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- Ajjan Godoy, Fátima Nadia
(författare)
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Biohybrid Polymer Electrodes for Renewable Energy Storage
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Daily and seasonally fluctuating energy supply and demand requires adequate energy storage solutions. In recent years electrochemical supercapacitors have attracted considerable attention due to their ability to both store and deliver electrical energy efficiently. Our efforts are focused on developing and optimizing sustainable organic electrode materials for supercapacitors based on renewable bioorganic materials, offering a cheap, environmentally friendly and scalable alternative to store energy. In particular, we are using the second most abundant biopolymer in nature, lignin (Lig), which is an insulating material. However, when used in combination with electroactive and conducting polymers such as polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT), the biohybrid electrodes PPy/Lig and PEDOT/Lig display significantly enhanced energy storage performance as compared to the pristine conducting polymers without the lignin. Redox cyclic voltammetry and galvanostatic charge/discharge measurements indicate that the enhanced performance is due to the additional pseudocapacitance generated by the quinone moieties in lignin. Moreover, a conjugated redoxpolymer poly(aminoanthraquinone) PAAQ, with intrinsic quinone functions and excellentstability, has been combined with lignin and PEDOT resulting in a trihybrid bioelectrode. PEDOT compensates the low conductivity of PAAQ and provides electrical pathways to the quinone groups. The electrochemically generated quinones undergo a two electron, two protonredox process within the biohybrid electrodes as revealed by FTIR spectroelectrochemistry.These remarkable features reveal the exciting potential of a full organic energy storage device with long cycle life. Therefore, supercapacitor devices were designed in symmetric or asymmetric two electrode configuration. The best electrochemical performance was achieved by the asymmetric supercapacitor based on PEDOT+Lignin/PAAQ as the positive electrode and PEDOT/PAAQ as the negative electrode. This device exhibits superior electrochemical performance and outstanding stability after 10000 charge/discharge cycles due to the synergistic effect of the two electrodes. Finally, we have characterized the response of this supercapacitor device when charged with the intermittent power supply from an organic photovoltaic module. We have designed charging/discharging conditions such that reserve power was available in the storage device at all times. This work has resulted in an inexpensive fully organic system witht he dual function of energy conversion and storage.
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| 5. |
- Andersson, Lars Mattias, 1976-
(författare)
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Electronic Transport in Polymeric Solar Cells and Transistors
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main topic of this dissertation is electronic charge transport in polymeric and molecular organic materials and material blends intended for solar cell applications. Charge transport in polymers is a strange beast and carrier mobility is rarely a well-defined number. Measurements on different sample geometries and under different conditions tend to give different results and when everything is to be related to solar cell performance it is imperative that there is a way to correlate the results from different measurements. Polymer solar cells utilize composite materials for their function. This puts an additional twist on charge transport studies, as there will also be interaction between the different phases to take into account.Several measurement techniques have been used and their interrelationships as well as information on their relevance for solar cells have been investigated. Field effect transistors (FET) with an organic active layer have proved to be one of the more versatile measurement geometries and are also an interesting topic in itself. FETs are discussed both as a route for material characterization and as components. A main result correlates bias stress in organic field effect transistors with the electronic structure of the material.Power conversion efficiency in solar cells is discussed with respect to electrical properties. The interaction of different blend materials and the impact of stoichiometry on transport properties in the active layer have been investigated. Results indicate that charge transport properties frequently are a key determining factor for which material combinations and ratios that works best.Some work on the conductive properties of nano-fibers coated with semiconducting polymers has also been done and is briefly discussed. The conductive properties of nano-fibers have been studied through potential imaging.
