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- 2019
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Tidskriftsartikel (refereegranskat)
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- Cheng, Hao-Wen, et al.
(författare)
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Realizing Efficient Charge/Energy Transfer and Charge Extraction in Fullerene-Free Organic Photovoltaics via a Versatile Third Component
- 2019
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Ingår i: Nano letters (Print). - : AMER CHEMICAL SOC. - 1530-6984 .- 1530-6992. ; 19:8, s. 5053-5061
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Tidskriftsartikel (refereegranskat)abstract
- Solution-processed organic photovoltaics (OPVs) based on bulk-heterojunctions have gained significant attention to alleviate the increasing demend of fossil fuel in the past two decades. OPVs combined of a wide bandgap polymer donor and a narrow bandgap nonfullerene acceptor show potential to achieve high performance. However, there are still two reasons to limit the OPVs performance. One, although this combination can expand from the ultraviolet to the near-infrared region, the overall external quantum efficiency of the device suffers low values. The other one is the low open-circuit voltage (V-OC) of devices resulting from the relatively downshifted lowest unoccupied molecular orbital (LUMO) of the narrow bandgap. Herein, the approach to select and incorporate a versatile third component into the active layer is reported. A third component with a bandgap larger than that of the acceptor, and absorption spectra and LUMO levels lying within that of the donor and acceptor, is demonstrated to be effective to conquer these issues. As a result, the power conversion efficiencies (PCEs) are enhanced by the elevated short-circuit current and V-OC; the champion PCEs are 11.1% and 13.1% for PTB7-Th:IEICO-4F based and PBDB-T:Y1 based solar cells, respectively.
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- Sommar, Jonas, et al.
(författare)
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Seasonal variations in metallic mercury (Hg0) vapor exchange overbiannual wheat–corn rotation cropland in the North China Plain
- 2016
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Ingår i: Biogeosciences. - : European Geosciences Union (EGU). - 1726-4170 .- 1726-4189. ; 13:7, s. 2029-2049
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Tidskriftsartikel (refereegranskat)abstract
- Air surface gas exchange of Hg-0 was measured in five approximately bi-weekly campaigns (in total 87 days) over a wheat corn rotation cropland located on the North China Plain (NCP) using the relaxed eddy accumulation (REA) technique. The campaigns were separated over the duration of a full-year period (2012-2013) aiming to capture the flux pattern over essential growing stages of the planting system with a low homogeneous topsoil Hg content (similar to 45 ng g(-1)). Contrasting pollution regimes influenced air masses at the site and corresponding Hg-0 concentration means (3.3 in late summer to 6.2 ng m(-3) in winter) were unanimously above the typical hemispheric background of 1.5-1.7 ng m(-3) during the campaigns. Extreme values in bi-directional net Hg-0 exchange were primarily observed during episodes of peaking Hg-0 concentrations. In tandem with under-canopy chamber measurements, the above-canopy REA measurements provided evidence for a balance between Hg-0 ground emissions and uptake of Hg-0 by the developed canopies. During the wheat growing season covering similar to 2 / 3 of the year at the site, net field-scale Hg emission prevailed for periods of active plant growth until canopy senescence (mean flux: 20.0 ng m(-3)), showing the dominance of Hg soil efflux during warmer seasons. In the final vegetative stage of corn and wheat, ground and above canopy Hg flux displayed inversed daytime courses with a near mid-day maximum (emission) and minimum (deposition), respectively. In contrast to wheat, Hg uptake of the corn canopy at this stage offset ground Hg emissions with additional removal of Hg from the atmosphere. Differential uptake of Hg between wheat (C-3 species) and corn (C-4 species) foliage is discernible from estimated Hg flux (per leaf area) and Hg content in mature cereal leaves, being a factor of >3 higher for wheat (at 120 ng g(-1) dry weight). Furthermore, this study shows that intermittent flood irrigation of the air-dry field induced a short pulse of Hg emission due to displacement of Hg present in the surface soil horizon. A more lingering effect of flood irrigation is however suppressed Hg soil emissions, which for wet soil (similar to 30 % vol) beneath the corn canopy was on average a factor of similar to 3 lower than that for drier soil (<10 % vol) within wheat stands Extrapolation of the campaign Hg flux data (mean: 7.1 ng m(-2) h(-1)) to the whole year suggests the wheat corn rotation cropland to be a net source of atmospheric Hg. The observed magnitude of annual wet deposition flux (similar to 8.8 mu g Hg m(-2)) accounted for a minor fraction of soil Hg evasion flux prevailing over the majority of the year. Therefore, we suggest that dry deposition of other forms of airborne Hg-0 constitutes the dominant pathway of Hg-0 input to this local ecosystem and that these deposited forms would be gradually transformed and re-emitted as Hg-0 rather than being sequestered here. In addition, after crop harvesting, the practice of burning agricultural residue with considerable Hg content rather than straw return management yields seasonally substantial atmospheric Hg-0 emissions from croplands in the NCP region.
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- Zhu, Wei, et al.
(författare)
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Global observations and modeling of atmosphere-surface exchange of elemental mercury : a critical review
- 2016
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 16:7, s. 4451-4480
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Forskningsöversikt (refereegranskat)abstract
- Reliable quantification of air-surface fluxes of elemental Hg vapor (Hg-0) is crucial for understanding mercury (Hg) global biogeochemical cycles. There have been extensive measurements and modeling efforts devoted to estimating the exchange fluxes between the atmosphere and various surfaces (e.g., soil, canopies, water, snow, etc.) in the past three decades. However, large uncertainties remain due to the complexity of Hg-0 bidirectional exchange, limitations of flux quantification techniques and challenges in model parameterization. In this study, we provide a critical review on the state of science in the atmosphere-surface exchange of Hg-0. Specifically, the advancement of flux quantification techniques, mechanisms in driving the air-surface Hg exchange and modeling efforts are presented. Due to the semi-volatile nature of Hg-0 and redox transformation of Hg in environmental media, Hg deposition and evasion are influenced by multiple environmental variables including seasonality, vegetative coverage and its life cycle, temperature, light, moisture, atmospheric turbulence and the presence of reactants (e.g., O-3, radicals, etc.). However, the effects of these processes on flux have not been fundamentally and quantitatively determined, which limits the accuracy of flux modeling. We compile an up-to-date global observational flux database and discuss the implication of flux data on the global Hg budget. Mean Hg-0 fluxes obtained by micrometeorological measurements do not appear to be significantly greater than the fluxes measured by dynamic flux chamber methods over unpolluted surfaces (p = 0.16, one-tailed, Mann-Whitney U test). The spatiotemporal coverage of existing Hg-0 flux measurements is highly heterogeneous with large data gaps existing in multiple continents (Africa, South Asia, Middle East, South America and Australia). The magnitude of the evasion flux is strongly enhanced by human activities, particularly at contaminated sites. Hg-0 flux observations in East Asia are comparatively larger in magnitude than the rest of the world, suggesting substantial re-emission of previously deposited mercury from anthropogenic sources. The Hg-0 exchange over pristine surfaces (e.g., background soil and water) and vegetation needs better constraints for global analyses of the atmospheric Hg budget. The existing knowledge gap and the associated research needs for future measurements and modeling efforts for the air-surface exchange of Hg-0 are discussed.
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