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  • 1.
    Blazinic, Vanja
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Ericsson, Leif
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Levine, Igal
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Opitz, Andreas
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Impact of intentional photo-oxidation of a donor polymer and PC70BM on solar cell performance2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, p. 22259-22271Article in journal (Refereed)
    Abstract [en]

    A short lifetime is the main factor hindering the wider implementation of low-cost organic photovoltaics in large-area and outdoor applications. Ingress of oxygen and water vapour through non-ideal encapsulation layers is a known cause of degradation for polymer/fullerene based solar cells. To better understand the origin of this performance degradation, we study the effect of intentional exposure of the photo-active layer to simulated sunlight (AM1.5) in air both on the solar cell performance and on the molecular semiconductor materials. Cathode-free thin films of a blend of the electron donor polymer poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) and the electron acceptor fullerene derivative [6,6]-phenyl-C70-butyric acid methyl ester (PC70BM) were exposed to simulated sunlight in air. Fourier-transform infrared spectra demonstrate the formation of carbonyl photo-oxidation products in the blend films, as well as in the pristine polymer and fullerene films. Solar cells prepared with photo-oxidized active layers show increasingly degraded electrical performance (lower short circuit current, open circuit voltage and fill factor) with increasing exposure time. The increased diode ideality factor indicates that trap-assisted recombination hinders device operation after exposure. The external quantum efficiency decreases drastically with increasing exposure time over the whole photon energy range, while the UV-vis absorption spectra of the blend films only show a mild photo-induced bleaching. This demonstrates that not only the photo-induced degradation of the solar cell performance is not predominantly caused by the loss in light absorption, but charge transport and collection are also hampered. This is explained by the fact that photo-oxidation of PC70BM causes bonds in its conjugated cage to break, as evidenced by the decreased ∏* intensity in C1s-NEXAFS spectra of PC70BM films. This degradation of unoccupied states of PC70BM will hinder the transport of photo-generated electrons to the electrode. Surface photovoltage spectroscopy gives direct evidence for gap states at the surface of a PC70BM film, formed after 2 hours of exposure and resulting in upward band bending at the PC70BM/air surface. These observations indicate that the photo-oxidation of PC70BM is likely to be the main cause of the performance degradation observed when the photoactive layer of a TQ1:PC70BM solar cell is intentionally exposed to light in air.

  • 2.
    Brumboiu, Iulia Emilia
    et al.
    KTH Royal Institute of Technology.
    Ericsson, Leif
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Blazinic, Vanja
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Opitz, Andreas
    Humboldt-Universität zu Berlin.
    Brena, Barbara
    Uppsala Universitet, Physics and Astronomy.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    The Photooxidation of PC60BM: New Insights from SpectroscopyManuscript (preprint) (Other academic)
    Abstract [en]

    In the quest towards more durable solution-processed solar cells, the stability of the active layer materials under operation conditions is important. While lifetimes of several years have been demonstrated for encapsulated organic solar cells, it is generally known that degradation events can be accounted for by air components (O2 and/or water vapour) leaking into the cell through a non-ideal sealing. Here we present a fundamental study of intentional photo-degradation of the electron-acceptor PC60BM ([6,6]-phenyl-C61-butyric acid methyl ester) in air, with the purpose of improving the understanding of the electronic effects of fullerene photo-oxidation. We have studied spincoated thin films of PC60BM by X-ray Photoelectron Spectroscopy, Near-edge X-ray Absorption Fine Structure spectroscopy, and Fourier Transform Infrared Spectroscopy, before and after exposing them to simulated sunlight in air. The changes observed in the spectra obtained by these complementary methods were compared with calculated spectra of a large set of possible oxidation products of PC60BM where oxygen atoms have been attached to the C60 cage. The best fit with experimental IR spectra of photodegraded PC60BM films was obtained for a linear combination of calculated spectra for two degradation products, a dicarbonyl and an anhydride, both with open cages with 58 carbon atoms, and the pristine PC60BM molecule. From this comparison, we conclude that the conjugation of the fullerene cage is disturbed by the formation of several carbonyl-based derivatives on the C60 cage, accompanied by a transition from sp2 to sp3-hybridized carbon. The π* resonance in the C1s NEXAFS spectrum was found to be a very sensitive probe for small changes to the fullerene cage, and FT-IR was needed in combination with O1s NEXAFS, to identify the oxidation products.

