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Sökning: WFRF:(Zheng Kaibo)

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1.
  • Zheng, Qian, et al. (författare)
  • Constructing InP/ZnSe Quantum Dots with Shell Gradient In3+ Doping for Photoelectrochemical Cells
  • 2024
  • Ingår i: ACS Energy Letters. - 2380-8195. ; 9:5, s. 2358-2366
  • Tidskriftsartikel (refereegranskat)abstract
    • Environmentally friendly InP/ZnSe core/shell quantum dots (QDs) with high absorption coefficients and tunable band gaps have demonstrated great potential for photoelectrochemical (PEC) water splitting. However, the tightly bound excitonic feature by inherent type I band alignment tends to reduce the charge separation efficiency, limiting their PEC performance. Herein, we devised heterovalent In3+ gradient doping in the ZnSe shell of InP QD to construct core/shell structural InP/ZnSe-G-In QDs. The In3+ dopant increased the Fermi level of the ZnSe shell; thus continuous semiconductor homojunction and band bending were formed by gradient composition doping, which accelerates the exciton separation through the built-in electric field. As a result, the PEC cells based on such QDs exhibited high photocurrent density of 8.7 mA/cm2, demonstrating one of the highest values for the InP-based QDs PEC cells. This work provides an effective strategy for the application of type I band structure QDs in solar energy conversion.
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2.
  • Cao, Yuehan, et al. (författare)
  • Dual Functions of O-Atoms in the g-C3N4/BO0.2N0.8Interface : Oriented Charge Flow In-Plane and Separation within the Interface to Collectively Promote Photocatalytic Molecular Oxygen Activation
  • 2020
  • Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 12:30, s. 34432-34440
  • Tidskriftsartikel (refereegranskat)abstract
    • The photocatalytic performance of two-dimensional materials is largely limited by the fast recombination of photogenerated charges. Herein, we design and fabricate a novel g-C3N4/BO0.2N0.8 van der Waals heterostructure to realize oriented charge flow in-plane and separation within the interface. On one hand, a B-C bond forms within the g-C3N4/BO0.2N0.8 interface after the introduction of O atoms. The B-C bond as the mediator bridges g-C3N4 and BO0.2N0.8 sides to enhance the effective separation of photogenerated charges. On the other hand, the existence of O atoms promotes the formation of a B-O-O-B intermediate to realize that molecular oxygen can directionally obtain electrons from the surface to generate O2-. As a result, BO0.2N0.8 instead of g-C3N4 is considered to be the main reaction side, and the energy barrier of NO3- generation is significantly decreased. The NO removal performance of g-C3N4/BO0.2N0.8 is enhanced and the NO2 generation is effectively controlled compared with that of g-C3N and g-C3N4/BN. This work could provide an effective and facile strategy to tune oriented charge transfer.
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3.
  • Huang, Zheng, et al. (författare)
  • Constructing type-II CuInSe2/CuInS2 core/shell quantum dots for high-performance photoelectrochemical cells
  • 2024
  • Ingår i: SCIENCE CHINA Materials. - 2095-8226. ; 67:1, s. 134-142
  • Tidskriftsartikel (refereegranskat)abstract
    • CuInSe2 (CISe) quantum dots (QDs) have shown promising applications in photoelectrochemical (PEC) cells due to their nontoxicity, high extinction coefficient, and wide optical absorption range; however, their low PEC performance prevents their applications due to insufficient charge carrier separation and severe charge recombination. Herein, CISe/CuInS2 (CISe/CIS) core/shell structured QDs are designed and constructed to promote charge separation and diminish interface defects. Afterward, the copper vacancy (VCu) state of CISe/CIS QDs is enriched by modulating the precursor molar ratios of In/Cu. Therefore, the radiative recombination of the conduction band edge electrons with the VCu localized holes becomes dominant and prolongs the carrier lifetime compared with intrinsic band-to-band recombination, thus promoting charge separation. Consequently, the VCu-rich CISe/CIS QD-based photoanode shows a high photocurrent density of 8.0 mA cm−2, which is one of the highest values reported for CISe QD-based PEC cells. This work provides an effective approach for promoting charge carrier separation and transfer through surface or intrinsic defect mediation for PEC applications of I–III–VI semiconductor nanocrystals.
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4.
  • Karlsson, Max, et al. (författare)
  • Mixed halide perovskites for spectrally stable and high-efficiency blue light-emitting diodes
  • 2021
  • Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Bright and efficient blue emission is key to further development of metal halide perovskite light-emitting diodes. Although modifying bromide/chloride composition is straightforward to achieve blue emission, practical implementation of this strategy has been challenging due to poor colour stability and severe photoluminescence quenching. Both detrimental effects become increasingly prominent in perovskites with the high chloride content needed to produce blue emission. Here, we solve these critical challenges in mixed halide perovskites and demonstrate spectrally stable blue perovskite light-emitting diodes over a wide range of emission wavelengths from 490 to 451 nanometres. The emission colour is directly tuned by modifying the halide composition. Particularly, our blue and deep-blue light-emitting diodes based on three-dimensional perovskites show high EQE values of 11.0% and 5.5% with emission peaks at 477 and 467 nm, respectively. These achievements are enabled by a vapour-assisted crystallization technique, which largely mitigates local compositional heterogeneity and ion migration.
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5.
  • Liu, Yang, et al. (författare)
  • Defect State Assisted Z-scheme Charge Recombination in Bi2O2CO3/Graphene Quantum Dot Composites for Photocatalytic Oxidation of NO
  • 2020
  • Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 3:1, s. 772-781
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, we explored the photoinduced charge carriers dynamics rationalizing the photocatalytic oxidation of NO over N-doped Bi2O2CO3/graphene quantum dots composites(N-BOC/GQDs) via time-resolved photoluminescence (TRPL). Under visible light illumination, only GQDs can be photoexcited and inject electrons to N-BOC within 0.5 ns. Under UV light irradiation, the interfacial Z-scheme heterojunction recombination between the electrons in N-BOC and holes in GQDs dominate the depopulation of excited states within 0.36 ns. Such efficient Z-scheme recombination regardless of the large energy difference (1.66 eV) is mediated by the interfacial oxygen vacany defect states characterized by both density functional theory calculations (DFT) and electron paramagnetic resonance (EPR) measurement. This finding provide a novel strategic view to improve the photocatalytic performance of the nanocomposite by interfacial engineering
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6.
  • Xie, Jiaqi, et al. (författare)
  • Sequentially N-Doped Acceptor Primer Layer Facilitates Electron Collection of Inverted Non-Fullerene Organic Solar Cells
  • Ingår i: Advanced Functional Materials. - 1616-301X.
  • Tidskriftsartikel (refereegranskat)abstract
    • In most non-fullerene organic solar cells comprising bulk-heterojunction active layers, the inter-domain connectivity of small-molecule acceptors is generally inferior to those of polymeric donors due to their intrinsic short-range ordering. This issue is even exacerbated by the physiochemical mismatch between acceptor-phases and metal-oxide electron transport layers in most inverted n-i-p devices, leading to inefficient electron collection. By pre-depositing an ultra-thin acceptor primer layer, it develops a novel acceptor-enriched-bottom active layer to reinforce the acceptor-phase continuity. It is however challenging to preserve the primer layer during non-orthogonal solvent processing. Thus, sequential n-type doping is implemented on the surface of the primer layer, which allows to slightly reduce the acceptor solubility by polarity regulation, as well as stabilize the film structure via strong π–π interaction between dopant/host acceptor. Upon acceptor enrichment, higher interfacial electron density enhances the built-in potential while the enlarged domains suppress both charge-transfer state and bimolecular recombination. Consequently, the champion device efficiency is greatly improved from ca. 16.1% to 18.0%, mainly resulting from the simultaneously elevated fill factor and short-circuit current density.
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7.
