Understanding and managing charge carrier recombination dynamics is crucial for optimizing the performance of metal halide perovskite optoelectronic devices.In this work,we introduce a machine learning-assisted intens...Understanding and managing charge carrier recombination dynamics is crucial for optimizing the performance of metal halide perovskite optoelectronic devices.In this work,we introduce a machine learning-assisted intensity-modulated two-photon photoluminescence microscopy approach for quantitatively mapping recombination processes in MAPbBr_(3) perovskite microcrystalline films at micrometer-scale resolution.To enhance model accuracy,a balanced classification sampling strategy was applied during the machine learning optimization stage.展开更多
Miniaturization of light-emitting diodes(LEDs) with sizes down to a few micrometers has become a hot topic in both academia and industry due to their attractive applications on self-emissive displays for high-definiti...Miniaturization of light-emitting diodes(LEDs) with sizes down to a few micrometers has become a hot topic in both academia and industry due to their attractive applications on self-emissive displays for high-definition televisions,augmented/mixed realities and head-up displays, and also on optogenetics, high-speed light communication, etc. The conventional top-down technology uses dry etching to define the LED size, leading to damage to the LED side walls.Since sizes of microLEDs approach the carrier diffusion length, the damaged side walls play an important role, reducing microLED performance significantly from that of large area LEDs. In this paper, we review our efforts on realization of microLEDs by direct bottom-up growth, based on selective area metal–organic vapor phase epitaxy. The individual LEDs based on either GaN nanowires or InGaN platelets are smaller than 1 μm in our approach. Such nano-LEDs can be used as building blocks in arrays to assemble microLEDs with different sizes, avoiding the side wall damage by dry etching encountered for the top-down approach. The technology of InGaN platelets is especially interesting since InGaN quantum wells emitting red, green and blue light can be grown on such platelets with a low-level of strain by changing the indium content in the InGaN platelets. This technology is therefore very attractive for highly efficient microLEDs of three primary colors for displays.展开更多
Because of the good thermal stability and superior carrier transport characteristics of formamidinium lead trihalide perovskite HC(NH_2)_2 PbX_3(FAPbX_3), it has been considered to be a better optoelectronic material ...Because of the good thermal stability and superior carrier transport characteristics of formamidinium lead trihalide perovskite HC(NH_2)_2 PbX_3(FAPbX_3), it has been considered to be a better optoelectronic material than conventional CH_3NH_3-PbX_3(MAPbX_3). Herein, we fabricated a FAPbBr_3 microcrystal-based photodetector that exhibited a good responsivity of 4000 A W-1 and external quantum efficiency up to 106% under one-photon excitation, corresponding to the detectivity greater than 1014 Jones. The responsivity is two orders of magnitude higher than that of previously reported formamidinium perovskite photodetectors. Furthermore, the FAPbBr_3 photodetector's responsivity to two-photon absorption with an 800-nm excitation source can reach 0.07 A W^(-1), which is four orders of magnitude higher than that of its MAPbBr_3 counterparts. The response time of this photodetector is less than 1 ms.This study provides solid evidence that FAPbBr_3 can be an excellent candidate for highly sensitive and fast photodetectors.展开更多
Maximizing ultrafast electron-transfer kinetics in semiconductor is pivotal but challenging for highefficiency solar-to-energy during the photocatalytic reaction process due to the intrinsic property of photocatalysts...Maximizing ultrafast electron-transfer kinetics in semiconductor is pivotal but challenging for highefficiency solar-to-energy during the photocatalytic reaction process due to the intrinsic property of photocatalysts with low surface electron density.Herein,a model photocatalyst CdS@Mo is synthesized through a typical hydrothermal method for modulating the ultrafast electron-transfer to enhance the surface electron density.X-ray absorption fine spectra(XAFS)reveal that Mo is coordinated with S atoms to form a Mo-S_(6) configuration which is different from common MoS_(2) and Mo foil structures.Based on the femtosecond transient absorption spectra(fs-TAS),it is found that the formation of Mo-S6 configuration contributes to the fast decay of CdS signal and Mo-S_(6) signal reactivation,illustrating the ultrafast electron-transfer(∼2.2 ps)from CdS to Mo-S_(6) configuration,which achieves the enhanced electron density of photocatalyst surface.Finally,a holistic photocatalytic performance evaluation discloses that the growing of Mo-S_(6) configuration obviously improves the photocatalytic hydrogen evolution(PHE)effi-ciency of CdS from 28.5 to 47.5 mmol g^(-1)h^(-1)with a solar-to-hydrogen(STH)efficiency of 0.10%which is seldomly discussed in the system containing sacrificial agents.This work opens a new path to modulate the surface electron density by tuning the ultrafast electron-transfer for enhancing reaction efficiency in electron-density-dependent systems.展开更多
Perovskites have attracted widespread attention for laser applications due to their excellent optoelectronic properties.However,perovskite lasers typically exhibit a wavelength shift as pump density increases.Here,we ...Perovskites have attracted widespread attention for laser applications due to their excellent optoelectronic properties.However,perovskite lasers typically exhibit a wavelength shift as pump density increases.Here,we report a pump-induced wavelength shift-free laser achieved using a perovskite nanoplatelet with mixed orthorhombic and tetragonal phase.At 293 K,the tetragonal-phase perovskite nanoplatelet laser exhibits a blue shift of~0.4 nmµJ^(-1)cm^(2)with increasing pump density.In contrast,at 80 K,the orthorhombic-phase perovskite nanoplatelet laser exhibits a red shift of~1 nmµJ^(-1)cm^(2).By stabilizing the perovskite nanoplatelet in a mixed orthorhombic-tetragonal phase at 163 K,the pump induced wavelength shifts are completely suppressed,resulting in a wavelength-stable laser.Additionally,the lasing threshold decreases from 18.4µJ cm^(−2)at room temperature to 4.5µJ cm^(−2)at 163 K.This study presents a promising strategy for achieving pump-insensitive wavelength stability in micro/nano lasers.展开更多
