Observation of an Ultrafast Exciton Transport Regime at Early Times in Quantum Dot Solids

Abstract Understanding and engineering exciton transport in quantum dot (QD) solids is both of fundamental interest and crucial to their broad applications in devices1-6. Till date, studies of exciton transport in QD solids on pico/nano-second timescales have led to the conclusion that closer packing of QDs enables faster exciton transport, while energetic/structural heterogeneity leads to reduction of exciton diffusivity over time7,8. Here we study PbS QD solids using transient absorption microscopy with 13 femtoseconds time resolution and 10 nm spatial precision. We find exciton diffusivities in the range of ~102 cm2 s-1 within the first few hundred femtoseconds after photoexcitation, followed by the transition to a slower transport regime with diffusivities in the range 10-1 to 1 cm2 s-1. Counterintuitively, the initial diffusivity is higher and the time before the transition to the slower transport phase is longer in QD solids with longer ligand lengths. This suggests a transition from early-time transport of delocalized excitons to later time hopping based transport of localized excitons, where QD packing density and heterogeneity accelerate the localization process. Our results reveal a new regime for exciton transport in QD solids and provide design rules to engineer desired transport properties in these systems on a range of timescales.

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Deciphering the role of quantum dot size in the ultrafast charge carrier dynamics at the perovskite–quantum dot interface

Journal of Materials Chemistry C ◽

10.1039/d0tc03835k ◽

2020 ◽

Vol 8 (42) ◽

pp. 14834-14844

Author(s):

Piotr Piatkowski ◽

Sofia Masi ◽

Pavel Galar ◽

Mario Gutiérrez ◽

Thi Tuyen Ngo ◽

...

Keyword(s):

Quantum Dot ◽

Charge Carrier ◽

Rate Constants ◽

Transient Absorption ◽

Carrier Dynamics ◽

Carrier Transfer ◽

Charge Carrier Dynamics ◽

Conduction Bands

Charge-carrier transfer (CT) from the perovskite host to PbS QDs were studied using fs-transient absorption and THz techniques. The CT rate constants increase with the size of QDs due to a change in the position of valence and conduction bands in PbS QDs.

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Ecological Succession of Bacterial Communities during Conventionalization of Germ-Free Mice

Applied and Environmental Microbiology ◽

10.1128/aem.05239-11 ◽

2012 ◽

Vol 78 (7) ◽

pp. 2359-2366 ◽

Cited By ~ 39

Author(s):

Merritt G. Gillilland ◽

John R. Erb-Downward ◽

Christine M. Bassis ◽

Michael C. Shen ◽

Galen B. Toews ◽

...

Keyword(s):

Bacterial Community ◽

16S Rrna ◽

Bacterial Communities ◽

Structural Heterogeneity ◽

Ecological Succession ◽

Rrna Gene ◽

Gi Tract ◽

Content Type ◽

Germ Free ◽

Over Time

ABSTRACTLittle is known about the dynamics of early ecological succession during experimental conventionalization of the gastrointestinal (GI) tract; thus, we measured changes in bacterial communities over time, at two different mucosal sites (cecum and jejunum), with germfree C57BL/6 mice as the recipients of cecal contents (input community) from a C57BL/6 donor mouse. Bacterial communities were monitored using pyrosequencing of 16S rRNA gene amplicon libraries from the cecum and jejunum and analyzed by a variety of ecological metrics. Bacterial communities, at day 1 postconventionalization, in the cecum and jejunum had lower diversity and were distinct from the input community (dominated by eitherEscherichiaorBacteroides). However, by days 7 and 21, the recipient communities had become significantly diverse and the cecal communities resembled those of the donor and donor littermates, confirming that transfer of cecal contents results in reassembly of the community in the cecum 7 to 21 days later. However, bacterial communities in the recipient jejunum displayed significant structural heterogeneity compared to each other or the donor inoculum or the donor littermates, suggesting that the bacterial community of the jejunum is more dynamic during the first 21 days of conventionalization. This report demonstrates that (i) mature input communities do not simply reassemble at mucosal sites during conventionalization (they first transform into a “pioneering” community and over time take on the appearance, in membership and structure, of the original input community) and (ii) the specific mucosal environment plays a role in shaping the community.

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Energy Transfer via Exciton Transport in Quantum Dot Based Self-Assembled Fractal Structures

The Journal of Physical Chemistry C ◽

10.1021/jp411456m ◽

2014 ◽

Vol 118 (9) ◽

pp. 4982-4990 ◽

Cited By ~ 9

Author(s):

César Bernardo ◽

I. Moura ◽

Y. Núnez Fernández ◽

Eduardo J. Nunes-Pereira ◽

Paulo J. G. Coutinho ◽

...

Keyword(s):

Energy Transfer ◽

Quantum Dot ◽

Fractal Structures ◽

Exciton Transport ◽

Self Assembled

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Ultrafast Dynamic Microscopy of Carrier and Exciton Transport

Annual Review of Physical Chemistry ◽

10.1146/annurev-physchem-042018-052605 ◽

2019 ◽

Vol 70 (1) ◽

pp. 219-244 ◽

Cited By ~ 31

Author(s):

Tong Zhu ◽

Jordan M. Snaider ◽

Long Yuan ◽

Libai Huang

Keyword(s):

Charge Transport ◽

Organic Solar Cells ◽

Transient Absorption ◽

Ultrafast Imaging ◽

Ultrafast Optical ◽

Ultrafast Dynamic ◽

Exciton Transport ◽

Solar Energy Harvesting ◽

Hybrid Perovskite ◽

Ultrafast Optical Spectroscopy

We highlight the recent progress in ultrafast dynamic microscopy that combines ultrafast optical spectroscopy with microscopy approaches, focusing on the application transient absorption microscopy (TAM) to directly image energy and charge transport in solar energy harvesting and conversion systems. We discuss the principles, instrumentation, and resolutions of TAM. The simultaneous spatial, temporal, and excited-state-specific resolutions of TAM unraveled exciton and charge transport mechanisms that were previously obscured in conventional ultrafast spectroscopy measurements for systems such as organic solar cells, hybrid perovskite thin films, and molecular aggregates. We also discuss future directions to improve resolutions and to develop other ultrafast imaging contrasts beyond transient absorption.

