| 1. |
- Andersson, Mattias, et al.
(författare)
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From short to long - Optical and electrical transients in photovoltaic bulk heterojunctions of polyfluorene/fullerenes
- 2009
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448 .- 0301-0104. ; 357:1-3, s. 120-123
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Tidskriftsartikel (refereegranskat)abstract
- We combine results from transient optical absorption in a bulk heterojunction polymer donor/fullerene acceptor material, obtained in the optical range as well as in the THz range, with results from electrical transients after a short light pulse, to present a unified interpretation of the transport of charge after the very first act of photoinduced charge transfer. We find that the mobility of charges is initially very high, but dramatically reduced with time, to arrive at values three orders of magnitude lower. We show that this can be understood as a consequence of the transport of hot charges by hopping through the density of states, from higher to lower energies.
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| 2. |
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| 3. |
- Homa, Bekele, et al.
(författare)
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Photogenerated charge carrier transport and recombination in polyfluorene/fullerene bilayer and blend photovoltaic devices
- 2009
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Ingår i: ORGANIC ELECTRONICS. - : Elsevier BV. - 1566-1199. ; 10:3, s. 501-505
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Tidskriftsartikel (refereegranskat)abstract
- Using extraction of photogenerated charge carriers by linearly increasing voltage (photo-CELIV), we investigated two key transport parameters in photovoltaic materials based on the donor APFO-3 and acceptor PCBM: the mobility and lifetime of photogenerated charge carriers, in bilayers of varying geometry and in blends with various acceptors loading. We find that mobility depends strongly on delay time for shorter delay time in all devices. The observed recombination kinetics is found to be monomolecular. The mean lifetime of charge carriers is 2-3 mu s in blends and is slightly greater than 4 mu s in bilayer devices. In addition, the implications of mobility and lifetime values on the collection efficiency of the devices are presented.
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| 4. |
- Krebs, Frederik C, et al.
(författare)
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A round robin study of flexible large-area roll-to-roll processed polymer solar cell modules
- 2009
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Ingår i: SOLAR ENERGY MATERIALS AND SOLAR CELLS. - : Elsevier BV. - 0927-0248. ; 93:11, s. 1968-1977
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Tidskriftsartikel (refereegranskat)abstract
- A round robin for the performance of roll-to-roll coated flexible large-area polymer solar-cell modules involving 18 different laboratories in Northern America, Europe and Middle East is presented. The study involved the performance measurement of the devices at one location (Riso DTU) followed by transportation to a participating laboratory for performance measurement and return to the starting location (Riso DTU) for re-measurement of the performance. It was found possible to package polymer solar-cell modules using a flexible plastic barrier material in such a manner that degradation of the devices played a relatively small role in the experiment that has taken place over 4 months. The method of transportation followed both air-mail and surface-mail paths.
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| 5. |
- Lindgren, Lars Johan, 1977, et al.
(författare)
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Synthesis, Characterization, and Devices of a Series of Alternating Copolymers for Solar Cells
- 2009
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Ingår i: CHEMISTRY OF MATERIALS. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 21:15, s. 3491-3502
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Tidskriftsartikel (refereegranskat)abstract
- In this study we report the synthesis, characterization. and photovoltaic properties of a series of six Conjugated polymers based on donor-acceptor-donor (DAD) structure. The polymers are obtained via Suzuki polymerization of different alkoxy-substituted DAD monomers together with a substituted fluorene or phenylene monomer. Application of polymers as light-harvesting and electron-donating materials in solar cells, in conjunction with both [60]PCBM and [70]PCBM as acceptors, show power-conversion efficiencies (PCEs) up to 2.9%, values obtained without extensive optimization work. Furthermore, atomic force microscopy and field-effect transistor (FET) mobility measurements of acceptor-polymer mixtures show that differences in substitution on the polymers affect morphology, mobility, and device performance. Within the series of polymers, all showing similar optical absorption and redox behavior, substituents play an important role in phase separation on a micrometer scale, which in turn has a large impact on device performance. The phase-separation behavior is clearly seen in [70]PCBM devices where the best-performing devices are obtained using the polymers with short alkoxy groups or no substituents together with a high speed of spin coating during device preparation.
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| 6. |
- Qin, Ruiping, et al.
(författare)
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A Planar Copolymer for High Efficiency Polymer Solar Cells
- 2009
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Ingår i: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 131:41, s. 14612-
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Tidskriftsartikel (refereegranskat)abstract
- An alternating copolymer, poly(2-(5-(5,6-bis(octyloxy)-4-(thiophen-2-yl)benzo[c][1,2,5]thiadiazol-7-yl)thiophen-2-yl)-9-octyt-9H-carbazole) (HXS-1), was designed, synthesized, and used as the donor material for high efficiency polymer solar cells. The close packing of the polymer chains in the solid state was confirmed by XRD. A J(sc) of 9.6 mA/cm(2), a V-proportional to of 0.81 V, an FF of 0.69, and a PCE of 5.4% were achieved with HXS-1 and [6,6]-phenyl C-71-butyric acid methyl ester (PC71BM) as a bulk heterojunction active layer spin-coated from a solvent mixture of 1,2-dichlorobenzene and 1,8-diodooctane (97.5:2.5) under air mass 1.5 global (AM 1.5 G) irradiation of 100 mW/cm(2).