As the field of metal halide perovskites matures,a range of compositionally different perovskite films has found a place in efficient optoelectronic devices.These films feature variable local structural stability,carr...As the field of metal halide perovskites matures,a range of compositionally different perovskite films has found a place in efficient optoelectronic devices.These films feature variable local structural stability,carrier diffusion,and recombination,while there is still a lack of easy-to-implement generic protocols for high-throughput characterization of these variable properties.Correlation clustering imaging(CLIM)is a recently developed tool that resolves peculiarities of local photophysics by assessing the dynamics of photoluminescence detected by wide-field optical microscopy.We demonstrate the capability of CLIM as a high-throughput characterization tool of perovskite films using MAPbI3(MAPI)and triple cation mixed halide(TCMH)perovskites as examples where it resolves the interplay of carrier diffusion,recombination,and defect dynamics.We found significant differences in the appearance of metastable defect states in these two films.Despite a better surface quality and larger grain size,MAPI films showed more pronounced effects of fluctuating defect states than did TCMH films.As CLIM shows a significant difference between materials known to lead to different solar cell efficiencies,it can be considered a tool for quality control of thin films for perovskite optoelectronic devices.展开更多
Photocatalysis plays a crucial role in harnessing renewable energy by efficiently converting solar energy into chemical energy.Adequate cognition of photogenerated charge carrier dynamics in photocatalysis is the key ...Photocatalysis plays a crucial role in harnessing renewable energy by efficiently converting solar energy into chemical energy.Adequate cognition of photogenerated charge carrier dynamics in photocatalysis is the key to realizing efficient solar energy utilization,and provides guidance for breaking through the efficiency bottleneck.However,a convincing correlation between those photophysical processes and the photocatalytic performance has yet been established due to the complexity of photocatalytic reactions.In this review,we overviewed the detailed ultrafast photophysics in photocatalysis based on three typical ultrafast spectroscopic techniques(TRPL,TA and TRIR),and put a special focus on the justification as well as the limitation on correlating those photophysics with the actual catalytic performance.The classification of carrier behaviors after photoexcitation as well as typical time-resolved spectroscopic characterization techniques are briefly introduced first.State-of-the-art studies on the excited state dynamics in photocatalysis and its correlation to catalytic performance are then systematically presented from three types of common photocatalysts including quantum dots,polymeric photocatalysts,and traditional semiconductors.Finally,a summary on the correlation between ultrafast photophysics and the final photocatalytic performance is provided,and challenges and limitations of current photophysical characterization to rationalize the catalytic performance are outlined.展开更多
具有低温升的高效散热方案是实现电泵浦激光的关键因素之一.高导热金刚石有望克服钙钛矿激光的散热限制.本文中,我们展示了一种可以将光泵浦过程中产生热量高效耗散的金刚石基底钙钛矿纳米片激光.此外,紧密光学束缚可以通过在纳米片和...具有低温升的高效散热方案是实现电泵浦激光的关键因素之一.高导热金刚石有望克服钙钛矿激光的散热限制.本文中,我们展示了一种可以将光泵浦过程中产生热量高效耗散的金刚石基底钙钛矿纳米片激光.此外,紧密光学束缚可以通过在纳米片和金刚石基底之间引入一层薄SiO_(2)间隔层而实现.该激光的品质因子高达~1962,激光阈值为52.19μJ cm^(-2).受益于金刚石基底,其泵浦能量密度相关温度灵敏度较低(~0.56±0.01 K cm~2μJ^(-1)).本工作有望促进电泵浦钙钛矿激光的发展.展开更多
Semiconductor nanowire （NW） solar cells with a single p-n junction have exhibited efficiency comparable to that of their planar counterparts with a substantial reduction in material consumption. Tandem geometry is a...Semiconductor nanowire （NW） solar cells with a single p-n junction have exhibited efficiency comparable to that of their planar counterparts with a substantial reduction in material consumption. Tandem geometry is a path toward the fabrication of devices with even higher efficiencies, for which a key step is the fabrication of tunnel （Esaki） diodes within NWs with the correct diameter, pitch, and material combination for maximized efficiency. InP/GaInP and GaInP/InP NW tunnel diodes with band gap combinations corresponding to high-efficiency solar energy harvesting were fabricated and their electrical characteristics and material properties were compared. Four different configurations, with respect to material composition and doping, were investigated. The NW arrays were grown with metal-organic vapor-phase epitaxy from Au particles by use of nano-imprint lithography, metal evaporation and lift-off. Electrical measurements showed that the NWs behave as tunnel diodes in both InP （bottom）/GaInP （top） and GaInP （bottom）/InP （top） configurations, exhibiting a maximum peak current density of 25 A/cm^2, and maximum peak to valley current ratio of 2.5 at room temperature. The realization of NW tunnel diodes in both InP/GaInP and GaInP/InP configurations represent an opportunity for the use of NW tandem solar cells, whose efficiency is independent of the growth order of the different materials, increasing the flexibility regarding dopant incorporation polarity.展开更多
X-ray microscopy is an essential imaging method in many scientific fields,which can be extended to three-dimensional(3D)using tomography.Recently,metal halide perovskite(MHP)nanomaterials have become a promising candi...X-ray microscopy is an essential imaging method in many scientific fields,which can be extended to three-dimensional(3D)using tomography.Recently,metal halide perovskite(MHP)nanomaterials have become a promising candidate for X-ray scintillators,due to their high light yield,high spatial resolution,and easy fabrication.Tomography requires many projections and therefore scintillators with excellent stability.This is challenging for MHPs,which often suffer from fast degradation under X-ray irradiation and ambient conditions.Here,we demonstrate that MHP scintillators of CsPbBr3 nanowires(diameter:60 nm,length:5–9μm)grown in anodized aluminum oxide(CsPbBr3 NW/AAO)have sufficient stability for X-ray micro-tomography.A tomogram was taken with a Cu X-ray source over 41 h(dose 4.2 Gyair).During this period the scintillator brightness fluctuated less than 5%,which enabled a successful reconstruction.A long-term study with 2 weeks of continuous X-ray exposure(37.5 Gyair)showed less than 14%fluctuations in brightness and no long-term degradation,despite variations in the ambient relative humidity from 7.4%RH to 34.2%RH.The resolution was stable at(180±20)lp·mm−1,i.e.,about 2.8 micron.This demonstrates that CsPbBr3 NW/AAO scintillators are promising candidates for high resolution X-ray imaging detectors.展开更多