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| 6. |
- Andersson, Mattias, 1973-
(författare)
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Colour Calibration of Trichromatic Capturing Devices
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In a time where there is an increasing demand for easily accessible and up-to-date information, digital printing has become a link between traditional printed media and electronic media. Over the last years, applications such as variable data printing, personalised printing and print on demand have changed the way in which printed matter is produced and handled. The print quality of products produced by digital printing systems has improved considerably in recent years. The main reason for this improvement is better printer hardware but the printing paper is still a very influential factor. The two major technologies, inkjet and electrophotography and their respective applications put very different demands on the paper, mechanically, chemically and optically. Nevertheless, the differences in print quality across digital printing systems are decreasing, except for one area − colour reproduction. The growth of the market of consumer colour imaging products, such as digital printers and desktop printers, has been enormous during the last years. As a consequence of this, consumer expectations on colour reproduction have risen significantly, as even very small failures in colour reproduction can drastically reduce the visual impression of an otherwise impeccably reproduced image. Therefore, as consumer expectations continue to rise, a high and repeatable quality of colour image reproduction is a growing challenge for producers of digital printing devices as well as for paper producers. However, this is impossible to achieve without precise methods and routines to measure colour reproduction quality. The use of spectrophotometers for colour measurements of printed substrates is widely spread among paper producers as well as within the printing industry. Spectrophotometers are precise instruments for point-wise measurements. However, the measurement procedure is very time-consuming and therefore, faster methods for colour measurements are longed-for. If the spectrophotometers used today could be replaced with trichromatic capturing devices such as flatbed scanners or digital cameras, colour characterisation would be not only faster, but also less expensive. In addition, if the trichromatic devices are colorimetrically calibrated, spatial image information can be combined with colour information, making it possible to measure quality attributes related to colour image rendering that are impossible to capture with point-wise measurements. Today, flatbed scanners and digital cameras provide robust and high-quality image capturing capabilities at a relatively low cost. Furthermore, scanner and camera-based systems for automated objective measurements of print quality parameters have already become widely used tools for print quality measurements of print-related properties such as print mottle, sharpness and bleeding. However, the colour calibration of trichromatic capturing devices is not free from obstacles. In colour calibrations, where the aim is to measure colour of printed matter, knowledge about the properties of the capturing device, the printing substrate, the printing process and the printer function are all of great importance. In the work presented here, methods for colour characterisation of printing processes are proposed as well as methods for colour characterisation and calibration of trichromatic capturing devices. Furthermore, the media dependency problem inherent to colour calibrations of trichromatic capturing devices is discussed. Examples are given on how properties of the printed substrate, such as the content of fluorescent whitening agents, influence colour calibrations as well as colour measurements in general.
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| 7. |
- Andersson, Viktor
(författare)
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Electron tomography and optical modelling for organic solar cells
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organic solar cells using carbon based materials have the potential to deliver cheap solar electricity. The aim is to be able to produce solar cells with common printing techniques on flexible substrates, and as organic materials can be made soluble in various solvents, they are well adapted to such techniques. There is a large variation of organic materials produced for solar cells, both small molecules and polymers. Alterations of the molecular structure induce changes of the electrical and optical properties, such as band gap, mobility and light absorption. During the development of organic solar cells, the step of mixing of an electron donor and an electron acceptor caused a leap in power conversion efficiency improvement, due to an enhanced exciton dissociation rate. Top performing organic solar cells now exhibit a power conversion efficiency of over 10%. Currently, a mix of a conjugated polymer, or smaller molecule, and a fullerene derivative are commonly used as electron donor and acceptor. Here, the blend morphology plays an important role. Excitons formed in either of the donor or acceptor phase need to diffuse to the vicinity of the donor-acceptor interface to efficiently dissociate. Exciton diffusion lengths in organic materials are usually in the order of 5-10 nm, so the phases should not be much larger than this, for good exciton quenching. These charges must also be extracted, which implies that a network connected to the electrodes is needed. Consequently, a balance of these demands is important for the production of efficient organic solar cells.Morphology has been found to have a significant impact on the solar cell behaviour and has thus been widely studied. The aim of this work has been to visualize the morphology of active layers of organic solar cells in three dimensions by the use of electron tomography. The technique has been applied to materials consisting of conjugated polymers blended with fullerene derivatives. Though the contrast in these blends is poor, three-dimensional reconstructions have been produced, showing the phase formation in three dimensions at the scale of a few nanometres. Several material systems have been investigated and preparation techniques compared.Even if excitons are readily dissociated and paths for charge extraction exist, the low charge mobilities of many materials put a limit on film thickness. Although more light could be absorbed by increased film thickness, performance is hampered due to increased charge recombination. A large amount of light is thus reflected and not used for energy conversion. Much work has been put into increasing the light absorption without hampering the solar cell performance. Aside from improved material properties, various light trapping techniques have been studied. The aim is here to increase the optical path length in the active layer, and in this way improve the absorption without enhanced extinction coefficient.At much larger dimensions, light trapping in solar cells with folded configuration has been studied by the use of optical modelling. An advantage of these V-cells is that two materials with complementing optical properties may be used together to form a tandem solar cell, which may be connected in either serial or parallel configuration, with maintained light trapping feature. In this work optical absorption in V-cells has been modelled and compared to that of planar ones.
