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| 2. |
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| 3. |
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| 4. |
- Anselmo, Ana Sofia, 1980-, et al.
(författare)
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Characterisation of vertical phase separation in polymer : fullerene blend films for photovoltaics by dSIMS and NEXAFS
- 2011
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Ingår i: E-MRS 2011 Spring Meeting. - Malden, MA : John Wiley & Sons. ; , s. 62-63
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Konferensbidrag (refereegranskat)abstract
- Morphological control and characterization of blend films is key in the development of viable polymer solar cells. Spontaneous formation of vertical compositional gradients during solution processing has been shown for polyfluorene:PCBM blends and rationalized with thermodynamic and kinetic models of nucleation and spinodal decomposition.[1, 2] The extent of vertical stratification is affected by polymer side-chain modification aimed at controlling polymer:fullerene miscibility.[3] Here we present high-resolution film morphology results for several polymer:fullerene systems as obtained from near-edge X-ray fine structure spectroscopy (NEXAFS) in partial and in total electron yield modes. Blend films were found to be polymer- enriched at the surface. Dynamic secondary ion mass spectrometry (dSIMS) and NEXAFS give compositional information at different depths, resulting in a more complete picture of the film morphology.
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| 5. |
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Anselmo, Ana Sofia, 1980-, et al.
(författare)
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Tuning the Vertical Phase Separation in Polyfluorene: Fullerene Blend Films by Polymer Functionalization
- 2011
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Ingår i: Chemistry of Materials. - Washington : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 23:9, s. 2295-2302
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Tidskriftsartikel (refereegranskat)abstract
- Achieving control over the nanomorphology of blend films of the fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester, PCBM, with light-absorbing conjugated polymers is an important challenge in the development of efficient solution-processed photovoltaics. Here, three new polyfluorene copolymers are presented, tailored for enhanced miscibility with the fullerene through the introduction of polymer segments with modified side chains, which enhance the polymer's polar character. The composition of the spincoated polymer:PCBM films is analyzed with dynamic secondary ion mass spectrometry (dSIMS). The dSIMS depth profiles demonstrate compositional variations perpendicular to the surface plane, as a result of vertical phase separation, directed by the substrate. These variations propagate to a higher degree through the film for the polymers with a larger fraction of modified side chains. The surface composition of the films is studied by Near-edge X-ray absorption fine structure spectroscopy (NEXAFS). Quantitative analysis of the NEXAFS spectra through a linear combination fit with the spectra of the pure components yields the surface composition. The resulting blend ratios reveal polymer-enrichment of the film surface for all three blends, which also becomes stronger as the polar character of the polymer increases. Comparison of the NEXAFS spectra collected with two different sampling depths shows that the vertical composition gradient builds up already in the first nanometers underneath the surface of the films. The results obtained with this new series of polymers shed light on the onset of formation of lamellar structures in thin polymer:PCBM films prepared from highly volatile solvents.
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| 10. |
- Armstrong, Emily J., et al.
(författare)
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A ground-state complex between methyl viologen and the fluorescent whitening agent 4,4 '-bis(2-sulfostyryl)-biphenyl disodium salt : a fluorescence spectroscopy study
- 2021
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Ingår i: Canadian journal of chemistry (Print). - : Canadian science publishing. - 0008-4042 .- 1480-3291. ; 99:7, s. 563-569
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Tidskriftsartikel (refereegranskat)abstract
- This study explores the quenching of the dianionic fluorescent whitening agent, NFW, by various substances, including methyl viologen (MV), in water and in the presence of beta-cyclodextrin (beta-CD). Results of a fluorescence spectro-scopic examination of the beta-CD-NFW system are presented. It was found that NFW forms a 1:1 inclusion complex with b-CD with an association constant of 2540 +/- 380 M-1. The included NFW fluorescent state is protected by the beta-CD cavity from a range of water-based quenchers (neutral, anionic, and cationic). Quenching proceeds near the diffusion-controlled limit in water for the quenchers tested with the exception of the dicationic MV. Methyl viologen is an extremely efficient quencher of NFW fluorescence with a nominal K-SV similar to 5.0 x 10(3) M-1 in water alone, corresponding to a nominal k(q) of similar to 4 x 10(12) M-1 s(-1), which exceeds the diffusion-controlled limit in this solvent. The quenching efficiency of MV is strongly suppressed in the presence of 10 mM beta-CD (K-SV = 105 +/- 12 M-1) and in the presence of NaCl (K-SV = 106 +/- 9 M-1 at 0.5 M salt). In the absence of CD or salt, there is a strong contribution from static quenching in the MV system; the presence of these additives suppresses the static quenching. Various results suggest the static quenching is due to formation of a ground-state complex between the dianion NFW and the dication MV.
