Electronic and Vibrational Coherences in Resonance Energy Transfer along MEH-PPV Chains at Room Temperature

Collini, Elisabetta; Scholes, Gregory D.

doi:10.1021/jp810757x

Cited by 114 publications

(138 citation statements)

References 223 publications

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“…6,7,48 We will show in an upcoming paper 49 that this unusually high PL quenching of thick P3HT films by thin PCBM overlayers results from a novel long-range exciton quenching mechanism. 50,51 The green triangles in Figure 5 show that upon thermal annealing, the PL intensity from P3HT/PCBM bilayers undergoes a slight increase, indicating a decrease in exciton quenching efficiency. This result is in direct contrast to the work of Drees et al, who observed that thermal annealing led to increased quenching of the PL from interdiffused blends of a poly(phenylene vinylene) derivative and C 60 .…”

Section: Resultsmentioning

confidence: 99%

Reappraising the Need for Bulk Heterojunctions in Polymer−Fullerene Photovoltaics: The Role of Carrier Transport in All-Solution-Processed P3HT/PCBM Bilayer Solar Cells

et al. 2009

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The most efficient organic solar cells produced to date are bulk heterojunction (BHJ) photovoltaic devices based on blends of semiconducting polymers such as poly(3-hexylthiophene-2,5-diyl) (P3HT) with fullerene derivatives such as [6,6]-penyl-C 61 -butyric-acid-methyl-ester (PCBM). The need for blending the two components is based on the idea that the exciton diffusion length in polymers like P3HT is only ∼10 nm, so that the polymer and fullerene components must be mixed on this length scale to efficiently split the excitons into charge carriers. In this paper, we show that the BHJ geometry is not necessary for high efficiency, and that all-solution-processed P3HT/PCBM bilayer solar cells can be nearly as efficient as BHJ solar cells fabricated from the same materials. We demonstrate that o-dichlorobenzene (ODCB) and dichloromethane serve nicely as a pair of orthogonal solvents from which sequential layers of P3HT and PCBM, respectively, can be spin-cast. Atomic force microscopy, various optical spectroscopies, and electron microscopy all demonstrate that the act of spin-coating the PCBM overlayer does not affect the morphology of the P3HT underlayer, so that our spin-cast P3HT/PCBM bilayers have a well-defined planar interface. Our fluorescence quenching experiments find that there is still significant exciton splitting in P3HT/PCBM bilayers even when the P3HT layer is quite thick. When we fabricated photovoltaic devices from these bilayers, we obtained photovoltaic power conversion efficiencies in excess of 3.5%. Part of the reason for this high efficiency is that we were able to separately optimize the roles of each component of the bilayer; for example, we found that thermal annealing has relatively little effect on the nature of P3HT layers spin-cast from ODCB, but that it significantly increases the crystallinity and thus the mobility of electrons through PCBM. Because the carriers in bilayer devices are generated at the planar P3HT/PCBM interface, we also were able to systematically vary the distance the carriers have to travel to be extracted at the electrodes by changing the layer thicknesses without altering the bulk mobility of either component or the nature of the interfaces. We found that devices have the best fill-factors when the transit times of electrons and holes through the two layers are roughly balanced. In particular, we found that the most efficient devices are made with P3HT layers that are about four times thicker than the PCBM layers, demonstrating that it is the conduction and the extraction of electrons through the fullerene that ultimately limit the performance of both bilayer and BHJ devices based on the P3HT/ PCBM material combination. Overall, we believe that polymer-fullerene bilayers provide several advantages over BHJ devices, including reduced carrier recombination and a much better degree of control over the properties of the individual components and interfaces during device fabrication.

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Section: Resultsmentioning

confidence: 99%

Reappraising the Need for Bulk Heterojunctions in Polymer−Fullerene Photovoltaics: The Role of Carrier Transport in All-Solution-Processed P3HT/PCBM Bilayer Solar Cells

et al. 2009

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“…Transient anisotropy decay directly probes the orientational dynamics of transition dipole moments in a system consisting of multiple chromophores and has been used in the analysis of the lifetimes of coherent energy transfer and associated quantum coherence [70][71][72][73][74][75][76]. Following Ref.…”

Section: F Anisotropy Decaymentioning

confidence: 99%

Theoretical characterization of excitation energy transfer in chlorosome light-harvesting antennae from green sulfur bacteria

et al. 2014

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We present a theoretical study of excitation dynamics in the chlorosome antenna complex of green photosynthetic bacteria based on a recently proposed model for the molecular assembly. Our model for the excitation energy transfer (EET) throughout the antenna combines a stochastic time propagation of the excitonic wave function with molecular dynamics simulations of the supramolecular structure, and electronic structure calculations of the excited states. We characterized the optical properties of the chlorosome with absorption, circular dichroism and fluorescence polarization anisotropy decay spectra. The simulation results for the excitation dynamics reveal a detailed picture of the EET in the chlorosome. Coherent energy transfer is significant only for the first 50 fs after the initial excitation, and the wavelike motion of the exciton is completely damped at 100 fs. Characteristic time constants of incoherent energy transfer, subsequently, vary from 1 ps to several tens of ps. We assign the time scales of the EET to specific physical processes by comparing our results with the data obtained from time-resolved spectroscopy experiments.

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“…In related areas of quantum transport, the intersite coherence was found to be of fundamental importance in electronic energy transfer in light harvesting complexes 28 and conjugated polymers. 29,30 It would be interesting if the intersite coherence can also be measured experimentally for charge carrier transport in organic materials.…”

Section: ͑8͒mentioning

confidence: 99%

“…Both the coherent and thermal assisted transport mechanisms are characterized within a unified theory, and the intersite coherence is found to have important implications for the charge carrier transport mechanism. The new method could also find wide applications in areas such as charge transport in DNA, 31 and exciton dynamics in conjugated polymers, 29,30 as well as many other problems mentioned in the introduction. …”

Section: ͑8͒mentioning

confidence: 99%

Communications: A nonperturbative quantum master equation approach to charge carrier transport in organic molecular crystals

Wang

Chen

Zheng

et al. 2010

The Journal of Chemical Physics

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We present a nonperturbative quantum master equation to investigate charge carrier transport in organic molecular crystals based on the Liouville space hierarchical equations of motion method, which extends the previous stochastic Liouville equation and generalized master equation methods to a full quantum treatment of the electron-phonon coupling. Diffusive motion of charge carriers in a one-dimensional model in the presence of nonlocal electron-phonon coupling was studied, and two different charge carrier diffusion mechanisms are observed for large and small average intermolecular couplings. The new method can also find applications in calculating spectra and energy transfer in various types of quantum aggregates where the perturbative treatments fail.

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Electronic and Vibrational Coherences in Resonance Energy Transfer along MEH-PPV Chains at Room Temperature

Cited by 114 publications

References 223 publications

Reappraising the Need for Bulk Heterojunctions in Polymer−Fullerene Photovoltaics: The Role of Carrier Transport in All-Solution-Processed P3HT/PCBM Bilayer Solar Cells

Reappraising the Need for Bulk Heterojunctions in Polymer−Fullerene Photovoltaics: The Role of Carrier Transport in All-Solution-Processed P3HT/PCBM Bilayer Solar Cells

Theoretical characterization of excitation energy transfer in chlorosome light-harvesting antennae from green sulfur bacteria

Communications: A nonperturbative quantum master equation approach to charge carrier transport in organic molecular crystals

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