Zero-dimensional environmentally friendly carbon quantum dots(CQDs)combined with two-di-mensional materials have a wide range of applications in optoelec-tronic devices.We combined steady-state and transient absorp-ti...Zero-dimensional environmentally friendly carbon quantum dots(CQDs)combined with two-di-mensional materials have a wide range of applications in optoelec-tronic devices.We combined steady-state and transient absorp-tion spectroscopies to study the energy transfer dynamics between CQDs and molybdenum disulfide(MoS_(2)).Transient absorption plots showed photoinduced absorption and stimulated emission features,which involved the intrinsic and defect states of CQDs.Adding MoS_(2)to CQDs solution,the lowest unoccupied molecular orbital of CQDs transferred energy to MoS_(2),which quenched the intrinsic emission at 390 nm.With addition of MoS_(2),CQD-MoS_(2)composites quenched defect emission at 490 nm and upward absorption,which originated from another energy transfer from the defect state.Two energy transfer paths between CQDs and MoS_(2)were efficiently manipulated by changing the concentration of MoS_(2),which laid a foundation for improving device performance.展开更多
Ultrafast extreme ultraviolet (XUV) transient absorption spectroscopy measures the time- and frequencydependent light losses after light–matter interactions. In the linear region, the matter response to an XUV light ...Ultrafast extreme ultraviolet (XUV) transient absorption spectroscopy measures the time- and frequencydependent light losses after light–matter interactions. In the linear region, the matter response to an XUV light field is usually determined by the complex refractive index ̃n. The absorption signal is directly related to the imaginary part of ̃n, namely, the absorption index. The real part of ̃n refers to the real refractive index, which describes the chromatic dispersion of an optical material. However, the real refractive index information is usually not available in conventional absorption experiments. Here, we investigate the refractive index line shape in ultrafast XUV transient absorption spectroscopy by using a scheme that the XUV pulse traverses the target gas jet off-center. The jet has a density gradient in the direction perpendicular to the gas injection direction, which induces deflection on the XUV radiation. Our experimental and theoretical results show that the shape of the frequency-dependent XUV deflection spectra reproduces the refractive index line profile. A typical dispersive refractive index line shape is measured for a single-peak absorption;an additional shoulder structure appears for a doublet absorption.Moreover, the refractive index line shape is controlled by introducing a later-arrived near-infrared pulse to modify the phase of the XUV free induction decay, resulting in different XUV deflection spectra. The results promote our understanding of matter-induced absorption and deflection in ultrafast XUV spectroscopy.展开更多
Small-molecule organic solar cell is a category of clean energy potential device since charge transfers between donor and acceptor.The morphologies,co-assembly behavior,interaction sites,and charge transfer of BTID-nF...Small-molecule organic solar cell is a category of clean energy potential device since charge transfers between donor and acceptor.The morphologies,co-assembly behavior,interaction sites,and charge transfer of BTID-nF(n=1,2)/PC71BM donor-acceptor system in the active layer of organic solar cell have been studied employing scanning tunneling microscopy(STM),scanning tunneling spectroscopy(STS),density functional theory(DFT)calculations,and transient absorption(TA)spectroscopy.The results show that BTID-1F and BTID-2F form bright strip structures,whereas BTID-nF(n=1,2)/PC71BM form ridge-like structures with each complex composed of one BTID-nF(n=1,2)molecule and four PC71BM molecules which adsorbed around the BTID-nF(n=1,2)molecule by S···πinteraction.With the assistance of S···πinteraction between BTID-nF(n=1,2)and PC71BM,BTID-nF(n=1,2)/PC71BM co-assembled ridge-like structures are more stable than the BTID-nF(n=1,2)ridge structures.To investigate the charge transfer of BTID-nF(n=1,2)/PC71BM system,STS measurements,DFT calculation,and TA spectroscopy are further performed.The results show that charge transfer occurs in BTID-nF(n=1,2)/PC71BM system with the electron transferring from BTID-nF(n=1,2)molecules to PC71BM.展开更多