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| 11. |
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| 12. |
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| 13. |
- Carlsson, Gunilla, 1962-, et al.
(författare)
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Polymer film formation studied with fluorescence microscopy
- 2009
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Konferensbidrag (refereegranskat)abstract
- One problem with water-based film-forming systems is the high heat of evaporation, yielding long drying times. Short drying times are commonly important, and solvents with high vapour pressures must be used. This fluorescence microscopy method has successfully been used for studies of low and high volume latex fractions, even for particles with a diameter as small as 100 nm. It is possible to perform statistical analyses from single particles traces, yielding information on interactions with other compounds, as well as changes in the environment of the particle. For fast-drying systems, film formation often occurs under non-equilibrium conditions. The microstructure, frequently due to uncompleted phase separation, is decisive for the film properties. Such microstructures have been found in polymer thin films for optoelectronic devices. Of special interest is the recognition of arrested states and so-called Levy walk diffusion at elevated concentrations, the concentration gradient being a consequence of the drying process
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| 14. |
- Cirillo, Emilio N.M., et al.
(författare)
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A lattice model approach to the morphology formation from ternary mixtures during the evaporation of one component
- 2019
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Ingår i: The European Physical Journal Special Topics. - : Springer. - 1951-6355 .- 1951-6401. ; 228:1, s. 55-68
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Tidskriftsartikel (refereegranskat)abstract
- Stimulated by experimental evidence in the field of solution-born thin films, we study the morphology formation in a three state lattice system subjected to the evaporation of one component. The practical problem that we address is the understanding of the parameters that govern morphology formation from a ternary mixture upon evaporation, as is the case in the fabrication of thin films from solution for organic photovoltaics. We use, as a tool, a generalized version of the Potts and Blume-Capel models in 2D, with the Monte Carlo Kawasaki-Metropolis algorithm, to simulate the phase behaviour of a ternary mixture upon evaporation of one of its components. The components with spin 1, −1 and 0 in the Blume-Capel dynamics correspond to the electron-acceptor, electron-donor and solvent molecules, respectively, in a ternary mixture used in the preparation of the active layer films in an organic solar cell. Furthermore, we introduce parameters that account for the relative composition of the mixture, temperature, and interaction between the species in the system. We identify the parameter regions that are prone to facilitate the phase separation. Furthermore, we study qualitatively the types of formed configurations. We show that even a relatively simple model, as the present one, can generate key morphological features, similar to those observed in experiments, which proves the method valuable for the study of complex systems.
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| 15. |
- Ericsson, Leif, 1964-, et al.
(författare)
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An experimental setup for dip-coating of thin films for organic solar cells under microgravity conditions
- 2021
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Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 92:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the design and testing of a custom-built experimental setup for dip-coating from volatile solutions under microgravity conditionsonboard an aircraft. Function and safety considerations for the equipment are described. The equipment proved to work well, both concerningthe safety and the preparation of thin films. No leakage of the solvents, nor the solvent vapors, was detected, not even in a situation with afluctuating gravitational field due to bad weather conditions. We have shown that the equipment can be used to prepare thin films of polymerblends, relevant for organic solar cells, from solution in a feasible procedure under microgravity conditions. The prepared films are similar tothe corresponding films prepared under 1 g conditions, but with differences that can be related to the absence of a gravitational field duringdrying of the applied liquid coating. We report on some introductory results from the characterization of the thin films that show differencesin film morphology and structure sizes.
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| 16. |
- Heidkamp, Hannah, 1986-, et al.
