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1.
J Am Chem Soc ; 2022 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-36416496

RESUMO

Although sulfide perovskites usually require high-temperature syntheses, we demonstrate that organosulfides can be used in the milder syntheses of halide perovskites. The zwitterionic organosulfide, cysteamine (CYS; +NH3(CH2)2S-), serves as both the X- site and A+ site in the ABX3 halide perovskites, yielding the first examples of 3D organosulfide-halide perovskites: (CYS)PbX2 (X- = Cl- or Br-). Notably, the band structures of (CYS)PbX2 capture the direct bandgaps and dispersive bands of APbX3 perovskites. The sulfur orbitals compose the top of the valence band in (CYS)PbX2, affording unusually small direct bandgaps of 2.31 and 2.16 eV for X- = Cl- and Br-, respectively, falling in the ideal range for the top absorber in a perovskite-based tandem solar cell. Measurements of the carrier dynamics in (CYS)PbCl2 suggest carrier trapping due to defects or lattice distortions. The highly desirable bandgaps, band dispersion, and improved stability of the organosulfide perovskites demonstrated here motivate the continued expansion and exploration of this new family of materials, particularly with respect to extracting photocurrent. Our strategy of combining the A+ and X- sites with zwitterions may offer more members in this family of mixed-anion 3D hybrid perovskites.

2.
J Phys Chem B ; 126(40): 7981-7991, 2022 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-36191182

RESUMO

Despite extensive studies, many questions remain about what structural and energetic factors give rise to the remarkable energy transport efficiency of photosynthetic light-harvesting protein complexes, owing largely to the inability to synthetically control such factors in these natural systems. Herein, we demonstrate energy transfer within a biomimetic light-harvesting complex consisting of identical chromophores attached in a circular array to a protein scaffold derived from the tobacco mosaic virus coat protein. We confirm the capability of energy transport by observing ultrafast depolarization in transient absorption anisotropy measurements and a redshift in time-resolved emission spectra in these complexes. Modeling the system with kinetic Monte Carlo simulations recapitulates the observed anisotropy decays, suggesting an inter-site hopping rate as high as 1.6 ps-1. With these simulations, we identify static disorder in orientation, site energy, and degree of coupling as key remaining factors to control to achieve long-range energy transfer in these systems. We thereby establish this system as a highly promising, bottom-up model for studying long-range energy transfer in light-harvesting protein complexes.


Assuntos
Biomimética , Vírus do Mosaico do Tabaco , Transferência de Energia , Complexos de Proteínas Captadores de Luz/química , Fotossíntese , Vírus do Mosaico do Tabaco/química
3.
Nat Mater ; 21(5): 497-499, 2022 05.
Artigo em Inglês | MEDLINE | ID: mdl-35505231
4.
Science ; 375(6587): 1422-1426, 2022 03 25.
Artigo em Inglês | MEDLINE | ID: mdl-35324292

RESUMO

Colloidal nanocrystals of metals, semiconductors, and other functional materials can self-assemble into long-range ordered crystalline and quasicrystalline phases, but insulating organic surface ligands prevent the development of collective electronic states in ordered nanocrystal assemblies. We reversibly self-assembled colloidal nanocrystals of gold, platinum, nickel, lead sulfide, and lead selenide with conductive inorganic ligands into supercrystals exhibiting optical and electronic properties consistent with strong electronic coupling between the constituent nanocrystals. The phase behavior of charge-stabilized nanocrystals can be rationalized and navigated with phase diagrams computed for particles interacting through short-range attractive potentials. By finely tuning interparticle interactions, the assembly was directed either through one-step nucleation or nonclassical two-step nucleation pathways. In the latter case, the nucleation was preceded by the formation of two metastable colloidal fluids.

5.
Nano Lett ; 21(8): 3540-3547, 2021 04 28.
Artigo em Inglês | MEDLINE | ID: mdl-33872014

RESUMO

Investigating the impact of nanoscale heterogeneity on heat transport requires a spatiotemporal probe of temperature on the length and time scales intrinsic to heat navigating nanoscale defects. Here, we use stroboscopic optical scattering microscopy to visualize nanoscale heat transport in disordered films of gold nanocrystals. We find that heat transport appears subdiffusive at the nanoscale. Finite element simulations show that tortuosity of the heat flow underlies the subdiffusive transport, owing to a distribution of nonconductive voids. Thus, while heat travels diffusively through contiguous regions of the film, the tortuosity causes heat to navigate circuitous pathways that make the observed mean-squared expansion of an initially localized temperature distribution appear subdiffusive on length scales comparable to the voids. Our approach should be broadly applicable to uncover the impact of both designed and unintended heterogeneities in a wide range of materials and devices that can affect more commonly used spatially averaged thermal transport measurements.