Axially heterostructured nanowires are a promising platform for next generation electronic and optoelectronic devices.Reports based on theoretical modeling have predicted more complex strain distributions and increase...Axially heterostructured nanowires are a promising platform for next generation electronic and optoelectronic devices.Reports based on theoretical modeling have predicted more complex strain distributions and increased critical layer thicknesses than in thin films,due to lateral strain relaxation at the surface,but the understanding of the growth and strain distributions in these complex structures is hampered by the lack of high-resolution characterization techniques.Here,we demonstrate strain mapping of an axially segmented GalnP-lnP 190 nm diameter nanowire heterostructure using scanning X-ray diffraction.We systematically investigate the strain distribution and lattice tilt in three different segment lengths from 45 to 170 nm,obtaining strain maps with about 10^-4 relative strain sensitivity.The experiments were performed using the 90 nm diameter nanofocus at the NanoMAX beamline,taking advantage of the high coherent flux from the first diffraction limited storage ring MAX IV.The experimental results are in good agreement with a full simulation of the experiment based on a three-dimensional(3D)finite element model.The largest segments show a complex profile,where the lateral strain relaxation at the surface leads to a dome-shaped strain distribution from the mismatched interfaces,and a change from tensile to compressive strain within a single segment.The lattice tilt maps show a cross-shaped profile with excellent qualitative and quantitative agreement with the simulations.In contrast,the shortest measured InP segment is almost fully adapted to the surrounding GalnP segments.展开更多
Multiple morphologies of colloidal perovskite nanocrystals(NCs)diversify their optical and electronic properties.Among them,the linear absorption cross-section(σ)is a primary parameter to determine their intrinsic ph...Multiple morphologies of colloidal perovskite nanocrystals(NCs)diversify their optical and electronic properties.Among them,the linear absorption cross-section(σ)is a primary parameter to determine their intrinsic photophysical features,and consequently,application potential.Herein,three morphologies of all-inorganic hybrid colloidal perovskite CsPbBr_(3)NCs,nanocubes(NBs),nanoplatelets(NLs),and nanowires(NWs),were targeted,and their linearσvalues were obtained through femtosecond transient absorption(TA)spectroscopy analysis.At high excitation energy well above the bandgap,theσper particle of all CsPbBr3 NCs linearly increased with the particle volume(VNC)regardless of the morphology with the value ofσ400=9.45×10^(4)cm^(−1)×VNC(cm^(2)).Density functional theory(DFT)calculation confirmed the negligible influence of shapes on the optical selection rules.The Einstein spontaneous emission coefficients calculated from theσvalues define the intrinsic radiative recombination rate.However,reduced size dependence is observed when the excitation energy is close to the bandgap(i.e.,at 460 nm)with the value ofσ460=2.82×10^(8)cm0.65×(VNC)0.45(cm^(2)).This should be ascribed to the discrete energy levels as well as lower density of states close to the band edge for perovskite NCs.These results provide in-depth insight into the optical characteristics for perovskite NCs.展开更多
Due to their superior photoluminescence(PL)quantum yield(QY) and tunable optical band gap,all-inorganic CsPbBr_3 perovskite quantum dots(QDs) have attracted intensive attention for the application in solar cells,light...Due to their superior photoluminescence(PL)quantum yield(QY) and tunable optical band gap,all-inorganic CsPbBr_3 perovskite quantum dots(QDs) have attracted intensive attention for the application in solar cells,light emitting diodes(LED),photodetectors and laser devices.In this scenario,the stability of such materials becomes a critical factor to be revealed.We hereby investigated the long-term stability of as-synthesized CsPbBr_3 QDs suspended in toluene at various environmental conditions.We found light illumination would induce drastic photo-degradation of CsPbBr_3 QDs.The steady-state spectroscopy,transmission electron microscopy(TEM),and X-ray diffraction(XRD)verified that CsPbBr_3 QDs tend to aggregate to form larger particles under continuous light soaking.In addition,decreasing PL QY of the QDs during light soaking indicates the formation of trap sites.Our work reveals that the main origin of instability in CsPbBr_3 QDs and provides reference to engineer such QDs towards optimal device application.展开更多
Ternary III-V nanowires （NWs） cover a wide range of wavelengths in the solar spectrum and would greatly benefit from being synthesized as position-controlled arrays for improved vertical yield, reproducibility, and ...Ternary III-V nanowires （NWs） cover a wide range of wavelengths in the solar spectrum and would greatly benefit from being synthesized as position-controlled arrays for improved vertical yield, reproducibility, and tunable optical absorption. Here, we report on successful selective-area epitaxy of metal-particle-free vertical InxGa1-xP NW arrays using metal-organic vapor phase epitaxy and detail their optical properties. A systematic growth study establishes the range of suitable growth parameters to obtain uniform NW growth over a large array. The optical properties of the NWs were characterized by room-temperature cathodoluminescence spectroscopy. Tunability of the emission wavelength from 870 nm to approximately 800 nm was achieved. Transmission electron microscopy and energy dispersive X-ray measurements performed on cross- section samples revealed a pure wurtzite crystal structure with very few stacking faults and a slight composition gradient along the NW growth axis.展开更多
Lead-free halide double perovskites have gathered wide scientific interest since they are environmentally friendly and stable.However,compared to the lead perovskites,their optoelectronic properties are compromised.He...Lead-free halide double perovskites have gathered wide scientific interest since they are environmentally friendly and stable.However,compared to the lead perovskites,their optoelectronic properties are compromised.Herein we report a series of bulk lead-free mixed Bi-In halide double perovskites:Cs2AgBi1-xInxCl6(0<x<1).The Cs2AgBi0.125In0.875Cl6breaks the parity-forbidden transition and retains direct band gap structure,having warm-white light emission,with photoluminescence quantum efficiency(PLQE)of 70.3%,much higher than the PLQE of reported lead perovskite materials.Its exciton self-trapping dynamics is investigated.Meanwhile,the Cs2AgBi0.125In0.875Cl6nanocrystals and Cs2AgBi0.125In0.875Cl6microcrystals can be synthesized by modified hot injection and rapid cooling crystallization,respectively.The size effect of Cs2AgBi0.125In0.875Cl6is studied on the photoluminescence(PL)property.Additionally,the bulk material exhibits excellent stability on exposure to light,humidity and air for more than 3 months.It is a promising candidate as highly efficient warm white-light emitting material for road lighting.展开更多
