Tailored exciton diffusion in organic photovoltaic cells for enhanced power conversion efficiency

Menke, S. Matthew; Luhman, Wade A.; Holmes, Russell J.

doi:10.1038/nmat3467

Cited by 196 publications

(224 citation statements)

References 39 publications

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“…44 Using eq 1, the calculated exciton migration length is found to be as high as 133.1 nm ((12.0 nm) with the assumption of isotropic transport giving us a lower limit for the exciton migration length in the stacks of the NPLs. This exciton migration length represents the longest one among all other colloidal semiconductor nanocrystals reported to date.…”

Section: Resultsmentioning

confidence: 99%

Stacking in Colloidal Nanoplatelets: Tuning Excitonic Properties

et al. 2014

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Cataloged from PDF version of article.Colloidal semiconductor quantum wells, also commonly known as nanoplatelets (NPLs), have arisen among the most promising materials for light generation and harvesting applications. Recently, NPLs have been found to assemble in stacks. However, their emerging characteristics essential to these applications have not been previously controlled or understood. In this report, we systematically investigate and present excitonic properties of controlled column-like NPL assemblies. Here, by a controlled gradual process, we show that stacking in colloidal quantum wells substantially increases exciton transfer and trapping. As NPLs form into stacks, surprisingly we find an order of magnitude decrease in their photoluminescence quantum yield, while the transient fluorescence decay is considerably accelerated. These observations are corroborated by ultraefficient Forster resonance energy transfer (FRET) in the stacked NPLs, in which exciton migration is estimated to be in the ultralong range (>100 nm). Homo-FRET (i.e., FRET among the same emitters) is found to be ultraefficient, reaching levels as high as 99.9% at room temperature owing to the close-packed collinear orientation of the NPLs along with their large extinction coefficient and small Stokes shift, resulting in a large Forster radius of similar to 13.5 nm. Consequently, the strong and long-range homo-FRET boosts exciton trapping in nonemissive NPLs, acting as exciton sink centers, quenching photoluminescence from the stacked NPLs due to rapid nonradiative recombination of the trapped excitons. The rate-equation-based model, which considers the exciton transfer and the radiative and nonradiative recombination within the stacks, shows an excellent match with the experimental data. These results show the critical significance of stacking control in NPL solids, which exhibit completely different signatures of homo-FRET as compared to that in colloidal nanocrystals due to the absence of inhomogeneous broadening

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Section: Resultsmentioning

confidence: 99%

Stacking in Colloidal Nanoplatelets: Tuning Excitonic Properties

et al. 2014

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“…Exciton transport is at the core of photosynthesis 2,3 and it similarly governs the operation of a wide array of nanostructured optoelectronic devices including molecular, polymeric and colloidal-quantumdot solar cells 4,5 , light-emitting diodes 6 and excitonic transistors 7 . For example, in molecular and polymeric solar cells, excitons are generated by absorption of sunlight, and must be moved efficiently to an interface where electron and hole are separated to produce charge buildup, leading to photovoltage and photocurrent.…”

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confidence: 99%

“…Likewise, the efficient transport of photogenerated excitons from the light-harvesting complex of a plant to the reaction centre is at the core of photosynthesis 2 . Understanding and manipulating the flow of excitons in such systems can enhance device performance 5 and can lead to development of next-generation excitonic technologies.…”

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confidence: 99%

Visualization of exciton transport in ordered and disordered molecular solids

et al. 2014

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Transport of nanoscale energy in the form of excitons is at the core of photosynthesis and the operation of a wide range of nanostructured optoelectronic devices such as solar cells, lightemitting diodes and excitonic transistors. Of particular importance is the relationship between exciton transport and nanoscale disorder, the defining characteristic of molecular and nanostructured materials. Here we report a spatial, temporal and spectral visualization of exciton transport in molecular crystals and disordered thin films. Using tetracene as an archetype molecular crystal, the imaging reveals that exciton transport occurs by random walk diffusion, with a transition to subdiffusion as excitons become trapped. By controlling the morphology of the thin film, we show that this transition to subdiffusive transport occurs at earlier times as disorder is increased. Our findings demonstrate that the mechanism of exciton transport depends strongly on the nanoscale morphology, which has wide implications for the design of excitonic materials and devices.

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“…For example, the malaria drug artemisinin is commercially produced with a key photochemical step 6 . In organic electronics, the complex physics of excitations is critical to device function [7][8][9][10][11][12][13] . High efficiencies have been reached for both organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs) [14][15][16][17] , yet a major barrier to the deployment of organic semiconductors is their functional lifetime 17 .…”

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confidence: 99%

Temporal mapping of photochemical reactions and molecular excited states with carbon specificity

et al. 2016

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Photochemical reactions are essential to a large number of important industrial and biological processes. A method for monitoring photochemical reaction kinetics and the dynamics of molecular excitations with spatial resolution within the active molecule would allow a rigorous exploration of the pathway and mechanism of photophysical and photochemical processes. Here we demonstrate that laser-excited muon pump-probe spin spectroscopy (photo-μSR) can temporally and spatially map these processes with a spatial resolution at the single-carbon level in a molecule with a pentacene backbone. The observed time-dependent light-induced changes of an avoided level crossing resonance demonstrate that the photochemical reactivity of a specific carbon atom is modified as a result of the presence of the excited state wavefunction. This demonstrates the sensitivity and potential of this technique in probing molecular excitations and photochemistry.

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Tailored exciton diffusion in organic photovoltaic cells for enhanced power conversion efficiency

Cited by 196 publications

References 39 publications

Stacking in Colloidal Nanoplatelets: Tuning Excitonic Properties

Stacking in Colloidal Nanoplatelets: Tuning Excitonic Properties

Visualization of exciton transport in ordered and disordered molecular solids

Temporal mapping of photochemical reactions and molecular excited states with carbon specificity

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