| 1. |
- Kiefer, David, 1989, et al.
(författare)
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Double doping of conjugated polymers with monomer molecular dopants
- 2019
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Ingår i: Nature Materials. - : Springer Science and Business Media LLC. - 1476-4660 .- 1476-1122. ; 18:2, s. 149-155
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Tidskriftsartikel (refereegranskat)abstract
- Molecular doping is a crucial tool for controlling the charge-carrier concentration in organic semiconductors. Each dopant molecule is commonly thought to give rise to only one polaron, leading to a maximum of one donor:acceptor charge-transfer complex and hence an ionization efficiency of 100%. However, this theoretical limit is rarely achieved because of incomplete charge transfer and the presence of unreacted dopant. Here, we establish that common p-dopants can in fact accept two electrons per molecule from conjugated polymers with a low ionization energy. Each dopant molecule participates in two charge-transfer events, leading to the formation of dopant dianions and an ionization efficiency of up to 200%. Furthermore, we show that the resulting integer charge-transfer complex can dissociate with an efficiency of up to 170%. The concept of double doping introduced here may allow the dopant fraction required to optimize charge conduction to be halved.
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| 2. |
- Refaa, Zakariaa, 1987, et al.
(författare)
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Thermo-optical performance of molecular solar thermal energy storage films
- 2022
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 310
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Tidskriftsartikel (refereegranskat)abstract
- Due to their potential for solar energy harvesting and storage, molecular solar thermal energy storage (MOST) materials are receiving wide attention from both the research community and the public. MOST materials absorb photons and convert their energy to chemical energy, which is contained within the bonds of the MOST molecules. Depending on the molecular structure, these materials can store up to 1 MJ/kg, at ambient temperature and with storage times ranging from minutes to several years. This work is the first to thoroughly investigate the potential of MOST materials for the development of energy saving windows. To this end, the MOST molecules are integrated into thin, optically transparent films, which store solar energy during the daytime and release heat at a later point in time. A combined experimental and modeling approach is used to verify the system's basic functionality and identify key parameters. Multi-physics modeling and simulation were conducted to evaluate the interaction of MOST films with light, both monochromatic and the entire solar spectrum, as well as the corresponding dynamic energy storage. The model was experimentally verified by studying the optical response of thin MOST films containing norbornadiene derivatives as a functional system. We found that the MOST films act as excellent UV shield and can store up to 0.37 kWh/m2 for optimized MOST molecules. Further, this model allowed us to screen various material parameters and develop guidelines on how to optimize the performance of MOST window films.
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| 3. |
- Kiefer, David, 1989, et al.
(författare)
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Enhanced n-Doping Efficiency of a Naphthalenediimide-Based Copolymer through Polar Side Chains for Organic Thermoelectrics
- 2018
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Ingår i: ACS Energy Letters. - : American Chemical Society (ACS). - 2380-8195. ; 3:2, s. 278-285
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Tidskriftsartikel (refereegranskat)abstract
- N-doping of conjugated polymers either requires a high dopant fraction or yields a low electrical conductivity because of their poor compatibility with molecular dopants. We explore n-doping of the polar naphthalenediimide–bithiophene copolymer p(gNDI-gT2) that carries oligoethylene glycol-based side chains and show that the polymer displays superior miscibility with the benzimidazole–dimethylbenzenamine-based n-dopant N-DMBI. The good compatibility of p(gNDI-gT2) and N-DMBI results in a relatively high doping efficiency of 13% for n-dopants, which leads to a high electrical conductivity of more than 10–1 S cm–1 for a dopant concentration of only 10 mol % when measured in an inert atmosphere. We find that the doped polymer is able to maintain its electrical conductivity for about 20 min when exposed to air and recovers rapidly when returned to a nitrogen atmosphere. Overall, solution coprocessing of p(gNDI-gT2) and N-DMBI results in a larger thermoelectric power factor of up to 0.4 μW K–2 m–1 compared to other NDI-based polymers.
