The evolution of meandering rivers continues to attract considerable attention in research and for practical applications, given that it is closely associated with the safety of river systems and ...riparian zones. There has been much discussion regarding the various channel planform features exhibited by meandering rivers under different river systems and riparian conditions. The Yimin River is a good example and is located southeast of the Hulun Buir Grassland, which is characterised by a fragile ecosystem and little anthropological activity along with active flow during the non-frozen season from May to November each year and relatively low sediment discharge compared with the Yellow River and Mississippi River. Improved analysis of the evolution of the Yimin River from 1975 to 2019 can support increased local species diversity and more effective flood risk and river management. With the combined Google Earth Engine (GEE) platform and the Geographic Information Systems (GIS) technique, remote sensing images, including Landsat images and global surface water data, are used to analyse the channel planform features of the freely meandering river channel in the middle and lower Yimin River. The results show that the percentage of low sinuosity channel bends was higher than that of high-sinuosity bends. Although the bends with an amplitude greater than 0.48 km and sinuosity greater than 2.3 have an evident upstream-skewed trend, the main channel planform features were downstream skewed with 1499 such bends. The river system conditions in the Yimin River, including lower sediment discharge and vegetation cover, are conducive to the development of downstream-skewed bends. The high-sinuosity bends were found to have a relatively larger ratio during 1981–2000, a period with higher mean annual streamflow compared with other time periods.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The room-temperature solvent–solvent extraction (SSE) concept is used for the deposition of hybrid-perovskite thin films over large areas. In this simple process, perovskite precursor solution is ...spin-coated onto a substrate, and instead of the conventional thermal annealing treatment, the coated substrate is immediately immersed in a bath of another solvent at room temperature. This results in efficient extraction of the precursor-solvent and induces rapid crystallization of uniform, ultra-smooth perovskite thin films. The mechanisms involved in the SSE process are studied further, and its versatility in depositing high quality thin films of controlled thicknesses (20 to 700 nm) and various compositions (CH 3 NH 3 PbI (3−x) Br x ; x = 0, 1, 2, or 3) is demonstrated. Planar perovskite solar cells (PSCs) based on SSE-deposited CH 3 NH 3 PbI 3 perovskite thin films deliver power conversion efficiency (PCE) up to 15.2%, and most notably an average PCE of 10.1% for PSCs with sub-100 nm semi-transparent perovskite thin films. The SSE method has generic appeal, and its key attributes—room-temperature process, rapid crystallization, large-area uniform deposition, film-thickness control, ultra-smoothness, and compositional versatility—make the SSE method potentially suitable for roll-to-roll scalable processing of hybrid-perovskite thin films for future multifunctional PSCs.
Sn‐based perovskites are promising Pb‐free photovoltaic materials with an ideal 1.3 eV bandgap. However, to date, Sn‐based thin film perovskite solar cells have yielded relatively low power ...conversion efficiencies (PCEs). This is traced to their poor photophysical properties (i.e., short diffusion lengths (<30 nm) and two orders of magnitude higher defect densities) than Pb‐based systems. Herein, it is revealed that melt‐synthesized cesium tin iodide (CsSnI3) ingots containing high‐quality large single crystal (SC) grains transcend these fundamental limitations. Through detailed optical spectroscopy, their inherently superior properties are uncovered, with bulk carrier lifetimes reaching 6.6 ns, doping concentrations of around 4.5 × 1017 cm−3, and minority‐carrier diffusion lengths approaching 1 µm, as compared to their polycrystalline counterparts having ≈54 ps, ≈9.2 × 1018 cm−3, and ≈16 nm, respectively. CsSnI3 SCs also exhibit very low surface recombination velocity of ≈2 × 103 cm s−1, similar to Pb‐based perovskites. Importantly, these key parameters are comparable to high‐performance p‐type photovoltaic materials (e.g., InP crystals). The findings predict a PCE of ≈23% for optimized CsSnI3 SCs solar cells, highlighting their great potential.