A bulk heterojunction in organic solar cells is where charge separation and recombination occur.Molecular orientation at the interface is one of the key factors that dictate solar cell efficiency.Although X-ray scatte...A bulk heterojunction in organic solar cells is where charge separation and recombination occur.Molecular orientation at the interface is one of the key factors that dictate solar cell efficiency.Although X-ray scattering-based methods can determine donor/acceptor domain orientations between an anisotropic phase and an isotropic fullerene-based phase,the rise of nonfullerene solar cells presents a new challenge in delineating local molecular directions at the interface between two anisotropic donor/acceptor domains.Here,we determine interfacial molecular orientations of three high-efficiency small molecule solar cells(ZR1:Y6,B1:BO-4 Cl,and BTR:BO-4 Cl)using polarization-selective transient absorption spectroscopy.The polarization anisotropy of charge separation dynamics indicates an angle of~90°between ZR1 and Y6 molecules at the interface,an angle close to 0°between B1 and BO-4 Cl,and random orientations between BTR and BO-4 Cl.These observations provide complementary information to X-ray scattering measurements and highlight polarization-selective transient absorption spectroscopy as a tool to probe interfacial structure and dynamics of key photophysical steps in energy conversion.展开更多
Over the past decade the integration of ultrafast spectroscopy with nanoscience has greatly propelled the development of nanoscience, as the key information gleaned from the mechanistic studies with the assistance of ...Over the past decade the integration of ultrafast spectroscopy with nanoscience has greatly propelled the development of nanoscience, as the key information gleaned from the mechanistic studies with the assistance of ultrafast spectroscopy enables a deeper understanding of the structure–function interplay and various interactions involved in the nanosystems.This mini-review presents an overview of the recent advances achieved in our ultrafast spectroscopy laboratory that address the ultrafast dynamics and related mechanisms in several representative nanomaterial complex systems by means of femtosecond time-resolved transient absorption spectroscopy. We attempt to convey instructive, consistent information regarding the important processes, pathways, dynamics, and interactions involved in the nanomaterial complex systems,most of which exhibit excellent performance in photocatalysis.展开更多
Antimony trisulfide(Sb_(2)S_(3)) solar cells suffer from large open circuit voltage deficits due to their intrinsic defects which limit the power conversion efficiency.Thus,it is important to elucidate these defects’...Antimony trisulfide(Sb_(2)S_(3)) solar cells suffer from large open circuit voltage deficits due to their intrinsic defects which limit the power conversion efficiency.Thus,it is important to elucidate these defects’ origin and defects at the interface.Here,we discover that sulfide radical defects have a significant impact on the performance of Sb_(2)S_(3)solar cells.Moreover,it has been illustrated that these defects at the CdS/Sb_(2)S_(3)interface can be reduced by optimizing the deposition process.A trap distribution model is used to quantify the defect density at the CdS/Sb_(2)S_(3)interface.It shows that the interface defects can be reduced by24% by improving the deposition process.This work reveals the importance of interface defects and guides the future optimization of Sb_(2)S_(3)solar cells.展开更多
Despite that organic-inorganic lead halide perovskites have attracted enormous scientific attention for energy conversion applications over the recent years,the influence of temperature and the type of the employed ho...Despite that organic-inorganic lead halide perovskites have attracted enormous scientific attention for energy conversion applications over the recent years,the influence of temperature and the type of the employed hole transport layer(HTL)on the charge carrier dynamics and recombination processes in perovskite photovoltaic devices is still largely unexplored.In particular,significant knowledge is missing on how these crucial parameters for radiative and non-radiative recombinations,as well as for efficient charge extraction vary among different perovskite crystalline phases that are induced by temperature variation.Herein,we perform micro photoluminescence(pPL)and ultrafast time resolved transient absorption spectroscopy(TAS)in Glass/Perovskite and two dierent Glass/ITO/HTL/Perovskite configurations at temperatures below room temperature,in order to probe the charge carrier dynamics of different perovskite crystalline phases,while considering also the effect of the employed HTL polymer.Namely,CH_(3)NH_(3)Pbb films were deposited on Glass,PEDOT:PSS and PTAA polymers,and the developed Glass/CH_(3)NH_(3)PbI_(3)and Glass/ITO/HTL/CH_(3)NH_(3)PbI_(3)architectures were studied from 85 K up to 215 K in order to explore the charge extraction dynamics of the CH_(3)NH_(3)PbI_(3)orthorhombic and tetragonal crystalline phases.It is observed an unusual blueshift of the bandgap with temperature and the dual emission at temperature below of 100 K and also,that the charge carrier dynamics,as expressed by hole injection times and free carrier recombination rates,are strongly depended on the actual pervoskite crystal phase,as well as,from the selected hole transport material.展开更多