  • Zou, Yatao, et al. (författare)
  • Manipulating crystallization dynamics through chelating molecules for bright perovskite emitters
  • 2021
  • Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Molecular additives are widely utilized to minimize non-radiative recombination in metal halide perovskite emitters due to their passivation effects from chemical bonds with ionic defects. However, a general and puzzling observation that can hardly be rationalized by passivation alone is that most of the molecular additives enabling high-efficiency perovskite light-emitting diodes (PeLEDs) are chelating (multidentate) molecules, while their respective monodentate counterparts receive limited attention. Here, we reveal the largely ignored yet critical role of the chelate effect on governing crystallization dynamics of perovskite emitters and mitigating trap-mediated non-radiative losses. Specifically, we discover that the chelate effect enhances lead-additive coordination affinity, enabling the formation of thermodynamically stable intermediate phases and inhibiting halide coordination-driven perovskite nucleation. The retarded perovskite nucleation and crystal growth are key to high crystal quality and thus efficient electroluminescence. Our work elucidates the full effects of molecular additives on PeLEDs by uncovering the chelate effect as an important feature within perovskite crystallization. As such, we open new prospects for the rationalized screening of highly effective molecular additives.
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8.
  • Abdellah, Mohamed, et al. (författare)
  • Drastic difference between hole and electron injection through the gradient shell of CdxSeyZn1−xS1−y quantum dots
  • 2017
  • Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 9:34, s. 12503-12508
  • Tidskriftsartikel (refereegranskat)abstract
    • Ultrafast fluorescence spectroscopy was used to investigate the hole injection in CdxSeyZn1-xS1-y gradient core-shell quantum dot (CSQD) sensitized p-type NiO photocathodes. A series of CSQDs with a wide range of shell thicknesses was studied. Complementary photoelectrochemical cell measurements were carried out to confirm that the hole injection from the active core through the gradient shell to NiO takes place. The hole injection from the valence band of the QDs to NiO depends much less on the shell thickness when compared to the corresponding electron injection to n-type semiconductor (ZnO). We simulate the charge carrier tunneling through the potential barrier due to the gradient shell by numerically solving the Schrodinger equation. The details of the band alignment determining the potential barrier are obtained from X-ray spectroscopy measurements. The observed drastic differences between the hole and electron injection are consistent with a model where the hole effective mass decreases, while the gradient shell thickness increases.
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9.
  • Alvarez, Sol Gutierrez, et al. (författare)
  • Charge Carrier Diffusion Dynamics in Multisized Quaternary Alkylammonium-Capped CsPbBr3 Perovskite Nanocrystal Solids
  • 2021
  • Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:37, s. 44742-44750
  • Tidskriftsartikel (refereegranskat)abstract
    • CsPbBr3 quantum dots (QDs) are promising candidates for optoelectronic devices. The substitution of oleic acid ( OA) and oleylamine ( OLA) capping agents with a quaternary alkylammonium such as di-dodecyl dimethyl ammonium bromide (DDAB) has shown an increase in external quantum efficiency (EQE) from 0.19% (OA/OLA) to 13.4% (DDAB) in LED devices. The device performance significantly depends on both the diffusion length and the mobility of photoexcited charge carriers in QD solids. Therefore, we investigated the charge carrier transport dynamics in DDAB-capped CsPbBr3 QD solids by constructing a bi-sized QD mixture film. Charge carrier diffusion can be monitored by quantitatively varying the ratio between two sizes of QDs, which varies the mean free path of the carriers in each QD cluster. Excited-state dynamics of the QD solids obtained from ultrafast transient absorption spectroscopy reveals that the photogenerated electrons and holes are difficult to diffuse among small-sized QDs (4 nm) due to the strong quantum confinement. On the other hand, both photoinduced electrons and holes in large-sized QDs (10 nm) would diffuse toward the interface with the small-sized QDs, followed by a recombination process. Combining the carrier diffusion study with a Monte Carlo simulation on the QD assembly in the mixture films, we can calculate the diffusion lengths of charge carriers to be similar to 239 +/- 16 nm in 10 nm CsPbBr3 QDs and the mobility values of electrons and holes to be 2.1 (+/- 0.1) and 0.69 (+/- 0.03) cm(2)/V s, respectively. Both parameters indicate an efficient charge carrier transport in DDAB-capped QD films, which rationalized the perfect performance of their LED device application.
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10.
  • Alvarez, Sol Laura Gutierrez, et al. (författare)
  • Morphology-Dependent One- and Two-Photon Absorption Properties in Blue Emitting CsPbBr3Nanocrystals
  • 2022
  • Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 13:22, s. 4897-4904
  • Tidskriftsartikel (refereegranskat)abstract
    • The linear and nonlinear optical parameters and morphologic dependence of CsPbBr3 nanocrystals (NCs) are crucial for device engineering. In particular, such information in asymmetric nanocrystals is still insufficient. We characterized the OPLA (σ1) and TPA cross sections (σ2) of a series CsPbBr3 nanocrystals with various aspect ratios (AR) using femtosecond transient absorption spectroscopy (TAS). The σ1 presents a linear volume dependence of all the samples, which agrees with the previous behavior in CsPbBr3 QDs. However, the σ2 values do not exhibit conventional power dependency of the crystal volume but are also modulated by the shape-dependent local field factors. In addition, the local field effect in CsPbBr3 NCs is contributed by their asymmetric morphologies and polar ionic lattices, which is more pronounced than in conventional semiconductor NCs. Finally, we revealed that the lifetimes of photogenerated multiexcitonic species of those nanocrystals feature identical morphology independence in both OPLA and TPA.
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11.
  • Amarotti, Edoardo, et al. (författare)
  • Direct Visualization of Confinement and Many-Body Correlation Effects in 2D Spectroscopy of Quantum Dots
  • Ingår i: Advanced Optical Materials. - 2195-1071.
  • Tidskriftsartikel (refereegranskat)abstract
    • The size tunable color of colloidal semiconductor quantum dots (QDs) is probably the most elegant illustration of the quantum confinement effect. As explained by the simple “particle-in-a-box” model, the transition energies between the levels increase when the “box” becomes smaller. To investigate quantum confinement effects, typically a well-defined narrow size distribution of the nanoparticles is needed. In this contribution, how coherent electronic two-dimensional spectroscopy (2DES) can directly visualize the quantum size effect in a sample with broad size distribution of QDs is demonstrated. The method is based on two features of the 2DES – the ability to resolve inhomogeneous broadening and the capability to reveal correlations between the states. In QD samples, inhomogeneous spectral broadening is mainly caused by the size distribution and leads to elongated diagonal peaks of the spectra. Since the cross peaks correlate the energies of two states, they allow drawing conclusions about the size dependence of the corresponding states. It is also found that the biexciton binding energy changes between 3 and 8 meV with the QD size. Remarkably, the size dependence is non-monotonic with a clear minimum.
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12.
  • An, Rui, et al. (författare)
  • Photostability and Photodegradation Processes in Colloidal CsPbI3 Perovskite Quantum Dots
  • 2018
  • Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:45, s. 39222-39227
  • Tidskriftsartikel (refereegranskat)abstract
    • All-inorganic CsPbI3 perovskite quantum dots (QDs) have attracted intense attention for their successful application in photovoltaics (PVs) and optoelectronics that are enabled by their superior absorption capability and great photoluminescence (PL) properties. However, their photostability remains a practical bottleneck and further optimization is highly desirable. Here, we studied the photostability of as-obtained colloidal CsPbI3 QDs suspended in hexane. We found that light illumination does induce photodegradation of CsPbI3 QDs. Steady-state spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and transient absorption spectroscopy verified that light illumination leads to detachment of the capping agent, collapse of the CsPbI3 QD surface, and finally aggregation of surface Pb0. Both dangling bonds containing surface and Pb0 serve as trap states causing PL quenching with a dramatic decrease of PL quantum yield. Our work provides a detailed insight about the correlation between the structural and photophysical consequences of the photodegradation process in CsPbI3 QDs and may lead to the optimization of such QDs toward device applications.