(författare)
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Morphology of P3HT and PCBM blends in thin films obtained with different deposition methods
- 2011
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Konferensbidrag (refereegranskat)abstract
- Patterns and structures, formed when a semiconducting polymer blend in solution is subject to controlled evaporation, have been of great interest due to their influence on the performance of organic devices. By controlling the processes of pattern formation, function properties of organic semiconductor structures can be tailored, allowing for facile manufacturing of the active layers in organic devices, e.g. solar cells.By analyzing the morphologies of polymer blends resulting from different deposition methods, a deeper insight into the pattern formation process can be acquired. In this study, we have analyzed the morphology of blends of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) formed upon solvent evaporation. We used the following deposition methods: dip-coating, droplet evaporation within a constrained geometry and drop-casting. Dip-coated films revealed various types of morphology depending on the coating speed. At low coating speeds, where evaporation is the dominant factor, well-ordered patterns were obtained. When increasing the coating speed, viscous forces become dominant over evaporation yielding optically homogenous films [2]. Morphologically similar structures to those observed at low coating speeds, were also obtained with spatially constrained droplets. The blend morphologies were analyzed with polarized, fluorescence and atomic force microscopy [1].References:[1] C. M. Björström Svanström, J. Rysz, A. Bernasik, A. Budkowski, F. Zhang, O. Inganäs, M. R. Andersson, K. O. Magnusson, J. J. Benson-Smith, J. Nelson, and E. Moons, Adv. Mat. 21, 4398-4403 (2009)[2] R. Z. Rogowski and A. A. Darhuber, Langmuir 26, 11485-93 (2010)
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| 17. |
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| 18. |
- Heidkamp, Hannah, 1986-, et al.
(författare)
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Morphology of polymer blends in films made by dip-coating
- 2011
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Konferensbidrag (refereegranskat)abstract
- Thin spincoated polymer films are used in various applications and there has been anincreasing demand to understand and get precise control over the film formation process. One of the most exciting applications is organic solar cells which have an active layer made of a polymer based blend. The film morphology has a strong effect on the efficiency of solar cells and therefore it is crucial to understand the film formation process in order to tailor thedesired morphology [1].In this study we are combining and comparing results from three different deposition processes: drop-casting, sphere-on-flat arrangement and dip-coating. We are using dip-coating to produce thin films of polymer blends with different morphologies under controlled conditions. The main goal is to gain a deeper insight into the processes that occur while solvent evaporates and to understand why certain structures are formed.Drop-casting allows for little control of the structure formation. In the sphere-on-flat arrangement a droplet of a solution is constrained between a half-sphere and the substrate, which provides more controllable conditions for the deposition process. For more precise control, dip-coating can be used, where a substrate is withdrawn from a solution at a constant speed.In this study we have used the polymer poly(3-hexylthiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) dissolved in toluene. These components are the model system for studies on organic solar cells [1]. The dip-coated films show a wide variety of morphologies depending on the coating speed. This dependence can be rationalized by the different mechanisms occurring at low and high speeds: At low speeds, evaporation is dominant, [2] resulting in well ordered patterns. At high speeds, viscous forces become dominant, [2] yielding optically homogeneous films.[1] G. Dennler, M. C. Scharber, C. J. Brabec, Adv. Mat. 21, 1323-1338 (2009)[2] R. Z. Rogowski and A. A. Darhuber, Langmuir 26, 11485-93 (2010)
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| 19. |
- Heidkamp, Hannah, 1986-, et al.
(författare)
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Polymer film formation studied with fluorescence microscopy and AFM
- 2010
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Ingår i: Molecular Processes at Solid Surfaces. ; , s. 49-
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Konferensbidrag (refereegranskat)abstract
- Thin polymer films are used in many applications such as paint, paper coatings and electronic devices. For these applications, it is important to have knowledge about the film formation process, since it affect the film morphology and the morphology is important for the applications.One method for studying film formation in situ is fluorescence microscopy. By labeling a target molecule or particle with a fluorophore, the targets movements can be traced as the solvent evaporates [1-3]. If information gained from studies of particle movements during film formation and wet state behavior are combined, information about the film formation process can be obtained. Examination of the final film surfaces with regular light microscopy and AFM gives additional information about the film formation.These methods have been used for studying the formation of negatively charged latex films. It was shown that the films are greatly affected by adding positively charged surfactants [4-5]. Since latex is a water-based system it has relatively long drying times. Systems based on high-vapor pressure organic solvents have much shorter drying times and the film formation occurs under non-equilibrium conditions. This results in incomplete phase separation, which in turn gives microstructures in the film. These microstructures are of great interest since they affect the properties of the film and its function [6-7]. Our aim is to develop the methods used for latex studies in order to be able to apply them to study film formation of polymer blends used for photovoltaic applications. The goal is to get more knowledge about the film forming process and a deeper understanding about the mechanisms behind the formation of microstructures.[1] Carlsson G., Warszynski P., van Stam J., J. Colloid Interface Sci., 2003, 267, 500-508[2] Carlsson G., van Stam J., Nord. Pulp Pap. Res. J., 2005, 20, 192-199[3] Carlsson G., Järnström L., van Stam J., J. Colloid Interface Sci., 2006, 298, 162-171[4] Heidkamp H., Master thesis, Karlstad University 2009.[5] Paakkonen, J., Master thesis, Karlstad University 2010.[6] Björström C.M., Magnusson K.O., Moons E., Synth. Metals, 2005, 152, 109-112[7] Moons E., J. Phys.: Condens. Matter, 2002, 14, 12235-12260
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| 20. |
- Hillerström, Anna, et al.