One-dimensional nanowire is an important candidate for lead-halide perovskite-based photonic detectors and solar cells. Its surface population, diameter, and growth direction, etc., are critical for device performance...One-dimensional nanowire is an important candidate for lead-halide perovskite-based photonic detectors and solar cells. Its surface population, diameter, and growth direction, etc., are critical for device performance. In this research,we carried out a detailed study on electron transfer process at the interface of nanowire CH_(3) NH_(3) PbI_(3)(N-MAPbI_(3))/Phenyl C61 butyric acid methyl-ester synonym(PCBM), as well as the interface of compact CH_(3) NH_(3) PbI_(3)(C-MAPbI_(3))/PCBM by transient absorption spectroscopy. By comparing the carrier recombination dynamics of N-MAPbI_(3), N-MAPbI_(3)/PCBM,C-MAPbI_(3), and C-MAPbI_(3)/PCBM from picosecond(ps) to hundred nanosecond(ns) time scale, it is demonstrated that electron transfer at N-MAPbI_(3)/PCBM interface is less efficient than that at C-MAPbI_(3)/PCBM interface. In addition, electron transfer efficiency at C-MAPbI_(3)/PCBM interface was found to be excitation density-dependent, and it reduces with photo-generation carrier concentration increasing in a range from 1.0 × 1018 cm^(-3)–4.0 × 1018 cm^(-3). Hot electron transfer,which leads to acceleration of electron transfer between the interfaces, was also visualized as carrier concentration increases from 1.0 × 10^(18) cm^(-3)–2.2 × 10^(18) cm^(-3).展开更多
The excited-state intramolecular proton transfer of 2-(2-hydroxyphenyl)benzoxazole dye in different solvents is investigated using ultrafast femtosecond transient absorption spectroscopy combined with quantum chemical...The excited-state intramolecular proton transfer of 2-(2-hydroxyphenyl)benzoxazole dye in different solvents is investigated using ultrafast femtosecond transient absorption spectroscopy combined with quantum chemical calculations.Conformational conversion from the syn-enol configuration to the keto configuration is proposed as the mechanism of excited-state intramolecular proton transfer.The duration of excited-state intramolecular proton transfer is measured to range from 50 fs to 200 fs in different solvents.This time is strongly dependent on the calculated energy gap between the N-S;and T-S;structures in the S;state.Along the proton transfer reaction coordinate,the vibrational relaxation process on the S;state potential surface is observed.The duration of the vibrational relaxation process is determined to be from8.7 ps to 35 ps dependent on the excess vibrational energy.展开更多
Electron donors(EDs)are widely used to improve the H 2 production performance of Schottky junction photocatalysts,but the functions of EDs are still unknown from the perspective of electron transfer dy-namics.Herein,P...Electron donors(EDs)are widely used to improve the H 2 production performance of Schottky junction photocatalysts,but the functions of EDs are still unknown from the perspective of electron transfer dy-namics.Herein,Pt nanocluster-decorated CdS nanorod is successfully prepared to construct a typical CdS/Pt Schottky junction.Pt nanoclusters with a diameter of∼2 nm are deposited on the surface of CdS nanorods by in situ photoreduction at sub-zero temperature.The CdS/Pt photocatalyst using lactic acid shows a higher H_(2)production rate of 4762μmol g^(-1)h^(-1)compared to that using methanol,tri-ethanolamine,and glycerol.To understand the cause,the dynamics of photogenerated carriers in CdS/Pt photocatalysts during ED-assisted H_(2)production are revealed by femtosecond transient absorption spec-troscopy.Among the four organic EDs,lactic acid enables the fastest electron transfer rate of 1.8×10^(9)s^(-1)and the highest electron transfer efficiency of 76%at the CdS/Pt interface due to the most efficient hole consumption.This work sheds light on the importance of efficient interfacial electron transfer for im-proving the photocatalytic performance of Schottky junction photocatalysts.展开更多
Singlet fission(SF)is an appealing process where one photoexcited singlet transforms to two triplets,which can overcome thermalization energy loss and improve solar cell efficiency.However,it remains unclear how inter...Singlet fission(SF)is an appealing process where one photoexcited singlet transforms to two triplets,which can overcome thermalization energy loss and improve solar cell efficiency.However,it remains unclear how intermolecular coupling,which is subject to molecular stacking,controls SF pathways and dynamics.Here,we prepared polymorph rubrene single crystals with different stacking geometries,including orthorhombic(Orth.),triclinic(Tri.),and monoclinic(Mono.)phases.By micro-area ultrafast spectroscopy,we find that Orth.and Tri.phases with closerπ-πstacking exhibit co-existing coherent and incoherent SF channels while loosely stacked Mono.phase shows only incoherent SF.Furthermore,incoherent SF is thermally activated in Orth.but barrierless in Mono.and Tri.phases.Quantum mechanical calculation reveals that different electronic coupling strength in different phases leads to different SF dynamics.This study demonstrates that molecular stacking governs SF dynamics through electronic coupling,providing guidance for designing efficient SF materials via crystal structural engineering.展开更多
