Search

Low band gap D-A conjugated PNs consisting of 2-ethylhexyl cyclopentadithiophene co-polymerized with 2,1,3-benzothiadiazole (for nano-PCPDTBT) or 2,1,3-benzoselenadiazole (for nano-PCPDTBSe) have been developed. The PNs are stable in aqueous media and showed no significant toxicity up to 1 mg · mL(-1) . Upon exposure to 808 nm light, the PNs generated temperatures above 50 °C. Photothermal ablation studies of the PNs with RKO and HCT116 colorectal cancer cells were performed. At concentrations above 100 µg · mL(-1) for nano-PCPDTBSe, cell viability was less than 20%, while at concentrations above 62 µg · mL(-1) for nano-PCPDTBT, cell viability was less than 10%. The results of this work demonstrate that low band gap D-A conjugated polymers 1) can be formed into nanoparticles that are stable in aqueous media; 2) are non-toxic until stimulated by IR light and 3) have a high photothermal efficiency., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The synthesis and characterization of a soluble high molecular weight copolymer based on 4,8-bis(1-pentylhexyloxy)benzo[1,2-b:4,5-b']dithiophene and 2,1,3-benzoxadiazole is presented. High efficiency organic photovoltaic (OPV) devices comprised of this polymer and phenyl-C(71) -butyric acid methyl ester (PC(71) BM) were fabricated by additive processing with 1-chloronapthalene (CN). When the active layer is cast from pristine chlorobenzene (CB), power conversion efficiencies (PCEs) average 1.41%. Our best condition-using 2% chloronapthalene as a solvent additive in CB-results in an average PCE of 5.65%, with a champion efficiency of 6.05%., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The mechanical response, the force-indentation relationship, in normal force spectroscopy measurements carried out on individual polysaccharide encapsulated bacteria is modeled using three increasingly refined approaches that consider the elastic response of the bacterium and cantilever in combination with a fluid (hydrodynamic) model for the polysaccharide layer. For the hydrodynamic description of the polysaccharide layer, several increasingly realistic models are described in detail, together with numerical solution techniques. These models range from one-dimensional, Newtonian, to two-dimensional, axisymmetric, fully viscoelastic (Phan-Thien/Tanner). In all cases, the models rigorously consider the time-dependent rheological-mechanical coupling between the elastic and fluid viscoelastic physical components of the experimental setup. Effects of inherent variability in geometrical and material properties of the bacterium and polysaccharide layer on the measurable response are quantified. A parametric investigation of the force-indentation relationship highlights the importance of accurate knowledge of the rheology of the extracellular polysaccharides. We also draw conclusions about the design and evaluation of force spectroscopy experiments on single encapsulated bacteria. Supported by model calculations, we also point the way to methods of in vivo rheological characterization of the extracellular polysaccharide as a preferable alternative to characterization after its removal from the native environment.

In this paper, experimentally obtained force curves on Staphylococcus aureus are compared with a previously developed model that incorporates hydrodynamic effects of extracellular polysaccharides together with the elastic response of the bacterium and cantilever. Force-displacement curves were predicted without any adjustable parameters. It is demonstrated that experimental results can be accurately described by our model, especially if viscoelastic effects of the extracellular polysaccharide layer are taken into account. Polysaccharide layer viscoelasticity was treated by means of a multimode Phan-Thien/Tanner (PTT) constitutive equation. Typical maximum relaxation times range from 0.2 to 2 s, whereas the corresponding zero-shear-rate viscosities are 6-9 Pa.s, based on published, steady-state rheological measurements on Staphylococcus aureus polysaccharide extracted from its native environment. The bacterial elastic constant is found to be in the range 0.02-0.4 N/m, corresponding to bacterial wall Young's moduli in the range of a few hundred MPa. Repeatability of measurements performed on different bacteria is found to be only fair, due to large individuum variability, whereas repetitions of measurements on the same bacterium showed high reproducibility. Improved force-indentation curve predictions are expected if transient rheological characterization of extracellular polysaccharides is available. More desirable however is the direct, in vivo rheological characterization of the extracellular polysaccharide. A model-based analysis of experimental force-indentation curves shows that appreciable further experimental improvements are still necessary to achieve this goal.