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| 8. |
- Asplund, Maria, 1978-
(författare)
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Conjugated Polymers for Neural Interfaces : Prospects, possibilities and future challenges
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Within the field of neuroprosthetics the possibility to use implanted electrodes for communication with the nervous system is explored. Much effort is put into the material aspects of the electrode implant to increase charge injection capacity, suppress foreign body response and build micro sized electrode arrays allowing close contact with neurons. Conducting polymers, in particular poly(3,4-ethylene dioxythiophene) (PEDOT), have been suggested as materials highly interesting for such neural communication electrodes. The possibility to tailor the material both mechanically and biochemically to suit specific applications, is a substantial benefit with polymers when compared to metals. PEDOT also have hybrid charge transfer properties, including both electronic and ionic conduction, which allow for highly efficient charge injection. Part of this thesis describes a method of tailoring PEDOT through exchanging the counter ion used in electropolymerisation process. Commonly used surfactants can thereby be excluded and instead, different biomolecules can be incorporated into the polymer. The electrochemical characteristics of the polymer film depend on the ion. PEDOT electropolymerised with heparin was here determined to have the most advantageous properties. In vitro methods were applied to confirm non-cytotoxicity of the formed PEDOT:biomolecular composites. In addition, biocompatibility was affirmed for PEDOT:heparin by evaluation of inflammatory response and neuron density when implanted in rodent cortex. One advantage with PEDOT often stated, is its high stability compared to other conducting polymers. A battery of tests simulating the biological environment was therefore applied to investigate this stability, and especially the influence of the incorporated heparin. These tests showed that there was a decline in the electroactivity of PEDOT over time. This also applied in phosphate buffered saline at body temperature and in the absence of other stressors. The time course of degradation also differed depending on whether the counter ion was the surfactant polystyrene sulphonate or heparin, with a slightly better stability for the former. One possibility with PEDOT, often overlooked for biological applications, is the use of its semi conducting properties in order to include logic functions in the implant. This thesis presents the concept of using PEDOT electrochemical transistors to construct textile electrode arrays with in-built multiplexing. Using the electrolyte mediated interaction between adjacent PEDOT coated fibres to switch the polymer coat between conducting and non conducting states, then transistor function can be included in the conducting textile. Analogue circuit simulations based on experimentally found transistor characteristics proved the feasibility of these textile arrays. Developments of better polymer coatings, electrolytes and encapsulation techniques for this technology, were also identified to be essential steps in order to make these devices truly useful. In summary, this work shows the potential of PEDOT to improve neural interfaces in several ways. Some weaknesses of the polymer and the polymer electronics are presented and this, together with the epidemiological data, should point in the direction for future studies within this field.
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| 9. |
- Asplund, Maria, et al.
(författare)
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Construction of wire electrodesand 3D woven logicas a potential technology forneuroprosthetic implants
- 2008
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Ingår i: IEEE Transactions on Biomedical Engineering. - 0018-9294 .- 1558-2531.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- New strategies to improve neuron coupling to neuroelectronic implants are needed. In particular, tomaintain functional coupling between implant and neurons, foreign body response like encapsulation must meminimized. Apart from modifying materials to mitigate encapsulation it has been shown that with extremely thinstructures, encapsulation will be less pronounced. We here utilize wire electrochemical transistors (WECTs) usingconducting polymer coated fibers. Monofilaments down to 10 μm can be successfully coated and weaved intocomplex networks with built in logic functions, so called textile logic. Such systems can control signal patterns at alarge number of electrode terminals from a few addressing fibres. Not only is fibre size in the range where lessencapsulation is expected but textiles are known to make successful implants because of their soft and flexiblemechanical properties. Further, textile fabrication provides versatility and even three dimensional networks arepossible. Three possible architectures for neuroelectronic systems are discussed. WECTs are sensitive to dehydrationand materials for better durability or improved encapsulation is needed for stable performance in biologicalenvironments.
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| 10. |
- Bergqvist, Jonas, et al.
(författare)
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Determination of optical constants and phase transition temperatures in polymer fullerene thin films for polymer solar cells
- 2012
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Plastic photovoltaics combining semiconducting polymers with fullerene derivatives have the potentialto become the first cost efficient solar cells able to compete with fossil fuels. The maximum powerconversion efficiency is already 8.3%[1] , and new polymers arrive frequently in the search for efficienciesof 10%. As a first step in the screening of candidate materials, the optical constants of the purepolymer as well as the polymer blend with fullerenes are determined from Variable Angle SpectroscopicEllipsometry (VASE), using Tauc-Lorentz oscillator models, throughout the solar spectrum. Thesemodels are then used to predict the upper limits to photocurrent generation in devices, in transfermatrix simulations of the multilayer thin film photovoltaic devices. This forms an essential step in thechoice of materials for optimization in devices.Materials optics measurements are also used to deduce the phase diagram of polymer and polymerblend films. The glass transition temperature is very important for plastic solar cells and mustbe higher than the 80C a device can reach to avoid degradation during operation. Temperaturedependent ellipsometric measurements has proven to be a feasible way to determine phase transitionsin polymer thin films[2] . These transitions are displayed as a sudden change of the volumetricexpansion coefficient, and are manifested by an abrupt increase of thickness at the phase transitiontemperature. For thickness determination a Cauchy model is applied to the transparent infrared partof the spectra.References1. Z. He, C. Zhong, X. Huang, W-Y. Wong, H. Wu, L. Chen, S. Su, Y Cao, Advanced Materials 23, 4636(2011)2. M. Campoy-Quiles, P.G. Etchegoin, D.D.C. Bradley, Synthetic Metals 155, 279(2005)
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