Assuntos
Temperatura Alta , Nanopartículas , Ouro , Temperatura
6.
Soft Matter ; 16(41): 9578-9589, 2020 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-32974626

RESUMO

We induce and investigate the coarsening and melting dynamics of an initially static nanoparticle colloidal monolayer at an ionic liquid-vacuum interface, driven by a focused, scanning electron beam. Coarsening occurs through grain interface migration and larger-scale motions such as grain rotations, often facilitated by sliding dislocations. The progressive decrease in area fraction that drives melting of the monolayer is explained using an electrowetting model whereby particles at the interface are solvated once their accumulating charge recruits sufficient counterions to subsume the particle. Subject to stochastic particle removal from the monolayer, melting is recapitulated in simulations with a Lennard-Jones potential. This new driving mechanism for colloidal systems, whose dynamical timescales we show can be controlled with the accelerating voltage, opens the possibility to manipulate particle interactions dynamically without need to vary particle intrinsic properties or surface treatments. Furthermore, the decrease in particle size availed by electron imaging presents opportunities to observe force and time scales in a lesser-explored regime intermediate between typical colloidal and molecular systems.

7.
J Phys Chem Lett ; 11(12): 4849-4858, 2020 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-32510954

RESUMO

Semicrystalline polymers constitute some of the most widely used materials in the world, and their functional properties are intimately connected to their structure on a range of length scales. Many of these properties depend on the micro- and nanoscale heterogeneous distribution of crystalline and amorphous phases, but this renders the interpretation of ensemble averaged measurements challenging. We use superlocalized widefield single-particle tracking in conjunction with AFM phase imaging to correlate the crystalline morphology of lithium-triflate-doped poly(ethylene oxide) thin films to the motion of individual fluorescent probes at the nanoscale. The results demonstrate that probe motion is intrinsically isotropic in amorphous regions and that, without altering this intrinsic diffusivity, closely spaced, often parallel, crystallite fibers anisotropically constrain probe motion along intercalating amorphous channels. This constraint is emphasized by the agreement between crystallite and anisotropic probe trajectory orientations. This constraint is also emphasized by the extent of the trajectory confinement correlated to the width of the measured gaps between adjacent crystallites. This study illustrates with direct nanoscale correlations how controlled and periodic arrangement of crystalline domains is a promising design principle for mass transport in semicrystalline polymer materials without compromising their mechanical stability.

8.
J Chem Phys ; 152(23): 230901, 2020 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-32571034

RESUMO

We present a perspective on recent observations of the photoinduced phase separation of halides in multi-component lead-halide perovskites. The spontaneous phase separation of an initial homogeneous solid solution under steady-state illumination conditions is found experimentally to be reversible, stochastic, weakly dependent on morphology, yet strongly dependent on composition and thermodynamic state. Regions enriched in a specific halide species that form upon phase separation are self-limiting in size, pinned to specific compositions, and grow in number in proportion to the steady-state carrier concentration until saturation. These empirical observations of robustness rule out explanations based on specific defect structures and point to the local modulation of an existing miscibility phase transition in the presence of excess charge carriers. A model for rationalizing existing observations based on the coupling between composition, strain, and charge density fluctuations through the formation of polarons is reviewed.

9.
ACS Nano ; 14(4): 4792-4804, 2020 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-32208676

RESUMO

Metal nanocrystals exhibit important optoelectronic and photocatalytic functionalities in response to light. These dynamic energy conversion processes have been commonly studied by transient optical probes to date, but an understanding of the atomistic response following photoexcitation has remained elusive. Here, we use femtosecond resolution electron diffraction to investigate transient lattice responses in optically excited colloidal gold nanocrystals, revealing the effects of nanocrystal size and surface ligands on the electron-phonon coupling and thermal relaxation dynamics. First, we uncover a strong size effect on the electron-phonon coupling, which arises from reduced dielectric screening at the nanocrystal surfaces and prevails independent of the optical excitation mechanism (i.e., inter- and intraband). Second, we find that surface ligands act as a tuning parameter for hot carrier cooling. Particularly, gold nanocrystals with thiol-based ligands show significantly slower carrier cooling as compared to amine-based ligands under intraband optical excitation due to electronic coupling at the nanocrystal/ligand interfaces. Finally, we spatiotemporally resolve thermal transport and heat dissipation in photoexcited nanocrystal films by combining electron diffraction with stroboscopic elastic scattering microscopy. Taken together, we resolve the distinct thermal relaxation time scales ranging from 1 ps to 100 ns associated with the multiple interfaces through which heat flows at the nanoscale. Our findings provide insights into optimization of gold nanocrystals and their thin films for photocatalysis and thermoelectric applications.

