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Convenient, rapid, and accurate detection of chemical and biomolecules would be a great benefit to medical, pharmaceutical, and environmental sciences. Many chemical and biosensors based on metal nanoparticles (NPs) have been developed. However, as a result of the inconvenience and complexity of most of the current preparation techniques, surface plasmon-based test papers are not as common as, for example, litmus paper, which finds daily use. In this paper, we propose a convenient and practical technique, based on the photothermal effect, to fabricate the plasmonic test paper. This technique is superior to other reported methods for its rapid fabrication time (a few seconds), large-area throughput, selectivity in the positioning of the NPs, and the capability of preparing NP arrays in high density on various paper substrates. In addition to their low cost, portability, flexibility, and biodegradability, plasmonic test paper can be burned after detecting contagious biomolecules, making them safe and eco-friendly.

The aim of this study is to quantitatively investigate the effect of different fullerene type (PC60BM and PC70BM) on various morphological structures and power conversion efficiency (PCE) in the bulk heterojunction (BHJ) P3HT/PCxBM solar cells. The solar cells are fabricated by spin coating without thermal annealing. The quantitative investigations of three-dimensional self- organized nanostructures are performed by using combined grazing- incidence small- and wide-angle X-ray scattering technique (GISAXS/GIWAXS). Two types of nanostructures are observed due to the phase separation in the BHJ films during the processing. They include (1) intercalated PCxBM molecules around boundary of P3HT crystalline domain and within amorphous domain and (2) aggregated PCxBM clusters in PCxBM domains. The lamellar spacing of P3HT crystalline domains in P3HT/PC70BM is larger than that in P3HT/PC60BM. This result indicates more interfacial areas are generated between PC70BM and P3HT at the molecular scale for more efficient charge separation. On the other hand, the size, volume fraction, partial attachment, and spatial distribution of PC60BM clusters are larger than that of PC70BM clusters, which reveals more efficient electron transport in P3HT/PC60BM. We deduce the correlation between nanostructures and PCE (3.25% and 2.64%, respectively, for P3HT/ PC70BM and P3HT/PC60BM). The structure of fullerene intercalated with P3HT rather than the size of fullerene cluster plays a major role in the PCE performance of BHJ solar cell without thermal annealing.

We have developed multi-walled carbon nanotube/liquid crystalline epoxy composites and studied the effects of incorporation carbon nanotubes (CNTs) on the morphology, thermal and mechanical properties of the composites. The CNTs are functionalized by liquid crystalline (LC) 4,4′-bis(2,3-epoxypropoxy) biphenyl (BP) epoxy resin for the ease of dispersion and the formation of long range ordered structure. The epoxy functionalized CNT (ef-CNT) were dispersed in the LC BP epoxy resin that can be thermal cured with an equivalent of 4,4′-diamino-diphenylsulfone to form composite. The curing process was monitored by polarized optical microscopy. The results indicate the LC resin was aligned along the CNTs to form fiber with dendritic structure initially then further on to obtain micro-sized spherical crystalline along with fibrous crystalline. With homogeneous dispersion and strong interaction between nanotubes and matrix, the composite containing 2.00 wt.% ef-CNT exhibits excellent thermal and mechanical properties. When the amount of ef-CNT exceeds 2.00 wt.%, vitrification stage of curing is fast reached, which lowers the degree of conversion. As compared with the neat resin, the composite containing 2.00 wt.% ef-CNT increases the glass transition temperature by 70.0 °C, the decomposition temperature by 13.8 °C, the storage modulus by 40.9%, and the microhardness by 63.3%.

Both the performance and stability are the two major tasks for scientists to tackle in polymer solar cells. We introduce 3-hydroxyflavone (3-HF), a free-radical scavenging agent, as an additive in poly(3-hexythiophene):(6,6)-phenyl C61 butyric acid methyl ester (P3HT:PCBM) blend forming new photoactive material, which is used as an active layer in inverted solar cell devices. It was found that the addition of an adequate amount of 3-HF enhances the photocurrent, which is due to the improved carrier mobility. A power conversion efficiency (PCE) of the device has improved from 2.57% to 3.05%. In addition, 3-HF can further stabilize the inverted solar cell performance with a 85% retaining of its original PCE over a month in ambient condition as compared to the additive-free device of a value of 57%. Thus, incorporating 3-HF as an additive is an effective and simple method to approach the goal of high PCE while maintaining stable ambient operation.

