| 1. |
- Campoy-Quiles, M., et al.
(author)
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On the determination of anistropy in polymer thin films : A comparative study of optical techniques
- 2008
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In: Physica Status Solidi. C: Current Topics in Solid State Physics. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 1862-6351. ; 5:5, s. 1270-1273
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Journal article (peer-reviewed)abstract
- We have used seven different techniques to measure the anisotropic refractive index of poly(vinylcarbazole) films. These techniques are: two types of variable angle spectroscopic ellipsometry (VASE) with multiple sample analysis, Interference enhanced VASE, Transmittance combined with VASE, Polarised Reflectance, beta-scan VASE, and prism coupling. We have found the average ordinary and extraordinary indices at 633 nm to be no = nTE = 1.675 ± 0.008, and ne = nTM = 1.722 ± 0.018, respectively, consistent amongst methods and conclusive on the magnitude of Δn in polymer films.
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| 2. |
- Escobar Teran, Freddy, et al.
(author)
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Enhancing the Conductivity of the Poly(3,4-ethylenedioxythiophene)-Poly(styrenesulfonate) Coating and Its Effect on the Performance of Yarn Actuators
- 2020
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In: Advanced Intelligent Systems. - : Wiley-Blackwell. - 2640-4567. ; 2:5
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Journal article (peer-reviewed)abstract
- Nonconductive commercial viscose yarns have been coated with a commercial conducting poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) layer providing electrical conductivity which allowed a second coating of the electroactive conducting polymer polypyrrole through electropolymerization to develop textile yarns actuators. To simplify the PEDOT coating process and at the same time make this process more suitable for application in industry, a new coating method is developed and the properties of the PEDOT-PSS conducting layer is optimized, paying attention on its effect on the actuation performance. The effect of the concentration of an additive such as dimethylsulfoxide (DMSO) on actuation, and of PEDOT:PSS layers, is investigated. Results show that on improving this conducting layer, better performance than previously developed yarn-actuators is obtained, with strains up to 0.6%. This study provides a simple and efficient fabrication method toward soft, textile-based actuators for wearables and assistive devices with improved features.
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| 3. |
- Inganaes, Olle, et al.
(author)
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Alternating fluorene copolymer-fullerene blend solar cells
- 2005
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In: Optical Science and Engineering. ; 99, s. 387-402
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Journal article (peer-reviewed)abstract
- We present a new class of alternating fluorene copolymers, which can be combined with a fullerene acceptor, to make polymer blends suitable for photovoltaic energy conversion. By choice of comonomers in the polymer, it is possible to engineer the optical absorption spectrum and to cover the wavelength range down to 900 nm. The transport properties of the polymers investigated so far are competitive with other polymers used in polymer solar cells and the mixing of polymers with acceptors in the form of fullerenes is extensive. These polymers are therefore of interest in the future developments of high-performance polymer solar cells. [on SciFinder (R)]
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| 4. |
- Inganäs, Olle, 1951-, et al.
(author)
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Alternating fluorene copolymer/fullerene blend solar cells
- 2005. - 1
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In: Organic Photovoltaics. - Boca Raton, FL, USA : CRC Press. - 082475963X - 9780824759636 ; , s. 387-402
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Book chapter (other academic/artistic)abstract
- Recently developed organic photovoltaics (OPVs) show distinct advantages over their inorganic counterparts due to their lighter weight, flexible shape, versatile materials synthesis and device fabrication schemes, and low cost in large-scale industrial production. Although many books currently exist on general concepts of PV and inorganic PV materials and devices, few are available that offer a comprehensive overview of recently fast developing organic and polymeric PV materials and devices.Organic Photovoltaics: Mechanisms, Materials, and Devicesfills this gap. The book provides an international perspective on the latest research in this rapidly expanding field with contributions from top experts around the world. It presents a unified approach comprising three sections: General Overviews; Mechanisms and Modeling; and Materials and Devices. Discussions include sunlight capture, exciton diffusion and dissociation, interface properties, charge recombination and migration, and a variety of currently developing OPV materials/devices. The book also includes two forewords: one by Nobel Laureate Dr. Alan J. Heeger, and the other by Drs. Aloysius Hepp and Sheila Bailey of NASA Glenn Research Center.Organic Photovoltaics equips students, researchers, and engineers with knowledge of the mechanisms, materials, devices, and applications of OPVs necessary to develop cheaper, lighter, and cleaner renewable energy throughout the coming decades.
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| 5. |
- Martinez, Jose Gabriel, Dr. 1986-, et al.