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13.
  • Aydin, C., et al. (författare)
  • Synthesis, diffused reflectance and electrical properties of nanocrystalline Fe-doped ZnO via sol-gel calcination technique
  • 2013
  • Ingår i: Optics and Laser Technology. - : Elsevier BV. - 0030-3992. ; 48, s. 447-452
  • Tidskriftsartikel (refereegranskat)abstract
    • The nanocrystalline ZnO:Fe semiconductor oxides were successfully synthesized via the sol-gel calcination method. Structural, optical and electrical properties of the investigated samples were characterized by various techniques such as atomic force microscopy (AFM), UV-vis absorption and electrical transport measurements. The optical band gap for undoped ZnO (3.19 eV) decreases (2.75 eV) with increasing Fe-doped ZnO (20%). The temperature dependences of the electrical conductivities of undoped ZnO and Fe-doped ZnO were measured and analyzed by Arrhenius equation. The electrical conductivity of the samples decreases with the increase of Fe doping ratio; hence, the electrical conductivity mechanism is controlled by thermally activated processes. To support the nanostructure of Fe-doped ZnO, AFM micrographs were performed. (C) 2012 Elsevier Ltd. All rights reserved.
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14.
  • Bamini, Sesha, et al. (författare)
  • Time-resolved terahertz spectroscopy reveals the influence of charged sensitizing quantum dots on the electron dynamics in ZnO
  • 2017
  • Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:8, s. 6006-6012
  • Tidskriftsartikel (refereegranskat)abstract
    • Photoinitiated charge carrier dynamics in ZnO nanoparticles sensitized by CdSe quantum dots is studied using transient absorption spectroscopy and time-resolved terahertz spectroscopy. The evolution of the transient spectra shows that electron injection occurs in a two-step process, where the formation of a charge transfer state (occurring in several picoseconds) is followed by its dissociation within tens of picoseconds. The photoconductivity of electrons injected into the ZnO nanoparticles is lower than that of charges photogenerated directly in ZnO. We conclude that the motion of injected electrons in ZnO nanoparticles is strongly influenced by their interaction with positive charges left in the sensitizing quantum dots.
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15.
  • Becker, Christiane, et al. (författare)
  • Nanophotonic enhanced perovskite-silicon solar cell devices
  • 2019
  • Ingår i: ; , s. 858-859
  • Konferensbidrag (refereegranskat)abstract
    • Perovskite-silicon tandem solar cells are a promising concept for overcoming the limits of conventional silicon single-junction technology. Light management is doubtless a key issue for further boosting efficiency. We discuss the impact of photonic nanostructures on the optical performance of perovskite-silicon devices. We experimentally and numerically demonstrate shallow antireflective nanotextures, which are compatible with perovskite solution processing. We further showcase enhanced photon up-conversion using perovskite nanoparticles interacting with photonic nanostructures and discuss the applicability for spectral conversion of sunlight.
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16.
  • Becker, Christiane, et al. (författare)
  • Nanophotonic-Enhanced Two-Photon-Excited Photoluminescence of Perovskite Quantum Dots
  • 2018
  • Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 5:11, s. 4668-4676
  • Tidskriftsartikel (refereegranskat)abstract
    • All-inorganic CsPbBr3 perovskite colloidal quantum dots have recently emerged as a promising material for a variety of optoelectronic applications, among others for multiphoton-pumped lasing. Nevertheless, high irradiance levels are generally required for such multiphoton processes. One strategy to enhance the multiphoton absorption is taking advantage of high local light intensities using photonic nanostructures. Here, we investigate two-photon-excited photoluminescence of CsPbBr3 perovskite quantum dots on a silicon photonic crystal slab. By systematic excitation of optical resonances using a pulsed near-infrared laser beam, we observe an enhancement of two-photon-pumped photoluminescence by more than 1 order of magnitude when comparing to using a bulk silicon film. Experimental and numerical analyses allow relating these findings to near-field enhancement effects on the nanostructured silicon surface. The results reveal a promising approach for significantly decreasing the required irradiance levels for multiphoton processes being of advantage in applications such as biomedical imaging, lighting, and solar energy.
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17.
  • Bi, Chenghao, et al. (författare)
  • Spontaneous Self-Assembly of Cesium Lead Halide Perovskite Nanoplatelets into Cuboid Crystals with High Intensity Blue Emission
  • 2019
  • Ingår i: Advanced Science. - : Wiley. - 2198-3844. ; 6:13
  • Tidskriftsartikel (refereegranskat)abstract
    • Colloidal all-inorganic perovskite nanocrystals have gained significant attention as a promising material for both fundamental and applied research due to their excellent emission properties. However, reported photoluminescence quantum yields (PL QYs) of blue-emitting perovskite nanocrystals are rather low, mostly due to the fact that the high energy excitons for such wide bandgap materials are easily captured by interband traps, and then decay nonradiatively. In this work, it is demonstrated how to tackle this issue, performing self-assembly of 2D perovskite nanoplatelets into larger size (≈50 nm × 50 nm × 20 nm) cuboid crystals. In these structures, 2D nanoplatelets being isolated from each other within the cuboidal scaffold by organic ligands constitute multiple quantum wells, where exciton localization on potential disorder sites helps them to bypass nonradiative channels present in other platelets. As a result, the cuboid crystals show an extremely high PL QY of 91% of the emission band centered at 480 nm. Moreover, using the same synthetic method, mixed-anion CsPb(Br/Cl) 3 cuboid crystals with blue emission peaks ranging from 452 to 470 nm, and still high PL QYs in the range of 72–83% are produced.
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18.
  • Canton, Sophie E., et al. (författare)
  • Ultrafast Jahn-Teller Photoswitching in Cobalt Single-Ion Magnets
  • 2023
  • Ingår i: Advanced Science. - 2198-3844. ; 10:21
  • Tidskriftsartikel (refereegranskat)abstract
    • Single-ion magnets (SIMs) constitute the ultimate size limit in the quest for miniaturizing magnetic materials. Several bottlenecks currently hindering breakthroughs in quantum information and communication technologies could be alleviated by new generations of SIMs displaying multifunctionality. Here, ultrafast optical absorption spectroscopy and X-ray emission spectroscopy are employed to track the photoinduced spin-state switching of the prototypical complex [Co(terpy)2]2+ (terpy = 2,2′:6′,2″-terpyridine) in solution phase. The combined measurements and their analysis supported by density functional theory (DFT), time-dependent-DFT (TD-DFT) and multireference quantum chemistry calculations reveal that the complex undergoes a spin-state transition from a tetragonally elongated doublet state to a tetragonally compressed quartet state on the femtosecond timescale, i.e., it sustains ultrafast Jahn-Teller (JT) photoswitching between two different spin multiplicities. Adding new Co-based complexes as possible contenders in the search for JT photoswitching SIMs will greatly widen the possibilities for implementing magnetic multifunctionality and eventually controlling ultrafast magnetization with optical photons.
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19.
  • Cao, Kequan, et al. (författare)
  • Constructing ZnTe Spherical Quantum Well for Efficient Light Emission
  • 2024
  • Ingår i: Nano Letters. - 1530-6984.
  • Tidskriftsartikel (refereegranskat)abstract
    • ZnTe colloidal semiconductor nanocrystals (NCs) have shown promise for light-emitting diodes (LEDs) and displays, because they are free from toxic heavy metals (Cd). However, so far, their low photoluminescence (PL) efficiency (∼30%) has hindered their applications. Herein, we devised a novel structure of ZnTe NCs with the configuration of ZnSe (core)/ZnTe (spherical quantum well, SQW)/ZnSe (shell). The inner layer ZnTe was grown at the surface of ZnSe core with avoiding using highly active and high-risk Zn sources. Due to the formation of coherently strained heterostructure which reduced the lattice mismatch, and the thermodynamic growth of ZnTe, the surface or interface defects were suppressed. A high PL efficiency of >60% was obtained for the green light-emitting ZnSe/ZnTe/ZnSe SQWs after ZnS outer layer passivation, which is the highest value for colloidal ZnTe-based NCs. This work paves the way for the development of novel semiconductor NCs for luminescent and display applications.