GaSb-based nanowires in a gate-all-around geometry are good candidates for binary p-type transistors,however they require the introduction of compressive strain to enhance the transport properties.Here,we for the firs...GaSb-based nanowires in a gate-all-around geometry are good candidates for binary p-type transistors,however they require the introduction of compressive strain to enhance the transport properties.Here,we for the first time demonstrate epitaxial GaSb-GaASxSb1-x core-shell nanowires with a compressively strained core.Both axial and hydrostatic strain in GaSb core have been measured by X-ray diffraction(XRD)and Raman scattering,respectively.The optimal sample,almost without plastic relaxation,has an axial strain of-0.88%and a hydrostatic strain of-1.46%,leading to a noticeable effect where the light hole band is calculated to be 33.4 meV above the heavy hole band at the T-point.This valence band feature offers more light holes to contribute the transport process,and thus may provide enhanced hole mobility by reducing both the interband scattering and the hole effective mass.Our results show that lattice-mismatched epitaxial core-shell heterostructures of high quality can also be realized in the promising yet demanding GaSb-based system.展开更多
The highest resolution of images of soft matter and biological materials is ultimately limited by modification of the structure,induced by the necessarily high energy of short-wavelength radiation.Imaging the inelasti...The highest resolution of images of soft matter and biological materials is ultimately limited by modification of the structure,induced by the necessarily high energy of short-wavelength radiation.Imaging the inelastically scattered X-rays at a photon energy of 60 keV(0.02 nm wavelength)offers greater signal per energy transferred to the sample than coherent-scattering techniques such as phase-contrast microscopy and projection holography.We present images of dried,unstained,and unfixed biological objects obtained by scanning Compton X-ray microscopy,at a resolution of about 70 nm.This microscope was realised using novel wedged multilayer Laue lenses that were fabricated to sub-ångström precision,a new wavefront measurement scheme for hard X rays,and efficient pixel-array detectors.The doses required to form these images were as little as 0.02%of the tolerable dose and 0.05%of that needed for phase-contrast imaging at similar resolution using 17 keV photon energy.The images obtained provide a quantitative map of the projected mass density in the sample,as confirmed by imaging a silicon wedge.Based on these results,we find that it should be possible to obtain radiation damage-free images of biological samples at a resolution below 10 nm.展开更多
Atomically precise gold nanoclusters with diameters of 1–3 nm have attracted considerable research interests in the past decade because they fill the gap between small organic-metal complexes(<1 nm)and metal nanop...Atomically precise gold nanoclusters with diameters of 1–3 nm have attracted considerable research interests in the past decade because they fill the gap between small organic-metal complexes(<1 nm)and metal nanoparticles(>3 nm).Au13 nanocluster with icosahedral structure is a ubiquitous unit widely applied in nanocluster assembly.In this minireview,we introduce the optical properties of gold nanoclusters constructed from Au_(13) units.We first discuss the optical absorption and photoluminescence of Au_(13),Au_(25),Au_(37),and Au_(60) clusters.We then discuss the ultrafast dynamics,the detailed excited-state deactivation processes,and the origin of coherent oscillations of the Au13 homologous clusters.Finally,we provide our outlook on the future direction on this topic.展开更多
The exploitation of ultrafast electron dynamics in quantum cascade lasers(QCLs)holds enormous potential for intense,compact mode-locked terahertz(THz)sources,squeezed THz light,frequency mixers,and comb-based metrolog...The exploitation of ultrafast electron dynamics in quantum cascade lasers(QCLs)holds enormous potential for intense,compact mode-locked terahertz(THz)sources,squeezed THz light,frequency mixers,and comb-based metrology systems.Yet the important sub-cycle dynamics have been notoriously difficult to access in operational THz QCLs.Here,we employ high-field THz pulses to perform the first ultrafast two-dimensional spectroscopy of a free-running THz QCL.Strong incoherent and coherent nonlinearities up to eight-wave mixing are detected below and above the laser threshold.These data not only reveal extremely short gain recovery times of 2 ps at the laser threshold,they also reflect the nonlinear polarization dynamics of the QCL laser transition for the first time,where we quantify the corresponding dephasing times between 0.9 and 1.5 ps with increasing bias currents.A density-matrix approach reproducing the emergence of all nonlinearities and their ultrafast evolution,simultaneously,allows us to map the coherently induced trajectory of the Bloch vector.The observed high-order multi-wave mixing nonlinearities benefit from resonant enhancement in the absence of absorption losses and bear potential for a number of future applications,ranging from efficient intracavity frequency conversion,mode proliferation to passive mode locking.展开更多
基金financial support from Swedish Energy Agency grant 50709-1Swedish Research Council grant 2021-05207+2 种基金KAW WISE/WASP grant 01-22Olle Engkvist foundation grant 235-0422Light and Materials profile area at Lund University(Young Investigator Synergy Award,2023)。
文摘Understanding and managing charge carrier recombination dynamics is crucial for optimizing the performance of metal halide perovskite optoelectronic devices.In this work,we introduce a machine learning-assisted intensity-modulated two-photon photoluminescence microscopy approach for quantitatively mapping recombination processes in MAPbBr_(3) perovskite microcrystalline films at micrometer-scale resolution.To enhance model accuracy,a balanced classification sampling strategy was applied during the machine learning optimization stage.