(author)
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Woven and knitted artificial muscles for wearable devices
- 2019
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Conference paper (other academic/artistic)abstract
- Diseases of the nervous system, traumas, or natural causes can reduce human muscle capacity. Robotic exoskeletons are forthcoming to support the movement of body parts, e.g. assist walking or aid rehabilitation. Current available devices are rigid and driven by electric motors or pneumatic actuators, making them noisy, heavy, stiff and noncompliant. We are developing textile based assistive devices that can be worn like clothing being light, soft, compliant and comfortable. We have merged advanced textile technology with electroactive polymers. By knitting and weaving electroactive yarns, we are developing soft textile actuators ("Knitted Muscles") that can be used in wearable assistive devices. We will present the latest progress increase the performance and to rationalise the fabrication. In addition we will show some demonstrators of the textile exoskeletons.
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| 6. |
- Persson, Nils-Krister, 1966-
(author)
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Optical modelling of conjugated polymers : from materials to devices
- 2005
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Doctoral thesis (other academic/artistic)abstract
- Measurements and modelling of theoretical properties of polymer-based photovoltaic devices, PPVDs, are the subjects of this thesis. Modelling refers both to modelling of materials, based on extraction of the dielectric function, and to modelling of devices by computer simulation of the optical electrical field inside PPVDs. PPVDs include polymer-based solar cells, a promising technology for energy generation and the theme for the this thesis.The conjugated polymers studied here arc built from fluorencs, PF, or thiophenes, PT, and combinations thereof in the form of different derivatives and copolymers, such as DAD blocks with alternating donor, acceptor, donor moieties. The latter are referred to as low-band gap materials and have absorption spectra that match the solar spectrum better than earlier generations of polymers.PPVDs operate according to the principle of transforming incoming photons to useful current: i.e. there is an optical side and an electrical side to the performance of PPVDs.This work is an effort taking a holistic perspective of the optical side and shows that simulation can save both materials and labour.It is demonstrated that variable-angle spectroscopic ellipsometry, SE, is a valuable tool for the characterisation of the optical linear response of this kind of materials. Using SE, the fully complex-valued index of refraction for wavelengths spanning from ultraviolet to infrared has been determined for a number of pure conjugated polymers as well as blends with polymer and acceptor-acting fullerenes. SE was also used for morphological studies, such as confirming spin-introduced uniaxiality - more pronounced for longer pure chains, somewhat suppressed for blends with fullerenes - and it was shown that traditional: effective mean field approximations fail in composing the material from its constituents indicating a more complicated morphology than expected. Methodological developments include a "sneaking method" suitable for band gap materials by which no assumptions about an underlying parameterisation are necessary. Another development is the introduction of quantum chemistry as a valuable tool for ellipsometric modelling. The position and relative magnitude of Lorentz peaks can be predicted and hence the dielectric function of the studied low-band gap DAD copolymer can be reconstructed.A tool for calculating the optical electrical field in these sandwich-like structures has been developed which includes polychromatic, solar-light distributed irradiation, and fully account for reflection and transmission at all interior interfaces, giving rise to interference not obeying the often assumed Beer-Lambert decay. The model enables calculation of spatially and wavelength resolved absorption profiles, of integrated absorbed energy, energy redistribution charts, upper estimates of quantum efficiencies, and the possibility of performing sensitivity analysis. The simulation also allows for optimisation by finding the set of layer thicknesses giving the highest absorption. The optical simulation has also been merged with electrical calculations in order both to give a more complete understanding of the device and also to de-couple the optical and electrical phenomena. The latter allows bottlenecks to be identified. For example, mobilities arc too low and have to be increased in coming generation of materials. In one study the coherent situation is expanded to the more general including both coherent and incoherent light addition. From this, tandem structures have been analysed. This tool is also valuable for optics in general.
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| 7. |
- Persson, Nils-Krister, 1966-, et al.