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| 4. |
- Mauri, Massimiliano, 1987, et al.
(författare)
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Click chemistry-type crosslinking of a low-conductivity polyethylene copolymer ternary blend for power cable insulation
- 2020
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Ingår i: Polymer International. - : Wiley. - 1097-0126 .- 0959-8103. ; 69:4, s. 404-412
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Tidskriftsartikel (refereegranskat)abstract
- High-voltage direct-current power cables are vital for the efficient transport of electricity derived from renewable sources of energy. The most widely used material for high-voltage power cable insulation - low-density polyethylene (LDPE) - is usually crosslinked with peroxides, a process that releases unwanted by-products. Hence, by-product-free crosslinking concepts that mitigate the associated increase in electrical conductivity are in high demand. Click chemistry-type crosslinking of polyethylene copolymer mixtures that contain glycidyl methacrylate and acrylic acid co-monomers is a promising alternative, provided that the curing reaction can be controlled. Here, we demonstrate that the rate of the curing reaction can be adjusted by tuning the number of epoxy and carboxyl groups. Both dilution of copolymer mixtures with neat LDPE and the selection of copolymers with a lower co-monomer content have an equivalent effect on the curing speed. Ternary blends that contain 50 wt% of neat LDPE feature an extended extrusion window of up to 170 degrees C. Instead, at 200 degrees C rapid curing is possible, leading to thermosets with a low direct-current electrical conductivity of about 10(-16) S cm(-1) at an electric field of 20 kV mm(-1) and 70 degrees C. The conductivity of the blends explored here is comparable to or even lower than values measured for both ultraclean LDPE and a peroxide-cured commercial crosslinked polyethylene grade. Hence, click chemistry curing represents a promising alternative to radical crosslinking with peroxides. (c) 2019 Society of Chemical Industry
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| 5. |
- Untilova, Viktoriia, et al.
(författare)
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High Thermoelectric Power Factor of Poly(3-hexylthiophene) through In-Plane Alignment and Doping with a Molybdenum Dithiolene Complex
- 2020
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 53:15, s. 6314-6321
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Tidskriftsartikel (refereegranskat)abstract
- We report a record thermoelectric power factor of up to 160 μW m-1 K-2 for the conjugated polymer poly(3-hexylthiophene) (P3HT). This result is achieved through the combination of high-temperature rubbing of thin films together with the use of a large molybdenum dithiolene p-dopant with a high electron affinity. Comparison of the UV-vis-NIR spectra of the chemically doped samples to electrochemically oxidized material reveals an oxidation level of 10%, i.e., one polaron for every 10 repeat units. The high power factor arises due to an increase in the charge-carrier mobility and hence electrical conductivity along the rubbing direction. We conclude that P3HT, with its facile synthesis and outstanding processability, should not be ruled out as a potential thermoelectric material. ©
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| 6. |
- Beretta, Davide, et al.