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Quantitative Analysis of Trap-State-Mediated Exciton Transport in Perovskite-Shelled PbS Quantum Dot Thin Films Using Photocarrier Diffusion-Wave Nondestructive Evaluation and Imaging

The Journal of Physical Chemistry C ◽

10.1021/acs.jpcc.6b04468 ◽

2016 ◽

Vol 120 (26) ◽

pp. 14416-14427 ◽

Cited By ~ 14

Author(s):

Lilei Hu ◽

Zhenyu Yang ◽

Andreas Mandelis ◽

Alexander Melnikov ◽

Xinzheng Lan ◽

...

Keyword(s):

Thin Films ◽

Quantitative Analysis ◽

Quantum Dot ◽

Nondestructive Evaluation ◽

Trap State ◽

Diffusion Wave ◽

Exciton Transport ◽

Pbs Quantum Dot

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Inverting Transient Absorption Data to Determine Transfer Rates in Quantum Dot–TiO2 Heterostructures

The Journal of Physical Chemistry C ◽

10.1021/jp512500g ◽

2015 ◽

Vol 119 (11) ◽

pp. 6337-6343 ◽

Cited By ~ 12

Author(s):

Tess R. Senty ◽

Scott K. Cushing ◽

Congjun Wang ◽

Christopher Matranga ◽

Alan D. Bristow

Keyword(s):

Quantum Dot ◽

Transient Absorption ◽

Absorption Data ◽

Transfer Rates

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Non-Equilibrium Carrier Transport in Strongly Coupled Quantum Dot Solids and Heterostructures

10.21203/rs.3.rs-146013/v1 ◽

2021 ◽

Author(s):

Mengxia Liu ◽

Sachin Dev Verma ◽

Zhilong Zhang ◽

Jooyoung Sung ◽

Akshay Rao

Keyword(s):

Quantum Dot ◽

Carrier Transport ◽

Transient Absorption ◽

High Mobility ◽

Full Potential ◽

Strongly Coupled ◽

Transport Length ◽

Energetic Disorder ◽

Colloidal Quantum Dot ◽

Non Equilibrium

Abstract Understanding and controlling carrier dynamics in colloidal quantum dot (CQD) solids is crucial for unlocking their full potential for optoelectronic applications. The recent development of solution-processing methods to incorporate CQDs into high-mobility semiconducting matrices opens new routes to control simultaneously electronic coupling and packing uniformity in CQD solids. However, the fundamental nature of carrier transport in such systems remains elusive. Here we report the direct visualisation of carrier propagation in metal-halide exchanged PbS CQD solids and quantum-dot-in-perovskite (QDiP) heterostructures via transient absorption microscopy. We reveal three distinct transport regimes: an initial band-like transport persisting over hundreds of femtoseconds, an Auger-assisted sub-diffusive transport before thermal equilibrium is achieved, and a final hopping regime at longer times. The band-like transport was observed to correlate strongly with the extent of carrier delocalisation and the degree of energetic disorder. By tailoring the perovskite content in heterostructures, we obtained a band-like transport length of 90 nm at room temperature and an equivalent diffusivity of up to 106 cm2 s-1 – which is four orders of magnitude higher than the steady-state values obtained for PbS CQD solids. These findings not only shed light on the non-equilibrium dynamics in CQD solids and their influence on carrier transport, but also introduce promising strategies to harness non-equilibrium transport phenomena for more efficient optoelectronic devices.

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Temporal tracking of quantum-dot apatite across in vitro mycorrhizal networks shows how host demand can influence fungal nutrient transfer strategies

The ISME Journal ◽

10.1038/s41396-020-00786-w ◽

2020 ◽

Cited By ~ 2

Author(s):

Anouk van’t Padje ◽

Loreto Oyarte Galvez ◽

Malin Klein ◽

Mark A. Hink ◽

Marten Postma ◽

...

Keyword(s):

Quantum Dot ◽

Correlation Spectroscopy ◽

Image Correlation ◽

Nutrient Transfer ◽

Plant Host ◽

Local Conditions ◽

Fungal Partner ◽

Transfer Strategies ◽

Over Time

Abstract Arbuscular mycorrhizal fungi function as conduits for underground nutrient transport. While the fungal partner is dependent on the plant host for its carbon (C) needs, the amount of nutrients that the fungus allocates to hosts can vary with context. Because fungal allocation patterns to hosts can change over time, they have historically been difficult to quantify accurately. We developed a technique to tag rock phosphorus (P) apatite with fluorescent quantum-dot (QD) nanoparticles of three different colors, allowing us to study nutrient transfer in an in vitro fungal network formed between two host roots of different ages and different P demands over a 3-week period. Using confocal microscopy and raster image correlation spectroscopy, we could distinguish between P transfer from the hyphae to the roots and P retention in the hyphae. By tracking QD-apatite from its point of origin, we found that the P demands of the younger root influenced both: (1) how the fungus distributed nutrients among different root hosts and (2) the storage patterns in the fungus itself. Our work highlights that fungal trade strategies are highly dynamic over time to local conditions, and stresses the need for precise measurements of symbiotic nutrient transfer across both space and time.

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