| 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. |
- 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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| 3. |
- Andersson, Mattias, 1985, et al.
(författare)
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Additive-like amounts of HDPE prevent creep of molten LDPE: Phase-behavior and thermo-mechanical properties of a melt-miscible blend
- 2017
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Ingår i: Journal of Polymer Science, Part B: Polymer Physics. - : Wiley. - 1099-0488 .- 0887-6266. ; 55:2, s. 146-156
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Tidskriftsartikel (refereegranskat)abstract
- Low-density polyethylene (LDPE) is the preferred type of polyolefin for many medical and electrical applications because of its superior purity and cleanliness. However, the inferior thermo-mechanical properties as compared to, for example, high-density polyethylene (HDPE), which arise because of the lower melting temperature of LDPE, constitute a significant drawback. Here, we demonstrate that the addition of minute amounts of HDPE to a LDPE resin considerably improves the mechanical integrity above the melting temperature of LDPE. A combination of dynamic mechanical analysis and creep experiments reveals that the addition of as little as 1 to 2 wt% HDPE leads to complete form stability above the melting temperature of LDPE. The investigated LDPE/HDPE blend is found to be miscible in the melt, which facilitates the formation of a solid-state microstructure that features a fine distribution of HDPE-rich lamellae. The absence of creep above the melting temperature of LDPE is rationalized with the presence of tie chains and trapped entanglements that connect the few remaining crystallites.
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| 4. |
- Andersson, Mattias, 1985, et al.
(författare)
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Highly Insulating Polyethylene Blends for High-Voltage Direct-Current Power Cables
- 2017
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Ingår i: ACS Macro Letters. - : American Chemical Society (ACS). - 2161-1653. ; 6:2, s. 78-82
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Tidskriftsartikel (refereegranskat)abstract
- The insulation of state-of-the-art extruded high-voltage direct-current (HVDC) power cables is composed of cross-linked low-density polyethylene. Driven by the search for sustainable energy solutions, concepts that improve the ability to withstand high electrical fields and, ultimately, the power transmission efficiency are in high demand. The performance of a HVDC insulation material is limited by its residual electrical conductivity. Here, we demonstrate that the addition of small amounts of high-density polyethylene (HDPE) to a low-density polyethylene (LDPE) resin results in a drastic reduction in DC conductivity. An HDPE content as low as 1 wt % is found to introduce a small population of thicker crystalline lamellae, which are finely distributed throughout the material. The change in nanostructure correlates with a decrease in DC conductivity by approximately 1 order of magnitude to about 10(-15) S m(-1) at high electric fields of 30 and 40 kV mm(-1) and elevated temperature of 70 degrees C. This work opens up an alternative design concept for the insulation of HVDC power cables.
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| 5. |
- Andersson, Mattias, 1985, et al.
(författare)
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Invariant Dielectric Strength upon Addition of Low Amounts of HDPE to LDPE
- 2016
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Ingår i: Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP. - 0084-9162. ; 2016-December, s. 711-714
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Konferensbidrag (refereegranskat)abstract
- Blending of polyethylenes permits to combine the superior mechanical properties of high-density material with the higher purity that is associated with low-density resins. Mixing different polyethylene architectures offers a lot of advantages, but for electrical applications it is important that there is no detrimental effect on the resulting dielectric strength. Here, the nanostructure of crosslinked blends that comprise low-and high-density polyethylene (LDPE and HDPE) is explored. Despite the presence of higher-melting lamellae the formation of electrical trees under alternating current (AC) conditions is found to be invariant for the investigated HDPE content of 1 to 10 wt%. This observation suggests that the use of polyethylene blends is feasible for AC electrical applications.
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| 6. |
- Hynynen, Jonna, 1987, et al.
(författare)
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Enhanced Electrical Conductivity of Molecularly p-Doped Poly(3-hexylthiophene) through Understanding the Correlation with Solid-State Order
- 2017
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Ingår i: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 50:20, s. 8140-8148
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Tidskriftsartikel (refereegranskat)abstract
- Molecular p-doping of the conjugated polymer poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4TCNQ) is a widely studied model system. Underlying structure property relationships are poorly understood because processing and doping are often carried out simultaneously. Here, we exploit doping from the vapor phase, which allows us to disentangle the influence of processing and doping. Through this approach, we are able to establish how the electrical conductivity varies with regard to a series of predefined structural parameters. We demonstrate that improving the degree of solid-state order, which we control through the choice of processing solvent and regioregularity, strongly increases the electrical conductivity. As a result, we achieve a value of up to 12.7 S cm(-2) for P3HT:F4TCNQ, We determine the F4TCNQ anion concentration and find that the number of (bound + mobile) charge carriers of about 10(-4) mol cm(-3) is not influenced by the degree of solid-state order. Thus, the observed increase in electrical conductivity by almost 2 orders of magnitude can be attributed to an increase in charge-carrier mobility to more than 10(-1) cm(2) V-1 s(-1). Surprisingly, in contrast to charge transport in undoped P3HT, we find that the molecular weight of the polymer does not strongly influence the electrical conductivity, which highlights the need for studies that elucidate structure property relationships of strongly doped conjugated polymers.
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| 7. |
- Hynynen, Jonna, 1987, et al.