  • 3.
    Brumboiu, Iulia Emilia
    et al.
    Department of Physics and Astronomy, Uppsala University, SE-75120 Uppsala, Sweden.
    Ericsson, Leif K.E.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Eriksson, Olle
    Department of Physics and Astronomy, Uppsala University, SE-75120 Uppsala, Sweden.
    Brena, Barbara
    Department of Physics and Astronomy, Uppsala University, SE-75120 Uppsala, Sweden.
    The influence of oxygen adsorption on the NEXAFS and core-level XPS spectra of the C60 derivative PCBM2015In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, p. 054306-Article in journal (Refereed)
  • 4. Chavhan, Sudam D.
    et al.
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Ericsson, Leif
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Beyer, Paul
    Hofmann, Alexander
    Brütting, Wolfgang
    Opitz, Andreas
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Low temperature processed NiOx hole transport layers for efficient polymer solar cells2017In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 44, p. 59-66Article in journal (Refereed)
  • 5.
    Ciammaruchi, Laura
    et al.
    Parc Mediterani de la Technologia, ICFO.
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Galagan, Yulia
    TNO Solliance, Eindhoven, Netherlands.
    Stability of organic solar cells with PCDTBT donor polymer: An interlaboratory study2018In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 33, no 13, p. 1909-1924Article in journal (Refereed)
    Abstract [en]

    This work is part of the interlaboratory collaboration to study the stability of organic solar cells containing PCDTBT polymer as a donor material. The varieties of the OPV devices with different device architectures, electrode materials, encapsulation, and device dimensions were prepared by seven research laboratories. Sets of identical devices were aged according to four different protocols: shelf lifetime, laboratory weathering under simulated illumination at ambient temperature, laboratory weathering under simulated illumination, and elevated temperature (65 degrees C) and daylight outdoor weathering under sunlight. The results generated in this study allow us to outline several general conclusions related to PCDTBT-based bulk heterojunction (BHJ) solar cells. The results herein reported can be considered as practical guidance for the realization of stabilization approaches in BHJ solar cells containing PCDTBT.

  • 6.
    Farinhas, Joana
    et al.
    Inst Super Tecn, Inst Telecomunicacoes, Av Rovisco Pais, P-1049001 Lisbon, Portugal..
    Oliveira, Ricardo
    Inst Super Tecn, Inst Telecomunicacoes, Av Rovisco Pais, P-1049001 Lisbon, Portugal..
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Ericsson, Leif
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Morgado, Jorge
    Inst Super Tecn, Inst Telecomunicacoes, Av Rovisco Pais, P-1049001 Lisbon, Portugal.;Univ Lisbon, Inst Super Tecn, Dept Bioengn, Av Rovisco Pais, P-1049001 Lisbon, Portugal..
    Charas, Ana
    Inst Super Tecn, Inst Telecomunicacoes, Av Rovisco Pais, P-1049001 Lisbon, Portugal..
    Efficient ternary organic solar cells based on immiscible blends2017In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 41, p. 130-136Article in journal (Refereed)
    Abstract [en]