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%.

We study the effects of the morphology of gold film on the unusual modulation of surface plasmon resonance (SPR) and surface-enhanced Raman scattering (SERS) using the periodic nanostructures of P3...

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

The selection of carrier transporting layer in polymer solar cells is an important issue because the nature and direction of carrier transport can be manipulated by inserting different functional layers in the device structure. In this work, we report a very efficient inverted polymer solar cell (PSC) system based on regioregular poly(3-hexylthiophene) and a n-type acceptor, bis-indene[C60]. With a pair of metal oxides and the insertion of TiO2 nanorods electron collecting layer between the ZnO thin film and the active layer, the device efficiency can be greatly improved. The contact area between the active layer and the electron collecting layer, as well as the thickness of active layer, can be increased with the incorporation of TiO2 nanorods. As a result, photocurrent can be enhanced due to more absorption of light and more charge separation interface. In addition, the larger contact area and the crystalline TiO2 nanorods provide a more efficient transporting route for the carriers to the cathode. The most efficient device demonstrated shows a high power conversion efficiency of 5.6% with the inverted structure.

The external quantum efficiencies of P3HT:PCBM blend solar cells decrease significantly when they are bent or illuminated at large incident angles because of (i) optical anisotropy of the P3HT:PCBM films—primarily because a mismatch between the direction of the electric field of the incoming light and the orientation of the P3HT:PCBM blend nanocrystallites results in a significant reduction in the amount of TM-polarized light absorbed and (ii) interfacial reflection of multilayer structures – primarily because the outermost air–flexible substrate interface exhibits a distinct refractive index difference – at large incident angles. Textured moth-eye structures fabricated by nanoimprint lithography on the flexible substrates of organic solar cells reduce the degree of interfacial reflection at high incident angles; they should allow more TE-polarized light to absorb in the P3HT:PCBM films (active layers) of the organic solar cells.

We report the synthesis of N-doped TiO(2) nanofibers and high photocatalytic efficiency in generating hydrogen from ethanol-water mixtures under UV-A and UV-B irradiation. Titanate nanofibers synthesized by hydrothermal method are annealed in air and/or ammonia to achieve N-doped anatase fibers. Depending on the synthesis route, either interstitial N atoms or new N-Ti bonds appear in the lattice, resulting in slight lattice expansion as shown by XPS and HR-TEM analysis, respectively. These nanofibers were then used as support for Pd and Pt nanoparticles deposited with wet impregnation followed by calcination and reduction. In the hydrogen generation tests, the N-doped samples were clearly outperforming their undoped counterparts, showing remarkable efficiency not only under UV-B but also with UV-A illumination. When 100 mg of catalyst (N-doped TiO(2) nanofiber decorated with Pt nanoparticles) was applied to 1 L of water-ethanol mixture, the H(2) evolution rates were as high as 700 μmol/h (UV-A) and 2250 μmol/h (UV-B) corresponding to photo energy conversion percentages of ∼3.6 and ∼12.3%, respectively.

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.

A new class of nanocomposite has been fabricated from liquid crystalline (LC) epoxy resin of 4,4′-bis(2,3-epoxypropoxy) biphenyl (BP), 4,4′-diamino-diphenyl sulfone (DDS), and multiwalled carbon nanotubes (CNTs). The surface of the CNTs was functionalized by LC epoxy resin (ef-CNT). The ef-CNT can be blended well with the BP that is further cured with an equivalent of DDS to form nanocomposite. We have studied the curing kinetics of this nanocomposite using isothermal and nonisothermal differential scanning calorimetry (DSC). The dependence of the conversion on time can fit into the autocatalytic model before the vitrification, and then it becomes diffusion control process. The reaction rate increases and the activation energy decreases with increasing concentration of the ef-CNT. At 10 wt % of ef-CNT, the activation energy of nanocomposite curing is lowered by about 20% when compared with the neat BP/DDS resin. If the ef-CNT was replaced by thermal-insulating TiO2 nanorods on the same weight basis, the decrease of activation energy was not observed. The result indicates the accelerating effect on the nanocomposite was raised from the high-thermal conductivity of CNT and aligned LC epoxy resin. However, at ef-CNT concentration higher than 2 wt %, the accelerating effect of ef-CNTs also antedates the vitrification and turns the reaction to diffusion control driven. As the molecular motions are limited, the degree of cure is lowered. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