The effects of varying nanotube loading/concentration in carbon nanotube-poly(3-octylthiophene) blends used as thin film photovoltaic cells, have been studied. The network of single walled nanotubes clearly aids in exciton separation and modifies carrier mobility within the active layer as suggested by a bulk heterojunction model. Further, modifications to the metal-polymer interface occur with the addition of nanotubes leading to variations in the observed VOC of the photovoltaic cells. Finally, the "nanocomposite" devices exhibit significant enhancements to external power conversion efficiencies, with the overall efficiency strongly dependent on device design parameters such as the addition of buffer layers.

In this work, the application of an aluminum (Al)/multiwall carbon nanotube (MWCNT)/Al, multilayered electrode to flexible, high-efficiency, alternating current driven organic electroluminescent devices (AC-OEL), is reported. The electrode is fabricated by sandwiching a spray-cast nanonetwork film of MWCNTs between two evaporated layers of Al. The resulting composite film facilitates a uniform charge distribution across a robust crack-free electrode under various bending angles. It is demonstrated that these composite electrodes stabilize the power efficiency of flexible devices for bending angles up to 120°, with AC-OEL device power efficiencies of ≈22 lm W−1 at luminances of ≈4000 cd m−2 (using no output coupling). Microscopic examination of the Al/MWCNTs/Al electrode after bending of up to 1300 cycles suggests that the nanotubes significantly enhance the mechanical properties of the thin Al layers while providing a moderate modification to the work function of the metal. While the realization of robust, high-brightness, and high-efficiency AC-OEL devices is potentially important in their future lighting applications, it is anticipated that this to also have significant impact in standard organic light emitting diodes lighting applications. [ABSTRACT FROM AUTHOR]

In this work, the effects of electrode modification by calcium (Ca) on the performance of AC field induced polymer electroluminescence (FIPEL) devices are studied. The FIPEL device with Ca/Al electrode exhibits 550 cd m-2, which is 27.5 times higher than that of the device with only an Al electrode (20 cd m-2). Both holes and electrons are injected from one electrode in our FIPEL device. We found that the electron injection can be significantly enhanced by a Ca modification on the Al electrode without greatly affecting the hole injection. Therefore, the electrons and holes can be effectively recombined in the emissive layer to form more excitons under the AC voltage, leading to effective light emission. The device emitted much brighter light than other AC-based organic EL devices. This result provides an easy and effective way to improve FIPEL performance. [ABSTRACT FROM AUTHOR]

Bulk-heterojunction (BHJ) solar cells utilizing P3HT:PCBM composite loaded with niobium-doped zinc oxide nanoparticles (Nb/ZnO NPs) produced by flame spray pyrolysis were fabricated. The devices loaded with and without Nb/ZnO NPs were compared. It was found that niobium doping led to a slight increase in open circuit voltage and an increase in short-circuit current. The effect of co-solvent (1,3,5-trichlorobenzene; TCB) in chlorobenzene in the polymer solution was also investigated on the morphology and performance of a P3HT:PCBM and P3HT:PCBM:Nb/ZnO bulk-heterojunction solar cells. The device efficiency was improved due to a good quality of the thin film nanostructure and annealing time. [ABSTRACT FROM AUTHOR]

The potential of gold nanorods to act as 'antennae' in organic photovoltaic devices and improve performance by enhancing the optical field within the device has been examined. Gold nanorods were blended into the buffer layer of standard poly (3-hexothiopene) (P3HT): 6, 6-phenyl C61-butyric acid methyl ester (PCBM) photovoltaic cells. Increases in both the broad spectrum absorption and device fill factors (as compared to solar cells without nanorods) were observed. A comparison of the internal resistance and absorption allows estimation of what part in the change in performance can be attributed to greater absorption and increases in buffer layer conductivity. [ABSTRACT FROM AUTHOR]

