oxygen vacancies which can partially reduce Fe3+ and result in relatively high dielectric constant (6252 at 100 kHz) and ionic conductivity (>10−2 S cm−1 at 650 °C). The BFO is coated with an yttria-stabilized zirconia (YSZ) protective layer to avoid hydrogen reduction of BFO. This bilayer electrolyte exhibits a 1.6 times increase in maximum power density as compared with pure YSZ when a Ni–YSZ anode and lanthanum strontium cobalt ferrite (LSCF) cathode are used in the fuel cell at 650 °C.

Optic neuropathy is one of the leading causes of irreversible blindness caused by retinal ganglion cell (RGC) degeneration. The development of induced pluripotent stem cell (iPSC)-based therapy opens a therapeutic window for RGC degeneration, and tissue engineering may further promote the efficiency of differentiation process of iPSCs. The present study was designed to evaluate the effects of a novel biomimetic polybenzyl glutamate (PBG) scaffold on culturing iPSC-derived RGC progenitors. The iPSC-derived neural spheres cultured on PBG scaffold increased the differentiated retinal neurons and promoted the neurite outgrowth in the RGC progenitor layer. Additionally, iPSCs cultured on PBG scaffold formed the organoid-like structures compared to that of iPSCs cultured on cover glass within the same culture period. With RNA-seq, we found that cells of the PBG group were differentiated toward retinal lineage and may be related to the glutamate signaling pathway. Further ontological analysis and the gene network analysis showed that the differentially expressed genes between cells of the PBG group and the control group were mainly associated with neuronal differentiation, neuronal maturation, and more specifically, retinal differentiation and maturation. The novel electrospinning PBG scaffold is beneficial for culturing iPSC-derived RGC progenitors as well as retinal organoids. Cells cultured on PBG scaffold differentiate effectively and shorten the process of RGC differentiation compared to that of cells cultured on coverslip. The new culture system may be helpful in future disease modeling, pharmacological screening, autologous transplantation, as well as narrowing the gap to clinical application.

We report the development of low moisture permeation and transparent dense polyacrylate/silica nanocomposite material that can exhibit both superhydrophobic and oleophobic (omniphobic) properties. The material was prepared by a three-step process. The first step involved the preparation of UV polymerizable solventless hybrid resin and the fabrication of nanocomposite. The hybrid resin consisted of a mixture of acrylate monomer, initiator, and acrylate-modified different size silica nanoparticles. The second step was to roughen the surface of the nanocomposite with unique nanotexture by oxygen plasma. In the third step, we applied a low surface tension fluoro monolayer on the treated surface. The nanocomposite exhibits desired superhydrophobicity and oleophobicity with a water contact angle of 158.2° and n-1-octadecene contact angle of 128.5°, respectively; low moisture permeation of 1.44 g·mm/m(2)·day; and good transparency (greater than 82% at 450-800 nm for ~60 μm film). The material has potential applications in optoelectronic encapsulation, self-cleaning coating, etc.

Controlling the nonlamellar and bicontinuous nanostructures through changing volume fraction is a well-developed technique for coil–coil block copolymer, but it is not always effective for rod–coil block copolymer due to strong rod–rod interaction. Versatile self-assembly morphology of rod–coil copolymer can be achieved by simultaneously adjusting the rod–rod interaction, rod–coil interaction, and conformational asymmetry. This approach has been investigated by using poly(3-alkylthiophene)-b-poly(methyl methacrylate) as a model. By altering the alkyl side chain of polythiophene from linear hexyl to longer dodecyl and to branch 2-ethylhexyl, both rod–coil and rod–rod interaction are decreased with increasing spatial occupation of alkyl side chain which have been quantitatively determined for this type of rod–coil copolymer. With tunable conformational asymmetry, competition between rod–rod and rod–coil interactions, and crystallization-driven force, the presence of versatile morphology, i.e., lamellar and ...