10.
J Phys Chem Lett ; 11(7): 2624-2629, 2020 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-32191469

RESUMO

Mn2+ doping of lead halide perovskites has garnered recent interest because it produces stable orange luminescence in tandem with perovskite emission. Here, we observe enhanced Mn2+ luminescence at the edges of Mn2+-doped CsPbCl3 perovskite microplates and suggest an explanation for its origin using the high spatiotemporal resolution of time-resolved cathodoluminescence (TRCL) imaging. We reveal two luminescent decay components that we attribute to two different Mn2+ populations. While each component appears to be present both near the surface and in the bulk, the origin of the intensity variation stems from a higher proportion of the longer lifetime component near the perovskite surface. We suggest that this higher emission is caused by an increased probability of electron-hole recombination on Mn2+ near the perovskite surface due to an increased trap concentration there. This observation suggests that such surface features have yet untapped potential to enhance emissive properties via control of surface-to-volume ratio.

11.
J Phys Chem A ; 124(9): 1867-1876, 2020 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-32096402

RESUMO

Inorganic lead halide perovskite nanostructures show promise as the active layers in photovoltaics, light emitting diodes, and other optoelectronic devices. They are robust in the presence of oxygen and water, and the electronic structure and dynamics of these nanostructures can be tuned through quantum confinement. Here we create aligned bundles of CsPbBr3 nanowires with widths resulting in quantum confinement of the electronic wave functions and subject them to ultrafast microscopy. We directly image rapid one-dimensional exciton diffusion along the nanowires, and we measure an exciton trap density of roughly one per nanowire. Using transient absorption microscopy, we observe a polarization-dependent splitting of the band edge exciton line, and from the polarized fluorescence of nanowires in solution, we determine that the exciton transition dipole moments are anisotropic in strength. Our observations are consistent with a model in which splitting is driven by shape anisotropy in conjunction with long-range exchange.

12.
Annu Rev Phys Chem ; 71: 1-30, 2020 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-31756129

RESUMO

We review recent advances in the characterization of electronic forms of energy transport in emerging semiconductors. The approaches described all temporally and spatially resolve the evolution of initially localized populations of photogenerated excitons or charge carriers. We first provide a comprehensive background for describing the physical origin and nature of electronic energy transport both microscopically and from the perspective of the observer. We introduce the new family of far-field, time-resolved optical microscopies developed to directly resolve not only the extent of this transport but also its potentially temporally and spatially dependent rate. We review a representation of examples from the recent literature, including investigation of energy flow in colloidal quantum dot solids, organic semiconductors, organic-inorganic metal halide perovskites, and 2D transition metal dichalcogenides. These examples illustrate how traditional parameters like diffusivity are applicable only within limited spatiotemporal ranges and how the techniques at the core of this review,especially when taken together, are revealing a more complete picture of the spatiotemporal evolution of energy transport in complex semiconductors, even as a function of their structural heterogeneities.

13.
Nat Mater ; 19(1): 56-62, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31591529

RESUMO

The ability of energy carriers to move between atoms and molecules underlies biochemical and material function. Understanding and controlling energy flow, however, requires observing it on ultrasmall and ultrafast spatio-temporal scales, where energetic and structural roadblocks dictate the fate of energy carriers. Here, we developed a non-invasive optical scheme that leverages non-resonant interferometric scattering to track tiny changes in material polarizability created by energy carriers. We thus map evolving energy carrier distributions in four dimensions of spacetime with few-nanometre lateral precision and directly correlate them with material morphology. We visualize exciton, charge and heat transport in polyacene, silicon and perovskite semiconductors and elucidate how disorder affects energy flow in three dimensions. For example, we show that morphological boundaries in polycrystalline metal halide perovskites possess lateral- and depth-dependent resistivities, blocking lateral transport for surface but not bulk carriers. We also reveal strategies for interpreting energy transport in disordered environments that will direct the design of defect-tolerant materials for the semiconductor industry of tomorrow.