(författare)
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Enhanced Thermoelectric Power Factor of Tensile Drawn Poly(3-hexylthiophene)
- 2019
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Ingår i: ACS Macro Letters. - : American Chemical Society (ACS). - 2161-1653. ; 8:1, s. 70-76
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Tidskriftsartikel (refereegranskat)abstract
- © 2018 American Chemical Society. The thermoelectric power factor of a broad range of organic semiconductors scales with their electrical conductivity according to a widely obeyed power law, and therefore, strategies that permit this empirical trend to be surpassed are highly sought after. Here, tensile drawing of the conjugated polymer poly(3-hexylthiophene) (P3HT) is employed to create free-standing films with a high degree of uniaxial alignment. Along the direction of orientation, sequential doping with a molybdenum tris(dithiolene) complex leads to a 5-fold enhancement of the power factor beyond the predicted value, reaching up to 16 μW m-1 K-2 for a conductivity of about 13 S cm-1. Neither stretching nor doping affect the glass transition temperature of P3HT, giving rise to robust free-standing materials that are of interest for the design of flexible thermoelectric devices.
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| 8. |
- Hynynen, Jonna, 1987, et al.
(författare)
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Influence of crystallinity on the thermoelectric power factor of P3HT vapour-doped with F4TCNQ
- 2018
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 8:3, s. 1593-1599
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Tidskriftsartikel (refereegranskat)abstract
- Doping of the conjugated polymer poly(3-hexylthiophene) (P3HT) with the p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) is a widely used model system for organic thermoelectrics. We here study how the crystalline order influences the Seebeck coefficient of P3HT films doped with F4TCNQ from the vapour phase, which leads to a similar number of F4TCNQ anions and hence (bound + mobile) charge carriers of about 2 × 10 -4 mol cm -3 . We find that the Seebeck coefficient first slightly increases with the degree of order, but then again decreases for the most crystalline P3HT films. We assign this behaviour to the introduction of new states in the bandgap due to planarisation of polymer chains, and an increase in the number of mobile charge carriers, respectively. Overall, the Seebeck coefficient varies between about 40 to 60 μV K -1 . In contrast, the electrical conductivity steadily increases with the degree of order, reaching a value of more than 10 S cm -1 , which we explain with the pronounced influence of the semi-crystalline nanostructure on the charge-carrier mobility. Overall, the thermoelectric power factor of F4TCNQ vapour-doped P3HT increases by one order of magnitude, and adopts a value of about 3 μW m -1 K -2 in the case of the highest degree of crystalline order.
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| 9. |
- Hynynen, Jonna, 1987
(författare)
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Interplay of Nanostructure and Molecular Doping of Poly(3-hexylthiophene)
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The accelerating growth of the number of inter-connected small devices, which together make up the so-called Internet of Things, is increasing the need for autonomous power sources. Heat is an abundant and often wasted source of energy. Thermoelectric generators could be used to harvest this waste energy. Small devices could potentially be powered by low-grade heat sources using flexible plastic thermoelectric generators. This thesis discusses thermoelectric plastics and in particular the semiconducting polymer poly(3-hexylthiophene) (P3HT). P3HT is a model conjugated polymer that is commercially available and has become an important reference material for the study of optoelectronic processes in organic semiconductors. At first, I investigated isotropic thin films of P3HT doped with 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). I chose doping from the vapour phase as this allowed me to disentangle the influence of polymer processing and doping. I demonstrate that by improving the degree of solid state order of P3HT it is possible to strongly increase the electrical conductivity, which enhances the thermoelectric power factor from 0.2 to 2.7 μW m-1 K-2. Secondly, I explored the impact of orientation on the thermoelectric properties of P3HT. I chose to study highly anisotropic thin films of P3HT, aligned using a high temperature rubbing technique. Further, I investigated free-standing bulk tapes that where uniaxially oriented through tensile drawing. Sequential doping from solution with F4TCNQ or a molybdenum dithiolene complex allowed me to preserve the anisotropy of both thin films and stretched tapes. I found that orientation of the polymer allows to further increase the thermoelectric properties in the direction of alignment. As a result, a power factor of 16 μW m-1 K-2 for tensile drawn tapes and ~ 100 μW m-1 K-2 for rubbed thin films is obtained. Furthermore, oriented P3HT tapes show no change in the glass transition temperature of about 20 C upon doping with a molybdenum dithiolene complex, which suggests that tensile drawing can be used to prepare flexible thermoelectric materials.
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| 10. |
- Hynynen, Jonna, 1987, et al.
(författare)
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'Lignin and extractives first' conversion of lignocellulosic residual streams using UV light from LEDs
- 2021
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Ingår i: Green Chemistry. - : Royal Society of Chemistry (RSC). - 1463-9262 .- 1463-9270. ; 23, s. 8251-8259
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Tidskriftsartikel (refereegranskat)abstract
- Lignocellulosic biomass, especially lignin and extractives, has the potential to substitute fossil precursors in the chemical industry. The conversion of lignin has been intensively researched, but challenges remain as high temperatures and increased pressure are commonly used, which is not energy efficient. Lignin and wood extractives bear chromophoric groups that can absorb light in the ultraviolet (UV) region, which enables photochemical reactions. Ultraviolet light emitting diodes (UV-LEDs) are an emerging technology; they are cheap, versatile, and energy-efficient compared to existing mercury lamps. UV-LEDs were used in this study as a proof of concept for the valorisation of a lignocellulosic residual stream from the pulp and paper industry, sawdust. In a process at ambient temperature and pressure and without the use of a catalyst, we have shown that lignin and extractives can be valorised using light from UV-LEDs. Simplified lignin model compounds were used to pinpoint chemical reactions during irradiation, and to ease the analysis of the sawdust samples. The rate of conversion upon irradiation of the model compounds was found to be 0.7-2.3 g L-1 h(-1), depending on the concentration of the starting compounds.
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