基金supported by the Swedish Research Council (VR),the Foundation for Strategic Research (SSF),the Knut and Alice Wallenberg foundation (KAW),the Swedish Energy Agency and Sweden’s innovation agency (VINNOVA)。
文摘Miniaturization of light-emitting diodes(LEDs) with sizes down to a few micrometers has become a hot topic in both academia and industry due to their attractive applications on self-emissive displays for high-definition televisions,augmented/mixed realities and head-up displays, and also on optogenetics, high-speed light communication, etc. The conventional top-down technology uses dry etching to define the LED size, leading to damage to the LED side walls.Since sizes of microLEDs approach the carrier diffusion length, the damaged side walls play an important role, reducing microLED performance significantly from that of large area LEDs. In this paper, we review our efforts on realization of microLEDs by direct bottom-up growth, based on selective area metal–organic vapor phase epitaxy. The individual LEDs based on either GaN nanowires or InGaN platelets are smaller than 1 μm in our approach. Such nano-LEDs can be used as building blocks in arrays to assemble microLEDs with different sizes, avoiding the side wall damage by dry etching encountered for the top-down approach. The technology of InGaN platelets is especially interesting since InGaN quantum wells emitting red, green and blue light can be grown on such platelets with a low-level of strain by changing the indium content in the InGaN platelets. This technology is therefore very attractive for highly efficient microLEDs of three primary colors for displays.
基金the National Key R@D Program of China (Grant 2017YFA0204800)the National Natural Science Foundation of China (Grant Nos: 21533010, 21321091, 21525315, 91333116 and 21173169) for their financial supports
文摘Because of the good thermal stability and superior carrier transport characteristics of formamidinium lead trihalide perovskite HC(NH_2)_2 PbX_3(FAPbX_3), it has been considered to be a better optoelectronic material than conventional CH_3NH_3-PbX_3(MAPbX_3). Herein, we fabricated a FAPbBr_3 microcrystal-based photodetector that exhibited a good responsivity of 4000 A W-1 and external quantum efficiency up to 106% under one-photon excitation, corresponding to the detectivity greater than 1014 Jones. The responsivity is two orders of magnitude higher than that of previously reported formamidinium perovskite photodetectors. Furthermore, the FAPbBr_3 photodetector's responsivity to two-photon absorption with an 800-nm excitation source can reach 0.07 A W^(-1), which is four orders of magnitude higher than that of its MAPbBr_3 counterparts. The response time of this photodetector is less than 1 ms.This study provides solid evidence that FAPbBr_3 can be an excellent candidate for highly sensitive and fast photodetectors.
基金The National Natural Science Foundation of China(Nos.22178291,22209135,22002123,and 22311530118)the National Science Fund for the Distinguished Young Scholars(No.52325401)。
文摘Maximizing ultrafast electron-transfer kinetics in semiconductor is pivotal but challenging for highefficiency solar-to-energy during the photocatalytic reaction process due to the intrinsic property of photocatalysts with low surface electron density.Herein,a model photocatalyst CdS@Mo is synthesized through a typical hydrothermal method for modulating the ultrafast electron-transfer to enhance the surface electron density.X-ray absorption fine spectra(XAFS)reveal that Mo is coordinated with S atoms to form a Mo-S_(6) configuration which is different from common MoS_(2) and Mo foil structures.Based on the femtosecond transient absorption spectra(fs-TAS),it is found that the formation of Mo-S6 configuration contributes to the fast decay of CdS signal and Mo-S_(6) signal reactivation,illustrating the ultrafast electron-transfer(∼2.2 ps)from CdS to Mo-S_(6) configuration,which achieves the enhanced electron density of photocatalyst surface.Finally,a holistic photocatalytic performance evaluation discloses that the growing of Mo-S_(6) configuration obviously improves the photocatalytic hydrogen evolution(PHE)effi-ciency of CdS from 28.5 to 47.5 mmol g^(-1)h^(-1)with a solar-to-hydrogen(STH)efficiency of 0.10%which is seldomly discussed in the system containing sacrificial agents.This work opens a new path to modulate the surface electron density by tuning the ultrafast electron-transfer for enhancing reaction efficiency in electron-density-dependent systems.
基金supported by the National Natural Science Foundation of China(U21A20496,62174117)Fund Program for the Scientific Activities of Selected Returned Overseas Professionals in Shanxi Province(20230011)+5 种基金Research Program Supported by Shanxi-Zheda Institute of Advanced Materials and Chemical Engineering(2022SX-TD020)Central Government Guides Local Funds for Scientific and Technological Development(YDZJSX20231A010)State Key Laboratory Program of Quantum Optics and Quantum Optics Devices(KF202306)Zheng K acknowledges the research grants from the Denmark VILLUM FONDEND(VIL50350)Swedish Research Council(2021-05319)Swedish Foundation for International Cooperation in Research and Higher Education(STINT,CH2019-8248).
文摘Perovskites have attracted widespread attention for laser applications due to their excellent optoelectronic properties.However,perovskite lasers typically exhibit a wavelength shift as pump density increases.Here,we report a pump-induced wavelength shift-free laser achieved using a perovskite nanoplatelet with mixed orthorhombic and tetragonal phase.At 293 K,the tetragonal-phase perovskite nanoplatelet laser exhibits a blue shift of~0.4 nmµJ^(-1)cm^(2)with increasing pump density.In contrast,at 80 K,the orthorhombic-phase perovskite nanoplatelet laser exhibits a red shift of~1 nmµJ^(-1)cm^(2).By stabilizing the perovskite nanoplatelet in a mixed orthorhombic-tetragonal phase at 163 K,the pump induced wavelength shifts are completely suppressed,resulting in a wavelength-stable laser.Additionally,the lasing threshold decreases from 18.4µJ cm^(−2)at room temperature to 4.5µJ cm^(−2)at 163 K.This study presents a promising strategy for achieving pump-insensitive wavelength stability in micro/nano lasers.