14.
ACS Nano ; 13(4): 4538-4547, 2019 Apr 23.
Artigo em Inglês | MEDLINE | ID: mdl-30865421

RESUMO

Hexagonal boron nitride (h-BN) is a 2D, wide band gap semiconductor that has recently been shown to display bright room-temperature emission in the visible region, sparking immense interest in the material for use in quantum applications. In this work, we study highly crystalline, single atomic layers of chemical vapor deposition grown h-BN and find predominantly one type of emissive state. Using a multidimensional super-resolution fluorescence microscopy technique we simultaneously measure spatial position, intensity, and spectral properties of the emitters, as they are exposed to continuous wave illumination over minutes. As well as low emitter heterogeneity, we observe inhomogeneous broadening of emitter line-widths and power law dependency in fluorescence intermittency; this is strikingly similar to previous work on quantum dots. These results show that high control over h-BN growth and treatment can produce a narrow distribution of emitter type and that surface interactions heavily influence the photodynamics. Furthermore, we highlight the utility of spectrally resolved wide-field microscopy in the study of optically active excitations in atomically thin two-dimensional materials.

15.
Proc Natl Acad Sci U S A ; 115(47): 11929-11934, 2018 11 20.
Artigo em Inglês | MEDLINE | ID: mdl-30397127

RESUMO

Facile ionic transport in lead halide perovskites plays a critical role in device performance. Understanding the microscopic origins of high ionic conductivities has been complicated by indirect measurements and sample microstructural heterogeneities. Here, we report the direct visualization of halide anion interdiffusion in CsPbCl3-CsPbBr3 single crystalline perovskite nanowire heterojunctions using wide-field and confocal photoluminescence measurements. The combination of nanoscale imaging techniques with these single crystalline materials allows us to measure intrinsic anionic lattice diffusivities, free from complications of microscale inhomogeneity. Halide diffusivities were found to be between 10-13 and ∼10-12 cm2/second at about 100 °C, which are several orders of magnitudes lower than those reported in polycrystalline thin films. Spatially resolved photoluminescence lifetimes and surface potential measurements provide evidence of the central role of halide vacancies in facilitating ionic diffusion. Vacancy formation free energies computed from molecular simulation are small due to the easily deformable perovskite lattice, accounting for the high equilibrium vacancy concentration. Furthermore, molecular simulations suggest that ionic motion is facilitated by low-frequency lattice modes, resulting in low activation barriers for vacancy-mediated transport. This work elucidates the intrinsic solid-state ion diffusion mechanisms in this class of semisoft materials and offers guidelines for engineering materials with long-term stability in functional devices.

16.
Proc Natl Acad Sci U S A ; 115(36): 8889-8894, 2018 09 04.
Artigo em Inglês | MEDLINE | ID: mdl-30127004

RESUMO

Semiconductor p-n junctions are fundamental building blocks for modern optical and electronic devices. The p- and n-type regions are typically created by chemical doping process. Here we show that in the new class of halide perovskite semiconductors, the p-n junctions can be readily induced through a localized thermal-driven phase transition. We demonstrate this p-n junction formation in a single-crystalline halide perovskite CsSnI3 nanowire (NW). This material undergoes a phase transition from a double-chain yellow (Y) phase to an orthorhombic black (B) phase. The formation energies of the cation and anion vacancies in these two phases are significantly different, which leads to n- and p- type electrical characteristics for Y and B phases, respectively. Interface formation between these two phases and directional interface propagation within a single NW are directly observed under cathodoluminescence (CL) microscopy. Current rectification is demonstrated for the p-n junction formed with this localized thermal-driven phase transition.

17.
J Phys Chem Lett ; 9(14): 3998-4005, 2018 Jul 19.
Artigo em Inglês | MEDLINE | ID: mdl-29979045

RESUMO

Photoinduced phase separation in mixed halide perovskites emerges from their electro-mechanical properties and high ionic conductivities, resulting in photoinduced I--rich charge carrier traps that diminish photovoltaic performance. Whether photoinduced phase separation stems from the polycrystalline microstructure or is an intrinsic material property has been an open question. We investigate the nanoscale photoinduced behavior of single-crystal mixed Br-/I- methylammonium (MA+) lead halide perovskite (MAPb(Br xI1- x)3) nanoplates, eliminating effects from extended structural defects. Even in these nanoplates, we find that phase separation occurs, resulting in I--rich clusters that are nucleated stochastically and stabilized by polarons. Upon lowering the electron-phonon coupling strength by partially exchanging MA+ for Cs+, a phase-separated steady state is not reached, nevertheless transient I- clustering still occurs. Our results, supported by multiscale modeling, demonstrate that photoinduced phase separation is an intrinsic property of mixed halide perovskites, the extent and dynamics of which depends on the electron-phonon coupling strength.

