Colloidal semiconductor nanocrystals have generated tremendous interest because of their solution processability and robust tunability. Among such nanocrystals, the colloidal quantum dot (CQD) draws ...the most attention for its well-known quantum size effects. In the last decade, applications of CQDs have been booming in electronics and optoelectronics, especially in photovoltaics. Electronically doped semiconductors are critical in the fabrication of solar cells, because carefully designed band structures are able to promote efficient charge extraction. Unlike conventional semiconductors, diffusion and ion implantation technologies are not suitable for doping CQDs. Therefore, researchers have creatively developed alternative doping methods for CQD materials and devices. In order to provide a state-of-the-art summary and comprehensive understanding to this research community, we focused on various doping techniques and their applications for photovoltaics and demystify them from different perspectives. By analyzing two classes of CQDs, lead chalcogenide CQDs and perovskite CQDs, we compared different working scenarios of each technique, summarized the development in this field, and raised our own future perspectives.
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•Ten methods were applied to estimate baseflow in Yiluo River watershed.•Yiluo River was a typical “Groundwater-dependent River”.•The mechanism of the methods generated a critical ...impact on separation.•Baseflow and baseflow index showed significant spatiotemporal variation.
Baseflow is the stable part of streamflow meeting the ecological water requirement of the watershed in dry season. Baseflow separation plays a vital role in maintaining the biodiversity of watershed ecosystem. However, research systematically on spatiotemporal variety in watershed scale in baseflow separation is not well documented. In this study, we chose six hydrometric stations in the Yiluo River watershed and carried ten methods (in the group of HYSEP, UKIH and digital filter methods) to isolate the daily runoff data from 2002 to 2021. Two evaluation indicators (Nash-Sutcliffe efficiency coefficient and relative error) were applied to measure the accuracy of those methods. The results showed that the Yiluo River had the average annual baseflow of 10.73 × 108 m3 and average baseflow index (BFI) of 0.42. The UKIH and Eckhardt filtering method methods were fit for the Yiluo River watershed. Temporally, BFI in the wet season (average of 0.35) was smaller than the dry season (average of 0.49). As to the interannual scale, the baseflow in the wet year accounted for nearly a half (49 %) of whole twenty years. Spatially, the BFI of lower reaches (0.35 in Heishiguan) was higher than upper reaches (0.30 in Dongwan and 0.24 in Lushi) on the same river. Nearly half river runoff was from the groundwater recharge and suggests that the Yiluo River is a heavily “Groundwater-dependent River”. Those results of this study can enhance the understanding of spatiotemporal changes of baseflow separations in watershed scale and provide the important references to the international readers.
•C:N, N:P, and C:P ratios decreased with soil depth in a mature subtropical forest.•C-N spatially declined in correlation with depth, whereas C-P and N-P increased.•Spatial variation in soil C, N, ...and P density was driven by different environmental factors at the landscape scale.
As the balance of multiple chemical substances in ecological interactions, stoichiometry of soil carbon (C), nitrogen (N) and phosphorus (P) is critical for forest sustainability. Soil depth is critical in regulating soil C-N-P stoichiometry; however, the vertical pattern of soil C-N-P stoichiometry remains unclear at the local scale in mature subtropical forests. Here, we sampled 555 soil columns from 185 grids at three soil depths (i.e., 0–20, 20–40, and 40–60 cm) in a mature subtropical evergreen forest of eastern China. We found the C:N, N:P, and C:P ratios decreased with increasing soil depth. However, the strength of bivariate correlations among C, N, and P converged from the top to the deepest soil layer. Such vertical convergence was jointly driven by decreasing C-N (R2 as 0.84, 0.80, and 0.76) and increasing C-P (R2 as 0.11, 0.26, and 0.31) correlations from 0–20 to 40–60 cm depths. Further analyses with a structural equation model showed that the spatial variations in C, N, and P were influenced by different environmental factors. For example, the spatial variations in soil organic C and total N in the top soil layer were largely influenced by soil pH, whereas the spatial variation in total P was jointly influenced by topographical, biotic, and soil factors. Our results validate the important impact of soil depth on soil C-N-P stoichiometry at the landscape scale. The converging bivariate correlations between C, N and P along the increasing soil depth indicate the depth-dependent roles of different nutrient elements in soil C cycling.
Theory suggests that intraspecific trait variability may promote species coexistence when competitively inferior species have higher intraspecific trait variability than their superior competitors. ...Here, we provide empirical evidence for this phenomenon in tree seedlings. We evaluated intraspecific variability and plastic response of ten traits in 6750 seedlings of ten species in a three-year greenhouse experiment. While we observed no relationship between intraspecific trait variability and species competitiveness in competition-free homogeneous environments, an inverse relationship emerged under interspecific competition and in spatially heterogeneous environments. We showed that this relationship is driven by the plastic response of the competitively inferior species: Compared to their competitively superior counterparts, they exhibited a greater increase in trait variability, particularly in fine-root traits, in response to competition, environmental heterogeneity and their combination. Our findings contribute to understanding how interspecific competition and intraspecific trait variability together structure plant communities.
Biochar application to soils may increase carbon (C) sequestration due to the inputs of recalcitrant organic C. However, the effects of biochar application on the soil greenhouse gas (GHG) fluxes ...appear variable among many case studies; therefore, the efficacy of biochar as a carbon sequestration agent for climate change mitigation remains uncertain. We performed a meta‐analysis of 91 published papers with 552 paired comparisons to obtain a central tendency of three main GHG fluxes (i.e., CO2, CH4, and N2O) in response to biochar application. Our results showed that biochar application significantly increased soil CO2 fluxes by 22.14%, but decreased N2O fluxes by 30.92% and did not affect CH4 fluxes. As a consequence, biochar application may significantly contribute to an increased global warming potential (GWP) of total soil GHG fluxes due to the large stimulation of CO2 fluxes. However, soil CO2 fluxes were suppressed when biochar was added to fertilized soils, indicating that biochar application is unlikely to stimulate CO2 fluxes in the agriculture sector, in which N fertilizer inputs are common. Responses of soil GHG fluxes mainly varied with biochar feedstock source and soil texture and the pyrolysis temperature of biochar. Soil and biochar pH, biochar applied rate, and latitude also influence soil GHG fluxes, but to a more limited extent. Our findings provide a scientific basis for developing more rational strategies toward widespread adoption of biochar as a soil amendment for climate change mitigation.