Blending with a homopolymer is an effective approach to tailor the microphase-separated morphology of block copolymers. It has been established for the blends of coil–coil diblock copolymer (A-b-B) with the corresponding homopolymer (h-A) that h-A can be solubilized uniformly into A mcirodomain to induce structure transformation when its molecular weight is smaller than that of the A block, i.e., α = Mh-A/Mb-A < 1. Here we examine if the microdomain structure of a rod–coil diblock copolymer, poly(2,5-diethylhexyloxy-1,4-phenylenevinylene)-block-poly(methyl methacrylate) (DEH-PPV-b-PMMA), may be systematically tuned by blending with PMMA hompolymer (h-PMMA). The blends over the major composition window were found to undergo macrophase separation even when the value of α was as low as 0.3. The phase separation led to the formation of a copolymer-rich phase and a homopolymer-rich phase, in which microphase separation occurred, yielding a well-ordered lamellar structure and a sponge structure, respectively. T...

Colloid TiO(2) nanorods are used for solution-processable poly(3-hexyl thiophene): TiO(2) hybrid solar cell. The nanorods were covered by insulating ligand of oleic acid (OA) after sol-gel synthesis. Three more conducting pyridine type ligands: pyridine, 2,6-lutidine (Lut) and 4-tert-butylpyridine (tBP) were investigated respectively to replace OA. The power conversion efficiency (PCE) of the solar cell was increased because the electronic mobility of pyridine-type ligand-modified TiO(2) is higher than that of TiO(2)-OA. The enhancement of PCE is in the descending order of Lut > pyridine > tBP because of the effective replacement of OA by Lut. The PCE of solar cell can be further enhanced by ligand exchange of pyridine type ligand with conjugating molecule of 2-cyano-3-(5-(7-(thiophen-2-yl)-benzothiadiazol-4-yl) thiophen-2-yl) acrylic acid (W4) on TiO(2) nanorods because W4 has aligned bandgap with P3HT and TiO(2) to facilitate charge separation and transport. The electronic mobility of two-stage ligand exchanged TiO(2) is improved furthermore except Lut, because it adheres well and difficult to be replaced by W4. The amount of W4 on TiO(2)-tBP is 3 times more than that of TiO(2)-Lut (0.20 mol % vs. 0.06 mol %). Thus, the increased extent of PCE of solar cell is in the decreasing order of tBP > pyridine > Lut. The TiO(2)-tBP-W4 device has the best performance with 1.4 and 2.6 times more than TiO(2)-pyridine-W4 and TiO(2)-Lut-W4 devices, respectively. The pKa of the pyridine derivatives plays the major role to determine the ease of ligand exchange on TiO(2) which is the key factor mandating the PCE of P3HT:TiO(2) hybrid solar cell. The results of this study provide new insights of the significance of acid-base reaction on the TiO(2) surface for TiO(2)-based solar cells. The obtained knowledge can be extended to other hybrid solar cell systems.

Varying composition of π-donor/acceptor moieties has been considered as an effective strategy for fine-tuning of the electronic properties of D-A conjugated copolymers. In this study, the change of optoelectronic properties with the change of donor/acceptor ratios is investigated on the basis of first-principles density functional calculations. Copolymers containing moieties of similar π-electron donating and/or accepting capabilities, e.g., thiophene (T)-methoxythiophene (OT), exhibit a linear dependence of electronic properties (especially, HOMO/LUMO, band gap, and bandwidth) on the D/A content. In contrast, for strong D/A contrast systems, e.g., thiophene (T)-thienopyrazine (TP), the electronic properties vary nonlinearly with D/A compositions. However, when the block size of one parent monomer in a strong D/A contrast system is fixed, the variation of electronic properties shows a remarkable linear correlation against D/A compositions. We found that the deviation of electronic properties from a linear composition dependence is dominated by the strength of orbital interactions between D and A. Weak orbital interactions between D and A moieties tend to lead to a nonlinear composition dependence. Our results provide useful insights for band gap tuning through the adjustment of D/A compositions in D-A conjugated copolymers.

