| 21. |
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| 22. |
- 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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| 23. |
- 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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| 24. |
- 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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| 25. |
- 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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| 26. |
- 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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| 27. |
- 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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| 28. |
- 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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| 29. |
- 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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| 30. |
- Andersson, Mattias, et al.
(författare)
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Mixed C60/C70 based fullerene acceptors in polymer bulk-heterojunction solar cells
- 2012
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Ingår i: Organic Electronics: physics, materials, applications. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 13:12, s. 2856-2864
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Tidskriftsartikel (refereegranskat)abstract
- Different mixtures of identically substituted C60 and C70 based fullerens have been used as acceptors in three polymer: fullerene systems that strongly express various performance limiting aspects of bulk heterojunction solar cells. Results are correlated with, and discussed in terms of e.g. morphology, charge separation, and charge transport. In these systems, there appears to be no relevant differences in either mobility or energy level positions between the identically substituted C60 and C70 based fullerenes tested. Examples of how fullerene mixtures influence the nano-morphology of the active layer are given. An upper limit to the open circuit voltage that can be obtained with fullerenes is also suggested.
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