(författare)
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Thermoelectrics: From history, a window to the future
- 2019
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Ingår i: Materials Science and Engineering: R: Reports. - : Elsevier BV. - 0927-796X. ; 138
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Forskningsöversikt (refereegranskat)abstract
- Thermoelectricity offers a sustainable path to recover and convert waste heat into readily available electric energy, and has been studied for more than two centuries. From the controversy between Galvani and Volta on the Animal Electricity, dating back to the end of the XVIII century and anticipating Seebeck's observations, the understanding of the physical mechanisms evolved along with the development of the technology. In the XIX century Ørsted clarified some of the earliest observations of the thermoelectric phenomenon and proposed the first thermoelectric pile, while it was only after the studies on thermodynamics by Thomson, and Rayleigh's suggestion to exploit the Seebeck effect for power generation, that a diverse set of thermoelectric generators was developed. From such pioneering endeavors, technology evolved from massive, and sometimes unreliable, thermopiles to very reliable devices for sophisticated niche applications in the XX century, when Radioisotope Thermoelectric Generators for space missions and nuclear batteries for cardiac pacemakers were introduced. While some of the materials adopted to realize the first thermoelectric generators are still investigated nowadays, novel concepts and improved understanding of materials growth, processing, and characterization developed during the last 30 years have provided new avenues for the enhancement of the thermoelectric conversion efficiency, for example through nanostructuration, and favored the development of new classes of thermoelectric materials. With increasing demand for sustainable energy conversion technologies, the latter aspect has become crucial for developing thermoelectrics based on abundant and non-toxic materials, which can be processed at economically viable scales, tailored for different ranges of temperature. This includes high temperature applications where a substantial amount of waste energy can be retrieved, as well as room temperature applications where small and local temperature differences offer the possibility of energy scavenging, as in micro harvesters meant for distributed electronics such as sensor networks. While large scale applications have yet to make it to the market, the richness of available and emerging thermoelectric technologies presents a scenario where thermoelectrics is poised to contribute to a future of sustainable future energy harvesting and management. This work reviews the broad field of thermoelectrics. Progress in thermoelectrics and milestones that led to the current state-of-the-art are presented by adopting an historical footprint. The review begins with an historical excursus on the major steps in the history of thermoelectrics, from the very early discovery to present technology. A panel on the theory of thermoelectric transport in the solid state reviews the transport theory in complex crystal structures and nanostructured materials. Then, the most promising thermoelectric material classes are discussed one by one in dedicated sections and subsections, carefully highlighting the technological solutions on materials growth that have represented a turning point in the research on thermoelectrics. Finally, perspectives and the future of the technology are discussed in the framework of sustainability and environmental compatibility. © 2018 Elsevier B.V.
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| 7. |
- Campbell, PJ, et al.
(författare)
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Pan-cancer analysis of whole genomes
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 578:7793, s. 82-
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Tidskriftsartikel (refereegranskat)abstract
- Cancer is driven by genetic change, and the advent of massively parallel sequencing has enabled systematic documentation of this variation at the whole-genome scale1–3. Here we report the integrative analysis of 2,658 whole-cancer genomes and their matching normal tissues across 38 tumour types from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA). We describe the generation of the PCAWG resource, facilitated by international data sharing using compute clouds. On average, cancer genomes contained 4–5 driver mutations when combining coding and non-coding genomic elements; however, in around 5% of cases no drivers were identified, suggesting that cancer driver discovery is not yet complete. Chromothripsis, in which many clustered structural variants arise in a single catastrophic event, is frequently an early event in tumour evolution; in acral melanoma, for example, these events precede most somatic point mutations and affect several cancer-associated genes simultaneously. Cancers with abnormal telomere maintenance often originate from tissues with low replicative activity and show several mechanisms of preventing telomere attrition to critical levels. Common and rare germline variants affect patterns of somatic mutation, including point mutations, structural variants and somatic retrotransposition. A collection of papers from the PCAWG Consortium describes non-coding mutations that drive cancer beyond those in the TERT promoter4; identifies new signatures of mutational processes that cause base substitutions, small insertions and deletions and structural variation5,6; analyses timings and patterns of tumour evolution7; describes the diverse transcriptional consequences of somatic mutation on splicing, expression levels, fusion genes and promoter activity8,9; and evaluates a range of more-specialized features of cancer genomes8,10–18.
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| 8. |
- Derewjanko, Dennis, et al.
