| 1. |
- Bentham, James, et al.
(författare)
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A century of trends in adult human height
- 2016
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Ingår i: eLIFE. - 2050-084X. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Being taller is associated with enhanced longevity, and higher education and earnings. We reanalysed 1472 population-based studies, with measurement of height on more than 18.6 million participants to estimate mean height for people born between 1896 and 1996 in 200 countries. The largest gain in adult height over the past century has occurred in South Korean women and Iranian men, who became 20.2 cm (95% credible interval 17.522.7) and 16.5 cm (13.319.7) taller, respectively. In contrast, there was little change in adult height in some sub-Saharan African countries and in South Asia over the century of analysis. The tallest people over these 100 years are men born in the Netherlands in the last quarter of 20th century, whose average heights surpassed 182.5 cm, and the shortest were women born in Guatemala in 1896 (140.3 cm; 135.8144.8). The height differential between the tallest and shortest populations was 19-20 cm a century ago, and has remained the same for women and increased for men a century later despite substantial changes in the ranking of countries.
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| 2. |
- Bentham, James, et al.
(författare)
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A century of trends in adult human height
- 2016
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Ingår i: eLIFE. - : eLife Sciences Publications Ltd. - 2050-084X. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Being taller is associated with enhanced longevity, and higher education and earnings. We reanalysed 1472 population-based studies, with measurement of height on more than 18.6 million participants to estimate mean height for people born between 1896 and 1996 in 200 countries. The largest gain in adult height over the past century has occurred in South Korean women and Iranian men, who became 20.2 cm (95% credible interval 17.5–22.7) and 16.5 cm (13.3– 19.7) taller, respectively. In contrast, there was little change in adult height in some sub-Saharan African countries and in South Asia over the century of analysis. The tallest people over these 100 years are men born in the Netherlands in the last quarter of 20th century, whose average heights surpassed 182.5 cm, and the shortest were women born in Guatemala in 1896 (140.3 cm; 135.8– 144.8). The height differential between the tallest and shortest populations was 19-20 cm a century ago, and has remained the same for women and increased for men a century later despite substantial changes in the ranking of countries.
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| 3. |
- 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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| 4. |
- Anselmo, Ana Sofia, 1980-
(författare)
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Materials aspects in spin-coated films for polymer photovoltaics
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polymer-based photovoltaics have the potential to contribute to boosting photovoltaic energy conversion overall. Besides allowing large-area inexpensive processing, polymeric materials have the added benefit of opening new market applications for photovoltaics due to their low-weight and interesting mechanical properties. The energy conversion efficiency values of polymer photovoltaics have reached new record values over the past years. It is however crucial that stability issues are addressed together with efficiency optimization. Understanding fundamental materials aspects is key in both areas.In the work presented in this thesis, the morphology of polymer:fullerene films and its influence on device performance was studied, as well as the effect of light exposure on the surface of fullerene films. Several polyfluorene copolymers were used for the morphology studies, where the effects of changing spin-coating solvent and of side chain engineering were investigated with dynamic secondary ion mass spectrometry (dSIMS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Polymer-enriched surfaces were found in all blend films, even in the cases with homogeneous distributions in the bulk. Side chain engineering of the polymer led to gradual changes in the compositional variations perpendicular to the surface, and to slight variations in the photocurrent. The electronic structure of the fullerene derivative PCBM was studied in detail and the spectroscopic fingerprint of the materials was analysed by comparison with theoretically simulated spectra. Photo-stability studies done in air showed that the surface of fullerene films underwent severe damages at the molecular level, which is evident from changes in the valence band and X-ray absorption spectra. These changes were explained by transitions from sp2-type to sp3 hybridization of the carbon atoms in the cage that resulted in the destruction of the fullerene cage.
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| 5. |
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| 6. |
- Anselmo, Ana Sofia, 1980-, et al.