    Organic photovoltaic cells based on ternary blends of materials with complementary properties represent an approach to improve the photon-absorption and/or charge transport within the devices. However, the more complex nature of the ternary system, i.e. in diversity of materials' properties and morphological features, complicates the understanding of the processes behind such optimizations. Here, organic photovoltaic cells with wider absorption spectrum composed of two electron-donor polymers, F8T2, poly(9,9-dioctylfluorene-alt-bithiophene), and PTB7, poly([4,8-bis[(2'-ethylhexyl) oxy] benzo[1,2-b: 4,5-b'] dithiophene-2,6-diyl][3-fluoro-2-[(2'-ethylhexyl) carbonyl] thieno[3,4-b] thiophenediyl]), mixed with [6,6]-phenyl-C-61-butyric acid methyl ester (PC61BM) are investigated. We demonstrate an improvement of 25% in power conversion efficiency in comparison with the most efficient binary blend control devices. The active layers of these ternary cells exhibit gross phase separation, as determined by Atomic Force Microscopy (AFM) and Synchrotron-based Scanning Transmission X-ray Microscopy (STXM).

  • 7.
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Materials and Device Engineering for Efficient and Stable Polymer Solar Cells2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Polymer solar cells form a promising technology for converting sunlight into electricity, and have reached record efficiencies over 10% and lifetimes of several years. The performance of polymer solar cells depends strongly on the distribution of electron donor and acceptor materials in the active layer. To achieve longer lifetimes, degradation processes in the materials have to be understood. In this thesis, a set of complementary spectroscopy and microscopy techniques, among which soft X-ray techniques have been used to determine the morphology of polymer:fullerene based active layers. We have found that the morphology of TQ1:PC70BM films is strongly influenced by the processing solvent and the use of solvent additives. We have also found, by using soft X-ray techniques, that not only the light-absorbing polymer TQ1, but also the fullerene is susceptible to photo-degradation in air. Moreover, the fullerene degradation is accelerated in the presence of the polymer. Additionally, this thesis addresses the role of the interfacial layers for device performance and stability. The commonly used hole transport material PEDOT:PSS has the advantage of being solution processable at room temperature, but this layer is also known to contribute to the device degradation. We have found that low-temperature processed NiOx is a promising alternative to PEDOT:PSS, leading to improved device performance. Even for encapsulated polymer solar cells, some photo-induced degradation of the electrical performance is observed and is found to depend on the nature of the hole transport material. We found a better initial stability for solar cells with MoO3 hole transport layers than with PEDOT:PSS. In the pursuit of understanding the initial decrease in electrical performance of PEDOT:PSS-based devices, simulations were performed, from which a number of degradation sources could be excluded.

  • 8.
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Morphology and material stability in polymer solar cells2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Polymer solar cells are promising in that they are inexpensive to produce, and due to their mechanical flexibility have the potential for use in applications not possible for more traditional types of solar cells. The performance of polymer solar cells depends strongly on the distribution of electron donor and acceptor material in the active layer. Understanding the connection between morphology and performance as well as how to control the morphology, is therefore of great importance. Furthermore, improving the lifetime of polymer solar cells has become at least as important as improving the efficiency.

     

    In this thesis, the relation between morphology and solar cell performance is studied, and the material stability for blend films of the thiophene-quinoxaline copolymer TQ1 and the fullerene derivatives PCBM and PC70BM. Atomic force microscopy (AFM) and scanning transmission X-ray microscopy (STXM) are used to investigate the lateral morphology, secondary ion mass spectrometry (SIMS) to measure the vertical morphology and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to determine the surface composition. Lateral phase-separated domains are observed whose size is correlated to the solar cell performance, while the observed TQ1 surface enrichment does not affect the performance. Changes to the unoccupied molecular orbitals as a result of illumination in ambient air are observed by NEXAFS spectroscopy for PCBM, but not for TQ1. The NEXAFS spectrum of PCBM in a blend with TQ1 changes more than that of pristine PCBM. Solar cells in which the active layer has been illuminated in air prior to the deposition of the top electrode exhibit greatly reduced electrical performance. The valence band and absorption spectrum of TQ1 is affected by illumination in air, but the effects are not large enough to account for losses in solar cell performance, which are mainly attributed to PCBM degradation at the active layer surface.