(författare)
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Ibuprofen loading into mesostructured silica using liquid carbon dioxide as a solvent
- 2009
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Ingår i: Green Chemistry. - : Royal Society of Chemistry (RSC). - 1463-9262 .- 1463-9270. ; 11:5, s. 662-667
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Tidskriftsartikel (refereegranskat)abstract
- It has been demonstrated that the pharmaceutical molecule, Ibuprofen, can be loaded into mesoporous silica using liquid (near-critical) carbon dioxide as the solvent, and that the resulting material had a high Ibuprofen content (300 mg Ibuprofen/g SiO2). A high enrichment (300 times) of Ibuprofen in the pores was observed in comparison to the Ibuprofen concentration in the solution. When similar experiments were performed in CO2 (l) mixed with minor amounts (5 mol-%) of other organic cosolvents (cyclohexane, acetone or methanol), a significantly lower loading capacity of Ibuprofen into the mesoporous material was achieved. The drug-loaded mesoporous silica material was analyzed with Thermogravimetric Analysis (TGA), confocal Raman microscopy, X-ray Powder Diffraction (XRPD) and Scanning Electron Microscopy (SEM). It was found that the Ibuprofen loaded into the mesoporous silica host was amorphous and that Ibuprofen was present both at the surface and in the centre of the mesoporous silica particles. Furthermore, the SEM images did not reveal any large flakes of Ibuprofen molecules outside the mesoporous silica particles.
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| 21. |
- Hillerström, Anna, et al.
(författare)
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Solvent strategies for loading and release in mesoporous silica
- 2014
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Ingår i: Colloid and Interface Science Communications. - Amsterdam : Elsevier BV. - 2215-0382. ; 3, s. 5-8
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Tidskriftsartikel (refereegranskat)abstract
- A model molecule, ibuprofen, was loaded in the pores of mesoporous silica by adsorption from nonpolar solvents (liquid carbon dioxide and cyclohexane) and from a polar solvent (methanol). It was sufficient with a very low concentration of ibuprofen in the nonpolar solvents to achieve maximum loading of ibuprofen in the mesoporous particles. When using liquid carbon dioxide, the pores of the mesoporous silica particles were filled completely with ibuprofen at a lower ibuprofen concentration than similar experiments performed with cyclohexane. When methanol was used, the maximum amount of loaded ibuprofen was never achieved. Furthermore, x-ray scattering showed that all ibuprofen loaded into the mesoporous particles were in an amorphous state. Ibuprofen was released from the mesoporous particles to water within a couple of minutes, regardless of solvent used for loading. It was found that the release of ibuprofen from mesoporous silica was much faster than that of crystalline ibuprofen.
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| 22. |
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| 23. |
- Holmes, Natalie P., et al.
(författare)
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Engineering Two-Phase and Three-Phase Microstructures from Water-Based Dispersions of Nanoparticles for Eco-Friendly Polymer Solar Cell Applications
- 2018
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 30:18, s. 6521-6531
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Tidskriftsartikel (refereegranskat)abstract
- Nanoparticle organic photovoltaics, a subfield of organic photovoltaics (OPV), has attracted increasing interest in recent years due to the eco-friendly fabrication of solar modules afforded by colloidal ink technology. Importantly, using this approach it is now possible to engineer the microstructure of the light absorbing/charge generating layer of organic photovoltaics; decoupling film morphology from film deposition. In this study, single-component nanoparticles of poly(3-hexylthiophene) (P3HT) and phenyl-C61 butyric acid methyl ester (PC61BM) were synthesized and used to generate a two-phase microstructure with control over domain size prior to film deposition. Scanning transmission X-ray microscopy (STXM) and electron microscopy were used to characterize the thin film morphology. Uniquely, the measured microstructure was a direct input for a nanoscopic kinetic Monte Carlo (KMC) model allowing us to assess exciton transport properties that are experimentally inaccessible in these single-component particles. Photoluminescence, UV-vis spectroscopy measurements, and KMC results of the nanoparticle thin films enabled the calculation of an experimental exciton dissociation efficiency (ηED) of 37% for the two-phase microstructure. The glass transition temperature (Tg) of the materials was characterized with dynamic mechanical thermal analysis (DMTA) and thermal annealing led to an increase in ηED to 64% due to an increase in donor-acceptor interfaces in the thin film from both sintering of neighboring opposite-type particles in addition to the generation of a third mixed phase from diffusion of PC61BM into amorphous P3HT domains. As such, this study demonstrates the higher level of control over donor-acceptor film morphology enabled by customizing nanoparticulate colloidal inks, where the optimal three-phase film morphology for an OPV photoactive layer can be designed and engineered.