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20.
  • Cao, Yuehan, et al. (författare)
  • Modulating electron density of vacancy site by single Au atom for effective CO2 photoreduction
  • 2021
  • Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The surface electron density significantly affects the photocatalytic efficiency, especially the photocatalytic CO2 reduction reaction, which involves multi-electron participation in the conversion process. Herein, we propose a conceptually different mechanism for surface electron density modulation based on the model of Au anchored CdS. We firstly manipulate the direction of electron transfer by regulating the vacancy types of CdS. When electrons accumulate on vacancies instead of single Au atoms, the adsorption types of CO2 change from physical adsorption to chemical adsorption. More importantly, the surface electron density is manipulated by controlling the size of Au nanostructures. When Au nanoclusters downsize to single Au atoms, the strong hybridization of Au 5d and S 2p orbits accelerates the photo-electrons transfer onto the surface, resulting in more electrons available for CO2 reduction. As a result, the product generation rate of AuSA/Cd1−xS manifests a remarkable at least 113-fold enhancement compared with pristine Cd1−xS.
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21.
  • Chen, Junsheng, et al. (författare)
  • Cation-Dependent Hot Carrier Cooling in Halide Perovskite Nanocrystals
  • 2019
  • Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 141:8, s. 3532-3540
  • Tidskriftsartikel (refereegranskat)abstract
    • Lead halide perovskites (LHPs) nanocrystals (NCs), owing to their outstanding photophysical properties, have recently emerged as a promising material not only for solar cells but also for lighting and display applications. The photophysical properties of these materials can be further improved by chemical engineering such as cation exchange. Hot carrier (HC) cooling, as one of the key photophysical processes in LHPs, can strongly influence performance of LHPs NCs based devices. Here, we study HC relaxation dynamics in LHP NCs with cesium (Cs), methylammonium (MA, CH 3 NH 3 + ), and formamidinium (FA, CH(NH 2 ) 2 + ) cations by using femtosecond transient absorption spectroscopy. The LHP NCs show excitation intensity and excitation energy-dependent HC cooling. We investigate the details of HC cooling in CsPbBr 3 , MAPbBr 3 , and FAPbBr 3 at three different excitation energies with low excitation intensity. It takes longer time for the HCs at high energy to relax (cool) to the band edge, compared to the HCs generated by low excitation energy. At the same excitation energy (350 nm, 3.54 eV), all the three LHP NCs show fast HC relaxation (<0.4 ps) with the cooling time and rate in the following order: CsPbBr 3 (0.39 ps, 2.9 meV/fs) > MAPbBr 3 (0.27 ps, 4.6 meV/fs) > FAPbBr 3 (0.21 ps, 5.8 meV/fs). The cation dependence can be explained by stronger interaction between the organic cations with the Pb-Br frameworks compared to the Cs. The revealed cation-dependent HC relaxation process is important for providing cation engineering strategies for developing high performance LHP devices.
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22.
  • Chen, Junsheng, et al. (författare)
  • Enhanced Size Selection in Two-Photon Excitation for CsPbBr3 Perovskite Nanocrystals
  • 2017
  • Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 8:20, s. 5119-5124
  • Tidskriftsartikel (refereegranskat)abstract
    • Cesium lead bromide (CsPbBr3) perovskite nanocrystals (NCs), with large two-photon absorption (TPA) cross-section and bright photoluminescence (PL), have been demonstrated as stable two-photon-pumped lasing medium. With two-photon excitation, red-shifted PL spectrum and increased PL lifetime is observed compared with one-photon excitation. We have investigated the origin of such difference using time-resolved laser spectroscopies. We ascribe the difference to the enhanced size selection of NCs by two-photon excitation. Because of inherent nonlinearity, the size dependence of absorption cross-section under TPA is stronger. Consequently, larger size NCs are preferably excited, leading to longer excited-state lifetime and red-shifted PL emission. In a broad view, the enhanced size selection in two-photon excitation of CsPbBr3 NCs is likely a general feature of the perovskite NCs and can be tuned via NC size distribution to influence their performance within NC-based nonlinear optical materials and devices.
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23.
  • Chen, Junsheng, et al. (författare)
  • Photo-stability of CsPbBr3 perovskite quantum dots for optoelectronic application
  • 2016
  • Ingår i: SCIENCE CHINA Materials. - : Springer Science and Business Media LLC. - 2095-8226 .- 2199-4501. ; 59:9, s. 719-727
  • Tidskriftsartikel (refereegranskat)abstract
    • Due to their superior photoluminescence (PL) quantum yield (QY) and tunable optical band gap, all-inorganic CsPbBr3 perovskite quantum dots (QDs) have attracted intensive attention for the application in solar cells, light emitting diodes (LED), photo detectors and laser devices. In this scenario, the stability of such materials becomes a critical factor. We hereby investigated the long-term stability of as-synthesized CsPbBr3 QDs suspended in toluene at various environmental conditions involving the light illumination, atmosphere, and temperature. We found light illumination would induce dramatic degradation of CsPbBr3 QDs reflecting as decreasing absorbance and PL intensity together with red-shifted emission band. Such light instability can be attributed to the photo-induced surface degradation and aggregation. The steady-state spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) technics verified that CsPbBr3 QDs trend 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. Such trap sites lead to the red-shifted emission with increasing PL lifetime. Our work reveals that the main origin of instability in CsPbBr3 QDs and provide reference to engineer such QDs towards optimal device application.
  •  
24.
  • Chen, Junsheng, et al. (författare)
  • Photostability of the Oleic Acid-Encapsulated Water-Soluble CdxSeyZn1-xS1-y Gradient Core-Shell Quantum Dots
  • 2017
  • Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 2:5, s. 1922-1929
  • Tidskriftsartikel (refereegranskat)abstract
    • Composite systems where quantum dots (QDs) are combined with other nanomaterials (e.g., gold nanorods) in aqueous solutions have attracted broad attention - both for their potential in applications and for studies of fundamental processes. However, high-quality QDs are typically prepared in organic solvents, and the transfer of QDs to an aqueous phase is needed to create the desired QD composites. Photostability of the transferred QDs - both the steady-state and photo-induced dynamic properties - is essential for studying the processes in the composites and for their applications. We present a detailed study of the photostability of aqueous CdxSeyZn1-xS1-y gradient core-shell QDs obtained by various approaches using linker exchange and surfactant encapsulation. Beside the steady-state photoluminescence (PL) emission stability, we also study changes in the PL decay. From the variety of the studied samples, the water-soluble QDs encapsulated by a double layer of oleic acid show superior properties, that is, stable PL emission and PL decay under continuous light or pulsed-laser light irradiation. We demonstrate that the double-layer encapsulation of QDs can be used to create QDs-metal nanoparticle composites.
  •  
25.
  • Chen, Junsheng, et al. (författare)
  • Size-And Wavelength-Dependent Two-Photon Absorption Cross-Section of CsPbBr3 Perovskite Quantum Dots
  • 2017
  • Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 8:10, s. 2316-2321
  • Tidskriftsartikel (refereegranskat)abstract
    • All-inorganic colloidal perovskite quantum dots (QDs) based on cesium, lead, and halide have recently emerged as promising light emitting materials. CsPbBr3 QDs have also been demonstrated as stable two-photon-pumped lasing medium. However, the reported two photon absorption (TPA) cross sections for these QDs differ by an order of magnitude. Here we present an in-depth study of the TPA properties of CsPbBr3 QDs with mean size ranging from 4.6 to 11.4 nm. By using femtosecond transient absorption (TA) spectroscopy we found that TPA cross section is proportional to the linear one photon absorption. The TPA cross section follows a power law dependence on QDs size with exponent 3.3 ± 0.2. The empirically obtained power-law dependence suggests that the TPA process through a virtual state populates exciton band states. The revealed power-law dependence and the understanding of TPA process are important for developing high performance nonlinear optical devices based on CsPbBr3 nanocrystals.