Quantum Junction Solar Cells Tang, Jiang; Liu, Huan; Zhitomirsky, David ...
Nano letters,
09/2012, Letnik:
12, Številka:
9
Journal Article
Recenzirano
Colloidal quantum dot solids combine convenient solution-processing with quantum size effect tuning, offering avenues to high-efficiency multijunction cells based on a single materials synthesis and ...processing platform. The highest-performing colloidal quantum dot rectifying devices reported to date have relied on a junction between a quantum-tuned absorber and a bulk material (e.g., TiO2); however, quantum tuning of the absorber then requires complete redesign of the bulk acceptor, compromising the benefits of facile quantum tuning. Here we report rectifying junctions constructed entirely using inherently band-aligned quantum-tuned materials. Realizing these quantum junction diodes relied upon the creation of an n-type quantum dot solid having a clean bandgap. We combine stable, chemically compatible, high-performance n-type and p-type materials to create the first quantum junction solar cells. We present a family of photovoltaic devices having widely tuned bandgaps of 0.6–1.6 eV that excel where conventional quantum-to-bulk devices fail to perform. Devices having optimal single-junction bandgaps exhibit certified AM1.5 solar power conversion efficiencies of 5.4%. Control over doping in quantum solids, and the successful integration of these materials to form stable quantum junctions, offers a powerful new degree of freedom to colloidal quantum dot optoelectronics.
Understanding the spatiotemporal nitrate retention in streambed is essential for developing management practices in reducing nitrate enrichment. However，the process of nitrate change in the profile ...of streambed at an elevated nitrate across a watershed scale is still not sufficiently investigated. In this study, we used a combination of hydraulic and hydro‐geochemistry methods to quantify total nitrate retention in streambeds of an agriculture‐intensive watershed in Central China. To conduct surface and groundwater measurements, we collected 1440 water samples for nitrate analysis from 40 shallow drilled wells during the dry and wet seasons from 2018 to 2020. The results showed a clear spatiotemporal variation of nitrate retention in streambed in the watershed. Spatially, nitrate retention in the midstream and downstream reaches was higher than that of the upstream reach. The lowest point of nitrate retention in downstream both in dry and wet seasons was at the depth of 0.75 m. While the lowest nitrate retention was found in midstream and upstream reaches, both in the dry and wet seasons at the depth between 1.5 and 2.5 m. Temporally, nitrate retention was higher in the wet season (1.56 μg N m−2d−1) than in dry season (1.41 μg N m−2d−1). DO min at 3 mg/L was found to the nitrate retention zero threshold in up and midstream. Water change fluxes and nitrate retention both have positive and negative relationship at watershed scale. Nitrate retention at the watershed scale was strongly affected by streambed lithology, precipitation, surface water ‐ groundwater exchange, and human activities. Those findings can provide reference for nitrate removal in international important agricultural areas.
The relationship between the nitrate retention with water fluxes and dissolve oxygen at the interface between surface water and groundwater.
Tuning the electronic bandgap of quantum dots via the quantum size-effect enables the tailored spectral response of quantum dot photodetectors, light emitting diodes, and solar cells. Chemically ...synthesized colloidal quantum dot (CQD) provides an option to produce such quantum material in an inexpensive way. Here, we propose an approach to fabricate filter-free narrowband photodetectors in near-infrared and mid-infrared regions using PbS and HgSe CQD materials, respectively. The spectrally selective bandpass response is implemented by taking advantage of the carrier collection narrowing effect using a photodiode device architecture. Narrower bandpass response in near-infrared region is further achieved employing blended PbS CQDs with different sizes. The external quantum efficiency spectra of these CQD detectors are comprehensively studied using numerical calculation.
Lead sulfide colloidal quantum dot (CQD) solar cells with a solar power conversion efficiency of 5.6% are reported. The result is achieved through careful optimization of the titanium dioxide ...electrode that serves as the electron acceptor. Metal‐ion‐doped sol‐gel‐derived titanium dioxide electrodes produce a tunable‐bandedge, well‐passivated materials platform for CQD solar cell optimization.
Due to the poor thermal stability of the lithium hexafluorophosphate (LiPF6) electrolyte system, commercial lithium-ion batteries (LIBs) are difficult for normal operation at high temperatures above ...55 °C. The limitation of the LiPF6 electrolyte severely limits the practical application of LIBs under extremely high temperatures conditions. Here, a high-concentration electrolyte based on lithium bis(fluorosufonyl)imide (LiFSI) as electrolyte salt and ethyl methyl carbonate (EMC) as solvent is proposed, which possesses superior electrochemical stability and thermal stability. The LiCoO2/graphite (Gr) pouch battery with the LiFSI high-concentration electrolyte (5.0 mol L−1 (M)) has been shown excellent cycling performance even at 100 °C, an impressive capacity retention of 87.7 % can be still maintained after 100 cycles at 1.0 C-rate. The superior high temperatures performance is mainly attributed to the unique solvated structure, along with the robust solid electrolyte interphase (SEI) rich in anions. This work presents an effective strategy for promoting the development of high-temperature lithium-ion batteries.
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