| 1. |
- Gadisa, Abay, et al.
(författare)
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Stoichiometry dependence of charge transport in polymer/methanofullerene and polymer/C70 derivative based solar cells
- 2006
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Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199. ; 7:4, s. 195-204
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Tidskriftsartikel (refereegranskat)abstract
- Charge transport in a near infrared absorbing polyfluorene copolymer (APFO-Green1) and its blends with methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM), and 3′-(3,5-bis-trifluoromethylphenyl)-1′-(4-nitrophenyl)pyrazolino[70]fullerene (BTPF70) is reported. PCBM and BTPF70 are electron acceptor and transporting molecules in polymer based solar cells. The BTPF70 has emerged as a new electron acceptor molecule that provides adequate exciton dissociation when blended with the low band gap polyfluorene copolymer APFO-Green1. Electron transport in both net PCBM and BTPF70 films are subjected to positional and energetic disorder, with the degree of disorder being more pronounced in BTPF70. On the other hand, mixing PCBM with conjugated polymers usually leads to increased hole mobility. We have investigated and compared the acceptor concentration dependence of charge transport in APFO-Green1/PCBM and APFO-Green1/BTPF70 blend films. For better understanding of the charge transport in the heterojunction films, the field and temperature dependence of hole transport in pure APFO-Green1 films has also been studied. It is observed that the behavior of hole mobility in the blend layer is sensitive to the acceptor type. For APFO-Green1/PCBM hole only devices, the hole mobility attains a local maximum at 67 wt.% of PCBM, while on the contrary mixing any amount of BTPF70 with APFO-Green1 results into degradation of hole transport. Electron transport in both blends, however, increases monotonically as a function of acceptor loading.
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| 2. |
- Inganäs, Olle, et al.
(författare)
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Low bandgap alternating polyfluorene copolymers in plastic photodiodes and solar cells
- 2004
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Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 79:1, s. 31-35
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Lindgren, L.J, et al.
(författare)
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Blue light-emitting diodes based on novel polyfluorene copolymers
- 2007
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 122-123:1-2, s. 610-613
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Tidskriftsartikel (refereegranskat)abstract
- This study presents the synthesis and characterisation of a series of fluorene-based conjugated copolymers, together with the preparation and characterisation of the corresponding light-emitting devices. The polymers consist of alkoxyphenyl-substituted fluorene units together with different amounts of a hole-transporting triphenylamine-substituted fluorene unit: 0%, 10%, 25% and 50%. All polymers (P0, P1, P2, and P3) show high photoluminescence efficiency (ηPL) and light emission (both PL and EL) in the blue spectral region. Electrochemical studies show improved hole injection as the ratio of the triphenylamine-substituted segment is increased. The electroluminescence quantum efficiencies (EQEs) of the devices increase six times going from P0 to P1. Compared with P1, polymers P2 and P3 show lower efficiencies in devices. These findings indicate the presence of an optimal polymer composition, where balance between the charge-carrier mobilities has been reached. © 2006 Elsevier B.V. All rights reserved.
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| 4. |
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| 5. |
- Persson, Nils-Krister, et al.
(författare)
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Optical limitations in thin-film low-band-gap polymer/fullerene bulk heterojunction devices
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:8, s. 083503-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
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| 7. |
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| 8. |
- von Kieseritzky, F, et al.
(författare)
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Regiospecifically alkylated oligothiophenes via structurally defined building blocks
- 2002
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Ingår i: Synthesis (Stuttgart). - 0039-7881 .- 1437-210X. ; :9, s. 1195-1200
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a new synthetic protocol for the unsymmetrically alkylated and halogenated terthiophenes 5 and 10. To demonstrate their usefulness as building blocks for well-defined oligothiophenes, we synthesized a series of seven new sexi-, septi- and octithiophenes. Terthiophene 5 could be dimerized to the didecylsexithiophene In6 and terthiophene 10 to sexithiophene Out6, respectively, by the use of nickel catalysis. Together with the bis-stannylated thiophenes 11 and 12, the septithiophenes In7 and Out7 as well as the octithiophenes In8 and Out8 could be obtained via Stille coupling methodology. We could also obtain the unsymmetrical sexithiophene Unsym6 by selective heterocoupling between one equivalent of terthiophene 5 and 10 each. All new sexi-, septi- and octithiophenes show high photoluminescence in solution, but the quantum yield drops sharply in thin films of the materials.
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| 9. |
- Wang, Xiangjun, 1964-, et al.
(författare)
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Dynamic Control of Surface Energy and Topography of Microstructured Conducting Polymer Films
- 2008
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24, s. 5942-5948
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Tidskriftsartikel (refereegranskat)abstract
- Microstructured polymer surfaces, including conducting and insulating polymers, have been prepared to achieve electrochemical control of the surface energy and topography. The reported surface switches include pillar- and mesh-like surface patterns of polypyrrole (PPy), poly(3,4-ethylene-dioxythiophene) (PEDOT), and photoresists. The structures have been evaluated by contact angle measurements and optical and scanning electron microscopy to determine the surfaces characteristics. These microstructured polymer surface switches can be electrochemically modified from dewetting to wetting conditions, with a maximum associated change of the water contact angle from 129° to 44°. This contact angle switching was observed for samples in which dynamic control of the surface topography and surface tension was coupled. Control of topography was achieved with a dynamic height-switching range of more than 3 ìm. In addition, dynamic control of anisotropic wetting is reported. Our experiments were carried out under conditions that are suitable for a biointerface, implying potential application in biotechnology and cell science. In particular, switching of the energy, chemistry, and topography of the surface, along with their associated orientation, are interesting features for dynamic (electronic) control of the seeding and proliferation for living cells. The technology reported promises for electronically controlled cell-growth within Petri dishes, well plates, and other cell-hosting tools.
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| 10. |
- Wang, Xiangjun, et al.
(författare)
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Electrophosphorescence from polythiophene blends light-emitting diodes
- 2003
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Konferensbidrag (refereegranskat)abstract
- Electrophosphorescence has been observed in phosphorescent blend polythiophene LEDs with poly(3-methyl-4-octyl-thiophene) (PMOT) as host, bis (2-phenylbenzothiazole) iridium acetylacetonate (BTIr) as the guest. Investigation of photoluminescence and quantum yields shows that energy transfer exists in the host-guest system and depends on guest concentration. Electroluminescence indicates that charge trapping effect also contributes to the formation of exciton at phosphorescent centers.
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