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  • 1.
    Björk, Per
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Persson, Nils-Krister
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Nilsson, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Åsberg, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Dynamics of complex formation between biological and luminescent conjugated polyelectrolytes - a surface plasmon resonance study2005In: Biosensors and Bioelectronics, ISSN 0956-5663, Vol. 20, no 9, p. 1764-1771Article in journal (Refereed)
    Abstract [en]

    A water-soluble polythiophene, POWT, with zwitterionic peptide like side chains possess good characteristics for biosensor applications. The zwitterionic side chains of the polymer can couple to biomolecules via electrostatic and hydrogen bonding. This creates possibilities to imprint biomolecules to spin-coated polymer films with maintained functionality, and use the resulting matrix as a biosensor. Polymer-biomolecular interaction studies done with surface plasmon resonance (SPR) reveal a well performing sensor matrix with high affinity for DNA hybridizations as well as for protein detection. The responses are distinct and very specific. A directional dependence of antibodies binding to POWT layer has also been observed. The polymer films have also been characterized by optical methods. Emission and absorption measurements in different buffer systems confirm that the polymer matrix can undergo structural and conformational changes on surfaces. The dielectric function in the interval 300–800 nm of POWT is reported, based on variable angle spectroscopic ellipsometry. This modeling reveals that a considerable amount of water is included in the material. The polymer layer possesses the characteristics needed for biochip applications and micro array techniques.

  • 2.
    Campoy-Quiles, M.
    et al.
    Experimental Solid State Physics Group, Blackett Laboratory, Imperial College London, UK.
    Nelson, J.
    Experimental Solid State Physics Group, Blackett Laboratory, Imperial College London, UK.
    Etchegoin, P.G.
    Experimental Solid State Physics Group, Blackett Laboratory, Imperial College London, UK.
    Bradley, D.D.C.
    Experimental Solid State Physics Group, Blackett Laboratory, Imperial College, UK.
    Zhokhavets, V
    Inst of Physics, Ilmenau Technical University, Germany.
    Gobsch, G.
    Inst of Physics, Ilmenau Technical University, Germany.
    Vaughan, H.
    Dept of Physics University of Durham, UK.
    Monkman, A,
    Dept of Physics, University of Durham, UK.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Persson, Nils-Krister
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Arwin, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Applied Optics . Linköping University, The Institute of Technology.
    Garriga, M.
    Inst de Ciència de Materials de Barcelona - CSIS, Campus de la UAB, Spain.
    Alonso, M.I.
    Inst de Ciència de Materials de Barcelona - CSIS, Campus de la UAB, Spain.
    Herrmann, G.
    Max Planck Institute for Polymer Research, Germany.
    Becker, M.
    Max Planck Institute for Polymer Research, Germany.
    Scholdei, W.
    Max Planck Institute for Polymer Research, Germany.
    Jahja, M.
    Max Planck Institute for Polymer Research, Germany.
    Bubeck, C.
    Max Planck Institute for Polymer Research, Germany.
    On the determination of anistropy in polymer thin films: A comparative study of optical techniques2008In: Physica Status Solidi. C: Current Topics in Solid State Physics, ISSN 1862-6351, Vol. 5, no 5, p. 1270-1273Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    Inganäs, Olle
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Svensson, M.
    Materials and Surface Chemistry, Chalmers University of Technology, 412 96 Göteborg, Sweden.
    Zhang, Fengling
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Gadisa, Abay
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Persson, Nils-Krister
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Wang, Xiangjun
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Andersson, M.R.
    Materials and Surface Chemistry, Chalmers University of Technology, 412 96 Göteborg, Sweden.
    Low bandgap alternating polyfluorene copolymers in plastic photodiodes and solar cells2004In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 79, no 1, p. 31-35Article in journal (Refereed)
    Abstract [en]

    We report a comparative study of plastic photodiodes using four different copolymers of fluorene, with a variation of alkyl side chain length and chemical structure. Photodiode materials are formed by blending the polymers with a fullerene derivative and spincoating the blend solution. A photovoltage of 1 V is obtained in devices, where the anode is a doped polymer and the cathode is LiF/Al. Monochromatic quantum efficiencies are better than 40% over most of the absorption range, and under solar light AM 1.5 simulation, we reach energy efficiencies beyond 2%. The high fill factors obtained in some of the devices indicate that these are of interest for more elaborate optimisation. Reasons for the benign electrical transport are discussed. © Springer-Verlag 2004.