(author)
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Optical optimization of polyfluorene-fullerene blend photodiodes
- 2005
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 97:3, s. 034503-1-034503-8
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Journal article (peer-reviewed)abstract
- Blends of polyfluorene-fullerenes are promising materials for polymer-based photovoltaic devices (PPVD). Using spectroscopic ellipsometry we deduce the dielectric function for the blend of the fullerene derivative [6,6]-phenyl-C 61-butyric acid methyl ester (PCBM) and the alternating polyfluorene copolymer, poly [2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1', 3'-benzothiadiazole)] DiO-PFDTBT (4:1 by weight), for the wavelength interval 250-1300 nm. n reaches above 2 and saturates to 1.9 for high wavelengths. Absorption starts at 720 nm (1.72 eV) and reaches a crest around 550 nm (2.25 eV). The spin coating introduces anisotropy in the blend, manifested in birefringence as well as in dichroism. The dielectric function for the blend versus its constituents is not additive. There are indications that the constituents lost their dielectric identity, as screening cannot explain the experimental data. Simulations of optical absorption inside a PPVD are performed for both monochromatic and polychromatic light, using an air mass 1.5 distributed solar irradiation. The model allows calculation of absorbed energies in absolute values in all layers within the device. An optimization is carried out with respect to the layer thicknesses. From a purely optical perspective there is no gain of optical absorbance in including an additional layer of acceptor. Spatially resolved energy dissipation within the device is presented for polychromatic light. Estimates for quantum efficiencies are derived. Experimental and theoretical results for reflectance are compared.
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| 8. |
- Persson, Nils-Krister, 1966-, et al.
(author)
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Organic tandem solar cells - modelling and predictions
- 2006
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In: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 90:20, s. 3491-3507
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Journal article (peer-reviewed)abstract
- Tandem combinations of organic photovoltaic devices are studied from an optical point of view. We unify coherent (wave-based) as well as incoherent (irradiance-based) light addition in our treatment of the incoming and reflected electromagnetic waves, and calculate the spatially resolved absorption profile in the cells. The model allows for any number and any order of thin and thick layers to be analysed. Irradiation is monochromatic or polychromatic, AM 1.5 or AM 1.0, and therefore applicable for solar cell simulation. The optical modelling is unified with electrical models of charge generation and transport in the solar cells. Through this, de-coupling of optical and electrical processes is possible. Moreover, the model allows identification of limiting processes in the devices. The model is applied to a tandem cell with copolymers of polyfluorene combined in bulk heterojunctions with fullerene acceptors, one device for high energy absorption and one for lower, where anodes and cathodes for the cells are semi-transparent metallic polymer layers. It is concluded that these materials do not at present have an electrical performance, which can be enhanced by the tandem cell combination.
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| 9. |
- Persson, Nils-Krister, 1966-, et al.
(author)
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Simulations of optical processes in organic photovoltaic devices
- 2005. - 1
-
In: Organic Photovoltaics. - Boca Raton, FL, USA : CRC Press. - 082475963X - 9780824759636 ; , s. 107-138
-
Book chapter (other academic/artistic)abstract
- Recently developed organic photovoltaics (OPVs) show distinct advantages over their inorganic counterparts due to their lighter weight, flexible shape, versatile materials synthesis and device fabrication schemes, and low cost in large-scale industrial production. Although many books currently exist on general concepts of PV and inorganic PV materials and devices, few are available that offer a comprehensive overview of recently fast developing organic and polymeric PV materials and devices.Organic Photovoltaics: Mechanisms, Materials, and Devicesfills this gap. The book provides an international perspective on the latest research in this rapidly expanding field with contributions from top experts around the world. It presents a unified approach comprising three sections: General Overviews; Mechanisms and Modeling; and Materials and Devices. Discussions include sunlight capture, exciton diffusion and dissociation, interface properties, charge recombination and migration, and a variety of currently developing OPV materials/devices. The book also includes two forewords: one by Nobel Laureate Dr. Alan J. Heeger, and the other by Drs. Aloysius Hepp and Sheila Bailey of NASA Glenn Research Center.Organic Photovoltaics equips students, researchers, and engineers with knowledge of the mechanisms, materials, devices, and applications of OPVs necessary to develop cheaper, lighter, and cleaner renewable energy throughout the coming decades.
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| 10. |
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| 11. |
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| 12. |
- Wang, Xiangjun, et al.
(author)
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Polymer solar cells with low-bandgap polymers blended with C70-derivative give photocurrent at 1 μm
- 2006
-
In: Thin Solid Films. - : Elsevier BV. - 0040-6090. ; 511-512, s. 576-580
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Journal article (peer-reviewed)abstract
- A new series of low-bandgap alternating polyfluorenes with different donor–acceptor–donor moieties have been synthesized. Electrochemical and optical absorption measurement show that onset bandgaps of these polymers range from 1.2 to 1.5 eV. These polymers, blended with a C70-derivative as acceptor, are used for solar cell fabrication. Devices show promising photovoltaic properties, and the spectral response of photocurrent covers all visible and near-infrared wavelength regions with its onset extended to 1 μm. The best data gives a photocurrent density of 3.4 mA/cm2, open circuit voltage of 0.58 V and power conversion efficiency of 0.7% under illumination of AM1.5 (1000 W/m2) from a solar simulator.
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