MAPbBr_(3)(MA=CH_(3)NH_(3)^(+))doping with bismuth increases electric conductivity,charge carrier density and photostability,reduces toxicity,and expands light absorption.However,Bi doping shortens excited-state lifet...MAPbBr_(3)(MA=CH_(3)NH_(3)^(+))doping with bismuth increases electric conductivity,charge carrier density and photostability,reduces toxicity,and expands light absorption.However,Bi doping shortens excited-state lifetimes due to formation of DY−charge recombination centers.Using nonadiabatic molecular dynamics and time-domain density functional theory,we demonstrate that the DY−center forms a deep,highly localized hole trap,which accelerates nonradiative relaxation ten-fold and is responsible for 90%of carrier losses.Hole trapping occurs by coupling between the valence band and the trap state,facilitated by the Br atoms surrounding the Bi dopant.Passivation of the DY−center with chlorines heals the local geometry distortion,eliminates the trap state,and makes the carrier lifetimes longer than even in pristine MAPbBr_(3).The decreased charge recombination arises from reduced nonadiabatic coupling and shortened coherence time,due to diminished electron–hole overlap around the passivated defect.Our study demonstrates accelerated nonradiative recombination in Bi-doped MAPbBr_(3),suggests a strategy for defect passivation and reduction of nonradiative energy losses,and provides atomistic insights into unusual defect properties of metal halide perovskites needed for rational design of high-performance perovskite solar cells and optoelectronic devices.展开更多
The composition of animal species and interactions among them are widely known to shape ecological communities and fine-scale(e.g.,<1 km)monitoring of animal communities is essential for understanding the relations...The composition of animal species and interactions among them are widely known to shape ecological communities and fine-scale(e.g.,<1 km)monitoring of animal communities is essential for understanding the relationships among animals and plants.Although the co-existence of large-and medium-sized species has been studied across different scales,research on fine-scale interactions of herbivores in deciduous broadleaf forests is limited.Camera trapping of large-and medium-sized mammals was carried out over a 1 year period within a 25 ha deciduous broadleaf forest dynamics plot in the Qinling Mountains,China.Fourteen species of large-and medium-sized mammals,including six carnivores,six ungulates,one primate and one rodent species were found.Kernel density estimations were used to analyse the diel or 24 h activity patterns of all species with more than 40 independent detections and general linear models were developed to explore the spatial relationships among the species.The combination of overlapping diel activity patterns and spatial associations showed obvious niche separation among six species:giant panda(Ailuropoda melanoleuca David),takin(Budorcas taxicolor Hodgson),Reeves’s muntjac(Muntiacus reevesi Ogilby),tufted deer(Elaphodus cephalophus Milne-Edwards),Chinese serow(Capricornis milneedwardsii David)and wild boar(Sus scrofa Linnaeus).Long-term fine-scale monitoring is useful for providing information about the co-existence of species and their interactions.The results demonstrate the importance for fine-scale monitoring of animals and plants for improving understanding of species interactions and community dynamics.展开更多
Based on molecular dynamics simulations,we have studied the wetting behaviors of water on the talc-like surface with different surface polarity by modifying the charge distribution of surface hydroxyl(–OH)groups.With...Based on molecular dynamics simulations,we have studied the wetting behaviors of water on the talc-like surface with different surface polarity by modifying the charge distribution of surface hydroxyl(–OH)groups.With the change of the charge of the hydrogen atom(denoted asδq)in–OH group,the contact angle decreases from 91°to 50°and then remains constant.On the surfaces with the larger charge of hydrogen atoms(δ_(q)≥0.2 e),a water droplet is formed above a water monolayer,which is exactly contacted on the surface.Each water molecule in the monolayer forms one hydrogen bond(H bond)with surface–OH groups,without participating in any H bond with the water molecules within the monolayer or with the water molecules above the monolayer.The polarity of the–OH group also has a great influence on the dynamic behaviors of the interface water,such as residence time,hydrogen bond lifetime and selfdiffusion coefficient.The diffusion of water molecules in the water monolayer near the highly polar surface is greatly suppressed,and the residence time of water molecules in the water monolayer even exceeds 12 ns.展开更多
基金the Beijing Science Foundation(No.2212031)the National Natural Science Foundation of China(Nos.51861135101,21973006,21573022,21688102 and 21590801)R.L.acknowledges the Recruitment Program of Global Youth Experts of China and the Beijing Normal University Startup.O.V.P.acknowledges funding from the U.S.Department of Energy(No.DE SC0014429).