The interface property has been one of the critical issues in developing hybrid polymer/metal oxide solar cells. We synthesize a conjugated oligomer, an amine- and bromine-terminated 3-hexyl thiophene (O3HT-(Br)NH 2 ), to modify the ZnO-nanorod (ZnO-NR) surface in hybrid polymer/ZnO-NR photovoltaic cells. This oligomer is of the same repeat unit structure as and ∼1/12 the contour length of that of the light-harvesting polymer. In addition to passivate the NR surface, the presence of this conjugated oligomer enhances the electron mobility, and drives larger hole density toward the anodic surface for collection. The improved charge transport property of the hybrid is presumably a result of modulating the nanomorphology of the bi-carrier transport network induced by the conjugated oligomer. As a result, there is a large enhancement in photocurrent and photovoltage leading to an improved device performance of ∼35%.

High mobility channel thin-film-transistor (TFT) is crucial for both display and future generation integrated circuit. We report a new metal-oxide TFT that has an ultra-thin 4.5 nm SnO2 thickness for both active channel and source-drain regions, very high 147 cm2/Vs field-effect mobility, high ION/IOFF of 2.3 × 107, small 110 mV/dec sub-threshold slope and a low VD of 2.5 V for low power operation. This mobility is already better than chemical-vapor-deposition grown multi-layers MoS2 TFT. From first principle quantum-mechanical calculation, the high mobility TFT is due to strongly overlapped orbitals.

We offer a novel approach to improve the performance of P3HT/TiO2 hybrid photovoltaic devices by incorporating either hydroxyl- or amino-functionalized silica nanodots (SND–OH or SND–NH2) into the hole transport layer of the PEDOT:PSS. The SNDs serve as screens between conducting polymer and ionomer PSS to improve the phase separation and charge transport of the PEDOT:PSS hole transport layer. The power conversion efficiency (PCE) was thus improved by 1.45 and 2.61 fold for devices fabricated with PEDOT:PSS containing 1 wt % of SND–OH (SND–OH device) and 1 wt % of SND–NH2 (SND–NH2 device), respectively, when compared with the devices fabricated by neat PEDOT:PSS. The increase in PCE arises from an increase in short circuit currents, which are affected by the phase separation of PEDOT:PSS with possessing incorporated SNDs. The low surface potential of hydroxyl-functionalized SNDs (SND–OH) is easily aggregated in the PEDOT:PSS solution and forms large-sized phase separation in the PEDOT:PSS film. The aggreg...

A series of all-conjugated diblock copolythiophenes of poly(3-hexylthiophene)-b-poly(3-thiophene hexylacetate) (P3HT-b-P3THA) were synthesized via modified sequential Grignard metathesis polymerization. The living P3HT was formed first, then reacting with the monomer of P3THA. By using 2-bromo-3-hexyloxycarbonylmethylene-5-iodothiophene instead of dibromo monomer in metal exchange reaction and by controlling the polymerization temperature relatively low at 16–20 °C, the reaction between carboxylate group and Grignard reagent can be minimized and the polymerization can be controlled; low PDI ( 95%), and well-controlled block ratios of block copolymer were obtained. The introduction of carboxylate group in the side chain of one of the monomers, and controlling the side-chain length difference by only three atoms between two monomers, there are profound effects on the optical and electrochemical properties and morphologies of the block copolymers. The electron-withdrawing carboxy...

The charge recombination rate in poly(3-hexyl thiophene)/TiO(2) nanorod solar cells is demonstrated to correlate to the morphology of the bulk heterojunction (BHJ) and the interfacial properties between poly(3-hexyl thiophene) (P3HT) and TiO(2). The recombination resistance is obtained in P3HT/TiO(2) nanorod devices by impedance spectroscopy. Surface morphology and phase separation of the bulk heterojunction are characterized by atomic force microscopy (AFM). The surface charge of bulk heterojunction is investigated by Kelvin probe force microscopy (KPFM). Lower charge recombination rate and lifetime have been observed for the charge carriers in appropriate heterostructures of hybrid P3HT/TiO(2) nanorod processed via high boiling point solvent and made of high molecular weight P3HT. Additionally, through surface modification on TiO(2) nan,orod, decreased recombination rate and longer charge carrier lifetime are obtained owing to creation of a barrier between the donor phases (P3HT) and the acceptor phases (TiO(2)). The effect of the film morphology of hybrid and interfacial properties on charge carrier recombination finally leads to different outcome of photovoltaic I-V characteristics. The BHJ fabricated from dye-modified TiO(2) blended with P3HT exhibits 2.6 times increase in power conversion efficiency due to the decrease of recombination rate by almost 2 orders of magnitude as compared with the BHJ made with unmodified TiO(2). In addition, the interface heterostructure, charge lifetime, and device efficiency of P3HT/TiO(2) nanorod solar cells are correlated.