(författare)
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Delocalization Enhances Conductivity at High Doping Concentrations
- 2022
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-3028 .- 1616-301X. ; 32:20
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Tidskriftsartikel (refereegranskat)abstract
- Many applications of organic semiconductors require high electrical conductivities and hence high doping levels. Therefore, it is indispensable for effective material design to have an accurate understanding of the underlying transport mechanisms in this regime. In this study, own and literature experimental data that reveal a power-law relation between the conductivity and charge density of strongly p-doped conjugated polymers are combined. This behavior cannot consistently be described with conventional models for charge transport in energetically disordered materials. Here, it is shown that the observations can be explained in terms of a variable range hopping model with an energy-dependent localization length. A tight-binding model is used to quantitatively estimate of the energy-dependent localization length, which is used in an analytical variable range hopping model. In the limit of low charge densities, the model reproduces the well-known Mott variable range hopping behavior, while for high charge densities, the experimentally observed superlinear increase in conductivity with charge density is reproduced. The latter behavior occurs when the Fermi level reaches partially delocalized states. This insight can be anticipated to lead to new strategies to increase the conductivity of organic semiconductors.
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| 9. |
- Hofmann, Anna, 1987, et al.
(författare)
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All-Polymer Conducting Fibers and 3D Prints via Melt Processing and Templated Polymerization
- 2020
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Ingår i: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8252 .- 1944-8244. ; 12:7, s. 8713-8721
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Tidskriftsartikel (refereegranskat)abstract
- Because of their attractive mechanical properties, conducting polymers are widely perceived as materials of choice for wearable electronics and electronic textiles. However, most state-of-the-art conducting polymers contain harmful dopants and are only processable from solution but not in bulk, restricting the design possibilities for applications that require conducting micro-to-millimeter scale structures, such as textile fibers or thermoelectric modules. In this work, we present a strategy based on melt processing that enables the fabrication of nonhazardous, all-polymer conducting bulk structures composed of poly(3,4-ethylenedioxythiophene) (PEDOT) polymerized within a Nafion template. Importantly, we employ classical polymer processing techniques including melt extrusion followed by fiber spinning or fused filament 3D printing, which cannot be implemented with the majority of doped polymers. To demonstrate the versatility of our approach, we fabricated melt-spun PEDOT:Nafion fibers, which are highly flexible, retain their conductivity of about 3 S cm(-1) upon stretching to 100% elongation, and can be used to construct organic electrochemical transistors (OECTs). Furthermore, we demonstrate the precise 3D printing of complex conducting structures from OECTs to centimeter-sized PEDOT:Nafion figurines and millimeter-thick 100-leg thermoelectric modules on textile substrates. Thus, our strategy opens up new possibilities for the design of conducting, all-polymer bulk structures and the development of wearable electronics and electronic textiles.
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| 10. |
- Hofmann, Anna, 1987, et al.
(författare)
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Chemical Doping of Conjugated Polymers with the Strong Oxidant Magic Blue
- 2020
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Ingår i: Advanced Electronic Materials. - : Wiley. - 2199-160X .- 2199-160X. ; 6:8
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Tidskriftsartikel (refereegranskat)abstract
- Molecular doping of organic semiconductors is a powerful tool for the optimization of organic electronic devices and organic thermoelectric materials. However, there are few redox dopants that have a sufficiently high electron affinity to allow the doping of conjugated polymers with an ionization energy of more than 5.3 eV. Here, p-doping of a broad palette of conjugated polymers with high ionization energies is achieved by using the strong oxidant tris(4-bromophenyl)ammoniumyl hexachloroantimonate (Magic Blue). In particular diketopyrrolopyrrole (DPP)-based copolymers reach a conductivity of up to 100 S cm−1 and a thermoelectric power factor of 10 µW m−1 K−2. Further, both electron paramagnetic resonance (EPR) as well as a combination of spectroelectrochemistry and chronoamperometry is used to estimate the charge-carrier density of the polymer PDPP-3T doped with Magic Blue. A molar attenuation coefficient of 6.0 ± 0.2 × 103 m2 mol−1 is obtained for the first polaronic sub-bandgap absorption of electrochemically oxidized PDPP-3T. Comparison with chemically doped PDPP-3T suggests a charge-carrier density on the order of 1026 m−3, which yields a charge-carrier mobility of up to 0.5 cm2 V−1 s−1 for the most heavily doped material.
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