基金support of Marie Skłodowska-Curie postdoctoral fellowship(No.101151427,SPS_Nano)from the European Union’s Horizon Europe program,short stay abroad grant(K257023N)travel grant(K147824N)from Research Foundation-Flanders(FWO)。
文摘As the field of metal halide perovskites matures,a range of compositionally different perovskite films has found a place in efficient optoelectronic devices.These films feature variable local structural stability,carrier diffusion,and recombination,while there is still a lack of easy-to-implement generic protocols for high-throughput characterization of these variable properties.Correlation clustering imaging(CLIM)is a recently developed tool that resolves peculiarities of local photophysics by assessing the dynamics of photoluminescence detected by wide-field optical microscopy.We demonstrate the capability of CLIM as a high-throughput characterization tool of perovskite films using MAPbI3(MAPI)and triple cation mixed halide(TCMH)perovskites as examples where it resolves the interplay of carrier diffusion,recombination,and defect dynamics.We found significant differences in the appearance of metastable defect states in these two films.Despite a better surface quality and larger grain size,MAPI films showed more pronounced effects of fluctuating defect states than did TCMH films.As CLIM shows a significant difference between materials known to lead to different solar cell efficiencies,it can be considered a tool for quality control of thin films for perovskite optoelectronic devices.
基金supported by the National Science Fund for Distinguished Young Scholars(52325401)the National Key R&D Project of China(2020YFA0710000)+7 种基金the National Natural Science Foundation of China(22178291,22309152,22311530118,22209135)the National High-end Foreign Experts Recruitment Program(G2022036015L)the Sichuan High-end Foreign Experts Recruitment Program(23RCYJ0029)the International Science and Technology Cooperation project of Chengdu(2021-GH02-00052-HZ)Special Project for the Central Government to Guide the Development of Local Science and Technology in Sichuan Province(22ZYZYTS0231)the Scientific Research Starting Project of SWPU(2021QHZ028)Swedish Foundation for International Cooperation in Research and Higher Education(STINT,CH2019-8179)support from research grant(VIL50350)from VILLUM FONDEN,Denmark,and Swedish Research Council(2021-05319).
文摘Photocatalysis plays a crucial role in harnessing renewable energy by efficiently converting solar energy into chemical energy.Adequate cognition of photogenerated charge carrier dynamics in photocatalysis is the key to realizing efficient solar energy utilization,and provides guidance for breaking through the efficiency bottleneck.However,a convincing correlation between those photophysical processes and the photocatalytic performance has yet been established due to the complexity of photocatalytic reactions.In this review,we overviewed the detailed ultrafast photophysics in photocatalysis based on three typical ultrafast spectroscopic techniques(TRPL,TA and TRIR),and put a special focus on the justification as well as the limitation on correlating those photophysics with the actual catalytic performance.The classification of carrier behaviors after photoexcitation as well as typical time-resolved spectroscopic characterization techniques are briefly introduced first.State-of-the-art studies on the excited state dynamics in photocatalysis and its correlation to catalytic performance are then systematically presented from three types of common photocatalysts including quantum dots,polymeric photocatalysts,and traditional semiconductors.Finally,a summary on the correlation between ultrafast photophysics and the final photocatalytic performance is provided,and challenges and limitations of current photophysical characterization to rationalize the catalytic performance are outlined.
基金supported by the National Natural Science Foundation of China(U21A20496,61922060,61775156,61805172,12104334,62174117,and 61905173)the Key Research and Development Program of Shanxi Province(202102150101007)+5 种基金Shanxi-Zheda Institute of Advanced Materials and Chemical Engineering Program(2022SX-TD020)the Natural Science Foundation of Shanxi Province(20210302123154 and 20210302123169)the Research Project Supported by Shanxi Scholarship Council of China(2021-033)the Research Project Supported by Shanxi-Zheda Institute of Advanced Materials and Chemical Engineering(2021SXFR008)the Introduction of Talents Special Project of Lvliang City(Rc2020206 and Rc2020207)support from China Scholarship Council(202006935009)。
文摘具有低温升的高效散热方案是实现电泵浦激光的关键因素之一.高导热金刚石有望克服钙钛矿激光的散热限制.本文中,我们展示了一种可以将光泵浦过程中产生热量高效耗散的金刚石基底钙钛矿纳米片激光.此外,紧密光学束缚可以通过在纳米片和金刚石基底之间引入一层薄SiO_(2)间隔层而实现.该激光的品质因子高达~1962,激光阈值为52.19μJ cm^(-2).受益于金刚石基底,其泵浦能量密度相关温度灵敏度较低(~0.56±0.01 K cm~2μJ^(-1)).本工作有望促进电泵浦钙钛矿激光的发展.
文摘Semiconductor nanowire （NW） solar cells with a single p-n junction have exhibited efficiency comparable to that of their planar counterparts with a substantial reduction in material consumption. Tandem geometry is a path toward the fabrication of devices with even higher efficiencies, for which a key step is the fabrication of tunnel （Esaki） diodes within NWs with the correct diameter, pitch, and material combination for maximized efficiency. InP/GaInP and GaInP/InP NW tunnel diodes with band gap combinations corresponding to high-efficiency solar energy harvesting were fabricated and their electrical characteristics and material properties were compared. Four different configurations, with respect to material composition and doping, were investigated. The NW arrays were grown with metal-organic vapor-phase epitaxy from Au particles by use of nano-imprint lithography, metal evaporation and lift-off. Electrical measurements showed that the NWs behave as tunnel diodes in both InP （bottom）/GaInP （top） and GaInP （bottom）/InP （top） configurations, exhibiting a maximum peak current density of 25 A/cm^2, and maximum peak to valley current ratio of 2.5 at room temperature. The realization of NW tunnel diodes in both InP/GaInP and GaInP/InP configurations represent an opportunity for the use of NW tandem solar cells, whose efficiency is independent of the growth order of the different materials, increasing the flexibility regarding dopant incorporation polarity.
基金This project received funding from the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation program(Grant 801847).
文摘X-ray microscopy is an essential imaging method in many scientific fields,which can be extended to three-dimensional(3D)using tomography.Recently,metal halide perovskite(MHP)nanomaterials have become a promising candidate for X-ray scintillators,due to their high light yield,high spatial resolution,and easy fabrication.Tomography requires many projections and therefore scintillators with excellent stability.This is challenging for MHPs,which often suffer from fast degradation under X-ray irradiation and ambient conditions.Here,we demonstrate that MHP scintillators of CsPbBr3 nanowires(diameter:60 nm,length:5–9μm)grown in anodized aluminum oxide(CsPbBr3 NW/AAO)have sufficient stability for X-ray micro-tomography.A tomogram was taken with a Cu X-ray source over 41 h(dose 4.2 Gyair).During this period the scintillator brightness fluctuated less than 5%,which enabled a successful reconstruction.A long-term study with 2 weeks of continuous X-ray exposure(37.5 Gyair)showed less than 14%fluctuations in brightness and no long-term degradation,despite variations in the ambient relative humidity from 7.4%RH to 34.2%RH.The resolution was stable at(180±20)lp·mm−1,i.e.,about 2.8 micron.This demonstrates that CsPbBr3 NW/AAO scintillators are promising candidates for high resolution X-ray imaging detectors.