The aggregation and photoinduced excited state dynamics of organic π-conjugated molecules play a vital role in solar energy conversion and applications.This work investigates how solvent polarity affects the aggregat...The aggregation and photoinduced excited state dynamics of organic π-conjugated molecules play a vital role in solar energy conversion and applications.This work investigates how solvent polarity affects the aggregation behavior and the photophysical process of perylene diimide dimer(PDI-II).The results show that the conjugations between PDI intramolecular chromophores are more likely to generate excimer,and the conjugations between PDI intermolecular chromophores are more likely to experience symmetry-breaking charge separation.Our study can provide a reference for the design of high-efficiency solar energy conversion materials.展开更多
Fundamental understandings on the dynamics of charge carriers and excitonic quasiparticles in semiconductors are of central importance for both many-body physics and promising optoelectronic and photonic applications....Fundamental understandings on the dynamics of charge carriers and excitonic quasiparticles in semiconductors are of central importance for both many-body physics and promising optoelectronic and photonic applications.Here,we investigated the carrier dynamics and many-body interactions in two-dimensional(2D)transition metal dichalcogenides(TMDs),using monolayer WS2 as an example,by employing femtosecond broadband pump-probe spectroscopy.Three time regimes for the exciton energy renormalization are unambiguously revealed with a distinct red-blue-red shift upon above-bandgap optical excitations.We attribute the dominant physical process in the three typical regimes to free carrier screening effect,Coulombic exciton-exciton interactions and Auger photocarrier generation,respectively,which show distinct dependence on the optical excitation wavelength,pump fluences and/or lattice temperature.An intrinsic exciton radiative lifetime of about 1.2 picoseconds(ps)in monolayer WS2 is unraveled at low temperature,and surprisingly the efficient Auger nonradiative decay of both bright and dark excitons puts the system in a nonequilibrium state at the nanosecond timescale.In addition,the dynamics of trions at low temperature is observed to be significantly different from that of excitons,e.g.,a long radiative lifetime of^108.7 ps at low excitation densities and the evolution of trion energy as a function of delay times.Our findings elucidate the dynamics of excitonic quasiparticles and the intricate many-body physics in 2D semiconductors,underpinning the future development of photonics,valleytronics and optoelectronics based on 2D semiconductors.展开更多
The relaxation paths for triphenylamine(TPA)-2,3-dicyanopyrazino phenanthrene(DCPP), which has a pull-push structure, were investigated via steady-state, time-resolved spectroscopy involving transient absorption a...The relaxation paths for triphenylamine(TPA)-2,3-dicyanopyrazino phenanthrene(DCPP), which has a pull-push structure, were investigated via steady-state, time-resolved spectroscopy involving transient absorption and time-correlated single photon counting. By changing the solvent polarity we found that an intramolecular charge transfer(ICT) state acting as a "bright" state was responsible for the fluorescence character of TPA-DCPP. Meanwhile, a "dark" state gradually appeared and competed with the ICT state. This was likely to be responsible for the polarity-dependent evolution of fluorescence intensity and fluorescence lifetime. The temperature-dependent fluorescence character of the TPA-DCPP in toluene exhibited ICT processes at high temperatures prior to the relaxation path from the initial excited state to the ground state. Our results provide useful insight into the optoelectronic properties of these kinds of molecules.展开更多
基金supported by the National Natural Science Foundation of China(No.61805134 and No.11974229)Applied Basic Research Program in Shanxi Province,China(No.201801D221016 and No.202103021223254)+2 种基金Scientific and Technological Innovation Pro-grams of Higher Education Institutions in Shanxi(No.2020L0235 and No.2021L257)Linfen Key Re-search and Development Program(No.2028)Graduate Innovation Project in Shanxi Province(No.2022Y498).