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| 7. |
- Andersson, Mattias, et al.
(författare)
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Intrinsic and extrinsic influences on the temperature dependence of mobility in conjugated polymers
- 2008
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 9:5, s. 569-574
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Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence of charge carrier mobility in conjugated polymers and their blends with fullerenes is investigated with different electrical methods, through field effect transistor (FET), space charge limited current (SCLC) and charge extraction (CELIV) measurements. Simple models, such as the Gaussian disorder model (GDM), are shown to accurately predict the temperature behavior, and a good correlation between the different measurement methods is obtained. Inconsistent charge carrier concentrations in the modeling are explained through intrinsic non-equilibrium effects, and are responsible for the limited applicability of existing numerical models. A severe extrinsic influence from water in FETs with a hydrophilic insulator interface is also demonstrated. The presence of water leads to a significant overestimate of the disorder in the materials from measurements close to room temperature and erratic behavior in the 150-350 K range. To circumvent this problem it is shown to be necessary to measure under ultra high vacuum (UHV) conditions. © 2008 Elsevier B.V. All rights reserved.
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| 8. |
- Andersson, Lars Mattias, et al.
(författare)
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Non-equilibrium effects on electronic transport in organic field effect transistors
- 2007
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Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 8:4, s. 423-430
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Tidskriftsartikel (refereegranskat)abstract
- Non-ideal behavior in organic field effect transistors, in particular threshold voltage drift and light sensitivity, is argued to be due to intrinsic carrier dynamics. The discussion is based on the theory for hopping transport within a Gaussian density of states. Carrier concentration is shown to be of fundamental importance, and the time required to reach equilibrium at different bias is responsible for device behavior, with implications for mobility evaluation. Experimental results from various conjugated polymers in a field effect transistor illustrate the theory.
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| 9. |
- Andersson, Lars Mattias, et al.
(författare)
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Stoichiometry, mobility, and performance in bulk heterojunction solar cells
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:7, s. 071108-
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Tidskriftsartikel (refereegranskat)abstract
- Bipolar transport in blends of a copolymer of fluorene, thiophene and electron accepting groups, and the substituted fullerene [6,6]-phenyl-C61-butyric acid methylester have been studied through charge extraction by linearly increasing voltage on solar cells and with field effect transistors. Between 10% and 90% polymer has been used and the results show a clear correlation to solar cell performance. Optimal solar cells comprise 20% polymer and have a power conversion efficiency of 3.5%. The electron mobility is increasing strongly with fullerene content, but is always lower than the hole mobility, thus explaining the low amount of polymer in optimized devices.
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| 10. |
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| 11. |
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| 12. |
- Andersson, Lars Mattias, et al.
(författare)
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Acceptor influence on hole mobility in fullerene blends with alternating copolymers of fluorene
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 88, s. 082103-
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Tidskriftsartikel (refereegranskat)abstract
- Hole mobility in polyfluorene/fullerene blends has been studied with field effect transistors. Two different C60 derivatives and one C70 derivative have been investigated together with two different polyfluorenes. Mobility is presented as a function of acceptor loading at ratios suitable for photovoltaics and varies between 10–3 and 10–5 cm2 V–1 s–1 depending on the polymer/acceptor combination. The hole mobility is increased in blends with the commonly used acceptor [6-6]-phenyl-C61-butyric acid methylester (PCBM). With related C60 and C70 derivatives the hole mobility is decreased under the same circumstances.
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| 13. |
- Andersson, Lars Mattias, et al.
(författare)
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Bipolar transport observed through extraction currents on organic photovoltaic blend materials
- 2006
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89, s. 142111-
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Tidskriftsartikel (refereegranskat)abstract
- Both electron and hole mobilities have been simultaneously measured through charge extraction by linearly increasing voltage on polymer heterojunction solar cells with varying stoichiometry of polymer and acceptor. The polymer is a low band gap copolymer of fluorene, thiophene, and electron accepting groups named APFO-Green 5, and the acceptor is [6,6]-phenyl-C61-butyric acid methylester. Results are correlated to field effect transistor measurements on the same material system. A monotonous increase in mobility for both carrier types is observed with increased acceptor loading.
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| 14. |
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| 15. |
- Chen, Miaoxiang, 1962-, et al.
(författare)
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High carrier mobility in low band gap polymer-based field-effect transistors
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 87:25, s. 252105-1-252105-3
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Tidskriftsartikel (refereegranskat)abstract
- A conjugated polymer with a low band gap of 1.21 eV, i.e., absorbing infrared light, is demonstrated as active material in field-effect transistors (FETs). The material consists of alternating fluorene units and low band gap segments with electron donor-acceptor-donor units composed of two electron-donating thiophene rings attached on both sides of a thiadiazolo-quinoxaline electron-acceptor group. The polymer is solution-processable and air-stable; the resulting FETs exhibit typical p-channel characteristics and field-effect mobility of 0.03 cm2 V−1 s−1.
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