(författare)
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Molecular Orientation and Composition at the Surface of Spin-Coated Polyfluorene:Fullerene Blend Films
- 2013
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Ingår i: Journal of Polymer Science Part B. - Hoboken, New Jersey : John Wiley & Sons. - 0887-6266 .- 1099-0488. ; 51:3, s. 176-182
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Tidskriftsartikel (refereegranskat)abstract
- The surface composition in spin-coated films of polyfluorene:fullerene blends was determined quantitatively by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. By comparing partial and total electron yield spectra, we found vertical compositional differences in the surface region. Furthermore, the orientation of the polymer chains was investigated by variable-angle NEXAFS. Blend films of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole] with [6,6]-phenyl-C61-butyric acid methyl ester in two different blend ratios were studied. Results showed polymer enrichment of the surfaces for films with a polymer:fullerene weight ratio of 20:80 and of 50:50, spin-coated from both chlorobenzene and chloroform solutions. The angular dependence of the NEXAFS spectra of the pure polymer films showed a preferential plane-on orientation, which was slightly stronger in the subsurface region than at the surface. In blend films, this orientational preference was less pronounced and the difference between surface and subsurface vanished
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| 7. |
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| 8. |
- Anselmo, Ana Sofia, 1980-, et al.
(författare)
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Photodegradation of the electronic structure of PCBM and C60 films in air
- 2016
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Ingår i: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 652, s. 220-224
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Tidskriftsartikel (refereegranskat)abstract
- Fullerenes are common electron acceptors in organic solar cells. Here the photostability in air of the electronic structures of spin-coated PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) and evaporated C60 films are studied using ultraviolet photoelectron spectroscopy (UPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. After exposing these materials in air to simulated sunlight, the filled and empty molecular orbitals are strongly altered, indicating that the conjugated π-system of the C60-cage has degraded. Even a few minutes in normal lab light induces changes. These results stress the importance of protecting fullerene-based films from light and air during processing, operation, and storage.
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| 9. |
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| 10. |
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| 11. |
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| 12. |
- Anselmo, Ana Sofia, 1980-
(författare)
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The morphology of polyfluorene : fullerene blend films for photovoltaic applications
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polymer photovoltaic systems whose photoactive layer is a blend of a semiconducting polymer with a fullerene derivative in a bulk heterojunction configuration are amongst the most successful organic photovoltaic devices nowadays. The three-dimensional organization in these layers (the morphology) plays a crucial role in the performance of the devices. Detailed characterization of this organization at the nanoscale would provide valuable information for improving future material and architectural design and for device optimization.In this thesis, the results of morphology studies of blends of several polyfluorene copolymers (APFOs) blended with a fullerene derivative are presented. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy was combined with dynamic Secondary Ion Mass Spectrometry (dSIMS) for surface and in-depth characterization of the blend films. NEXAFS was performed using two different electron detection methods, partial (PEY) and total (TEY) electron yield, which provide information from different depth regimes. Quantitative compositional information was obtained by fitting the spectra of the blend films with a linear combination of the spectra of films of the pure components. In blends of APFO3 with PCBM in two different blend ratios (1:1 and 1:4 of polymer:fullerene) NEXAFS data show the existence of compositional gradients in the vertical direction for both blend ratios, with clear polymer enrichment of the free surface. A series of APFOs with systematic changes in the side-chains was studied and it was shown that those small modifications can affect polymer:fullerene interaction and induce vertical phase separation. Polymer-enrichment of the free surface was clearly identified, in accordance with surface energy minimization mechanisms, and a compositional gradient was revealed already in the first few nanometers of the surface of the blend films. dSIMS showed that this vertical phase separation propagates throughout the film. It was possible to determine that as the polar character of the polymer increases, and thus the polymer:fullerene miscibility is improved, the tendency for vertical phase separation becomes stronger.
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| 13. |
- 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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| 14. |
- Belova, Valentina, et al.