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...

We present a simple approach by using mixed solvent to control the morphology of poly(3-hexylthiophene) (P3HT)/TiO2 nanorod hybrid bulk heterojunction solar cells without any post-treatment. The effects of the controlled morphology on the optical and electrical properties are investigated. It has been a challenge to disperse polar inorganic nanocrystals at a relative high concentration into a relative nonpolar polymer. The use of mixed solvent which consists of pyridine (a poor solvent for P3HT), dichloromethane, and chloroform (a good solvent for P3HT) modifies the nanoscale morphology of P3HT/TiO2 nanorod hybrids, resulting in highly crystalline P3HT domains with well-dispersed TiO2 nanorods within polymer matrix. Study of photophysics reveals that charge carrier could form from emissive species upon photoexcitation and such a process is more efficient in highly ordered P3HT prepared by mixed solvent method. In the P3HT/TiO2 hybrid film, the formation of a bicontinuous phase-separated morphology largely...

In this study, we demonstrate optical properties of multilayer system in an organic solar cell based on poly (3-hexylthiophene) (P3HT) and 6,6-phenyl C61-butyric acid methyl ester (PCBM) with semitransparent anode through thermal annealing effect. The optical absorption is enhanced via optimizing annealing treatment which further elevates near-field electric field amplitude. The electric field amplitude at the interface (active layer/semitransparent anode) is enhanced after thermal annealing corresponding to effective absorption near to semitransparent anode. Moreover, the thickness of the active layer is optimized via optical thin-film model for enhancing the organic solar cell efficiency.

We report that ZnO nanorods (NRs) are grown on an organic layer of poly(3-hexylthiophene) (P3HT) using a modified seeding layer. Thus, ZnO NRs/P3HT heterojunction light-emitting diodes could be fabricated using the hydrothermal method, in which ZnO acts as an n-type material and P3HT as a p-type material. The ZnO NRs improve the electron transportation in the devices. A three-fold enhancement of current density of the device is observed due to the NRs formed on the P3HT. The electroluminescence (EL) of the optimized ZnO-based device is 1.5 times larger than that without NRs. The influence of the P3HT thickness for the EL spectrum is also discussed.

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.

We have developed Au/La(0.7)Sr(0.3)MnO(3) (Au/LSMO) periodic arrays with tunable surface plasmon properties that can be used as novel surface-enhanced Raman scattering (SERS) substrates. The periodic arrays are created by electron beam lithography of LSMO resist and metal film deposition. The LSMO electron beam resist is unique in that it exhibits either positive or negative resist behaviors depending on the electron beam dosage. Interestingly, surface plasmon behavior of the arrays can be controlled by just changing the electron beam dosage when presented with a fixed design pattern. Scanning confocal microscopy and spectral microreflectometry have been adapted to directly demonstrate this unique behavior. Furthermore, we show that our novel Au/LSMO array can be used as a high-sensitivity Raman scattering substrate. To illustrate this working principle, the Au/LSMO periodic array is applied to enhance the Raman scattering of a thin film containing 0.1 wt % poly-3-hexylthiophene (P3HT) in poly(methyl methacrylate) (PMMA). By controlling the geometry of the patterned substrate that exhibits gold surface plasmon near the excitation wavelength, we can enhance the intensity of Raman scattering of P3HT at 1350 cm(-1) up to 4 orders of magnitude as compared with previously generated planar Au substrates.