基金Open access funding provided by Lund University.
文摘Axially heterostructured nanowires are a promising platform for next generation electronic and optoelectronic devices.Reports based on theoretical modeling have predicted more complex strain distributions and increased critical layer thicknesses than in thin films,due to lateral strain relaxation at the surface,but the understanding of the growth and strain distributions in these complex structures is hampered by the lack of high-resolution characterization techniques.Here,we demonstrate strain mapping of an axially segmented GalnP-lnP 190 nm diameter nanowire heterostructure using scanning X-ray diffraction.We systematically investigate the strain distribution and lattice tilt in three different segment lengths from 45 to 170 nm,obtaining strain maps with about 10^-4 relative strain sensitivity.The experiments were performed using the 90 nm diameter nanofocus at the NanoMAX beamline,taking advantage of the high coherent flux from the first diffraction limited storage ring MAX IV.The experimental results are in good agreement with a full simulation of the experiment based on a three-dimensional(3D)finite element model.The largest segments show a complex profile,where the lateral strain relaxation at the surface leads to a dome-shaped strain distribution from the mismatched interfaces,and a change from tensile to compressive strain within a single segment.The lattice tilt maps show a cross-shaped profile with excellent qualitative and quantitative agreement with the simulations.In contrast,the shortest measured InP segment is almost fully adapted to the surrounding GalnP segments.
基金supported by the National Natural Science Foundation of China (NSFC, U1862111)China Scholarship Council (201706990062)+4 种基金Independent Research Fund Denmark-Nature Sciences (DFF-7014-00302)Independent Research Fund Denmark-Sapere Aude starting grant (7026-00037A)Swedish Research Council VR starting grant (2017-05337), grants VR2018-06011, and VR201805090the Research Fund for international Young Scientists from NSFC, China (21950410515)Swedish Energy Agency
文摘Multiple morphologies of colloidal perovskite nanocrystals(NCs)diversify their optical and electronic properties.Among them,the linear absorption cross-section(σ)is a primary parameter to determine their intrinsic photophysical features,and consequently,application potential.Herein,three morphologies of all-inorganic hybrid colloidal perovskite CsPbBr_(3)NCs,nanocubes(NBs),nanoplatelets(NLs),and nanowires(NWs),were targeted,and their linearσvalues were obtained through femtosecond transient absorption(TA)spectroscopy analysis.At high excitation energy well above the bandgap,theσper particle of all CsPbBr3 NCs linearly increased with the particle volume(VNC)regardless of the morphology with the value ofσ400=9.45×10^(4)cm^(−1)×VNC(cm^(2)).Density functional theory(DFT)calculation confirmed the negligible influence of shapes on the optical selection rules.The Einstein spontaneous emission coefficients calculated from theσvalues define the intrinsic radiative recombination rate.However,reduced size dependence is observed when the excitation energy is close to the bandgap(i.e.,at 460 nm)with the value ofσ460=2.82×10^(8)cm0.65×(VNC)0.45(cm^(2)).This should be ascribed to the discrete energy levels as well as lower density of states close to the band edge for perovskite NCs.These results provide in-depth insight into the optical characteristics for perovskite NCs.
基金supported by the National Priorities Research Program from the Qatar National Research Fund(a member of Qatar Foundation)(NPRP7-227-1-034)the Swedish Foundation for International Cooperation in Research and Higher Education(STINT,CH2015-6232)the Academy of Finland,and the Program of Study Abroad for Young Teachers by Agricultural University of Hebei
文摘Due to their superior photoluminescence(PL)quantum yield(QY) and tunable optical band gap,all-inorganic CsPbBr_3 perovskite quantum dots(QDs) have attracted intensive attention for the application in solar cells,light emitting diodes(LED),photodetectors and laser devices.In this scenario,the stability of such materials becomes a critical factor to be revealed.We hereby investigated the long-term stability of as-synthesized CsPbBr_3 QDs suspended in toluene at various environmental conditions.We found light illumination would induce drastic photo-degradation of CsPbBr_3 QDs.The steady-state spectroscopy,transmission electron microscopy(TEM),and X-ray diffraction(XRD)verified that CsPbBr_3 QDs tend to aggregate to form larger particles under continuous light soaking.In addition,decreasing PL QY of the QDs during light soaking indicates the formation of trap sites.Our work reveals that the main origin of instability in CsPbBr_3 QDs and provides reference to engineer such QDs towards optimal device application.
文摘Ternary III-V nanowires （NWs） cover a wide range of wavelengths in the solar spectrum and would greatly benefit from being synthesized as position-controlled arrays for improved vertical yield, reproducibility, and tunable optical absorption. Here, we report on successful selective-area epitaxy of metal-particle-free vertical InxGa1-xP NW arrays using metal-organic vapor phase epitaxy and detail their optical properties. A systematic growth study establishes the range of suitable growth parameters to obtain uniform NW growth over a large array. The optical properties of the NWs were characterized by room-temperature cathodoluminescence spectroscopy. Tunability of the emission wavelength from 870 nm to approximately 800 nm was achieved. Transmission electron microscopy and energy dispersive X-ray measurements performed on cross- section samples revealed a pure wurtzite crystal structure with very few stacking faults and a slight composition gradient along the NW growth axis.
