| 61. |
- Hellström, Stefan, 1978, et al.
(författare)
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Synthesis and characterization of three small band gap conjugated polymers for solar cell applications
- 2010
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Ingår i: Polymer Chemistry. - : Royal Society of Chemistry (RSC). - 1759-9954 .- 1759-9962. ; 1:8, s. 1272-1280
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Tidskriftsartikel (refereegranskat)abstract
- We report on a new series of small band gap conjugated polymers utilizing donor-acceptor-donor substructures in the polymer backbone to broaden and extend the optical absorption to longer wavelengths. Three polymers were prepared by Suzuki polymerization, using the same donor-acceptor-donor segment but with different comonomers. The goal was to investigate how the optical and electronic properties of the polymers were influenced by the different comonomers. Electrochemical spectroscopy, using square-wave voltammetry, shows that increasing the electron-donating strength of the comonomer will raise the HOMO energy level of the polymer, resulting in a decreased band gap. This result is also manifested by comparing open-circuit voltages from the corresponding laboratory fabricated solar cells. The best performing photovoltaic cell, based on APFO-Green15/[60]PCBM (1 : 4 w/w), reached a J(sc) of 4.2 mA cm(-2), a V-oc of 0.73 V, and a FF of 0.54, giving a PCE of 1.7%.
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| 62. |
- Hou, Lintao, et al.
(författare)
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Lateral Phase Separation Gradients in Spin-Coated Thin Films of High-Performance Polymer: Fullerene Photovoltaic Blends
- 2011
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-3028 .- 1616-301X. ; 21:16, s. 3169-3175
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Tidskriftsartikel (refereegranskat)abstract
- In this study, it is demonstrated that a finer nanostructure produced under a rapid rate of solvent removal significantly improves charge separation in a high-performance polymer: fullerene bulk-heterojunction blend. During spin-coating, variations in solvent evaporation rate give rise to lateral phase separation gradients with the degree of coarseness decreasing away from the center of rotation. As a result, across spin-coated thin films the photocurrent at the first interference maximum varies as much as 25%, which is much larger than any optical effect. This is investigated by combining information on the surface morphology of the active layer imaged by atomic force microscopy, the 3D nanostructure imaged by electron tomography, film formation during the spin coating process imaged by optical interference and photocurrent generation distribution in devices imaged by a scanning light pulse technique. The observation that the nanostructure of organic photovoltaic blends can strongly vary across spin-coated thin films will aid the design of solvent mixtures suitable for high molecular-weight polymers and of coating techniques amenable to large area processing.
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| 63. |
- Hou, Qiong, et al.
(författare)
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A triphenylamine-based four-armed molecule for solution-processed organic solar cells with high photo-voltage
- 2013
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Ingår i: JOURNAL OF MATERIALS CHEMISTRY A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 1:16, s. 4937-4940
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Tidskriftsartikel (refereegranskat)abstract
- A new four-armed molecule Th-4(DTPAB) with a triphenylamine-benzothiadiazole-triphenylamine unit as the core and 4-hexylthiophene as arms was synthesized. Solution-processed organic solar cells based on blends of Th-4(DTPAB) and PC71BM demonstrate a power conversion efficiency of 3.18% with a high open circuit voltage of 0.96 V.
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| 64. |
- Hultmark, Sandra, 1994, et al.
(författare)
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Suppressing Co-Crystallization of Halogenated Non-Fullerene Acceptors for Thermally Stable Ternary Solar Cells
- 2020
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-3028 .- 1616-301X. ; 30:48
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Tidskriftsartikel (refereegranskat)abstract
- While photovoltaic blends based on non-fullerene acceptors are touted for their thermal stability, this type of acceptor tends to crystallize, which can result in a gradual decrease in photovoltaic performance and affects the reproducibility of the devices. Two halogenated indacenodithienothiophene-based acceptors that readily co-crystallize upon mixing are studied, which indicates that the use of an acceptor mixture alone does not guarantee the formation of a disordered mixture. The addition of the donor polymer to the acceptor mixture readily suppresses the crystallization, which results in a fine-grained ternary blend with nanometer-sized domains that do not coarsen due to a high Tg ≈ 200 °C. As a result, annealing at temperatures of up to 170 °C does not markedly affect the photovoltaic performance of ternary devices, in contrast to binary devices that suffer from acceptor crystallization in the active layer. The results indicate that the ternary approach enables the use of high-temperature processing protocols, which are needed for upscaling and high-throughput fabrication of organic solar cells. Further, ternary devices display a stable photovoltaic performance at 130 °C for at least 205 h, which indicates that the use of acceptor mixtures allows to fabricate devices with excellent thermal stability.
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| 65. |
- Inganaes, Olle, et al.
(författare)
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Alternating fluorene copolymer-fullerene blend solar cells
- 2005
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Ingår i: Optical Science and Engineering. ; 99, s. 387-402
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Tidskriftsartikel (refereegranskat)abstract
- We present a new class of alternating fluorene copolymers, which can be combined with a fullerene acceptor, to make polymer blends suitable for photovoltaic energy conversion. By choice of comonomers in the polymer, it is possible to engineer the optical absorption spectrum and to cover the wavelength range down to 900 nm. The transport properties of the polymers investigated so far are competitive with other polymers used in polymer solar cells and the mixing of polymers with acceptors in the form of fullerenes is extensive. These polymers are therefore of interest in the future developments of high-performance polymer solar cells. [on SciFinder (R)]
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| 66. |
- Inganäs, Olle, et al.