  •  
26.
  • Chen, Junsheng, et al. (författare)
  • Surface plasmon inhibited photo-luminescence activation in CdSe/ZnS core-shell quantum dots
  • 2016
  • Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 28:25
  • Tidskriftsartikel (refereegranskat)abstract
    • In a composite film of Cdx Sey Zn1-x S1-y gradient core-shell quantum dots (QDs) and gold nanorods (NRs), the optical properties of the QDs are drastically affected by the plasmonic nanoparticles. We provide a careful study of the two-step formation of the film and its morphology. Subsequently we focus on QD luminescence photoactivation - a process induced by photochemical changes on the QD surface. We observe that even a sparse coverage of AuNRs can completely inhibit the photoactivation of the QDs' emission in the film. We demonstrate that the inhibition can be accounted for by a rapid energy transfer between QDs and AuNRs. Finally, we propose that the behavior of emission photoactivation can be used as a signature to distinguish between energy and electron transfer in the QD-based materials.
  •  
27.
  • Chen, Yani, et al. (författare)
  • 2D Ruddlesden-Popper Perovskites for Optoelectronics
  • 2018
  • Ingår i: Advanced Materials. - : Wiley. - 0935-9648. ; 30:2, s. 1703487-1703487
  • Tidskriftsartikel (refereegranskat)abstract
    • Conventional 3D organic-inorganic halide perovskites have recently undergone unprecedented rapid development. Yet, their inherent instabilities over moisture, light, and heat remain a crucial challenge prior to the realization of commercialization. By contrast, the emerging 2D Ruddlesden-Popper-type perovskites have recently attracted increasing attention owing to their great environmental stability. However, the research of 2D perovskites is just in their infancy. In comparison to 3D analogues, they are natural quantum wells with a much larger exciton binding energy. Moreover, their inner structural, dielectric, optical, and excitonic properties remain to be largely explored, limiting further applications. This review begins with an introduction to 2D perovskites, along with a detailed comparison to 3D counterparts. Then, a discussion of the organic spacer cation engineering of 2D perovskites is presented. Next, quasi-2D perovskites that fall between 3D and 2D perovskites are reviewed and compared. The unique excitonic properties, electron-phonon coupling, and polarons of 2D perovskites are then be revealed. A range of their (opto)electronic applications is highlighted in each section. Finally, a summary is given, and the strategies toward structural design, growth control, and photophysics studies of 2D perovskites for high-performance electronic devices are rationalized.
  •  
28.
  • Chen, Yani, et al. (författare)
  • Composition Engineering in Two-Dimensional Pb-Sn-Alloyed Perovskites for Efficient and Stable Solar Cells
  • 2018
  • Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:25, s. 21343-21348
  • Tidskriftsartikel (refereegranskat)abstract
    • Environmentally friendly tin (Sn)-based metallic halide perovskites suffer from oxidation and morphological issues. Here, we demonstrate the composition engineering of Pb-Sn-alloyed two-dimensional (2D) Ruddlesden-Popper perovskites, (BA)2(MA)3Pb4-xSnxI13, for efficient and stable solar cell applications. Smooth thin films with high surface coverage are readily formed without using any additive owing to the self-assembly characteristic of 2D perovskites. It is found that Sn plays a significant role in improving the crystallization and crystal orientation while narrowing the bandgap of Pb-Sn 2D perovskites. Photophysical studies further reveal that the optimal Sn ratio (25 mol %) based sample exhibits both minimized trap density and weakened quantum confinement for efficient charge separation. Consequently, the optimized (BA)2(MA)3Pb3SnI13-based solar cells yield the best power conversion efficiency close to 6% with suppressed hysteresis.
  •  
29.
  • Chen, Yani, et al. (författare)
  • Tailoring Organic Cation of 2D Air-Stable Organometal Halide Perovskites for Highly Efficient Planar Solar Cells
  • 2017
  • Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6832. ; 7:18
  • Tidskriftsartikel (refereegranskat)abstract
    • 2D perovskites have recently been shown to exhibit significantly improved environmental stability. Derived from their 3D analogues, 2D perovskites are formed by inserting bulky alkylammonium cations in-between the anionic layers. However, these insulating organic spacer cations also hinder charge transport. Herein, such a 2D perovskite, (iso-BA)2(MA)3Pb4I13, that contains short branched-chain spacer cations (iso-BA+) and shows a remarkable increase of optical absorption and crystallinity in comparison to the conventional linear one, n-BA+, is designed. After applying the hot-casting (HC) technique, all these properties are further improved. The HC (iso-BA)2(MA)3Pb4I13 sample exhibits the best ambient stability by maintaining its initial optical absorption after storage of 840 h in an environmental chamber at 20 °C with a relative humidity of 60% without encapsulation. More importantly, the out-of-plane crystal orientation of (iso-BA)2(MA)3Pb4I13 film is notably enhanced, which increases cross-plane charge mobility. As a result, the highest power conversion efficiencies (PCEs) measured from for current density versus voltage curves afford 8.82% and 10.63% for room-temperature and HC-processed 2D perovskites based planar solar cells, respectively. However, the corresponding steady-state PCEs are remarkably lower, which is presumably due to the significant hysteresis phenomena caused by low charge extraction efficiency at interfaces of C60/2D perovskites.
  •  
30.
  • Cheng, Chunyan, et al. (författare)
  • Near-Unity Quantum Yield ZnSeTe Quantum Dots Enabled by Controlling Shell Growth for Efficient Deep-Blue Light-Emitting Diodes
  • Ingår i: Advanced Functional Materials. - 1616-301X.
  • Tidskriftsartikel (refereegranskat)abstract
    • Core–shell structural ZnSeTe/ZnSe/ZnS quantum dots (QDs) have attracted great attention for advanced illumination and displays because of their environmentally friendly composition, but still suffering from poor photoluminescence (PL) and electroluminescence (EL) performance due to severe non-radiative charge recombination. Herein, a stepwise injection shell growth process to manipulate the monomer concentration and ensure adequate growth interval is devised, which enables the controllable uniform epitaxial growth of ZnSe and ZnS shells on the ZnSeTe core, thus relieving the lattice distortion and defects to greatly suppress the non-radiative charge recombination. The ZnSeTe/ZnSe/ZnS QDs presented deep-blue emission at 448 nm with narrow full width at half maximum (FWHM, 23 nm), and near-unity PL quantum yield (PLQY, ≈100%) The light-emitting diodes (LEDs) based on the QDs exhibited a high external quantum efficiency (EQE) of 10.9%, a maximum brightness of 10240 cd cm−2, and a high current efficiency of 7.9 cd A−1, demonstrating a good performance for deep blue QDs LEDs (QLEDs) This shell growth strategy will be an effective approach to achieving efficient QDs and QLEDs.
  •  
31.
  • Corani, Alice, et al. (författare)
  • Ultrafast Dynamics of Hole Injection and Recombination in Organometal Halide Perovskite Using Nickel Oxide as p-Type Contact Electrode.