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| 24. |
- Holmes, Natalie P., et al.
(författare)
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Unravelling donor–acceptor film morphologyformation for environmentally-friendly OPV inkformulations
- 2019
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Ingår i: Green Chemistry. - : Royal Society of Chemistry. - 1463-9262 .- 1463-9270. ; 21:18, s. 5090-5103
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Tidskriftsartikel (refereegranskat)abstract
- The challenge of coating organic photovoltaics (OPV) from green solvents is to achieve the requirednanostructured interpenetrating network of donor and acceptor domains based on a rational choice ofsolvent approach as opposed to the usual trial-and-error methods. We demonstrate here that we canachieve a bicontinuous interpenetrating network with nanoscale phase separation for the chosen donor–acceptor material system poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl]:phenyl-C61 butyric acid methyl ester (TQ1:PC61BM) when processing from green solvent ink formulations.This structure is achieved by first calculating the Hansen solubility parameters (HSP) of the donor andacceptor materials, followed by careful choice of solvents with selective relative solubilities for the twomaterials based on the desired order of precipitation necessary for forming a nanostructured interdigitatednetwork morphology. We found that the relative distances in Hansen space (Ra) between TQ1 andthe primary solvent, on the one hand, and PC61BM and the primary solvent, on the other hand, could becorrelated to the donor–acceptor morphology for the formulations based on the solvents d-limonene,anisole, and 2-methyl anisole, as well as the halogenated reference solvent o-dichlorobenzene. Thisnanostructured blend film morphology was characterised with scanning transmission X-ray microscopy(STXM) and transmission electron microscopy (TEM), and the film surface composition was analysed bynear edge X-ray absorption fine structure (NEXAFS) spectroscopy. Hansen solubility theory, based onsolution thermodynamics, has been used and we propose an HSP-based method that is a general platformfor the rational design of ink formulations for solution-based organic electronics, in particular facilitatingthe green solvent transition of organic photovoltaics. Our results show that the bulk heterojunctionmorphology for a donor–acceptor system processed from customised solvent mixtures can be predictedby the HSP-based method with good reliability.
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| 25. |
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| 26. |
- Jalan, Ishita, 1991-, et al.
(författare)
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Donor-acceptor polymer complex formation in solution confirmed by spectroscopy and atomic-scale modelling
- 2023
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 11:27, s. 9316-9326
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Tidskriftsartikel (refereegranskat)abstract
- In all-polymer solar cells, high performance is attributed to the fine-grained morphology of the film in the active layer. However, the mechanism by which this fine-grained morphology is achieved remains unknown. Polymeric non-fullerene acceptors have the potential to restrict the self-aggregation, typical of non-fullerene small molecule acceptors. Here we employed a blend of the polymeric acceptor PF5-Y5 and the donor polymer PBDB-T to investigate the balance between molecular interactions in solution. Temperature-dependent absorption spectra show evidence of temperature-induced disaggregation of both donor and acceptor polymers, where the donor polymer disaggregation depends on the solvent polarity. Concentration-dependent fluorescence spectra of blend solutions display blue-shifted acceptor emission upon dilution, similar to that observed in acceptor solutions, and a decreased tendency for charge transfer from donor to acceptor upon dilution. Excitation spectra of dilute blend solutions contain an increased contribution to the long-wavelength acceptor emission, as compared to pure acceptor solutions, from a chromophore that absorbs in a region where the donor does not absorb. These observations can be explained by donor-acceptor complexation in dilute blend solutions, that is stabilized in more polar solvents. Moreover, the near IR-region of the absorption spectrum could be matched with the calculated electronic excitations of donor-acceptor complexes of PBDB-T and PF5-Y5 oligomers. The results corroborate that the interaction between segments of the donor and acceptor polymer chains favours the formation of donor-acceptor charge transfer complexes, stabilized by hybridization of the molecular orbitals, which reduces the electronic energy. The proposed donor-acceptor complex formation competes with the donor and acceptor self-aggregation and is influenced by the solvent environment. These pre-formed donor-acceptor complexes in low-concentration solutions can be expected to have important consequences on the film morphology of all-polymer blends. The results from this joint experimental-theoretical spectroscopy study provide insights that can guide the design of compatible donor and acceptor polymers for future high-performance organic solar cells.