Abstract: Highly conductive, highly transparent thin films have been fabricated from polymer–single walled carbon nanotube blends. Using poly-3,4-ethylenedioxythiophene doped with poly(styrenesulfonate) as a host material, excellent dispersion of single wall nanotubes could be achieved enhancing the conductivity with relatively low loadings <3wt%. Raman spectroscopy indicates that there is little bundling of the single wall nanotubes in the matrix and that the nanotubes are sensitive to residual stress within the film. As the host bulk conductivity is increased, enhancements of the overall composite conductivity are observed to be proportional. These results suggest that the energy barrier to nanotube–nanotube carrier hopping within the matrix can be modified in accordance with a heterogeneous conduction model. [Copyright &y& Elsevier]

The authors have fabricated thin film polymer photovoltaics using 1-(3-methoxycarbonyl)propyl-1-phenyl-(6,6)C61 within regioregular poly(3-hexylthiophene) bulk heterojunction absorbing layers. Using thermal annealing at temperatures approaching the glass transition temperature, they have examined the formation of nanodomains within the matrix. These domains modify charge transport pathways in such a way as to allow for the efficient use of thicker absorbing layers. This results in a nearly 20% gain in overall performance for this polymer system with external power efficiencies exceeding 6%. [ABSTRACT FROM AUTHOR]

The effects of annealing and fullerene loading in regioregular poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) based bulk heterojunction photovoltaics have been investigated. Under specific loading and annealing conditions, a combination of morphological and electronic factors can be brought to play to achieve optimal filling factors, open-circuit voltage (Voc), and short-circuit current density (Jsc). We demonstrate that this occurs at surprisingly low loadings of PCBM and annealing temperatures nearing the melting point of the polymer. Further, we report power conversion efficiencies approaching 5% in the P3HT:PCBM system. [ABSTRACT FROM AUTHOR]

A C[sub 60]-based poly(phenylene vinylene) (PPV) dyad poly{(2,5-di-pentoxyl-phenylene)-4diylvinylene-3,6-[9-(1-azafulleroid-pro pyl)-carbazolenevinylene]} (PPV-AFCAR) and an emissive conjugated polymer poly{1,4[2-(3,7-dimethyloctyloxy)-3,5,6-trimethoxy]phenylene vinylene} (POMPV) were prepared to investigate the role of [60]fullerene in conjugated polymer composites. Multilayer organic light-emitting devices with the configuration of indium tin oxide/ poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/blends/2-(4-biphenylyl)-5-(4-tert-butylphenyl)-l,3,4-oxadiazo le(Bu-PBD)/LiF/A1 were fabricated using PPV-AFCAR as a dopant and POMPV as an emissive material. [ABSTRACT FROM AUTHOR]

The article presents a response to M.K. Riede and colleagues' comment on the paper "Roles of donor and acceptor nanodomains in 6% efficient thermally annealed polymer photovoltaics." The study examined the role of morphology in organic solar cells. The morphology created in the nanophase is compatible with thicker films, thereby raising the overall performance of the device.

Nanocomposite cathode structures with the aim of combining mechanical and electronic properties to achieve better performance in an organic flexible are examined by D. L. Carroll and team on page 4397. A flexible high‐efficiency alternating current (AC) driven field‐induced polymer electroluminescent) device is chosen as the platform system with the understanding that this approach to organic devices clearly points to organic light emitting diodes, organic thin‐film transistors, and other flexible systems. [ABSTRACT FROM AUTHOR]

In this work, the emission characteristics of a blue fluorophor poly(9, 9-dioctylfluorene) (PFO) combined with a red emitting dye: Bis(2-methyl-dibenzo[f,h]quinoxaline)(acetylacetonate)iridium (III) [Ir(MDQ)2(acac)], are examined in two different asymmetric white alternating current field-induced polymer electroluminescent (FIPEL) device structures. The first is a top-contact device in which the triplet transfer is observed resulting in the concentration-dependence of the emission similar to the standard organic light-emitting diode (OLED) structure. The second is a bottom-contact device which, however, exhibits concentration-independence of emission. Specifically, both dye emission and polymer emission are found for the concentrations as high as 10% by weight of the dye in the emitter. We attribute this to the significant different carrier injection characteristics of the two FIPEL devices. Our results suggest a simple and easy way to realize high-quality white emission. [ABSTRACT FROM AUTHOR]