文摘Zero-dimensional environmentally friendly carbon quantum dots(CQDs)combined with two-di-mensional materials have a wide range of applications in optoelec-tronic devices.We combined steady-state and transient absorp-tion spectroscopies to study the energy transfer dynamics between CQDs and molybdenum disulfide(MoS_(2)).Transient absorption plots showed photoinduced absorption and stimulated emission features,which involved the intrinsic and defect states of CQDs.Adding MoS_(2)to CQDs solution,the lowest unoccupied molecular orbital of CQDs transferred energy to MoS_(2),which quenched the intrinsic emission at 390 nm.With addition of MoS_(2),CQD-MoS_(2)composites quenched defect emission at 490 nm and upward absorption,which originated from another energy transfer from the defect state.Two energy transfer paths between CQDs and MoS_(2)were efficiently manipulated by changing the concentration of MoS_(2),which laid a foundation for improving device performance.
基金support of the Joint Centre for Extreme Photonics.Funding:This work is supported by the start-up grant of ShanghaiTech University,Double First-Class Initiative Fund of ShanghaiTech University,Shanghai Rising-Star Program(22QA1406200)National Natural Science Foundation of China(12274297,92250303)+7 种基金Shanghai Science and Technology Program(21511105000)NSERC Discovery Grant program(RGPIN-327147-2012)by the U.S.Army Research Office through Award W911NF-14-1-0383Part of this research used Beamline 03U of the Shanghai Synchrotron Radiation Facilitysupported by the ME2 project under contract no.11227902the National Natural Science Foundation of China.Y.F.and C.J.are supported by the National Natural Science Foundation of China(12274230,91950102,and 11834004)Funding of NJUST(TSXK2022D005)H.X.is supported by the National Natural Science Foundation of China(12074063 and 12264003)。
文摘Ultrafast extreme ultraviolet (XUV) transient absorption spectroscopy measures the time- and frequencydependent light losses after light–matter interactions. In the linear region, the matter response to an XUV light field is usually determined by the complex refractive index ̃n. The absorption signal is directly related to the imaginary part of ̃n, namely, the absorption index. The real part of ̃n refers to the real refractive index, which describes the chromatic dispersion of an optical material. However, the real refractive index information is usually not available in conventional absorption experiments. Here, we investigate the refractive index line shape in ultrafast XUV transient absorption spectroscopy by using a scheme that the XUV pulse traverses the target gas jet off-center. The jet has a density gradient in the direction perpendicular to the gas injection direction, which induces deflection on the XUV radiation. Our experimental and theoretical results show that the shape of the frequency-dependent XUV deflection spectra reproduces the refractive index line profile. A typical dispersive refractive index line shape is measured for a single-peak absorption;an additional shoulder structure appears for a doublet absorption.Moreover, the refractive index line shape is controlled by introducing a later-arrived near-infrared pulse to modify the phase of the XUV free induction decay, resulting in different XUV deflection spectra. The results promote our understanding of matter-induced absorption and deflection in ultrafast XUV spectroscopy.
基金the National Basic Research Program of China(Nos.2017YFA0205000 and 2016YFA0200700)the National Natural Science Foundation of China(Nos.21773041,21972031,21301092,and 20962002)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB36000000).
文摘Small-molecule organic solar cell is a category of clean energy potential device since charge transfers between donor and acceptor.The morphologies,co-assembly behavior,interaction sites,and charge transfer of BTID-nF(n=1,2)/PC71BM donor-acceptor system in the active layer of organic solar cell have been studied employing scanning tunneling microscopy(STM),scanning tunneling spectroscopy(STS),density functional theory(DFT)calculations,and transient absorption(TA)spectroscopy.The results show that BTID-1F and BTID-2F form bright strip structures,whereas BTID-nF(n=1,2)/PC71BM form ridge-like structures with each complex composed of one BTID-nF(n=1,2)molecule and four PC71BM molecules which adsorbed around the BTID-nF(n=1,2)molecule by S···πinteraction.With the assistance of S···πinteraction between BTID-nF(n=1,2)and PC71BM,BTID-nF(n=1,2)/PC71BM co-assembled ridge-like structures are more stable than the BTID-nF(n=1,2)ridge structures.To investigate the charge transfer of BTID-nF(n=1,2)/PC71BM system,STS measurements,DFT calculation,and TA spectroscopy are further performed.The results show that charge transfer occurs in BTID-nF(n=1,2)/PC71BM system with the electron transferring from BTID-nF(n=1,2)molecules to PC71BM.