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 have studied the effect of annealing process on the performance of photovoltaic devices based on the bulk heterojunction of poly(3-hexylthiophene) and [6,6]-phenyl-C 61 butyric acid methyl ester (P3HT/PCBM). By means of atomic force microscopy (AFM) and scanning of near-field microscopy (SNOM), we can observe the morphology evolution of the annealed P3HT/PCBM composite films. We also studied the changes of optical properties by absorption spectroscopy and the changes of composition distribution of annealed composite films. The results indicate the P3HT in the composite film gradually becomes an ordered structure with annealing. The ordered P3HT facilitates the charge transport. However, the film exhibits a large-scale (1 μm) PCBM aggregation after annealing for an extended period of time. The disrupted bi-continous phase retards the charge transport. Thus, the device efficiency reaches the highest (2.308%) after annealing at 140 °C for 30 min but decreases to 0.810% after 60 min annealing.

Nanocomposites made from inorganic nanoparticles and polymers have many applications in optics, electronics and biomaterials. However, the glass transition temperature (Tg) of a nanocomposite is very difficult to measure accurately by conventional thermal analysis such as DSC or TMA when the concentration of the nanoparticle reaches a threshold of the percolation network. At this threshold stage, the phase transition in the nano domains of the matrix is too small to be detected by macroscale thermal analysis. We have developed a methodology basis on thermal atomic force microscope (AFM) to monitor the nanophase transition of the nanocomposite in situ upon heating. This method has demonstrated the capability in determining the Tg of a nanocomposite made by spherical SiO2 nanoparticles dispersed in polyacrylate. The threshold of the percolation network of this nanocomposite is at 40 wt% of SiO2 nanoparticles according to the results of refractive index, AFM, nanoindentation, DSC, TMA and TGA.

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.

We have studied the effect of polymer molecular weight on the performance of poly(3-hexylthiophene):TiO2 hybrid photovoltaic device using atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM). The atomic force microscopic studies show the nanoscale morphology of the hybrid film changes from small domain size rod-like structure to large domain nodule-like structure with increasing the molecular weight of poly(3-hexylthiophene). The studies of SNOM of hybrid film reveal that the large domain structure of the high-molecular-weight P3HT hybrid film exhibits continuous absorption mapping as opposite to the discontinuous absorption mapping of the low-molecular-weight P3HT hybrid film. Both results suggest the improvement in device efficiency from high-molecular-weight P3HT is due to the formation of large domain structure with increased carrier mobility and light harvesting.

We have fabricated a photovoltaic (PV) device based on the polymer blends of (poly(3-hexylthiophene) (P3HT)/polymethylmethacrylate (PMMA)) and inorganic TiO 2 nanorod bulk heterojunction. The optimized photovoltaic device with 1.6 wt% PMMA concentration has a power conversion efficiency of 0.65% under simulated AM 1.5 illumination (100 mW/cm 2 ), which is 38% more efficient than the device without the incorporation of PMMA. Furthermore, the PMMA-included device gives a short-circuit current density of 2.57 mA/cm 2 , an open-circuit voltage of 0.53 V, and a fill factor of 0.48. Our studies have shown that having optimal PMMA concentration in the photovoltaic devices helps to smoothen the surface of the hybrid thin film, broaden the absorption spectrum, and improve the electrical conductivity. The results implying improvement in cell performance can be illustrated using atomic force microscopy (AFM), a UV/vis spectrophotometer and electrical measurements.

A series of poly(diethylhexyloxy-p-phenylenevinylene-b-methyl methacrylate) (DEH-PPV-b-PMMA) polymers with narrow polydispersity (PDI < 1.1) were synthesized using Siegrist polycondensation and anionic polymerizations followed by “click” chemistry. Alkyne-terminated DEH-PPV and azido-terminated PMMA were synthesized first, and then the two functionalized polymers underwent 1,3-cycloaddition reaction to obtain copolymers. Both the conversion of the end-functionalization of the homopolymers and the yield of the “click” reaction were higher than 98% as determined by 1H nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). Transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies reveal the details of copolymer morphology. The DEH-PPV-b-PMMA system presented here has higher block segregation strength than many previously studied rod−coil block copolymers yet still shows experimentally accessible phase transitions with respect to temperature. As a result, thi...