The heterojunction of poly(3-hexylthiophene) (P3HT) and TiO2 in hybrid solar cells is systematically engineered with four cyanoacrylic acid-containing conjugated molecules with various lowest unoccupied molecular orbital (LUMO) levels, WL-1 to WL-4, which are prepared by the formylation of thiophene derivatives in a Vilsmeier–Haack reaction, followed by treatment with cyanoacetic acid. The optical characteristics, redox properties, and intrinsic dipole moments of these interfacial modifiers (IMs) are examined using UV-vis spectrophotometry, cyclic voltammetry, and density functional theory calculations. Using cyanoacrylic acid as a terminal anchoring group in IMs increases the electron affinity in regions close to the titania surface and forms a molecular dipole that is orientated away from the TiO2 surface, enabling both open-circuit voltage (VOC) and short-circuit current density to be increased simultaneously. Photovoltaic measurements demonstrate that VOC increases with the dipole moment of IMs along the molecular backbone. Moreover, the external quantum efficiency (EQE) spectra display a bimodal distribution, revealing that both IMs and P3HT contribute to the photocurrent. The EQE at 570 nm is identified as characteristic of P3HT. More importantly, the LUMO of the IMs decisively determines the dissociation efficiency of P3HT excitons. The device based on P3HT/WL-4/TiO2 exhibits the highest power conversion efficiency of 2.87%.

Low-temperature thermal chemical vapor deposition (thermal CVD) synthesis of multi-walled carbon nanotubes (MWCNTs) was studied using a large variety of different precursor compounds. Cyclopentene oxide, tetrahydrofuran, methanol, and xylene: methanol mixture as oxygen containing heteroatomic precursors, while xylene and acetylene as conventional hydrocarbon feedstocks were applied in the experiments. The catalytic activity of Co, Fe, Ni, and their bi-as well as tri-metallic combinations were tested for the reactions. Low-temperature CNT growth occurred at 400 degrees C when using bi-metallic Co-Fe and tri-metallic Ni-Co-Fe catalyst (on alumina) and methanol or acetylene as precursors. In the case of monometallic catalyst nanoparticles, only Co (both on alumina and on silica) was found to be active in the low temperature growth (below 500 degrees C) from oxygenates such as cyclopentene oxide and methanol. The structure and composition of the achieved MWCNTs products were studied by scanning and transmission electron microscopy (SEM and TEM) as well as by Raman and X-ray photoelectron spectroscopy (XPS) and by X-ray diffraction (XRD). The successful MWCNT growth below 500 degrees C is promising from the point of view of integrating MWCNT materials into existing IC fabrication technologies. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

In this article, we report the syntheses and charac- terizations of a series of novel block polyelectrolytes, poly(sty- rene-block-sulfonated hydroxystyrene) (PS-b-sPHS), containing pendant sulfonic acid groups attached to the backbone via propyl spacers in the sPHS domain. PS-b-sPHS with various compositions were synthesized via anionic polymerization and the following analogous chemistry to achieve accurate control of molecular weight (Mw), narrow polydispersity and high degree of sulfonation. Proton exchange membranes (PEMs) were prepared from PS-b-sPHS with sulfonic acids in either po- tassium salts or tetra-alkylammonium salts via solvent casting and following treatments. Some unique morphologies, such as hallow channels and lamellar arrangement of strings of beads, were observed as a consequence of equilibrium between microphase separation and columbic interactions between pol- yelectrolytes. The transportation properties were found to closely relate to the morphologies of the PEMs. The combina- tion of microphase separation of block polyelectrolytes and freedom of movement of pendent alkylsulfonic acids was dem- onstrated to effectively enhance the proton transport and sup- press the methanol crossover for the PEMs, leading to the selectivity higher than Nafion 117 by five times at most. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2325-2338, 2011