基金financially supported from National Key R&D Program of China(2016YFA0200700)the National Natural Science Foundation of China(22071207,21721001,21805230,51873217,21734008,51773047,52073068)。
文摘A bulk heterojunction in organic solar cells is where charge separation and recombination occur.Molecular orientation at the interface is one of the key factors that dictate solar cell efficiency.Although X-ray scattering-based methods can determine donor/acceptor domain orientations between an anisotropic phase and an isotropic fullerene-based phase,the rise of nonfullerene solar cells presents a new challenge in delineating local molecular directions at the interface between two anisotropic donor/acceptor domains.Here,we determine interfacial molecular orientations of three high-efficiency small molecule solar cells(ZR1:Y6,B1:BO-4 Cl,and BTR:BO-4 Cl)using polarization-selective transient absorption spectroscopy.The polarization anisotropy of charge separation dynamics indicates an angle of~90°between ZR1 and Y6 molecules at the interface,an angle close to 0°between B1 and BO-4 Cl,and random orientations between BTR and BO-4 Cl.These observations provide complementary information to X-ray scattering measurements and highlight polarization-selective transient absorption spectroscopy as a tool to probe interfacial structure and dynamics of key photophysical steps in energy conversion.
基金support from the National Natural Science Foundation of China (21573211 and 21421063)the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB01020200)the Fundamental Research Funds for the Central Universities of China (WK2340000063)
文摘Over the past decade the integration of ultrafast spectroscopy with nanoscience has greatly propelled the development of nanoscience, as the key information gleaned from the mechanistic studies with the assistance of ultrafast spectroscopy enables a deeper understanding of the structure–function interplay and various interactions involved in the nanosystems.This mini-review presents an overview of the recent advances achieved in our ultrafast spectroscopy laboratory that address the ultrafast dynamics and related mechanisms in several representative nanomaterial complex systems by means of femtosecond time-resolved transient absorption spectroscopy. We attempt to convey instructive, consistent information regarding the important processes, pathways, dynamics, and interactions involved in the nanomaterial complex systems,most of which exhibit excellent performance in photocatalysis.
基金support from the National Key R&D Program of China(2019YFE0120300)the National Natural Science Foundation of China(NSFC,11904266,62204174 and 91850207)the Fundamental Research Funds for the Central Universities(2042021kf0202 and 2042021kf0069)。
文摘Antimony trisulfide(Sb_(2)S_(3)) solar cells suffer from large open circuit voltage deficits due to their intrinsic defects which limit the power conversion efficiency.Thus,it is important to elucidate these defects’ origin and defects at the interface.Here,we discover that sulfide radical defects have a significant impact on the performance of Sb_(2)S_(3)solar cells.Moreover,it has been illustrated that these defects at the CdS/Sb_(2)S_(3)interface can be reduced by optimizing the deposition process.A trap distribution model is used to quantify the defect density at the CdS/Sb_(2)S_(3)interface.It shows that the interface defects can be reduced by24% by improving the deposition process.This work reveals the importance of interface defects and guides the future optimization of Sb_(2)S_(3)solar cells.
文摘Despite that organic-inorganic lead halide perovskites have attracted enormous scientific attention for energy conversion applications over the recent years,the influence of temperature and the type of the employed hole transport layer(HTL)on the charge carrier dynamics and recombination processes in perovskite photovoltaic devices is still largely unexplored.In particular,significant knowledge is missing on how these crucial parameters for radiative and non-radiative recombinations,as well as for efficient charge extraction vary among different perovskite crystalline phases that are induced by temperature variation.Herein,we perform micro photoluminescence(pPL)and ultrafast time resolved transient absorption spectroscopy(TAS)in Glass/Perovskite and two dierent Glass/ITO/HTL/Perovskite configurations at temperatures below room temperature,in order to probe the charge carrier dynamics of different perovskite crystalline phases,while considering also the effect of the employed HTL polymer.Namely,CH_(3)NH_(3)Pbb films were deposited on Glass,PEDOT:PSS and PTAA polymers,and the developed Glass/CH_(3)NH_(3)PbI_(3)and Glass/ITO/HTL/CH_(3)NH_(3)PbI_(3)architectures were studied from 85 K up to 215 K in order to explore the charge extraction dynamics of the CH_(3)NH_(3)PbI_(3)orthorhombic and tetragonal crystalline phases.It is observed an unusual blueshift of the bandgap with temperature and the dual emission at temperature below of 100 K and also,that the charge carrier dynamics,as expressed by hole injection times and free carrier recombination rates,are strongly depended on the actual pervoskite crystal phase,as well as,from the selected hole transport material.