(författare)
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Evidence for Anisotropic Electronic Coupling of Charge Transfer States in Weakly Interacting Organic Semiconductor Mixtures
- 2017
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 139:25, s. 8474-8486
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Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive investigation of the charge-transfer (CT) effect in weakly interacting organic semiconductor mixtures. The donor-acceptor pair diindenoperylene (DIP) and N,N′-bis(2-ethylhexyl)-1,7-dicyanoperylene-3,4/9,10-bis(dicarboxyimide) (PDIR-CN2) has been chosen as a model system. A wide range of experimental methods was used in order to characterize the structural, optical, electronic, and device properties of the intermolecular interactions. By detailed analysis, we demonstrate that the partial CT in this weakly interacting mixture does not have a strong effect on the ground state and does not generate a hybrid orbital. We also find a strong CT transition in light absorption as well as in photo- and electroluminescence. By using different layer sequences and compositions, we are able to distinguish electronic coupling in-plane vs out-of-plane and, thus, characterize the anisotropy of the CT state. Finally, we discuss the impact of CT exciton generation on charge-carrier transport and on the efficiency of photovoltaic devices.
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| 15. |
- Brumboiu, Iulia E., et al.
(författare)
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Near-edge X-ray Absorption Fine Structure Study of the C60-derivative PCBM
- 2013
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Ingår i: Chemical Physics Letters. - Amsterdam : Elsevier BV. - 0009-2614 .- 1873-4448. ; 568-569, s. 130-134
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Tidskriftsartikel (refereegranskat)abstract
- The fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester plays a key role for electron transport in polymer solar cells. We have studied the unoccupied molecular orbitals of PCBM by near edge X-ray absorption fine structure spectroscopy and were able to assign the main resonances to molecular moieties by comparison with calculated sum spectra of individual carbons. We analyzed specifically the origin of the high-energy shoulder to the first π∗-resonance and identified contributions from the lowest-energy transition of a specific carbon in the phenyl and from transitions to higher unoccupied orbitals of the unmodified carbons in the C60-cage.
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| 16. |
- Dzwilewski, Andrzej, et al.
(författare)
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Light induced effects in PCBM:P3HT blend films
- 2012
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Ingår i: Hybrid and Organics Photovoltaics Conference. - SEFIN, Castelló (Spain). - 9788494018909 ; , s. 155-155
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Konferensbidrag (refereegranskat)
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| 17. |
- Dzwilewski, Andrzej, et al.
(författare)
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The effect of light exposure on P3HT:PCBM films : a NEXAFS study
- 2011
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Konferensbidrag (refereegranskat)abstract
- A simple photolithography method was developed for patterning organic field effect transistors (OFETs) prepared from blends of poly(3-hexylthiophene), P3HT, and [6,6]-phenyl-C61-butyric acid methyl ester, PCBM.(1) This Photo-induced and Resist-free Imprint patterning (PRI) technique allows also the single solution step production of organic CMOS circuits.(2) It consists of two subsequent processing steps: 1) exposure: photo-irradiation of the P3HT:PCBM blend by visible laser light and 2) development: rinsing of the film in an organic solvent mixture that is selective for PCBM. As a result, two electronically different materials are obtained, i.e. the exposed and developed (ED) material, and the unexposed and developed (UD) material. The method is based on the modification of the PCBM component in the irradiated area, which becomes effectively insoluble in the solvent mixture, while the PCBM in the non-irradiated area is removed during development. Therefore, we expect that the UD material is pure P3HT, a hypothesis that is confirmed by the p-type conductivity of the ED region. Near-Edge X-ray Absorption Fine Structure spectroscopy (NEXAFS) was used to determine the surface composition of these films. C K-edge NEXAFS spectra of pristine, photo-exposed, and developed blend films, as well as films of the pure components were measured at the synchrotron facility MAX-lab in Lund, Sweden. The spectra for P3HT and PCBM are significantly different and the components can be clearly distinguished in the blend spectra. From the relative intensities of the P3HT and PCBM peaks, the actual blend composition can be estimated, both on the surface, using partial electron yield (PEY), and deeper in the sub-surface region of the film, using total electron yield (TEY). From the similarity of the spectra of the UD blend sample and the pure P3HT sample, we conclude that the remaining material after washing the pristine blend is indeed P3HT, and the ED blend sample retains its two-component character. The surface composition of the blend films is significantly more polymer-rich than the bulk blend ratio used to prepare the film. Both for the pristine blend and the photo-exposed blend differences are observed between the PEY and TEY spectra, indicating the existence of a polymer-enriched surface. Such gradients in thin films of P3HT:PCBM blends have been observed by others using variable-angle spectroscopic ellipsometry,(3) NEXAFS,(4) and neutron reflectometry,(5) and also in other polymer:PCBM blends by dynamic secondary ion mass spectrometry (d-SIMS).(6)References (1) Dzwilewski, A.; Wagberg, T.; Edman, L. J. Am. Chem.Soc. 2009, 131, 4006. (2) Dzwilewski, A.; Matyba, P.; Edman, L. J. Phys. Chem. B 2010, 114, 135. (3) Campoy-Quiles, M., et al., Nature Materials 2008, 7,158-164 (4) Germack,D.S. et al., Appl. Phys. Lett. 2009, 94, 233303. (5) Kiel, J.W. et al., Soft Matter 2010, 6, 641-646. (6) Björström, C.M. et al, J. Phys.: Condens. Matter 2005, 17, L529-L534.