TiO2 nanofibers decorated with Pt and Pd nanoparticles have been synthesized and studied in various photocatalytic processes. Excellent photocatalytic behavior in the decomposition of organic dyes in water, degradation of organic stains on the surface of flexible freestanding cellulose/catalyst composite films and in generation of hydrogen from ethanol using both suspended and immobilized catalysts are demonstrated. The performance of the nanofiber-based TiO2 materials is competitive with—and in some cases outperforms—their conventional nanoparticle-based counterparts. In all cases, Pd-decorated TiO2 nanoparticles and nanofibers proved to be more efficient than their Pt-based counterparts, which could be explained on the basis of the formation of nano-sized Schottky interfaces at the contacts between TiO2 and metal nanoparticles. The feasibility of forming cellulose/catalyst composites provides a novel way of utilizing photocatalyst materials in large-area coatings and freestanding films.

In this paper, we present two different types of polymer/metal oxide nanocrystals hybrid photovoltaics. One is the poly(3-hexylthiophene) (P3HT)/TiO2 nanorods hybrid bulk heterojunction (BHJ) solar cell and the other is a nanostructured ZnO/P3HT hybrid solar cell. In a BHJ hybrid solar cell, the dispersed semiconducting nanocrystals lead to an increased interface area between polymer and nanocrystals, which can assist charge separation for photogenerated carriers, but at the expense of poorly formed conducting pathways for electron transport. In contrast, a nanostructured hybrid solar cell usually consists of rigidly connected nanocrystals, which can provide direct pathways for electron transport, but the interface area between polymer and nanocrystals is limited. We have demonstrated that through interface modification with effective molecules, the photovoltaic performance in both device structures can be largely improved by enhancing charge separation and suppressing interface recombination rate in the polymer/inorganic hybrids.

Hyperbranched polymers (HBPs) formed by the self-condensing vinyl polymerization (SCVP) or self-condensing ring-opening polymerization (SCROP) of monomer AB activated by stimuli with various reacti...

A novel photoluminescence electron beam resist made from the blend of poly(3-hexylthiophene) (P3HT) and poly(methyl methacrylate) (PMMA) has been successfully developed in this study. In order to optimize the resolution of the electron beam resist, the variations of nanophase separated morphology produced by differing blending ratios were examined carefully. Concave P3HT-rich island-like domains were observed in the thin film of the resist. The size of concave island-like domains decreased from 350 to 100 nm when decreasing the blending ratio of P3HT/PMMA from 1:5 to 1:50 or lower, concurrently accompanied by significant changes in optical properties and morphological behaviors. The lambda(max) of the film absorption is blue-shifted from 520 to 470 nm, and its lambda(max) of photoluminescence (PL) is also shifted from 660 to 550 nm. The radiative lifetime is shorter while the luminescence efficiency is higher when the P3HT/PMMA ratio decreases. These results are attributed to the quantum confinement effect of single P3HT chain isolated in PMMA matrix, which effectively suppresses the energy transfer between the well-separated polymer chains of P3HT. The factors affecting the resolution of the P3HT/PMMA electron beam resists were systematically investigated, including blending ratios and molecular weight. The photoluminescence resist with the best resolution was fabricated by using a molecular weight of 13 500 Da of P3HT and a blending ratio of 1:1000. Furthermore, high-resolution patterns can be obtained on both flat silicon wafers and rough substrates made from 20 nm Au nanoparticles self-assembled on APTMS (3-aminopropyltrimethoxysilane)-coated silicon wafers. Our newly developed electron beam resist provides a simple and convenient approach for the fabrication of nanoscale photoluminescent periodic arrays, which can underpin many optoelectronic applications awaiting future exploration.