文摘MAPbBr_(3)(MA=CH_(3)NH_(3)^(+))doping with bismuth increases electric conductivity,charge carrier density and photostability,reduces toxicity,and expands light absorption.However,Bi doping shortens excited-state lifetimes due to formation of DY−charge recombination centers.Using nonadiabatic molecular dynamics and time-domain density functional theory,we demonstrate that the DY−center forms a deep,highly localized hole trap,which accelerates nonradiative relaxation ten-fold and is responsible for 90%of carrier losses.Hole trapping occurs by coupling between the valence band and the trap state,facilitated by the Br atoms surrounding the Bi dopant.Passivation of the DY−center with chlorines heals the local geometry distortion,eliminates the trap state,and makes the carrier lifetimes longer than even in pristine MAPbBr_(3).The decreased charge recombination arises from reduced nonadiabatic coupling and shortened coherence time,due to diminished electron–hole overlap around the passivated defect.Our study demonstrates accelerated nonradiative recombination in Bi-doped MAPbBr_(3),suggests a strategy for defect passivation and reduction of nonradiative energy losses,and provides atomistic insights into unusual defect properties of metal halide perovskites needed for rational design of high-performance perovskite solar cells and optoelectronic devices.
基金This work was supported by the National Natural Science Foundation of China project(No 41671183).
文摘The composition of animal species and interactions among them are widely known to shape ecological communities and fine-scale(e.g.,<1 km)monitoring of animal communities is essential for understanding the relationships among animals and plants.Although the co-existence of large-and medium-sized species has been studied across different scales,research on fine-scale interactions of herbivores in deciduous broadleaf forests is limited.Camera trapping of large-and medium-sized mammals was carried out over a 1 year period within a 25 ha deciduous broadleaf forest dynamics plot in the Qinling Mountains,China.Fourteen species of large-and medium-sized mammals,including six carnivores,six ungulates,one primate and one rodent species were found.Kernel density estimations were used to analyse the diel or 24 h activity patterns of all species with more than 40 independent detections and general linear models were developed to explore the spatial relationships among the species.The combination of overlapping diel activity patterns and spatial associations showed obvious niche separation among six species:giant panda(Ailuropoda melanoleuca David),takin(Budorcas taxicolor Hodgson),Reeves’s muntjac(Muntiacus reevesi Ogilby),tufted deer(Elaphodus cephalophus Milne-Edwards),Chinese serow(Capricornis milneedwardsii David)and wild boar(Sus scrofa Linnaeus).Long-term fine-scale monitoring is useful for providing information about the co-existence of species and their interactions.The results demonstrate the importance for fine-scale monitoring of animals and plants for improving understanding of species interactions and community dynamics.
基金supported by the National Natural Science Foundation of China(Grant No.12022508,12074394,11674345)the Key Research Program of Chinese Academy of Sciences(Grant No.QYZDJ-SSW-SLH019)the Sichuan Science and Technology Program(Grant No.2017YJ0174)。
文摘Based on molecular dynamics simulations,we have studied the wetting behaviors of water on the talc-like surface with different surface polarity by modifying the charge distribution of surface hydroxyl(–OH)groups.With the change of the charge of the hydrogen atom(denoted asδq)in–OH group,the contact angle decreases from 91°to 50°and then remains constant.On the surfaces with the larger charge of hydrogen atoms(δ_(q)≥0.2 e),a water droplet is formed above a water monolayer,which is exactly contacted on the surface.Each water molecule in the monolayer forms one hydrogen bond(H bond)with surface–OH groups,without participating in any H bond with the water molecules within the monolayer or with the water molecules above the monolayer.The polarity of the–OH group also has a great influence on the dynamic behaviors of the interface water,such as residence time,hydrogen bond lifetime and selfdiffusion coefficient.The diffusion of water molecules in the water monolayer near the highly polar surface is greatly suppressed,and the residence time of water molecules in the water monolayer even exceeds 12 ns.