  • 2016
  • Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 7, s. 1096-1101
  • Tidskriftsartikel (refereegranskat)abstract
    • There is a mounting effort to use nickel oxide (NiO) as p-type selective electrode for organometal halide perovskite-based solar cells. Recently, an overall power conversion efficiency using this hole acceptor has reached 18%. However, ultrafast spectroscopic investigations on the mechanism of charge injection as well as recombination dynamics have yet to be studied and understood. Using time-resolved terahertz spectroscopy, we show that hole transfer is complete on the subpicosecond time scale, driven by the favorable band alignment between the valence bands of perovskite and NiO nanoparticles (NiO(np)). Recombination time between holes injected into NiO(np) and mobile electrons in the perovskite material is shown to be hundreds of picoseconds to a few nanoseconds. Because of the low conductivity of NiO(np), holes are pinned at the interface, and it is electrons that determine the recombination rate. This recombination competes with charge collection and therefore must be minimized. Doping NiO to promote higher mobility of holes is desirable in order to prevent back recombination.
  •  
32.
  • Dan, Meng, et al. (författare)
  • A dual-interfacial system with well-defined spatially separated redox-sites for boosting photocatalytic overall H2S splitting
  • 2021
  • Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 423
  • Tidskriftsartikel (refereegranskat)abstract
    • Integration of high activity, selectivity, and stability is urgently desired to achieve more ideal photocatalysts. Herein, we reported the rational design of MoS2-MnS@(InxCu1-x)2S3 (M-M@IC) catalysts with dual interface to integrate separated redox sites for boosting photocatalytic hydrogen sulphide (H2S) splitting and the resource utilization of sacrificial reagents (Na2S/Na2SO3). The spatially separated reduction (MnS) and oxidation (In2S3) sites in MnS/In2S3 heterojunction, on which MoS2 and Cu were selectively loaded, can drive electrons and holes near the surface to flow along opposite directions, while the heterojunction between MnS and In2S3 inhibits the bulk charge recombination. Furthermore, the introduction of Cu atoms creates a d-band center, which favours mass diffusion of reactants/products species and greatly facilitates sunlight response. The MoS2 serves to provide abundant sites for proton reduction due to the unsaturated-sulfur-edge-rich (US-rich) nature. As a result, the M−M@IC shows a state-of-the-art visible-light photocatalytic H2 evolution rate (126.5 mmol g-1h−1), inspiring stability of >50 h, and nearly 100% selectivity toward value-added Na2S2O3 production under optimized condition. This work opens up new opportunities for the construction and design of spatially separated catalytic site in photocatalysts.
  •  
33.
  • Dan, Meng, et al. (författare)
  • Beyond hydrogen production : Solar−driven H2S−donating value−added chemical production over MnxCd1−xS/CdyMn1−yS catalyst
  • 2021
  • Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373. ; 284
  • Tidskriftsartikel (refereegranskat)abstract
    • Simultaneous hydrogen (H2) evolution and value−added chemicals production are highly attractive but have not drawn enough attention. Here, we demonstrate a hydrogen sulphide (H2S)−induced product−targeting (HIPT) strategy for the coproduction of H2 and valuable chemical feedstocks from Na2S/Na2SO3 via overall H2S splitting using a MnxCd1−xS/CdyMn1−yS catalyst driven by visible light excitation. With this chemistry, 113 mmol g−1 h−1 of hydrogen evolution rate is achieved, surpassing most of the previously reported state-of-the-art photocatalyst, together with the production of value−added Na2S2O3 with nearly 100% selectivity. This work not only provides a good example for solar energy conversion via overall H2S splitting, but also offers new insights into the resource utilization of sacrificial donor (Na2S/Na2SO3) in various catalytic fields such as H2O splitting and CO2 reduction.
  •  
34.
  • Denk, Ondřej, et al. (författare)
  • Compressive imaging of transient absorption dynamics on the femtosecond timescale
  • 2019
  • Ingår i: Optics Express. - 1094-4087. ; 27:7, s. 10234-10246
  • Tidskriftsartikel (refereegranskat)abstract
    • Femtosecond spectroscopy is an important tool used for tracking rapid photoinduced processes in a variety of materials. To spatially map the processes in a sample would substantially expand the method’s capabilities. This is, however, difficult to achieve, due to the necessity of using low-noise detection and maintaining feasible data acquisition time. Here, we demonstrate realization of an imaging pump-probe setup, featuring sub-100 fs temporal resolution, by using a straightforward modification of a standard pump-probe technique, which uses a randomly structured probe beam. The structured beam, made by a diffuser, enabled us to computationally reconstruct the maps of transient absorption dynamics based on the concept of compressed sensing. We demonstrate the setup’s functionality in two proof-of-principle experiments, where we achieve spatial resolution of 20 μm. The presented concept provides a feasible route to imaging, by using the pump-probe technique and ultrafast spectroscopy in general.
  •  
35.
  • Denk, Ondrej, et al. (författare)
  • Speckle-based compressive imaging in ultrafast spectroscopy
  • 2019
  • Ingår i: Computational Optical Sensing and Imaging, COSI 2019. - 9781557528209 ; Part F170-COSI 2019
  • Konferensbidrag (refereegranskat)abstract
    • We present a straightforward implementation of compressive imaging in femtosecond pump-probe spectroscopy. By using laser speckles as random patterns we built a single-pixel camera experiment capable of imaging processes with temporal resolution <100 fs.
  •  
36.
  • Elsayed, Mohamed Hammad, et al. (författare)
  • Visible-light-driven hydrogen evolution using nitrogen-doped carbon quantum dot-implanted polymer dots as metal-free photocatalysts
  • 2021
  • Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373. ; 283
  • Tidskriftsartikel (refereegranskat)abstract
    • Given the photocatalytic properties of semiconducting polymers and carbon quantum dots (CQDs), we report a new structure for a metal-free photocatalytic system with a promising efficiency for hydrogen production through the combination of an organic semiconducting polymer (PFTBTA) and N-doped carbon quantum dots (NCQDs) covered by PS-PEGCOOH to produce heterostructured photocatalysts in the form of polymer dots (Pdots). This design could provide strong interactions between the two materials owing to the space confinement effect in nanometer-sized Pdots. Small particle size NCQDs are easy to insert inside the Pdot, which leads to an increase in the stability of the Pdot structure and enhances the hydrogen evolution rate by approximately 5-fold over that of pure PFTBTA Pdots. The photophysics and the mechanism behind the catalytic activity of our design are investigated by transient absorption measurement, demonstrating the role of NCQDs to enhance the charge separation and the photocatalytic efficiency of the PFTBTA Pdot.
  •  
37.
  • Geng, Huifang, et al. (författare)
  • Controlled synthesis of highly stable lead-free bismuth halide perovskite nanocrystals : tructures and photophysics
  • 2023
  • Ingår i: SCIENCE CHINA Materials. - : Springer Science and Business Media LLC. - 2095-8226 .- 2199-4501. ; 66:5, s. 2079-2089
  • Tidskriftsartikel (refereegranskat)abstract
    • Recently, cesium bismuth halide perovskites have emerged as potential substitutes to their counterparts, cesium lead halide perovskites, owing to their low toxicity. However, the photophysics of cesium-bismuth halides nanocrystals (NCs) have not yet been fully rationalized because their structures remain highly debated. The ultraviolet-visible (UV-vis) absorption along with other photophysical properties such as the nature and lifetime of the excited states vary considerably across the previous reports. Here, we successfully synthesize pure Cs3BiBr6 and Cs3Bi2Br9 NCs via a modified hot-injection method, where the structure can be easily controlled by tuning the reaction temperature. The UV-vis absorption spectrum of the pure Cs3Bi2Br9 NCs features two characteristic peaks originating from the absorption of the first exciton and second exciton, respectively, which ultimately clarifies the debate in the previous reports. Using femtosecond transient absorption spectroscopy, we systematically investigate the excited state dynamics of the Cs3Bi2Br9 NCs and reveal that the photoexcited carriers undergo a self-trapping process within 3 ps after excitation. More intriguingly, the Cs3Bi2Br9 NCs prepared by this method show much better photostability than those prepared by the ligand-assisted reprecipitation process. Photodetectors based on these Cs3Bi2Br9 NCs show a sensitive light response, demonstrating the definite potential for breakthrough optoelectronic applications. [Figure not available: see fulltext.].