Pb‐free CsSnI3 single crystal possesses superior optoelectronic properties compared to its polycrystalline thin film counterparts for photovoltaic application, uncovered using detailed optical spectroscopy, with a bulk carrier lifetimes of around 6.6 ns, doping concentrations of ≈4.5 × 1017 cm−3, minority‐carrier diffusion lengths approaching 1 µm, and surface recombination velocity of <2 × 103 cm s−1.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Owing to the worrying increase in carbon dioxide concentrations in the atmosphere, there is a need to electrify fossil-fuel–powered chemical processes such as the Haber-Bosch ammonia synthesis. ...Lithium-mediated electrochemical nitrogen reduction has shown preliminary promise but still lacks sufficient faradaic efficiency and ammonia formation rate to be industrially relevant. Here, we show that oxygen, previously believed to hinder the reaction, actually greatly improves the faradaic efficiency and stability of the lithium-mediated nitrogen reduction when added to the reaction atmosphere in small amounts. With this counterintuitive discovery, we reach record high faradaic efficiencies of up to 78.0 ± 1.3% at 0.6 to 0.8 mole % oxygen in 20 bar of nitrogen. Experimental x-ray analysis and theoretical microkinetic modeling shed light on the underlying mechanism.
Electron transport layer (ETL) is a functional layer of great significance for boosting the power conversion efficiency (PCE) of perovskite solar cells (PSCs). To date, it is still a challenge to ...simultaneously reduce the surface defects and improve the crystallinity in ETLs during their low‐temperature processing. Here, a novel strategy for the mediation of in situ regrowth of SnO2 nanocrystal ETLs is reported: introduction of controlled trace amounts of surface absorbed water on the fluorinated tin oxide (FTO) or indium–tin oxide (ITO) surfaces of the substrates using ultraviolet ozone (UVO) pretreatment. The optimum amount of adsorbed water plays a key role in balancing the hydrolysis–condensation reactions during the structural evolution of SnO2 thin films. This new approach results in a full‐coverage SnO2 ETL with a desirable morphology and crystallinity for superior optical and electrical properties, as compared to the control SnO2 ETL without the UVO pretreatment. Finally, the rigid and flexible PSC devices based on the new SnO2 ETLs yield high PCEs of up to 20.5% and 17.5%, respectively.
A novel strategy is reported where control over the surface‐adsorbed water on a transparent conducting oxide substrate is used to mediate the in situ nanocrystalline regrowth of a SnO2 electron transport layer (ETL) at near room temperature. The new ETL is key to achieving a high power conversion efficiency of 20.5% and 17.5% in rigid and flexible perovskite solar cells, respectively.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
On the basis of agency and resource dependence theories, this paper mainly discusses the relationship between the board and financial performance of nonprofit foundations (NPFs) in China. The data ...used in this study were obtained from the 2017 annual work report of 203 national public and private fundraising NPFs. Conclusions of this empirical research are as follows. Board size is positively correlated with organizational performance. The size of the supervisory board is positively associated with total and donation incomes. In public NPFs, a negative relationship exists between the average age of directors and total and donation incomes. Foundations with fewer government officials among their directors have a higher total income. In public fundraising NPFs, a positive relationship exists between the proportion of paid directors and total and donation incomes, whereas no correlation is observed in private fundraising NPFs. This study has significant implications for understanding the relationship between board composition and organizational performance among NPFs in China. This study focuses on the effective features of boards in NPFs to enhance competitiveness in access to public resources after the enactment of the Charity Law.
Plain language summary The article mainly discusses the relationship between the board and financial performance of nonprofit foundations (NPFs) in China. Using the data from the 2017 annual work report of 203 national public and private fundraising NPFs, this study measured organizational financial performance adopting the definition from Ritchie and Kolodinsky (2003) and choose 12 independent variables to represent board characteristics. Empirical research has indicated a correlation between some characteristics of the board of directors and organizational performance. Board size is positively correlated with organizational performance. The size of the supervisory board is positively associated with total and donation incomes. The average age of directors is negatively correlated with total income in public NPFs and with the donation income in all NPFs. In foundations with fewer government officials among all directors, they perform better in terms of total income. In public fundraising NPFs, the proportion of directors who receive remuneration is positively correlated with the total and donation incomes, whereas in private fundraising NPFs, they show no correlation. This study has several limitations that should be noted. The measurements of board characteristics and effectiveness did not cover all elements of nonprofit board and organizational effectiveness mentioned in the literature due to data unavailability. Another limitation is that the cross-sectional data could not establish the causal relationship between governance structure and organizational performance. For future research on performance of NPFs in China, scholars need to pay special attention to the changes in China’s charitable legal environment, which is an important background in this study.