  • 9.
    Hansson, Rickard
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Ericsson, Leif
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Holmes, Natalie P.
    Blazinic, Vanja
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Dastoor, Paul
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Opportunities and challenges in probing local composition of organic material blends for photovoltaics2017In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 32, no 10, p. 1982-1992Article in journal (Refereed)
  • 10.
    Hansson, Rickard
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Ericsson, Leif K.E.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Holmes, Natalie P.
    Centre for Organic Electronics, University of Newcastle, Callaghan, NSW 2308, Australia.
    Rysz, Jakub
    M. Smoluchowski Insitute of Physics, Jagiellonian University, Reymonta 4, Krakow 30–059, Poland.
    Opitz, Andreas
    Department of Physics, Humboldt-Universit¨at zu Berlin, 12489 Berlin, Germany.
    Campoy-Quiles, Mariano
    Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, Bellaterra, 08193, Spain.
    Wang, Ergang
    Chalmers University of Technology, 41296 Göteborg, Sweden.
    Barr, Matthew G.
    Centre for Organic Electronics, University of Newcastle, Callaghan, NSW 2308, Australia.
    Kilcoyne, A. L. David
    Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
    Zhou, Xiaojing
    Centre for Organic Electronics, University of Newcastle, Callaghan, NSW 2308, Australia.
    Dastoor, Paul
    Centre for Organic Electronics, University of Newcastle, Callaghan, NSW 2308, Australia.
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Vertical and lateral morphology effects on solar cell performance for a thiophene–quinoxaline copolymer:PC70BM blend2015In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, p. 6970-6979Article in journal (Refereed)
  • 11.
    Hansson, Rickard
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Lindqvist, Camilla
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Ericsson, Leif
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Opitz, Andreas
    Humboldt univ. .
    Wang, Ergang
    Chalmers.
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Photodegradation in air of the active layer components in a thiophene-quinoxaline copolymer:fullerene solar cell2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 16, p. 11132-11138Article in journal (Refereed)
    Abstract [en]

    We have studied the photo-degradation in air of a blend of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1), and how the photo-degradation affects the solar cell performance. Using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, changes to the electronic structure of TQ1 and PCBM caused by illumination in ambient air are investigated and compared between the pristine materials and the blend. The NEXAFS spectra show that the unoccupied molecular orbitals of TQ1 are not significantly changed by the exposure of pristine TQ1 to light in air, whereas those of PCBM are severely affected as a result of photo-induced degradation of PCBM. Furthermore, the photo-degradation of PCBM is accelerated by blending it with TQ1. While the NEXAFS spectrum of TQ1 remains unchanged upon illumination in air, its valence band spectrum shows that the occupied molecular orbitals are weakly affected. Yet, UV-Vis absorption spectra demonstrate photo-bleaching of TQ1, which is attenuated in the presence of PCBM in blend films. Illumination of the active layer of TQ1: PCBM solar cells prior to cathode deposition causes severe losses in electrical performance.