In this work, a high-performance alternating current (AC) filed-induced chromatic-stable white polymer electroluminescence (WFIPEL) device was fabricated by combining a fluorophor Poly(9,9-dioctylfluorene) (PFO)-based blue device with a yellow down-conversion layer (YAG:Ce). A maximum luminance of this down-conversion FIPEL device achieves 3230 cd m −2 , which is 1.41 times higher than the device without the down-conversion layer. A maximum current efficiency and power efficiency of the down-conversion WFIPEL device reach 19.7 cd A −1 at 3050 cd m −2 and 5.37 lm W −1 at 2310 cd m −2 respectively. To the best of our knowledge, the power efficiency is one of the highest reports for the WFIPEL up to now. Moreover, Commison Internationale de L’Eclairage (CIE) coordinates of (0.28, 0.30) is obtained by adjusting the thickness of the down-conversion layer to 30 μm and it is kept stable over the entire AC-driven voltage range. We believe that this AC-driven, down-conversion, WFIPEL device may offer an easy way towards future flat and flexible lighting sources. [ABSTRACT FROM AUTHOR]

A solution-processed, all-phosphor, three-color (i.e., blue, green, and red), alternating current-driven white field-induced polymer electroluminescent device (WFIPEL), with low operational voltage, high luminance, high efficiency, high color-rendering index (CRI), and excellent color-stability, was demonstrated. The devices employed poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) [P(VDF–TrFE–CFE)] dielectric modified by single-walled carbon nanotubes (SWNTs) to further improve the dielectric characteristics, as the insulating layer. This significantly lowers the driving voltage of the device. Moreover, hole-generation layer and electron-transporting layer with high conductivity were used to more efficiently form and confine excitons in the emissive layer. The resulting WFIPEL devices show significant improvements in performance as compared to previous reports. Specifically, the devices exhibit a low turn-on voltage of 10 V, a maximum luminance of 7210 cd m −2 , a maximum current efficiency and power efficiency of 33.8 cd A −1 and 10.5 lm W −1 , and a CRI of 82. The power efficiency is even 10 times higher than the highest previous report (1 lm W −1 ). [ABSTRACT FROM AUTHOR]

Highlights: [•] The emission characteristics of a white emitting ter-polymer combined with a red emitting dye was examined between AC-driven FIPEL devices. [•] Specifically, both dye emission and polymer emission were observed for concentrations as high as 30% of the dye in the emitter. [•] The CIE coordinates with a CCT between 2500K and 6500K and a CRI above 90 are easily obtained over a wide range of dye concentrations in FIPEL devices. [•] The high-color-quality white FIPEL devices offer great potential for cost-effective next generation lighting and display products. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the use of multi-walled carbon nanotubes (MWNTs) dispersed in an emissive layer of poly (N-vinylcarbazole) (PVK):fac-tris(2-phenylpyri-dine)iridium(III) [Ir(ppy)3] in alternating current (AC) field-induced polymer electroluminescence (FIPEL) devices. A symmetric device structure, with the polymer/MWNT composite between two dielectric layers, was used to study the effect of MWNTs on charge generation within the active layer. An asymmetric device structure, using one dielectric layer, was used to study band alignment effects of carbon nanotubes in charge injection from a contact. The presence of MWNTs within the emissive layer facilitates effective internal charge generation in the symmetric devices, as would be expected if they acted as a charge source. However, electron injection under AC-driven fields also increases in the asymmetric devices, suggesting a modification to band alignment. Increase in light emission of five times is achieved in composite devices compared to devices with the pure polymer. From the trends in behavior with nanotube loading, we suggest that the nanotubes effectively doped the polymer, modifying energy level alignment in the device and increasing field-induced polarization currents. The combined effects of electron injection and charge generation may pave the way for widespread use of MWNTs in high-performance FIPEL devices. [Copyright &y& Elsevier]