Removing the lead (Pb) from state-of-the-art perovskite solar cells (PSCs) while maintaining high power conversion efficiencies (PCEs) is a prominent step toward full commercialization. The field has ...identified tin (Sn) PSCs as a promising alternative, but the performance of these Sn PSCs are limited primarily by detrimental Sn(IV) self-doping. Herein, we demonstrate Sn PSCs with PCEs up to 14.7% via a surface-dedoping approach. This method features the chemo-thermal removal of Sn(IV) self-dopants that are found mainly accumulated on the surface of Sn perovskite thin films, and its optimization can avoid negative effects on film morphology. Using this method, we show about a 3-fold enhancement in carrier lifetime and a 2-fold reduction in trap density, underpinning the device’s efficiency improvement. The Sn PSCs are also stable, with a 92% PCE retention after 1,000 h of storage in a nitrogen-filled glovebox. This work paves a way for PSCs to achieve their technological potential without Pb involvement.
Display omitted
•A chemo-thermal dedoping approach is employed to reduce surface Sn(IV) self-doping•Complexation between FACl and SnI4 facilitate the Sn(IV) removal upon annealing•Surface dedoping leads to significant improvement in optoelectronic properties•Sn perovskite solar cells demonstrate high efficiencies up to 14.7%
The perovskite solar cell (PSC) is a revolutionary photovoltaic technology that has witnessed a soaring development in recent years. PSCs not only exhibit potential in generating grid electricity compared with other photovoltaic technologies but are also suitable for powering the internet of things (IoTs) and urban buildings. However, the broad deployment of PSCs still suffers from the presence of toxic lead (Pb). Attention has been drawn on tin (Sn) and other less toxic and more environmentally friendly metals to replace Pb. This work reports a new engineering concept, called chemo-thermal surface dedoping, to suppress the detrimental Sn(IV) self-doping, addressing a major hurdle in Pb-free PSCs. This study represents a significant material advancement progression (MAP) in understanding and tailoring Sn perovskite semiconductors that potentially benefits the development of numerous useful (opto)electronics and can be further leveraged to improve our future sustainable and smart society.
The detrimental self-doping due to Sn(II)-to-Sn(IV) oxidation remains a hurdle in the development of high-performance Pb-free Sn perovskite solar cells. A chemo-thermal dedoping process is therefore introduced to reduce the Sn(IV) self-dopants on the film surface. This process is enabled by organic-inorganic complexation between the FACl and Sn(IV) iodide components in perovskite, which facilitates Sn(IV) removal upon thermal annealing. The resultant Sn perovskite solar cells can show PCEs up to 14.7% as well as good device stability.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Perovskite solar cells (PSCs) based on thin films of organolead trihalide perovskites (OTPs) hold unprecedented promise for low-cost, high-efficiency photovoltaics (PVs) of the future. While PV ...performance parameters of PSCs, such as short circuit current, open circuit voltage, and maximum power, are always measured at the macroscopic scale, it is necessary to probe such photoresponses at the nanoscale to gain key insights into the fundamental PV mechanisms and their localized dependence on the OTP thin-film microstructure. Here we use photoconductive atomic force microscopy spectroscopy to map for the first time variations of PV performance at the nanoscale for planar PSCs based on hole-transport-layer free methylammonium lead triiodide (CH3NH3PbI3 or MAPbI3) thin films. These results reveal substantial variations in the photoresponse that correlate with thin-film microstructural features such as intragrain planar defects, grains, grain boundaries, and notably also grain-aggregates. The insights gained into such microstructure-localized PV mechanisms are essential for guiding microstructural tailoring of OTP films for improved PV performance in future PSCs.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
We demonstrate the feasibility of a nonsalt-based precursor pairinorganic HPbI3 solid and organic CH3NH2 gasfor the deposition of uniform CH3NH3PbI3 perovskite thin films. The strong ...room-temperature solid–gas interaction between HPbI3 and CH3NH2 induces transformative evolution of ultrasmooth, full-coverage perovskite thin films at a rapid rate (in seconds) from nominally processed rough, partial-coverage HPbI3 thin films. The chemical origin of this behavior is elucidated via in situ experiments. Perovskite solar cells, fabricated using MAPbI3 thin films thus deposited, deliver power conversion efficiencies up to 18.2%, attesting to the high quality of the perovskite thin films deposited using this transformative process.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
An efficient cascade copper-catalyzed intermolecular Ullmann-type C–N coupling/enamine condensation reaction is described, in which ortho-acylanilines and alkenyl iodides converted to ...multisubstituted quinolines in good to excellent yields.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
PDF