(författare)
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Alternating Copolymers and Alternative Device Geometries for Organic Photovoltaics
- 2012
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 41:SUPPL.2, s. 138-142
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Konferensbidrag (refereegranskat)abstract
- The efficiency of conversion of light to electrical energy with the help of conjugated polymers and molecules is rapidly improving. The optical absorption properties of these materials can be designed, and implemented via molecular engineering. Full coverage of the solar spectrum is thus feasible. Narrow absorption spectra allow construction of tandem solar cells. The poor transport properties of these materials require thin devices, which limits optical absorption. Alternative device geometries for these flexible materials compensate for the optical absorption by light trapping, and allow tandem cells.
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| 67. |
- Inganäs, Olle, 1951-, et al.
(författare)
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Alternating fluorene copolymer/fullerene blend solar cells
- 2005. - 1
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Ingår i: Organic Photovoltaics. - Boca Raton, FL, USA : CRC Press. - 082475963X - 9780824759636 ; , s. 387-402
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Recently developed organic photovoltaics (OPVs) show distinct advantages over their inorganic counterparts due to their lighter weight, flexible shape, versatile materials synthesis and device fabrication schemes, and low cost in large-scale industrial production. Although many books currently exist on general concepts of PV and inorganic PV materials and devices, few are available that offer a comprehensive overview of recently fast developing organic and polymeric PV materials and devices.Organic Photovoltaics: Mechanisms, Materials, and Devicesfills this gap. The book provides an international perspective on the latest research in this rapidly expanding field with contributions from top experts around the world. It presents a unified approach comprising three sections: General Overviews; Mechanisms and Modeling; and Materials and Devices. Discussions include sunlight capture, exciton diffusion and dissociation, interface properties, charge recombination and migration, and a variety of currently developing OPV materials/devices. The book also includes two forewords: one by Nobel Laureate Dr. Alan J. Heeger, and the other by Drs. Aloysius Hepp and Sheila Bailey of NASA Glenn Research Center.Organic Photovoltaics equips students, researchers, and engineers with knowledge of the mechanisms, materials, devices, and applications of OPVs necessary to develop cheaper, lighter, and cleaner renewable energy throughout the coming decades.
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| 68. |
- Inganäs, Olle, et al.
(författare)
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Alternating Polyfluorenes Collect Solar Light in Polymer Photovoltaics
- 2009
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Ingår i: ACCOUNTS OF CHEMICAL RESEARCH. - : American Chemical Society (ACS). - 0001-4842 .- 1520-4898. ; 42:11, s. 1731-1739
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Tidskriftsartikel (refereegranskat)abstract
- The effort to improve the energy conversion efficiency of polymer solar cells has led to the design of novel donor polymers. To improve open circuit photovoltages (OCVs) and the spectral coverage of the solar spectrum, researchers have looked for materials with high HOMO values, an easily modified electronic structure, and sufficient electronic transport within the polymers. One advance in design from our laboratories has been the development of a class of alternating polyfluorene copolymers (APFOs), which can be combined with fullerenes to make bulk heterojunction materials for photovoltaic conversion. This Account describes copolymers of fluorene that we designed to expand the range the optical absorption of solar cells to include wavelengths out to 1000 nm. In most cases, we combine these polymers with acceptors from the fullerene family, typically the phenyl C-61 butyric acid methyl ester (PCBM) molecule, to generate solar cell materials. The synthesis of alternating copolymers of fluorene with various donor-acceptor-don or elements provides the opportunity to shift both HOMO and LUMO, which we have followed by electrochemical spectroscopy. Moving the LUMO of the APFOs farther from the vacuum level eventually leads to a situation where the driving force for photo-induced charge transfer from polymer donor to fullerene acceptor goes to zero, resulting in inefficient charge generation. Moving the HOMO level closer to the vacuum level reduces the OCV of devices made from bulk heterojunction blends. As we move the bandgap toward lower energies and increase the overlap of optical absorption with the solar spectrum, both these events eventually occur. In devices based on these APFO/fullerene blends, the performance depends on the OCV, the photocurrent under solar illumination, and the fill factor. The fill factor is influenced by electrical transport and charge generation. Optimizing these parameters requires new solutions to the perennial conflict between optically thin devices, where electrical extraction of charge is not a limitation, and the optically thick devices, where extraction of charge is hampered by trapping and recombination. As a result, we have developed methods to trap light in optically thin devices. When the thin film flexible solar cells are folded, multiple reflection between adjacent solar cells leads to a longer path length for the photon through the devices and considerable improvement of the optical dissipation in the active material. These optical tricks also enable an alternative route to tandem devices, where two different bandgap materials are located on adjacent folds. Thus light not absorbed in one cell is reflected onto the next cell to produce an effective optical series arrangement. Using experiments and simulations of the light trapping effects, we demonstrate power conversion efficiency enhancements of up to a factor of 1.8.
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| 69. |
- Inganäs, Olle, et al.
(författare)
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Low bandgap alternating polyfluorene copolymers in plastic photodiodes and solar cells
- 2004
-
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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| 70. |
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