  • 4.
    Inganäs, Olle
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics.
    Zhang, Fengling
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics.
    Wang, Xiangjun
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics.
    Gadisa, Abay
    IPS/ÌFM Linköpings universitet.
    Persson, Nils-Krister
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics.
    Svensson, Mattias
    Chalmers Tekniska Högskola.
    Perzon, Erik
    Chalmers Tekniska Högskola.
    Mammo, W
    Chalmers Tekniska Högskola.
    Andersson, M.R.
    Chalmers Tekniska Högskola.
    Alternating fluorene copolymer/fullerene blend solar cells2005In: Organic Photovoltaics: Mechanisms, Materials and Devices / [ed] Sam-Shajing Sun, Niyazi Serdar Sariciftci, Boca Raton, FL, USA: CRC Press , 2005, 1, p. 387-402Chapter in book (Other academic)
    Abstract [en]

    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.

  • 5.
    Johansson, Tomas
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Persson, Nils-Krister
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Inganäs, Olle
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Moving Redox Fronts in Conjugated Polymers Studies from Lateral Electrochemistry in Polythiophenes2004In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 151, no 4Article in journal (Refereed)
    Abstract [en]

    The propagation speed of the front of electrochemical conversion, from semiconductor to highly doped polymer, in films of regioregular poly(3-hexylthiophene) spin cast on insulating substrates was analyzed. Propagation of the p-doped zone in polymer electrochromic devices was imaged simultaneously with recording of electrochemical data. The current is proportional to the propagation speed and has a Tafel-like behavior when taking the resistive drop in the film into account. The resistivity in the film, which gradually lowers the propagation speed, was used for determination of the conductivity of the p-doped polymer. By combining these values with the doping charge injected into the film during front migration we estimated the hole carrier mobility for different doping levels. © 2004 The Electrochemical Society.

  • 6.
    Martinez, Jose Gabriel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Mehraeen, Shayan
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Escobar, Freddy
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Aziz, Shazed
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Milad, Milad Asadi Miankafshe
    University of Borås, Borås, Sweden.
    Persson, Nils-Krister
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics.
    Jager, Edwin
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Woven and knitted artificial muscles for wearable devices2019Conference paper (Other academic)
    Abstract [en]

    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.

  • 7.
    Persson, Nils-Krister
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Optical modelling of conjugated polymers: from materials to devices2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    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.

    List of papers
    1. Optical modelling of a layered photovoltaic device with a polyfluorene derivative/fullerene as the active layer
    Open this publication in new window or tab >>Optical modelling of a layered photovoltaic device with a polyfluorene derivative/fullerene as the active layer
    2004 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 83, no 2-3, p. 169-186Article in journal (Refereed) Published
    Abstract [en]

    Here we report on optical modelling of organic photovoltaic devices having a layered geometry, with polyfluorene-copolymer as the active material and C60 as the acceptor. Thin film theory in a matrix formalism enables analysis of the impact of reflection and interference on the optical electric field. The model allows us to predict an optimal C60 thickness where concern has been taken for light being both polychromatic and distributed according to solar irradiation. Fundamental for light–matter interaction is the dielectric function. We have extracted it for two variants of a new polyfluorene copolymer, PFDTBT, from UV via visible to the nearest infrared, using spectroscopic ellipsometry (SE). n is found to be relatively high with a max-value above 2.1. The process of spin coating induces anisotropy in the polymer film.

    Keywords
    Ellipsometry, Fullerene, Modelling, Photovoltaic, Polyfluorene
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-45709 (URN)10.1016/j.solmat.2004.02.023 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
    2. Optical optimization of polyfluorene-fullerene blend photodiodes
    Open this publication in new window or tab >>Optical optimization of polyfluorene-fullerene blend photodiodes
    2005 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, no 3, p. 034503-1-034503-8Article in journal (Refereed) Published
    Abstract [en]

    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.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-28476 (URN)10.1063/1.1836005 (DOI)13623 (Local ID)13623 (Archive number)13623 (OAI)
    Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
    3. Optical properties of low band gap alternating copolyfluorenes for photovoltaic devices
    Open this publication in new window or tab >>Optical properties of low band gap alternating copolyfluorenes for photovoltaic devices
    Show others...
    2005 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 123, no 20, p. 204718-Article in journal (Refereed) Published
    Abstract [en]