  •  
38.
  • Ghosh, Supriya, et al. (författare)
  • Slower Auger Recombination in 12-Faceted Dodecahedron CsPbBr3 Nanocrystals
  • 2023
  • Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 14:4, s. 1066-1072
  • Tidskriftsartikel (refereegranskat)abstract
    • Over the past two decades, intensive research efforts have been devoted to suppressions of Auger recombination in metal-chalcogenide and perovskite nanocrystals (PNCs) for the application of photovoltaics and light emitting devices (LEDs). Here, we have explored dodecahedron cesium lead bromide perovskite nanocrystals (DNCs), which show slower Auger recombination time compared to hexahedron nanocrystals (HNCs). We investigate many-body interactions that are manifested under high excitation flux density in both NCs using ultrafast spectroscopic pump-probe measurements. We demonstrate that the Auger recombination rate due to multiexciton recombinations are lower in DNCs than in HNCs. At low and intermediate excitation density, the majority of carriers recombine through biexcitonic recombination. However, at high excitation density (>1018 cm-3) a higher number of many-body Auger process dominates over biexcitonic recombination. Compared to HNCs, high PLQY and slower Auger recombinations in DNCs are likely to be significant for the fabrication of highly efficient perovskite-based photonics and LEDs.
  •  
39.
  • Guo, Ruiqi, et al. (författare)
  • CuInSe2 Quantum Dots Hybrid Hole Transfer Layer for Halide Perovskite Photodetectors
  • 2018
  • Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:41, s. 35656-35663
  • Tidskriftsartikel (refereegranskat)abstract
    • A novel hybrid hole transport layer (HTL) of CuInSe2 quantum dots (QDs)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was developed to enhance the performance of halide metal perovskite (MAPbI3)-based photodetectors. The introduction of CuInSe2 QDs not only improved the wettability of the PEDOT:PSS HTL for the growth of perovskite crystals but also facilitated the transportation of holes from the perovskite to the HTL. As a result, both responsivity and detectivity of the device were increased dramatically by CuInSe2 QDs hybrid HTL, showing excellent photoresponsivity of 240 mA/W, larger ratio of photocurrent density to dark current density of 4.1 × 106, fast on-off switching properties of <0.02 s, and remarkable detectivity values of 1.02 × 1013 Jones at 580 nm and above 5.01 × 1012 Jones over the visible light region without an external bias voltage. In addition, the photodetectors also showed excellent thermal stability in the range of 10-110 °C. Therefore, a unique design idea of a hole transport material would be an anticipated direction for efficient halide metal perovskite-based devices.
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40.
  • Guo, Ruiqi, et al. (författare)
  • Exploiting Flexible Memristors Based on Solution-Processed Colloidal CuInSe2 Nanocrystals
  • 2020
  • Ingår i: Advanced Electronic Materials. - : Wiley. - 2199-160X. ; 6:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Compared to analogous bulk materials, colloidal nanocrystals have presented a powerful platform for building up electronic devices on the nano/micrometer scale and flexible portable electronic apparatus with the benefits of solution-based processing approach at room temperature. Herein, memristors based on CuInSe2 (CISe) colloidal nanocrystals prepared using a solution-based process at room temperature are constructed. The memristors exhibit obvious bipolar resistive switching performance with a high–low resistance ratio larger than 5.7 and a steady retention time over 104 s. This is attributed to the copper ion redox reaction and the migration of these ions under an applied electric field. When the SET voltage is reached, the ions are separated from one of the electrodes, and the memristor changes from a low-resistance state (LRS) to a high-resistance state (HRS). Conversely, when the voltage reaches the RESET voltage, the memristor switches from a HRS to a LRS. In addition, the flexible memristor can be fabricated by spincoating nanocrystal solution onto polyethylene terephthalate (PET) at room temperature, showing excellent reproducibility of the performance including 100 times of continuous operation, 104 s of reproducible reading, 600 times of antifatigue testing, and thermal stability up to 95 °C. The flexible devices demonstrate promising applications for portable electronic devices.
  •  
41.
  • Guo, Ruiqi, et al. (författare)
  • Manganese doped eco-friendly CuInSe2 colloidal quantum dots for boosting near-infrared photodetection performance
  • 2021
  • Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 403
  • Tidskriftsartikel (refereegranskat)abstract
    • CuInSe2 (CISe) colloidal quantum dots (QDs) display promising applications in photodetection especially within near-infrared (NIR) regions due to their high extinction coefficient and environmental-friendly. However, the high trap density and poor crystal quality introduced by the ternary structure result in low photodetection of CISe QDs devices. Herein, we dope transition metal manganese ions (Mn2+) into CISe QDs to tackle the above problems. Structural characterization results demonstrate the crystal quality of CISe QDs is improved by doping Mn2+ during the synthesis of QDs. The transient absorption (TA) spectroscopic study together with the space-charge-limited current (SCLC) measurements show the charge carrier lifetime of Mn-CISe QDs is much longer than that of the CISe QDs, due to the Mn2+ doping state serve as hole capturer forming a charge-compensated pair with the Cu2+ defect that makes the long-lived Cu2+ radiative recombination dominate. Furthermore, Mn2+ doping concurrently modifies the conduction band minimum and valence band maximum level of the QDs verified by the ultraviolet photoelectron spectroscopy (UPS), which determines the driving force for charge carrier transfer to acceptors. The optimal Mn2+ doping level (0.01 Mn:Cu feed ratio) balanced the above two factors in the QDs. The detector based on such Mn-CISe QDs exhibits responsivity of 30 mA/W and specific detectivity of 4.2 × 1012 Jones at near-infrared wavelength, the response speed of 0.76 µs, and suppressed dark current density of 1.6 × 10−10 A cm−2.
  •  
42.
  • Hansen, Thorsten, et al. (författare)
  • Orbital Topology Controlling Charge Injection in Quantum-Dot-Sensitized Solar Cells
  • 2014
  • Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 5:7, s. 1157-1162
  • Tidskriftsartikel (refereegranskat)abstract
    • Quantum-dot-sensitized solar cells are emerging as a promising development of dye-sensitized solar cells, where photostable semiconductor quantum dots replace molecular dyes. Upon photoexcitation of a quantum dot, an electron is transferred to a high-band-gap metal oxide. Swift electron transfer is crucial to ensure a high overall efficiency of the solar cell. Using femtosecond time-resolved spectroscopy, we find the rate of electron transfer to be surprisingly sensitive to the chemical structure of the linker molecules that attach the quantum dots to the metal oxide. A rectangular barrier model is unable to capture the observed variation. Applying bridge-mediated electron-transfer theory, we find that the electron-transfer rates depend on the topology of the frontier orbital of the molecular linker. This promises the capability of fine tuning the electron-transfer rates by rational design of the linker molecules.
  •  
43.
  • Hattori, Yocefu, et al. (författare)
  • Phonon-assisted hot carrier generation in plasmonic semiconductor systems
  • Ingår i: Nano letters (Print). - 1530-6984 .- 1530-6992.
  • Tidskriftsartikel (refereegranskat)abstract
    • Plasmonic materials have optical cross-sections that exceed by tenfold their geometric sizes, making them uniquely suitable to convert light into electrical charges. Har-vesting plasmon-generated hot carriers are of interest for the broad fields of photovoltaics and photocatalysis, however, their direct utilization is limited by their ultrafast thermaliza-tion in metals. To prolong the lifetime of hot carriers one can place acceptor materials, such as semiconductors, in direct contact with the plasmonic system. Herein, we report the ef-fect of operating temperature on hot electron generation and transfer to a suitable semiconductor. We found that an in-crease in the operation temperature improves hot electron harvesting in a plasmonic semiconductor hybrid system, con-trasting what is observed on photo-driven processes in non-plasmonic systems. The effect appears to be related to an en-hancement in hot carrier generation due to phonon coupling. This discovery provides a new strategy for optimization of photo-driven energy production and chemical synthesis.