基金supported by the National Natural Science Foundation of China (Grant Nos. 21503066 and 61904048)the Fundamental Research Project from Shenzhen Science and Technology Innovation Committee (Grant No. JCYJ20180302174021198)+2 种基金the Natural Science Foundation of Hebei ProvinceChina(Grant No. F2017201136)the Foundation of Hebei Educational Committee (Grant No. ZC2016003)。
文摘One-dimensional nanowire is an important candidate for lead-halide perovskite-based photonic detectors and solar cells. Its surface population, diameter, and growth direction, etc., are critical for device performance. In this research,we carried out a detailed study on electron transfer process at the interface of nanowire CH_(3) NH_(3) PbI_(3)(N-MAPbI_(3))/Phenyl C61 butyric acid methyl-ester synonym(PCBM), as well as the interface of compact CH_(3) NH_(3) PbI_(3)(C-MAPbI_(3))/PCBM by transient absorption spectroscopy. By comparing the carrier recombination dynamics of N-MAPbI_(3), N-MAPbI_(3)/PCBM,C-MAPbI_(3), and C-MAPbI_(3)/PCBM from picosecond(ps) to hundred nanosecond(ns) time scale, it is demonstrated that electron transfer at N-MAPbI_(3)/PCBM interface is less efficient than that at C-MAPbI_(3)/PCBM interface. In addition, electron transfer efficiency at C-MAPbI_(3)/PCBM interface was found to be excitation density-dependent, and it reduces with photo-generation carrier concentration increasing in a range from 1.0 × 1018 cm^(-3)–4.0 × 1018 cm^(-3). Hot electron transfer,which leads to acceleration of electron transfer between the interfaces, was also visualized as carrier concentration increases from 1.0 × 10^(18) cm^(-3)–2.2 × 10^(18) cm^(-3).
基金supported by the Natural Science Foundation of Hubei Province,China(Grant No.2020CFB468)the Guiding Project of Scientific Research Plan of Department of Education of Hubei Province,China(Grant No.B2020136)+1 种基金the National Key Research and Development Program of China(Grant No.2019YFA0307700)the National Natural Science Foundation of China(Grant Nos.11974381,11674355,and 21507027)。
文摘The excited-state intramolecular proton transfer of 2-(2-hydroxyphenyl)benzoxazole dye in different solvents is investigated using ultrafast femtosecond transient absorption spectroscopy combined with quantum chemical calculations.Conformational conversion from the syn-enol configuration to the keto configuration is proposed as the mechanism of excited-state intramolecular proton transfer.The duration of excited-state intramolecular proton transfer is measured to range from 50 fs to 200 fs in different solvents.This time is strongly dependent on the calculated energy gap between the N-S;and T-S;structures in the S;state.Along the proton transfer reaction coordinate,the vibrational relaxation process on the S;state potential surface is observed.The duration of the vibrational relaxation process is determined to be from8.7 ps to 35 ps dependent on the excess vibrational energy.
基金the National Key Research and Development Program of China(Nos.2022YFB3803600 and 2018YFB1502001)National Natural Science Foundation of China(Nos.22238009,51932007,U1905215,52073223,52173065,and 52202375)+2 种基金the Natural Science Foundation of Hubei Province of China(No.2022CFA001)China Postdoctoral Science Foundation(Nos.2021TQ0311 and 2021M702990)International Postdoc-toral Exchange Fellowship Program(No.PC2022051).
文摘Electron donors(EDs)are widely used to improve the H 2 production performance of Schottky junction photocatalysts,but the functions of EDs are still unknown from the perspective of electron transfer dy-namics.Herein,Pt nanocluster-decorated CdS nanorod is successfully prepared to construct a typical CdS/Pt Schottky junction.Pt nanoclusters with a diameter of∼2 nm are deposited on the surface of CdS nanorods by in situ photoreduction at sub-zero temperature.The CdS/Pt photocatalyst using lactic acid shows a higher H_(2)production rate of 4762μmol g^(-1)h^(-1)compared to that using methanol,tri-ethanolamine,and glycerol.To understand the cause,the dynamics of photogenerated carriers in CdS/Pt photocatalysts during ED-assisted H_(2)production are revealed by femtosecond transient absorption spec-troscopy.Among the four organic EDs,lactic acid enables the fastest electron transfer rate of 1.8×10^(9)s^(-1)and the highest electron transfer efficiency of 76%at the CdS/Pt interface due to the most efficient hole consumption.This work sheds light on the importance of efficient interfacial electron transfer for im-proving the photocatalytic performance of Schottky junction photocatalysts.