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| 27. |
- Jalan, Ishita, 1991-
(författare)
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Film morphology for organic solar cells : Effect of Solubility and Gravity Conditions
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organic photovoltaics is a promising environmentally friendly technology, due to their printability, light-weight nature and mechanical flexibility, and the possibility to use off-grid. Research and development in this field has resulted in power conversion efficiencies of over 15%. To further improve the efficiency, it is important to understand the connection between the morphology of the active layer and the performance of the device. This thesis focuses on understanding on a molecular level of the morphology formation in a thin coated film of a polymer bend, using two different approaches. One approach will focus on the thermodynamics of conjugated polymers in relation to the morphology, by using the Hansen solubility Parameters (HSP) and solution chemistry. The second approach focuses on understanding phase separation between the two polymers in the active layer. To be able to study phase separation, films were fabricated under microgravity conditions, as previous studies show that in these conditions phase separation mechanism is slowed down. Atomic force microscopy is used to characterize the resulting morphology of the thin films. Preliminary studies in this thesis showed that using HSP is a good tool, to understanding solvent-solute and solute-solute interactions in solution and to guide the final film morphology in relation to solubility. Furthermore, HSP is a good tool for the preliminary screening of alternative solvents and solvent blends for environmentally friendly processing solvents for upscaling. It was also found that dip coating of films under microgravity conditions provides a tool to study the early stages of the phase separation, as well as facilitate the study of the dependence of the morphology on the thicknesses of the coating. More work is needed to be able to separate the complex effect of hypergravity and to eliminate uncertainty concerning if the deposited wet film is completely dried under the microgravity phase.
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| 28. |
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| 29. |
- Jalan, Ishita, 1991-
(författare)
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Solution Chemistry and Morphological Properties for Organic Solar Cells : Exploring Alternative Solvents Using Microgravity and Modelling as Tools
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organic photovoltaics (OPVs) have the advantage of the accessibility of energy for all, due to facile and low-cost processing, with its low energy payback time compared to other technologies, therefore promising applications. Research and development have led to power conversion efficiencies of nearly 20% and now catching up to their inorganic counterparts. To enhance the efficiency even further, it is crucial to get an insight into the correlation between the active layer's morphology and the device's performance as well as how to control the morphology of the active layer.This thesis focuses on a molecular understanding of the morphology formation in a thin film of a polymer blend for OPVs. By using Hansen solubility parameters (HSP) and solution chemistry, the thermodynamics of the phase separation of conjugated polymers, both in solution and thin films, is investigated. Furthermore, to get a deeper understanding of the phase separation between the polymers in the active layer, films were prepared under microgravity conditions, as the phase separation is slowed down under such conditions. Atomic force microscopy combined with infrared spectroscopy was used to characterize the morphology of the dry film.Our results show that understanding solvent-solute and solute-solute interactions is key to comprehending morphology formation. Moreover, HSP proves to be a valuable tool for the initial screening of alternative solvents and solvent blends for more environmentally friendly processing and upscaling. It was found that microgravity conditions provide a tool to study the early stages of phase separation, as well as facilitate the study of the dependence of the morphology on the thicknesses of the film. Additional research is needed to separate the complex effects of gravity fluctuations and to eliminate uncertainty concerning the complete drying of the film under the microgravity phase.
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| 30. |
- Jalan, Ishita, et al.
(författare)
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Using solubility parameters to model more environmentally friendly solvent blends for organic solar cell active layers
- 2019
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 12:23, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- To facilitate industrial applications, as well as for environmental and health purposes, there is a need to find less hazardous solvents for processing the photoactive layer of organic solar cells. As there are vast amounts of possibilities to combine organic solvents and solutes, it is of high importance to find paths to discriminate among the solution chemistry possibilities on a theoretical basis. Using Hansen solubility parameters (HSP) offers such a path. We report on some examples of solvent blends that have been found by modelling HSP for an electron donor polymer (TQ1) and an electron acceptor polymer (N2200) to match solvent blends of less hazardous solvents than those commonly used. After the theoretical screening procedure, solubility tests were performed to determine the HSP parameters relevant for the TQ1:N2200 pair in the calculated solvent blends. Finally, thin solid films were prepared by spin-coating from the solvent blends that turned out to be good solvents to the donor-acceptor pair. Our results show that the blend film morphology prepared in this way is similar to those obtained from chloroform solutions.