18.
J Am Chem Soc ; 140(20): 6278-6287, 2018 05 23.
Artigo em Inglês | MEDLINE | ID: mdl-29741876

RESUMO

Creating artificial systems that mimic and surpass those found in nature is one of the great challenges of modern science. In the context of photosynthetic light harvesting, the difficulty lies in attaining utmost control over the energetics, positions and relative orientations of chromophores in densely packed arrays to transfer electronic excitation energy to desired locations with high efficiency. Toward achieving this goal, we use a highly versatile biomimetic protein scaffold from the tobacco mosaic virus coat protein on which chromophores can be attached at precise locations via linkers of differing lengths and rigidities. We show that minor linker modifications, including switching chiral configurations and alkyl chain shortening, lead to significant lengthening of the ultrafast excited state dynamics of the system as the linkers are shortened and rigidified. Molecular dynamics simulations provide molecular-level detail over how the chromophore attachment orientations, positions, and distances from the protein surface lead to the observed trends in system dynamics. In particular, we find that short and rigid linkers are able to sandwich water molecules between chromophore and protein, leading to chromophore-water-protein supracomplexes with intricately coupled dynamics that are highly dependent on their local protein environment. In addition, cyclohexyl-based linkers are identified as ideal candidates to retain rotational correlations over several nanoseconds and thus lock relative chromophore orientations throughout the lifetime of an exciton. Combining linker engineering with judicious placement of chromophores on the hydrated protein scaffold to exploit different chromophore-bath couplings provides a clear and effective path to producing highly controllable artificial light-harvesting systems that can increasingly mimic their natural counterparts, thus aiding to elucidate natural photosynthetic mechanisms.


Assuntos
Materiais Biomiméticos/química , Proteínas do Capsídeo/química , Corantes/química , Complexos de Proteínas Captadores de Luz/química , Vírus do Mosaico do Tabaco/química , Biomimética , Reagentes de Ligações Cruzadas/química , Cicloexanos/química , Transferência de Energia , Simulação de Dinâmica Molecular , Pigmentos Biológicos/química , Teoria Quântica , Água/química
19.
J Am Chem Soc ; 140(6): 2326-2335, 2018 02 14.
Artigo em Inglês | MEDLINE | ID: mdl-29392936

RESUMO

Singlet fission is the spin-conserving process by which a singlet exciton splits into two triplet excitons. Singlet fission occurs via a correlated triplet pair intermediate, but direct evidence of this state has been scant, and in films of TIPS-pentacene, a small molecule organic semiconductor, even the rate of fission has been unclear. We use polarization-resolved transient absorption microscopy on individual crystalline domains of TIPS-pentacene to establish the fission rate and demonstrate that the initially created triplets remain bound for a surprisingly long time, hundreds of picoseconds, before separating. Furthermore, using a broadband probe, we show that it is possible to determine absorbance spectra of individual excited species in a crystalline solid. We find that triplet interactions perturb the absorbance, and provide evidence that triplet interaction and binding could be caused by the π-stacked geometry. Elucidating the relationship between the lattice structure and the electronic structure and dynamics has important implications for the creation of photovoltaic devices that aim to boost efficiency via singlet fission.

20.
ACS Nano ; 11(10): 10583-10590, 2017 10 24.
Artigo em Inglês | MEDLINE | ID: mdl-28956598

RESUMO

In situ electron microscopy provides remarkably high spatial resolution, yet electron beam irradiation often damages soft materials and perturbs dynamic processes, requiring samples to be very robust. Here, we instead noninvasively image the dynamics of metal and polymer nanoparticles in a liquid environment with subdiffraction resolution using cathodoluminescence-activated imaging by resonant energy transfer (CLAIRE). In CLAIRE, a free-standing scintillator film serves as a nanoscale optical excitation source when excited by a low energy, focused electron beam. We capture the nanoscale dynamics of these particles translating along and desorbing from the scintillator surface and demonstrate 50 ms frame acquisition and a range of imaging of at least 20 nm from the scintillator surface. Furthermore, in contrast with in situ electron microscopy, CLAIRE provides spectral selectivity instead of relying on scattering alone. We also demonstrate through quantitative modeling that the CLAIRE signal from metal nanoparticles is impacted by multiplasmonic mode interferences. Our findings demonstrate that CLAIRE is a promising, noninvasive approach for super-resolution imaging for soft and fluid materials with high spatial and temporal resolution.

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