基金supported by the National Natural Science Foundation of China (21533010, 21525315)the National Key Research and Development Program of China (2017YFA0204800)+2 种基金DICP DMTO201601DICP ZZBS201703the Science Challenging Program (JCKY2016212A501)
文摘Lead-free halide double perovskites have gathered wide scientific interest since they are environmentally friendly and stable.However,compared to the lead perovskites,their optoelectronic properties are compromised.Herein we report a series of bulk lead-free mixed Bi-In halide double perovskites:Cs2AgBi1-xInxCl6(0<x<1).The Cs2AgBi0.125In0.875Cl6breaks the parity-forbidden transition and retains direct band gap structure,having warm-white light emission,with photoluminescence quantum efficiency(PLQE)of 70.3%,much higher than the PLQE of reported lead perovskite materials.Its exciton self-trapping dynamics is investigated.Meanwhile,the Cs2AgBi0.125In0.875Cl6nanocrystals and Cs2AgBi0.125In0.875Cl6microcrystals can be synthesized by modified hot injection and rapid cooling crystallization,respectively.The size effect of Cs2AgBi0.125In0.875Cl6is studied on the photoluminescence(PL)property.Additionally,the bulk material exhibits excellent stability on exposure to light,humidity and air for more than 3 months.It is a promising candidate as highly efficient warm white-light emitting material for road lighting.
基金This work was supported by the Swedish Research Council(VR)the Swedish Foundation for Strategic Research(SSF).
文摘GaSb-based nanowires in a gate-all-around geometry are good candidates for binary p-type transistors,however they require the introduction of compressive strain to enhance the transport properties.Here,we for the first time demonstrate epitaxial GaSb-GaASxSb1-x core-shell nanowires with a compressively strained core.Both axial and hydrostatic strain in GaSb core have been measured by X-ray diffraction(XRD)and Raman scattering,respectively.The optimal sample,almost without plastic relaxation,has an axial strain of-0.88%and a hydrostatic strain of-1.46%,leading to a noticeable effect where the light hole band is calculated to be 33.4 meV above the heavy hole band at the T-point.This valence band feature offers more light holes to contribute the transport process,and thus may provide enhanced hole mobility by reducing both the interband scattering and the hole effective mass.Our results show that lattice-mismatched epitaxial core-shell heterostructures of high quality can also be realized in the promising yet demanding GaSb-based system.
基金We thank Martin Domaracky,Florian Laucks,Jerome Carnis(CFEL)for support with controls and data acquisition software,Sabrina Bolmer,Harumi Nakatsutsumi,Tjark Delmas(CFEL)for technical work,Christian Hamm(AWI,Bremerhaven,Germany)for the diatom sample,Klara Gregorič(Univ.of Ljubljana,Slovenia)and Iosifina Sarrou for preparing the spirulina sample,and Miriam Barthelmeß(CFEL)for the silicon sample.We also thank X-Spectrum(Hamburg,Germany)for support with CdTe detectors.We acknowledge support by DESY(Hamburg,Germany),a member of the Helmholtz Association HGF and by the Cluster of Excellence‘Advanced Imaging of Matter’of the Deutsche Forschungsgemeinschaft(DFG)-EXC 2056-project ID 390715994.
文摘The highest resolution of images of soft matter and biological materials is ultimately limited by modification of the structure,induced by the necessarily high energy of short-wavelength radiation.Imaging the inelastically scattered X-rays at a photon energy of 60 keV(0.02 nm wavelength)offers greater signal per energy transferred to the sample than coherent-scattering techniques such as phase-contrast microscopy and projection holography.We present images of dried,unstained,and unfixed biological objects obtained by scanning Compton X-ray microscopy,at a resolution of about 70 nm.This microscope was realised using novel wedged multilayer Laue lenses that were fabricated to sub-ångström precision,a new wavefront measurement scheme for hard X rays,and efficient pixel-array detectors.The doses required to form these images were as little as 0.02%of the tolerable dose and 0.05%of that needed for phase-contrast imaging at similar resolution using 17 keV photon energy.The images obtained provide a quantitative map of the projected mass density in the sample,as confirmed by imaging a silicon wedge.Based on these results,we find that it should be possible to obtain radiation damage-free images of biological samples at a resolution below 10 nm.
基金Chinese Academy of Sciences,Grant/Award Number:YSBR-007。
文摘Atomically precise gold nanoclusters with diameters of 1–3 nm have attracted considerable research interests in the past decade because they fill the gap between small organic-metal complexes(<1 nm)and metal nanoparticles(>3 nm).Au13 nanocluster with icosahedral structure is a ubiquitous unit widely applied in nanocluster assembly.In this minireview,we introduce the optical properties of gold nanoclusters constructed from Au_(13) units.We first discuss the optical absorption and photoluminescence of Au_(13),Au_(25),Au_(37),and Au_(60) clusters.We then discuss the ultrafast dynamics,the detailed excited-state deactivation processes,and the origin of coherent oscillations of the Au13 homologous clusters.Finally,we provide our outlook on the future direction on this topic.
基金We acknowledge funding from the European Union under the Horizon 2020 research and innovation programs FET-Open grant ULTRAQCL 665158the French National Research Agency(ANR-18-CE24-0013-02-“TERASEL”)+1 种基金the Swedish Research Council(project 2017-04287)the EPSRC(UK)program grant“HyperTerahertz”(EP/P021859/1).
文摘The exploitation of ultrafast electron dynamics in quantum cascade lasers(QCLs)holds enormous potential for intense,compact mode-locked terahertz(THz)sources,squeezed THz light,frequency mixers,and comb-based metrology systems.Yet the important sub-cycle dynamics have been notoriously difficult to access in operational THz QCLs.Here,we employ high-field THz pulses to perform the first ultrafast two-dimensional spectroscopy of a free-running THz QCL.Strong incoherent and coherent nonlinearities up to eight-wave mixing are detected below and above the laser threshold.These data not only reveal extremely short gain recovery times of 2 ps at the laser threshold,they also reflect the nonlinear polarization dynamics of the QCL laser transition for the first time,where we quantify the corresponding dephasing times between 0.9 and 1.5 ps with increasing bias currents.A density-matrix approach reproducing the emergence of all nonlinearities and their ultrafast evolution,simultaneously,allows us to map the coherently induced trajectory of the Bloch vector.The observed high-order multi-wave mixing nonlinearities benefit from resonant enhancement in the absence of absorption losses and bear potential for a number of future applications,ranging from efficient intracavity frequency conversion,mode proliferation to passive mode locking.