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| 18. |
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| 19. |
- Hörmann, Ulrich, et al.
(författare)
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Voc from a Morphology Point of View : the Influence of Molecular Orientation on the Open Circuit Voltage of Organic Planar Heterojunction Solar Cells
- 2014
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Ingår i: Journal of physical chemistry C. - : American Chemical Society (ACS). - 1932-7455 .- 1932-7447. ; 118:46, s. 26462-26470
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Tidskriftsartikel (refereegranskat)abstract
- The film morphology and device performance of planar heterojunctionsolar cells based on the molecular donor material α-sexithiophene (6T) are investigated.Planar heterojunctions of 6T with two different acceptor molecules, the C60 fullerene anddiindenoperylene (DIP), have been prepared. The growth temperature of the 6T bottomlayer has been varied between room temperature and 100 °C for each acceptor. By meansof X-ray diffraction and X-ray absorption, we show that the crystallinity and the molecularorientation of 6T is influenced by the preparation conditions and that the 6T filmtemplates the growth of the subsequent acceptor layer. These structural changes areaccompanied by changes in the characteristic parameters of the correspondingphotovoltaic cells. This is most prominently observed as a shift of the open circuitvoltage (Voc): In the case of 6T/C60 heterojunctions, Voc decreases from 0.4 to 0.3 V,approximately, if the growth temperature of 6T is increased from room temperature to 100°C. By contrast, Voc increases from about 1.2 V to almost 1.4 V in the case of 6T/DIP solarcells under the same conditions. We attribute these changes upon substrate heating toincreased recombination in the C60 case while an orientation dependent intermolecular coupling seems to change the origin of the photovoltaic gap in the DIP case.
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| 20. |
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| 21. |
- Müller, Christian, et al.
(författare)
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Phase behaviour of liquid-crystalline polymer/fullerene organic photovoltaic blends : thermal stability and miscibility
- 2011
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Ingår i: Journal of Materials Chemistry. - : RSC Publishing. - 0959-9428 .- 1364-5501. ; 21, s. 10676-10684
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Tidskriftsartikel (refereegranskat)abstract
- The thermal behaviour of an organic photovoltaic (OPV) binary system comprised of a liquidcrystalline fluorene-based polymer and a fullerene derivative is investigated. We employ variabletemperature ellipsometry complemented by photo- and electroluminescence spectroscopy as well as optical microscopy and scanning force nanoscopy to explore phase transitions of blend thin films. The high glass transition temperature correlates with the good thermal stability of solar cells based on these materials. Furthermore, we observe partial miscibility of the donor and acceptor together with the tendency of excess fullerene derivative to segregate into exceedingly large domains. Thus, for charge generation less adequate bulk-heterojunction nanostructures are poised to develop if this mixture is exposed to more elevated temperatures. Gratifyingly, the solubility of the fullerene derivative in the polymer phase is found to decrease if a higher molecular-weight polymer fraction is employed, which offers routes towards improving the photovoltaic performance of non-crystalline OPV blends.
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