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| 31. |
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| 32. |
- Lindqvist, Camilla, et al.
(författare)
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Fullerene aggregation in thin films of polymer blends for solar cell applications
- 2018
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 11:11
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Tidskriftsartikel (refereegranskat)abstract
- We report on the effects of the film morphology on the fluorescence spectra for a thin film including a quinoxaline-based co-polymer (TQ1) and a fullerene derivative ([6,6]-phenyl-C71-butyric acid methyl ester-PC70BM). The ratio between the polymer and the fullerene derivative, as well as the processing solvent, were varied. Besides the main emission peak at 700 nm in the fluorescence spectra of thin films of this phase-separated blend, a broad emission band is observed with a maximum at 520-550 nm. The intensity of this emission band decreases with an increasing degree of mixing in the film and becomes most prominent in thicker films, films with high PC70BM content, and films that were spin-coated from solvents with lower PC70BM solubility. We assign this emission band to aggregated PC70BM.
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| 33. |
- Liu, Yanfeng, et al.
(författare)
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In Situ Optical Spectroscopy Demonstrates the Effect of Solvent Additive in the Formation of All-Polymer Solar Cells
- 2022
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 13:50, s. 11696-11702
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Tidskriftsartikel (refereegranskat)abstract
- 1-Chloronaphthalene (CN) has been a common solvent additive in both fullerene- A nd nonfullerene-based organic solar cells. In spite of this, its working mechanism is seldom investigated, in particular, during the drying process of bulk heterojunctions composed of a donor:acceptor mixture. In this work, the role of CN in all-polymer solar cells is investigated by in situ spectroscopies and ex situ characterization of blade-coated PBDB-T:PF5-Y5 blends. Our results suggest that the added CN promotes self-aggregation of polymer donor PBDB-T during the drying process of the blend film, resulting in enhanced crystallinity and hole mobility, which contribute to the increased fill factor and improved performance of PBDB-T:PF5-Y5 solar cells. Besides, the nonradiative energy loss of the corresponding device is also reduced by the addition of CN, corresponding to a slightly increased open-circuit voltage. Overall, our observations deepen our understanding of the drying dynamics, which may guide further development of all-polymer solar cells.
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| 34. |
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| 35. |
- Muntean, Stela Andrea, et al.
(författare)
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Quantitative analysis of phase formation and growth in ternary mixtures upon evaporation of one component
- 2022
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Ingår i: Physical review. E. - : American Physical Society. - 2470-0045 .- 2470-0053. ; 106:2
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Tidskriftsartikel (refereegranskat)abstract
- We perform a quantitative analysis of Monte Carlo simulation results of phase separation in ternary blends upon evaporation of one component. Specifically, we calculate the average domain size and plot it as a function of simulation time to compute the exponent of the obtained power law. We compare and discuss results obtained by two different methods, for three different models: two-dimensional (2D) binary-state model (Ising model), 2D ternary-state model with and without evaporation. For the ternary-state models, we study additionally the dependence of the domain growth on concentration, temperature and initial composition. We reproduce the expected 1/3 exponent for the Ising model, while for the ternary-state model without evaporation and for the one with evaporation we obtain lower values of the exponent. It turns out that phase separation patterns that can form in this type of systems are complex. The obtained quantitative results give valuable insights towards devising computable theoretical estimations of size effects on morphologies as they occur in the context of organic solar cells.
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| 36. |
- Olsson, Robert, et al.
(författare)
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Effects on ink setting in flexographic printing : coating polarity and dot gain
- 2006
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Ingår i: Nordic Pulp & Paper Research Journal. - Sundsval : Mittuniversitetet. - 0283-2631 .- 2000-0669. ; 21:5, s. 569-574
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Tidskriftsartikel (refereegranskat)abstract
- Research has been carried out to study the factors that affect ink setting, with particular focus on the effects of coating polarity and the printing pressure in flexographic printing. Different coating layers were prepared on non-porous polyester films. The coating colours were based on calcium carbonates of different particle sizes, lattices of different polarities and a carboxymethyl cellulose (CMC) thickener. Two latex films were prepared to characterise the surface tension properties through contact angle measurements, which were repeated several times for each latex film and testing fluid. The coating layers were printed in a laboratory printing press under different printing pressures using a water-based flexographic ink. Results showed different print densities for a given amount of ink transferred on the different substrates, with the latex character rather than the pore size of the substrates affecting the print density. Compared with the less polar substrate, the more polar substrate resulted in a higher print density. A non-linear relationship between physical dot enlargement and printing pressure was visualised, resulting from increasing printing form deformation. A mathematical model for printing plate deformation has been proposed that takes into account elastic deformations. It was found that the diameter of the printed halftone dot was larger in the print direction than in the cross print direction. (7 fig, 6 tab, 17 ref)
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| 37. |
- Setta, Mario, et al.