Here we report syntheses, photophysical properties, and morphologies of a series of coil-rod-coil ABA triblock copolymers containing highly regioregular poly(3-hexylthio- phene) (P3HT) as the central rod block. A new methodology, based on the coupling reaction between living polymeric anions (polystyrene, polyisoprene, and poly(methyl methacrylate)) and aldehyde terminated P3HT, was successfully developed to syn- thesize the triblock copolymers with low polydispersities. This coupling reaction was effective for building blocks with a variety of molecular weights; therefore, a good variation in composi- tions of the triblock copolymers could be feasibly achieved. The non-P3HT coil segments and the solvents were found to exhibit noticeable effects on morphologies of the spin-coated thin films. Attachment of the coil segments to P3HT did not change the optical absorption of the P3HT segment as the block copoly- mers were dissolved in solution regardless the chemical struc- ture and the molecular weight of the coil segment. Interestingly, different UV-vis absorption behaviors were observed for the spin-coated thin films of the block copolymers, which closely related to their morphologies. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3311-3322, 2010

In this study, we developed a novel sensing material fabricated using a poly(3-hexylthiophene) (P3HT)/poly(methyl methacrylate) (PMMA) blend fiber on a glass substrate. The sensing materials can easily be used for sensing toluene vapor detected from extinction spectral changes. The extinction spectra variation is noted from the absorption of volatile organic compounds in a highly specific surface area of fibrous coating. An electrospinning technique is applied to generate a nonwoven structure and uniaxial orientation by fibrous coating. The response of the uniaxially orientated fibrous film is even improved at several toluene vapor concentrations. The best detection limit of this well-aligned fibrous film is up to 200 ppm for toluene vapor.

In this study, we demonstrated a simple method of fabricating a high-performance surface-enhanced Raman scattering (SERS) substrate. Monodispersive SiO2 colloidal spheres were self-assembled on a silicon wafer, and then a silver layer was coated on it to obtain a Ag/SiO2 SERS substrate. The Ag/SiO2 SERS substrates were used to detect three kinds of plasticizer with different concentrations, namely, including bis(2-ethylhexyl)phthalate (DEHP), benzyl butyl phthalate (BBP), and dibutyl phthalate (DBP). The enhancement of Raman scattering intensity caused by surface plasmon resonance can be observed using the Ag/SiO2 SERS substrates. The Ag/SiO2 SERS substrate with a 150-nm-thick silver layer can detect plasticizers, and it satisfies the detection limit of plasticizers at 100 ppm. The developed highly sensitive Ag/SiO2 SERS substrates show a potential for the design and fabrication of functional sensors to identify the harmful plasticizers that plastic products release in daily life.

The redox characteristic of methylene blue in polyacrylate film has been investigated for applications in monitoring time and temperature. This monitoring capability is based on a color change from colorless to blue under exposure to air. The oxidation process is controlled by the air diffusion which is affected by the chemical structure of the polyacrylate. The activation energy of diffusion, which was calculated by Arrhenius equation, goes up with increasing the rigid structure of the polyacrylate. The results correlate well with the glass transition temperature of different polyacrylates. The unique feature of the methylene blue to change color under oxidation, can be used for the fabrication of low cost visual sensors for monitoring time and temperature.

Hyperbranched polymers obtained by the polymerization of monomers A 2 and B 3 in the presence of end-capping molecules AR with a first shell substitution effect, FSSE, on the monomer B 3 were investigated by a kinetic model. The profiles of the average degree of polymerization, degree of branching, and critical conversion under various compositions were calculated by a generating function method. It was found that, if groups B in excess of A, the curves of critical conversion A of 100%, at which a gelation occurs, based on the initial compositions with substitution effect differ from that with equal reactivity of the groups B. The weight-average degree of polymerization, DP ¯ w , and degree of branching, DB, increase with increasing of the reactivity ratio of B. On the other hand, when the initial groups B are lower than A, there is no apparent difference of the curves of critical conversion B of 100% between the polymerizations with and without FSSE. At high conversion of B, 99%, for example, the DP ¯ w and DB decrease with increasing of the end-capping molecules AR, but the DP ¯ w and DB are less influenced by the FSSE.