This work presents polymer photovoltaic devices based on poly(3-hexylthiophene) (P3HT) and TiO2 nanorod hybrid bulk heterojunctions. Interface modification of a TiO2 nanorod surface is conducted to yield a very promising device performance of 2.20% with a short circuit current density (J(sc)) of 4.33 mA/cm2, an open circuit voltage (V(oc)) of 0.78 V, and a fill factor (FF) of 0.65 under simulated A.M. 1.5 illumination (100 mW/cm2). The suppression of recombination at P3HT/TiO2 nanorod interfaces by the attachment of effective ligand molecules substantially improves device performance. The correlation between surface photovoltage and hybrid morphology is revealed by scanning Kelvin probe microscopy. The proposed method provides a new route for fabricating low-cost, environmentally friendly polymer/inorganic hybrid bulk heterojunction photovoltaic devices.

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

We have fabricated La0.6Ca0.4MnO3 periodic arrays exhibiting tunable optical properties and magnetic properties using nontoxic and environmentally friendly electron beam resist made from La0.6Ca0.4MnO3 sol-gel precursor. We studied their unique optical properties by using the spectral microreflectometer and their magnetic properties using the superconducting quantum interference device and magnetic force microscopy. Additionally, the resist has the ability to demonstrate both positive and negative resist behaviors depending on the electron beam dosage. With these special characteristics, we can fabricate periodic structure on a thin film possessing controlled optical reflectance properties with one fixed design electron beam pattern without changing the structural parameters but changing the electron beam dosage only. Our approach provides an uncomplicated route for the fabrication of nanometer scale magnetic patterns, which serve as the building blocks in the search for novel properties of periodic magnetic arrays.

We have investigated the enhancement of light absorption and carrier transport of poly(3-hexylthiophene) (P3HT) resulted from doping with multi-wall carbon nanotubes (MWNTs). The MWNTs were acid washed first, and then incorporated into P3HT homogenously. The MWNTs make P3HT unfolded with more alignment and thus increase light absorption as shown by the studies of AFM and UV–vis spectroscopy. The KFM data provides useful information to differentiate the work function of the MWNTs from P3HT and further show improved hole transporting behaviors. Based upon these results, the 0.01 wt% MWNTs doped P3HT/PCBM photovoltaic device shows an increase of 29% power conversion efficiency.

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.

A highly conductive poly(3,4-ethylenedioxythiophene) (PEDOT) film was prepared by in-situ oxidative polymerization on a glass substrate and adopted as the transparent anode of polymer solar cells that were based on a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C 61 butyric acid methyl ester (PCBM) as the photoactive layer. PEDOT anodes of various thicknesses were prepared for use in such devices. The resistance of the PEDOT and the transmitted light intensity of the irradiation varied with the thickness. The best devices exhibited a power conversion efficiency of 2.6% under simulated AM1.5G solar irradiation. Importantly, the conversion efficiency of incident photons to electrons in the device with the PEDOT anode was comparable to that with an ITO electrode, indicating the practicability of applying PEDOT as anode to fabricate high-efficiency flexible solar cells.

ARTICLE I NFO We have fabricated an arrayed CdSe quantum dots composite thin film that can enhance the photo- luminescence of CdSe under the 488 nm laser irradiation by tuning the gold surface plasmon resonance frequency. This thin film consists of a gold coated periodic array of hybrid material of CdSe and poly(methyl methacrylate) on indium tin oxide coated glass substrate. The main surface plasmon resonance was red shifted as we increased the column diameter of the array. By adjusting the column diameters and lattice constants of the array to coincide with the 488 nm excitation wavelength, an evident increase in luminescence intensity was obtained due to the surface plasmon resonance of gold. As a result of likely efficient energy transfer from gold surface plasmon resonance to CdSe, the photoluminescence intensity of CdSe has been increased to 248% at 570 nm. This composite film has many potential applications in high efficient optoelectronic devices.