基金National Natural Science Foundation of China,Grant/Award Numbers:22273084,22073045。
文摘Singlet fission(SF)is an appealing process where one photoexcited singlet transforms to two triplets,which can overcome thermalization energy loss and improve solar cell efficiency.However,it remains unclear how intermolecular coupling,which is subject to molecular stacking,controls SF pathways and dynamics.Here,we prepared polymorph rubrene single crystals with different stacking geometries,including orthorhombic(Orth.),triclinic(Tri.),and monoclinic(Mono.)phases.By micro-area ultrafast spectroscopy,we find that Orth.and Tri.phases with closerπ-πstacking exhibit co-existing coherent and incoherent SF channels while loosely stacked Mono.phase shows only incoherent SF.Furthermore,incoherent SF is thermally activated in Orth.but barrierless in Mono.and Tri.phases.Quantum mechanical calculation reveals that different electronic coupling strength in different phases leads to different SF dynamics.This study demonstrates that molecular stacking governs SF dynamics through electronic coupling,providing guidance for designing efficient SF materials via crystal structural engineering.
基金supported by the National Natural Science Foundation of China(No.U2032112).
文摘The aggregation and photoinduced excited state dynamics of organic π-conjugated molecules play a vital role in solar energy conversion and applications.This work investigates how solvent polarity affects the aggregation behavior and the photophysical process of perylene diimide dimer(PDI-II).The results show that the conjugations between PDI intramolecular chromophores are more likely to generate excimer,and the conjugations between PDI intermolecular chromophores are more likely to experience symmetry-breaking charge separation.Our study can provide a reference for the design of high-efficiency solar energy conversion materials.
基金Q.H.X.gratefully acknowledges the support from Singapore Ministry of Education via AcRF Tier 3 Programme(No.MOE2018-T3-1-002)Tier 2 project(No.MOE2017-T2-1-040)Singapore National Research Foundation via NRF-ANR project(No.NRF2017-NRF-ANR0052D-Chiral).
文摘Fundamental understandings on the dynamics of charge carriers and excitonic quasiparticles in semiconductors are of central importance for both many-body physics and promising optoelectronic and photonic applications.Here,we investigated the carrier dynamics and many-body interactions in two-dimensional(2D)transition metal dichalcogenides(TMDs),using monolayer WS2 as an example,by employing femtosecond broadband pump-probe spectroscopy.Three time regimes for the exciton energy renormalization are unambiguously revealed with a distinct red-blue-red shift upon above-bandgap optical excitations.We attribute the dominant physical process in the three typical regimes to free carrier screening effect,Coulombic exciton-exciton interactions and Auger photocarrier generation,respectively,which show distinct dependence on the optical excitation wavelength,pump fluences and/or lattice temperature.An intrinsic exciton radiative lifetime of about 1.2 picoseconds(ps)in monolayer WS2 is unraveled at low temperature,and surprisingly the efficient Auger nonradiative decay of both bright and dark excitons puts the system in a nonequilibrium state at the nanosecond timescale.In addition,the dynamics of trions at low temperature is observed to be significantly different from that of excitons,e.g.,a long radiative lifetime of^108.7 ps at low excitation densities and the evolution of trion energy as a function of delay times.Our findings elucidate the dynamics of excitonic quasiparticles and the intricate many-body physics in 2D semiconductors,underpinning the future development of photonics,valleytronics and optoelectronics based on 2D semiconductors.
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
基金Supported by the National Natural Science Foundation of China(Nos.51502109, 21573094, 11274142, 11474131), the Science and Technology Projects in the 13th Five-year Plan in the Education Department of Jilin Province, China(No.2016-402), the National Fund for Fostering Talents of Basic Science, China(No.J1103202) and the Chinese Scholarship Council for Providing Financial Support During Visiting University of California at Irvine, USA.
文摘The relaxation paths for triphenylamine(TPA)-2,3-dicyanopyrazino phenanthrene(DCPP), which has a pull-push structure, were investigated via steady-state, time-resolved spectroscopy involving transient absorption and time-correlated single photon counting. By changing the solvent polarity we found that an intramolecular charge transfer(ICT) state acting as a "bright" state was responsible for the fluorescence character of TPA-DCPP. Meanwhile, a "dark" state gradually appeared and competed with the ICT state. This was likely to be responsible for the polarity-dependent evolution of fluorescence intensity and fluorescence lifetime. The temperature-dependent fluorescence character of the TPA-DCPP in toluene exhibited ICT processes at high temperatures prior to the relaxation path from the initial excited state to the ground state. Our results provide useful insight into the optoelectronic properties of these kinds of molecules.