A series of low band gap, highly soluble alternating conjugated copoly- mers, comprised of 11,11,12,12-tetrahexylindenofluorene and thiophene derivatives (P1-P4), were synthesized via Pd-catalyzed Suzuki coupling reaction with very good yields. Described here are the synthesis, thermal, optical, and electrochemical properties of these new copolymers as potential new active materials for electronic and optoelectronic device applications. P1 and P2 have electron donating non-p- substituents with ethylenedioxy and propylenedioxy bridging the 3,3 positions of the cyclopentadithiophene groups; whereas P3 and P4 have electron withdrawing p- substituents (carbonyl and pyrazine groups on P3 and P4, respectively). For the main absorptions in UV-vis spectrum, P1 and P2 displayed more red absorptions in comparison with P3 and P4. Nevertheless, much suppressed quantum yields are exhibited by P3 and P4. The behaviors of P3 can be attributed to the significant charge transfer interactions between the p-substituents and the conjugated polymer backbone that leads to a less allowed optical transition between the ground and the lowest excited state. For P4, the weak fluoresence might associate with energy trans- fer from indenofluorene to the low band gap thiophene-pyrazinethiophene-thiophene (T-PT-T) unit. In comparison with the corresponding polymers containing fluorene instead of indenofluorene, the use of indenofluorene exhibited mixed effects on the optical properties and improved solubility. V C 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5044-5056, 2009

We conducted an extensive study on poly(3-hexylthiophene) (P3HT) in combination with titanium dioxide (TiO 2 ) nanorods hybrid material for polymer solar cell applications. The device performance critically depends on the morphology of the hybrid film that will be determined by the molecular weight of P3HT, the solvent type, the hybrid compositions, the surface ligand on the TiO 2 nanorods, film thickness, process conditions, and so on. The current–voltage characteristic of the device fabricated in air has shown a power conversion efficiency of 0.83% under air mass (AM) 1.5 illumination using high molecular weight (65,000 D) P3HT, high boiling point solvent trichlorobenzene, and pyridine-modified TiO 2 nanorods with a film thickness of about 100 nm. The Kelvin probe force microscopy (KPFM) study of hybrid films shows large-scale phase separation with domain size greater than 10 nm, which may be the main factor limiting device performance.

Well-defined poly(methyl methacrylate) (Mn ¼ 3630 g mol � 1 , PDI ¼ 1.06) with a primary benzylic bromide prepared using anionic polymerization was suc- cessfully transformed into diverse end-functionalities (x- carboxyl, x-hydroxy, x-methyl-vinyl, x-trimethylsilane, and x-glycidyl-ether) via ''click'' reaction. The bromine end-terminated poly(methyl methacrylate) was first sub- stituted by an azide function and sequentially was reacted with various functional alkynes (propiolic acid, propargyl alcohol, 2-methyl-1-buten-3-yne, propargyl tri- methylsilane, and propargyl glycidylether). In all the cases, 1 H-NMR, 13 C NMR, FT-IR, and GPC measure- ments show qualitative and quantitative transformation of the chain-end poly(methyl methacrylate) into the desired functionalities with high conversion (above 99%). V C 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 1571-1580, 2009

Article history: Received 23 June 2008 Accepted 2 October 2008 Available online 9O ctober 2008 Two classes of phosphonic acid-bearing organic molecules, 2-oligothiophene phosphonic acid and ω- (2-thienyl)alkyl phosphonic acid were adopted as interface modifiers (IMs) of the TiO2 surface, to increase its compatibility with poly(3-hexylthiophene) (P3HT). The self-assembled monolayers of these molecules on titania surface were characterized by making contact angle measurements and X-ray photoelectron spectroscopy (XPS). Atomic force microscopic (AFM) images revealed that the adsorption of IMs effectively smoothes the TiO2 surface. Both photoluminescence (PL) spectroscopy and PL lifetime measurements were made to investigate the photoinduced properties of the TiO2/IM/P3HT layered- junction. The PL quenching efficiency increased with the number of thiophene rings and as the alkyl chain-length in IMs decreased. Meanwhile, the decline in the PL lifetime followed a similar trend as the PL quenching efficiency. Additionally, the power conversion efficiency (PCE) of the ITO/TiO2/IM/P3HT/Au devices was examined by measuring their photocurrent density-applied voltage ( J -V )c urves. The experimental results indicated that the short-circuit current density ( J SC) increased with the number of thiophene units and as the hydrocarbon chain-length in IMs decreased. However, the open-circuit voltage (V OC) of the devices slightly fell as the energy level of the highest occupied molecular orbital (HOMO) of IM decreased. The PCE of the device with 2-terthiophene phosphonic acid was 2.5 times that of the device with 10-(2-thienyl)decyl phosphonic acid.