(författare)
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A mesoscopic lattice model for morphology formation in ternary mixtures with evaporation
- 2023
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Ingår i: Communications in nonlinear science & numerical simulation. - : Elsevier. - 1007-5704 .- 1878-7274. ; 119
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Tidskriftsartikel (refereegranskat)abstract
- We develop a mesoscopic lattice model to study the morphology formation in inter-acting ternary mixtures with the evaporation of one component. As concrete potentialapplication of our model, we wish to capture morphologies as they are typically arisingduring the fabrication of organic solar cells. In this context, we consider an evaporatingsolvent into which two other components are dissolved, as a model for a 2-componentcoating solution that is drying on a substrate. We propose a 3-spins dynamics to describethe evolution of the three interacting species. As main tool, we use a Monte CarloMetropolis-based algorithm, with the possibility of varying the system’s temperature,mixture composition, interaction strengths, and evaporation kinetics. The main novelty isthe structure of the mesoscopic model – a bi-dimensional lattice with periodic boundaryconditions, divided into square cells to encode a mesoscopic range interaction amongthe units. We investigate the effect of the model parameters on the structure of theresulting morphologies. Finally, we compare the results obtained with the mesoscopicmodel with corresponding ones based on an analogous lattice model with a short rangeinteraction among the units, i.e. when the mesoscopic length scale coincides with themicroscopic length scale of the lattice.
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| 38. |
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| 39. |
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| 40. |
- van Stam, Jan, 1958-, et al.
(författare)
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Morphology in Dip-Coated Blend Films for Photovoltaics Studied by UV/VIS Absorption and Fluorescence Spectroscopy
- 2018
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Ingår i: Organic Electronics and Photonics. - : SPIE-INT SOC OPTICAL ENGINEERING. - 9781510619012
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Konferensbidrag (refereegranskat)abstract
- Blend thin films, prepared by dip-coating, of polyfluorene (F8 or PFO), acting as an electron donor, and [6,6]-phenyl-C-61-butyric acid methyl ester (PC60BM), acting as the electron acceptor, have been characterized by UV/VIS absorption spectroscopy, static and dynamic fluorescence, and atomic force microscopy. Four different solvents were used for the film preparation; the monohalogenated fluorobenzene and chlorobenzene and their dihalogenated counterparts o-difluorobenzene and o-dichlorobenzene, respectively. Fluid mechanics calculations were used to determine the withdrawal speed for each solvent, in order to prepare wet films of comparable thicknesses. The resulting dry films were also of similar thicknesses. It was found that the choice of solvent influences the ability for F8 to form its beta-phase.
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| 41. |
- Yao, Nannan, et al.
(författare)
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In Situ Study the Dynamics of Blade-Coated All-Polymer Bulk Heterojunction Formation and Impact on Photovoltaic Performance of Solar Cells
- 2023
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Ingår i: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; , s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- All-polymer solar cells (all-PSCs) have achieved impressive progress by employing acceptors polymerized from well performing small-molecule non-fullerene acceptors. Herein, the device performance and morphology evolution in blade-coated all-PSCs based on PBDBT:PF5–Y5 blends prepared from two different solvents, chlorobenzene (CB), and ortho-xylene (o-XY) are studied. The absorption spectra in CB solution indicate more ordered conformation for PF5–Y5. The drying process of PBDBT:PF5–Y5 blends is monitored by in situ multifunctional spectroscopy and the final film morphology is characterized with ex situ techniques. Finer-mixed donor/acceptor nanostructures are obtained in CB-cast film than that in o-XY-cast ones, corresponding to more efficient charge generation in the solar cells. More importantly, the conformation of polymers in solution determines the overall film morphology and the device performance. The relatively more ordered structure in CB-cast films is beneficial for charge transport and reduced non-radiative energy loss. Therefore, to achieve high-performance all-PSCs with small energy loss, it is crucial to gain favorable aggregation in the initial stage in solution.
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