  •  
44.
  • Hattori, Yocefu, et al. (författare)
  • Phonon-Assisted Hot Carrier Generation in Plasmonic Semiconductor Systems
  • 2021
  • Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 21:2, s. 1083-1089
  • Tidskriftsartikel (refereegranskat)abstract
    • Plasmonic materials have optical cross sections that exceed by 10-fold their geometric sizes, making them uniquely suitable to convert light into electrical charges. Harvesting plasmon-generated hot carriers is of interest for the broad fields of photovoltaics and photocatalysis; however, their direct utilization is limited by their ultrafast thermalization in metals. To prolong the lifetime of hot carriers, one can place acceptor materials, such as semiconductors, in direct contact with the plasmonic system. Herein, we report the effect of operating temperature on hot electron generation and transfer to a suitable semiconductor. We found that an increase in the operation temperature improves hot electron harvesting in a plasmonic semiconductor hybrid system, contrasting what is observed on photodriven processes in nonplasmonic systems. The effect appears to be related to an enhancement in hot carrier generation due to phonon coupling. This discovery provides a new strategy for optimization of photodriven energy production and chemical synthesis.
  •  
45.
  • Hattori, Yocefu, et al. (författare)
  • Role of the Metal Oxide Electron Acceptor on Gold-Plasmon Hot-Carrier Dynamics and Its Implication to Photocatalysis and Photovoltaics
  • 2021
  • Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 4:2, s. 2052-2060
  • Tidskriftsartikel (refereegranskat)abstract
    • The recent discovery that metal nanoparticles can generate hot carriers upon light excitation is seen as a breakthrough in the fields of plasmonics and photonics. However, the high expectations for a plasmonic revolution in applications have been dampened by the ultrafast energy dissipation of surface plasmon polariton modes. While research aimed at suppressing loss mechanisms is still pursued, another research direction has emerged where charges are harnessed before they relax. Despite the effort, efficiencies of devices based on hot carriers harnessed from plasmonics are typically very low (a few percent), which is somehow paradoxical since efficiencies for electron injection efficiency have been reported to be in the range from 25% to 40% and hole injection up to 85%. This indicates that the low device performance relates to the undesirable charge back-transfer process, which happens in the picosecond time scale. In this context, we performed a comparative ultrafast spectroscopy investigation with gold nanoparticles in direct contact with different metal oxides, namely, TiO2, ZnO, SnO2, and Al:ZnO. Electron dynamics revealed the decisive role of metal/semiconductor interfaces and semiconductor electronic structure in electron injection efficiency and recombination, with significant implications to the fields of photocatalysis and photovoltaics.
  •  
46.
  • Hattori, Yocefu, et al. (författare)
  • Simultaneous Hot Electron and Hole Injection upon Excitation of Gold Surface Plasmon
  • 2019
  • Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 10:11, s. 3140-3146
  • Tidskriftsartikel (refereegranskat)abstract
    • We have successfully investigated the simultaneous injection of hot electrons and holes upon excitation of gold localized surface plasmon resonance (LSPR). The studies were performed on all-solid-state plasmonic system composed of titanium dioxide (TiO2)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) p-n junctions with gold nanoparticles (Au NPs). The study revealed that both charge carriers are transferred within 200 fs to the respective charge acceptors, exhibiting a free carrier transport behavior. We also confirmed that the transfer of charge carriers are accompanied by change in the initial relaxation dynamics of Au NPs.
  •  
47.
  • He, Yanmei, et al. (författare)
  • Direct Observation of Size-Dependent Phase Transition in Methylammonium Lead Bromide Perovskite Microcrystals and Nanocrystals
  • 2022
  • Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 7:44, s. 39970-39974
  • Tidskriftsartikel (refereegranskat)abstract
    • Methylammonium (MA) lead halide perovskites have been widely studied as active materials for advanced optoelectronics. As crystalline semiconductor materials, their properties are strongly affected by their crystal structure. Depending on their applications, the size of MA lead halide perovskite crystals varies by several orders of magnitude. The particle size can lead to different structural phase transitions and optoelectronic properties. Herein, we investigate the size effect for phase transition of MA lead bromide (MAPbBr3) by comparing the temperature-dependent neutron powder diffraction patterns of microcrystals and nanocrystals. The orthorhombic-to-tetragonal phase transition occurs in MAPbBr3microcrystals within the temperature range from 100 to 310 K. However, the phase transition is absent in nanocrystals in this temperature range. In this work, we offer a persuasive and direct evidence of the relationship between the particle size and the phase transition in perovskite crystals.
  •  
48.
  • He, Yanmei, et al. (författare)
  • Nature of Self-Trapped Exciton Emission in Zero-Dimensional Cs2ZrCl6 Perovskite Nanocrystals
  • 2023
  • Ingår i: The Journal of Physical Chemistry Letters. - 1948-7185. ; 14:34, s. 7665-7671
  • Tidskriftsartikel (refereegranskat)abstract
    • Low dimensional perovskite-inspired materials with self-tapped exciton (STE) emission have stimulated a surge of cutting-edge research in optoelectronics. Despite numerous efforts on developing versatile low-dimensional perovskite-inspired materials with efficient STE emissions, there is little emphasis on the intrinsic dynamics of STE-based broad emission in these materials. Here, we investigated the excited state dynamics in zero-dimensional (0D) Cs2ZrCl6 nanocrystals (NCs) with efficient blue STE emission. By using femtosecond transient absorption (fs-TA) spectroscopy, the ultrafast STE formation process within 400 fs is directly observed. Then, the formed STEs relax to an intermediate STE state with a lifetime of ∼180 ps before reaching the emissive STE state with a lifetime of ∼15 μs. Our work offers a comprehensive and precise dynamic picture of STE emission in low-dimensional metal halides and sheds light on extending their potential applications.
  •  
49.
  • Honarfar, Alireza, et al. (författare)
  • Photoexcitation dynamics in electrochemically charged CdSe quantum dots : From hot carrier cooling to auger recombination of negative trions
  • 2020
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:12, s. 12525-12531
  • Tidskriftsartikel (refereegranskat)abstract
    • Fulfilling the potential of colloidal semiconductor quantum dots (QDs) in electrically driven applications remains a challenge largely since operation of such devices involves charged QDs with drastically different photophysical properties compared to their well-studied neutral counterparts. In this work, the full picture of excited state dynamics in charged CdSe QDs at various time scales has been revealed via transient absorption spectroscopy combined with electrochemistry as a direct manipulation tool to control the negative charging of CdSe QDs. In trions, excited states of single charged QDs, the additional electron in the conduction band speeds up the hot electron cooling by enhanced electron-electron scattering followed by charge redistribution and polaron formation in a picosecond time scale. The trions are finally decayed by the Auger process in a 500 ps time scale. Double charging in QDs, on the other hand, decelerates the polaron formation process while accelerates the following Auger decay. Our work demonstrates the potential of photoelectrochemistry as a platform for ultrafast spectroscopy of charged species and paves the way for further studies to develop comprehensive knowledge of the photophysical processes in charged QDs more than the well-known Auger decay, facilitating their use in future optoelectronic applications.
  •  
50.
  • Honarfar, Alireza, et al. (författare)
  • Ultrafast dynamics in QD based photoelectrochemical cells
  • 2019
  • Ingår i: Physical Chemistry of Semiconductor Materials and Interfaces XVIII. - : SPIE. - 9781510628618 ; 11084
  • Konferensbidrag (refereegranskat)abstract
    • We have prepared electrodes for photo-electro-chemical cells which have enabled to pre-charge colloidal quantum dots in well-controlled fashion. Femtosecond transient absorption measurements were carried out revealing clear speed-up of the photo-induced charge carrier dynamics, particularly the recombination. Such studies allow to understand the behavior of light harvesting materials in operational conditions of optoelectronic devices giving new recipes for improvements.
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