    In a joint experimental and theoretical work the optical response and excited-state character of two novel conjugated polymers for photovoltaic applications are studied. The polymers, alternating polyfluorene (APFO) Green 1 and APFO Green 2, are both copolymers of fluorene, thiophene, and electron accepting groups. The band gaps are extended into the red and near infrared with onsets of 780 and 1000 nm, respectively, due to alternating donor and acceptor moieties along the polymer chain. Spectroscopic ellipsometry and subsequent modeling made it possible to extract the dielectric function in the range of 260-1200 nm. Semiempirical quantum chemical calculations (ZINDO) revealed the character of the main electronic transitions in the studied spectral region. The spectral band just above 400 nm was assigned to a delocalized π - π* transition for both polymers. The red band lying at 622 and 767 nm in the two polymers corresponds to an electronic state mainly occupying the acceptor units and having a strong charge-transfer character. We show that the ZINDO transition energies are valuable input to the application of Lorentz oscillators in modeling of the dielectric function of the polymer material.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-50343 (URN)10.1063/1.2087367 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
    4. Organic tandem solar cells - modelling and predictions
    Open this publication in new window or tab >>Organic tandem solar cells - modelling and predictions
    2006 (English)In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 90, no 20, p. 3491-3507Article in journal (Refereed) Published
    Abstract [en]

    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.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-35453 (URN)10.1016/j.solmat.2006.05.009 (DOI)26905 (Local ID)26905 (Archive number)26905 (OAI)
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
    5. Optical limitations in thin-film low-band-gap polymer/fullerene bulk heterojunction devices
    Open this publication in new window or tab >>Optical limitations in thin-film low-band-gap polymer/fullerene bulk heterojunction devices
    2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 8, p. 083503-Article in journal (Refereed) Published
    Abstract [en]

    Photovoltaic devices from the low-band-gap alternating copolymer APFO-Green1, blended with the fullerene derivative BTPF70 as electron acceptor, show a pronounced variation of the external quantum efficiency with varying thickness. Device simulation, based on ellipsometric characterization, reveals that this behavior is to be expected and valid also for most low-band-gap polymers and that it can be explained by optical interference. Requirements for materials suitable for wide spectral coverage in thin-film organic solar cells are delineated. Furthermore, the internal quantum efficiency is calculated to be ≈ 0.4.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-39410 (URN)10.1063/1.2736280 (DOI)48250 (Local ID)48250 (Archive number)48250 (OAI)
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2018-10-08
  • 8.
    Persson, Nils-Krister
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Arwin, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Applied Optics . Linköping University, The Institute of Technology.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Optical optimization of polyfluorene-fullerene blend photodiodes2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, no 3, p. 034503-1-034503-8Article in journal (Refereed)
    Abstract [en]

    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.

  • 9.
    Persson, Nils-Krister
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Organic tandem solar cells - modelling and predictions2006In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 90, no 20, p. 3491-3507Article in journal (Refereed)
    Abstract [en]

    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.

  • 10.
    Persson, Nils-Krister
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Inganäs, Olle
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics.
    Simulations of optical processes in organic photovoltaic devices2005In: Organic Photovoltaics: Mechanisms, Materials and Devices / [ed] Sam-Shajing Sun, Niyazi Serdar Sariciftci, Boca Raton, FL, USA: CRC Press , 2005, 1, p. 107-138Chapter in book (Other academic)
    Abstract [en]

    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.

  • 11.
    Persson, Nils-Krister
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Schubert, Mathias
    Universität Leipzig, Fakultät für Physik und Geowissenschaften, Institut für Experimentelle Physik II, AG Festkörperoptik und Akustik, Germany.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Optical modelling of a layered photovoltaic device with a polyfluorene derivative/fullerene as the active layer2004In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 83, no 2-3, p. 169-186Article in journal (Refereed)
    Abstract [en]

    Here we report on optical modelling of organic photovoltaic devices having a layered geometry, with polyfluorene-copolymer as the active material and C60 as the acceptor. Thin film theory in a matrix formalism enables analysis of the impact of reflection and interference on the optical electric field. The model allows us to predict an optimal C60 thickness where concern has been taken for light being both polychromatic and distributed according to solar irradiation. Fundamental for light–matter interaction is the dielectric function. We have extracted it for two variants of a new polyfluorene copolymer, PFDTBT, from UV via visible to the nearest infrared, using spectroscopic ellipsometry (SE). n is found to be relatively high with a max-value above 2.1. The process of spin coating induces anisotropy in the polymer film.

  • 12.
    Persson, Nils-Krister
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Sun, Mengtao
    Chemical Physics, Lund University, Lund, Sweden .
    Kjellberg, Pär
    Chemical Physics, Lund University, Lund, Sweden .
    Pullerits, Tänu
    Chemical Physics, Lund University, Lund, Sweden .
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Optical properties of low band gap alternating copolyfluorenes for photovoltaic devices2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 123, no 20, p. 204718-Article in journal (Refereed)
    Abstract [en]

    In a joint experimental and theoretical work the optical response and excited-state character of two novel conjugated polymers for photovoltaic applications are studied. The polymers, alternating polyfluorene (APFO) Green 1 and APFO Green 2, are both copolymers of fluorene, thiophene, and electron accepting groups. The band gaps are extended into the red and near infrared with onsets of 780 and 1000 nm, respectively, due to alternating donor and acceptor moieties along the polymer chain. Spectroscopic ellipsometry and subsequent modeling made it possible to extract the dielectric function in the range of 260-1200 nm. Semiempirical quantum chemical calculations (ZINDO) revealed the character of the main electronic transitions in the studied spectral region. The spectral band just above 400 nm was assigned to a delocalized π - π* transition for both polymers. The red band lying at 622 and 767 nm in the two polymers corresponds to an electronic state mainly occupying the acceptor units and having a strong charge-transfer character. We show that the ZINDO transition energies are valuable input to the application of Lorentz oscillators in modeling of the dielectric function of the polymer material.