  • 12.
    Hörmann, Ulrich
    et al.
    Institute of Physics, University of Augsburg, Universitätsstraße 1, 86135 Augsburg, Germany.
    Lorch, Christopher
    Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany.
    Hinderhofer, Alexander
    Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany.
    Gerlach, Alexander
    Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany.
    Gruber, Mark
    Institute of Physics, University of Augsburg, Universitätsstraße 1, 86135 Augsburg, Germany.
    Kraus, Julia
    Institute of Physics, University of Augsburg, Universitätsstraße 1, 86135 Augsburg, Germany.
    Sykora, Benedikt
    Institute of Physics, University of Augsburg, Universitätsstraße 1, 86135 Augsburg, Germany.
    Grob, Stefan
    Institute of Physics, University of Augsburg, Universitätsstraße 1, 86135 Augsburg, Germany.
    Linderl, Theresa
    Institute of Physics, University of Augsburg, Universitätsstraße 1, 86135 Augsburg, Germany.
    Wilke, Andreas
    Department of Physics, Humboldt University of Berlin, Brook-Taylor-Straße 15, 12489 Berlin, Germany.
    Opitz, Andreas
    Department of Physics, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Anselmo, Ana Sofia
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Ozawa, Yusuke
    Graduate School of Advanced Integration Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.
    Nakayama, Yasuo
    Graduate School of Advanced Integration Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.
    Ishii, Hisao
    Center for Frontier Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan and Graduate School of Advanced Integration Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.
    Koch, Norbert
    Department of Physics, Humboldt University of Berlin, Brook-Taylor-Straße 15, 12489 Berlin, Germany and Helmholtz-Zentrum Berlin für Materialien und Energie GmbH - BESSY II, Albert-Einstein-Straße 15, 12489 Berlin, Germany.
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Schreiber, Frank
    Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany.
    Brütting, Wolfgang
    Institute of Physics, University of Augsburg, Universitätsstraße 1, 86135 Augsburg, Germany.
    Voc from a Morphology Point of View: the Influence of Molecular Orientation on the Open Circuit Voltage of Organic Planar Heterojunction Solar Cells2014In: Journal of physical chemistry C, ISSN 1932-7455, Vol. 118, no 46, p. 26462-26470Article in journal (Refereed)
    Abstract [en]

    The film morphology and device performance of planar heterojunction

    solar cells based on the molecular donor material α-sexithiophene (6T) are investigated.

    Planar heterojunctions of 6T with two different acceptor molecules, the C60 fullerene and

    diindenoperylene (DIP), have been prepared. The growth temperature of the 6T bottom

    layer has been varied between room temperature and 100 °C for each acceptor. By means

    of X-ray diffraction and X-ray absorption, we show that the crystallinity and the molecular

    orientation of 6T is influenced by the preparation conditions and that the 6T film

    templates the growth of the subsequent acceptor layer. These structural changes are

    accompanied by changes in the characteristic parameters of the corresponding

    photovoltaic cells. This is most prominently observed as a shift of the open circuit

    voltage (Voc): In the case of 6T/C60 heterojunctions, Voc decreases from 0.4 to 0.3 V,

    approximately, if the growth temperature of 6T is increased from room temperature to 100

    °C. By contrast, Voc increases from about 1.2 V to almost 1.4 V in the case of 6T/DIP solar

    cells under the same conditions. We attribute these changes upon substrate heating to

    increased recombination in the C60 case while an orientation dependent intermolecular coupling seems to change the origin of the photovoltaic gap in the DIP case.

  • 13.
    Opitz, Andreas
    et al.
    Humboldt Univ, Inst Phys, D-10099 Berlin, Germany.;Humboldt Univ, IRIS Adlershof, D-10099 Berlin, Germany..
    Wilke, Andreas
    Humboldt Univ, Inst Phys, D-10099 Berlin, Germany.;Humboldt Univ, IRIS Adlershof, D-10099 Berlin, Germany..
    Amsalem, Patrick
    Humboldt Univ, Inst Phys, D-10099 Berlin, Germany.;Humboldt Univ, IRIS Adlershof, D-10099 Berlin, Germany..
    Oehzelt, Martin
    Humboldt Univ, Inst Phys, D-10099 Berlin, Germany.;Humboldt Univ, IRIS Adlershof, D-10099 Berlin, Germany.;Helmholtz Zentrum Berlin Mat & Energie GmbH, Bereich Erneuerbare Energien, Berlin, Germany..
    Blum, Ralf-Peter
    Humboldt Univ, Inst Phys, D-10099 Berlin, Germany.;Humboldt Univ, IRIS Adlershof, D-10099 Berlin, Germany..
    Rabe, Juergen P.
    Humboldt Univ, Inst Phys, D-10099 Berlin, Germany.;Humboldt Univ, IRIS Adlershof, D-10099 Berlin, Germany..
    Mizokuro, Toshiko
    Natl Inst Adv Ind Sci & Technol, Osaka, Japan..
    Hoermann, Ulrich
    Univ Augsburg, Inst Phys, D-86159 Augsburg, Germany..
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Koch, Norbert
    Humboldt Univ, Inst Phys, D-10099 Berlin, Germany.;Humboldt Univ, IRIS Adlershof, D-10099 Berlin, Germany.;Helmholtz Zentrum Berlin Mat & Energie GmbH, Bereich Erneuerbare Energien, Berlin, Germany..
    Organic heterojunctions: Contact-induced molecular reorientation, interface states, and charge redistribution2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 21291Article in journal (Refereed)
    Abstract [en]

    We reveal the rather complex interplay of contact-induced re-orientation and interfacial electronic structure-in the presence of Fermi-level pinning-at prototypical molecular heterojunctions comprising copper phthalocyanine (H16CuPc) and its perfluorinated analogue (F16CuPc), by employing ultraviolet photoelectron and X-ray absorption spectroscopy. For both layer sequences, we find that Fermi-level (E-F) pinning of the first layer on the conductive polymer substrate modifies the work function encountered by the second layer such that it also becomes E-F-pinned, however, at the interface towards the first molecular layer. This results in a charge transfer accompanied by a sheet charge density at the organic/organic interface. While molecules in the bulk of the films exhibit upright orientation, contact formation at the heterojunction results in an interfacial bilayer with lying and co-facial orientation. This interfacial layer is not EF-pinned, but provides for an additional density of states at the interface that is not present in the bulk. With reliable knowledge of the organic heterojunction's electronic structure we can explain the poor performance of these in photovoltaic cells as well as their valuable function as charge generation layer in electronic devices.

  • 14.
    van Stam, Jan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Lindqvist, Camilla
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Ericsson, Leif
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Fluorescence spectroscopy studies on polymer blend solutions and films for photovoltaics2015In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 483, p. 292-296Article in journal (Refereed)
  • 15.
    van Stam, Jan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Lindqvist, Camilla
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Ericsson, Leif
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Fluorescence and UV/VIS absorption spectroscopy studies on polymer blend films for photovoltaics2015In: Proceedings of SPIE: Physical Chemistry of Interfaces and Nanomaterials XIV / [ed] Hayes, SC; Bittner, ER, SPIE - International Society for Optical Engineering, 2015, Vol. 9549, p. 95490L1-95490L9Conference paper (Refereed)
  • 16.
    Züfle, Simon
    et al.
    Fluxim AG, Switzerland; Institute of Computational Physics, ZHAW, Switzerland.
    Hansson, Rickard
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Katz, Eugene A.
    The Ben-Gurion University of the Negev, Israel.
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Initial photo-degradation of PCDTBT:PC 70 BM solar cells studied under various illumination conditions: Role of the hole transport layer2019In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 183, no 1, p. 234-239Article in journal (Refereed)
    Abstract [en]

    ncapsulated organic solar cells often show a burn-in behaviour under illumination. This burn-in manifests itself as a rapid performance loss followed by a much slower progression of the degradation. Here we investigate the burn-in for PCDTBT:PC 70 BM solar cells under a wide range of illumination intensities. We find that increasing the sunlight concentration from 1 Sun to up to 100 Suns does not change the degradation behaviour, i.e. the dependence of all principal photovoltaic parameters on the dose of solar exposure (in Sun hours). This suggests that the degradation mechanisms under solar concentration (≤100 Suns) are the same as those observed under 1 Sun. This result makes it possible to use concentrated sunlight for accelerated stability assessment of these devices. We also find that devices with PEDOT:PSS as hole transport material show a rapid drop in open-circuit voltage of around 100 mV during the first Sun hour of light exposure. By replacing PEDOT:PSS with MoO 3 this initial process can be prevented and only the much slower part of the photo-degradation takes place.

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