  • 13.
    Persson, Nils-Krister
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Wang, Xiangjun
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Optical limitations in thin-film low-band-gap polymer/fullerene bulk heterojunction devices2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 8, p. 083503-Article in journal (Refereed)
    Abstract [en]

    Photovoltaic devices from the low-band-gap alternating copolymer APFO-Green1, blended with the fullerene derivative BTPF70 as electron acceptor, show a pronounced variation of the external quantum efficiency with varying thickness. Device simulation, based on ellipsometric characterization, reveals that this behavior is to be expected and valid also for most low-band-gap polymers and that it can be explained by optical interference. Requirements for materials suitable for wide spectral coverage in thin-film organic solar cells are delineated. Furthermore, the internal quantum efficiency is calculated to be ≈ 0.4.

  • 14.
    Schubert, Mattias
    et al.
    Inst for Experimental Physics II University of Leipzig.
    Bundesmann, C.
    Inst for Experimental Physics University of Leipzig.
    Jacopic, G.
    JOANNEUM Research Forschungsgesellschaft mbH, Austria.
    Maresch, H.
    JOANNEUM Research Forschungsgesellschaft Mbh, Austria.
    Arwin, Hans
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Optics .
    Persson, Nils-Krister
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Zhang, Fengling
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Inganäs, Olle
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Infrared ellipsometry characterization of conducting thin organic films2004In: Elsevier Science, ISSN 1626-3200, Vol. 455-456, p. 295-300Article in journal (Refereed)
  • 15.
    Schubert, Mattias
    et al.
    Fakultät für Physik und Geowissenschaften Institut für Experimentelle Physik II, Leipzig.
    Bundesmann, C.
    Fakultät für Physik und Geowissenschaften Institut für Experimentelle Physik II, Leipzig.
    v. Wenckstern, H.
    Fakultät für Physik und Geowissenschaften Istitut für Experimentelle Physik II, Leipzig.
    Jakopic, G.
    Institut für Nanostrukturierte Materialien und Photonik JOHANNEUM Research Forschungsgesellschaft mbH.
    Haase, A.
    Institut für Nanostrukturierte Materialien und Photonik JOANNEUM Research Forschungsgesellschaft mbH.
    Persson, Nils-Krister
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Zhang, Fengling
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Arwin, Hans
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Optics .
    Inganäs, Olle
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics .
    Carrier redistribution in organic/inorganic (poly(3,4-ethylenedioxy thiophene/poly(styrenesulfonate)polymer)-Si) heterojunction determined from infrared ellipsometry2004In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 84, p. 1311-1313Article in journal (Refereed)
  • 16.
    Tvingstedt, Kristofer
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Rahachou, Aliaksandr
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Persson, Nils-Krister
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Zozoulenko, Igor V.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Surface plasmon increased absorption in polymer photovoltaic cells2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 11, p. 113514 -Article in journal (Refereed)
    Abstract [en]

    The authors demonstrate the triggering of surface plasmons at the interface of a metal grating and a photovoltaic bulk heterojunction blend of alternating polyfluorenes and a fullerene derivative. An increased absorption originating from surface plasmon resonances is confirmed by experimental reflection studies and theoretical modeling. Plasmonic resonances are further confirmed to influence the extracted photocurrent from devices. More current is generated at the wavelength position of the plasmon resonance peak. High conductivity polymer electrodes are used to build inverted sandwich structures with top anode and bottom metal grating, facilitating for triggering and characterization of the surface plasmon effects.

  • 17.
    Wang, Xiangjun
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Perzon, Erik
    Mammo, Wendimagegn
    Oswald, Frédéric
    Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, Toledo, Spain.
    Admassie, Shimelis
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Persson, Nils-Krister
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Langa, Fernando
    Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, Toledo, Spain.
    Andersson, Mats R.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Polymer solar cells with low-bandgap polymers blended with C70-derivative give photocurrent at 1 μm2006In: Thin Solid Films, ISSN 0040-6090, Vol. 511-512, p. 576-580Article in journal (Refereed)
    Abstract [en]

    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.

1 - 17 of 17
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