A Shift from Diffusion Assisted to Energy Transfer Controlled Fluorescence Quenching in Polymer–Fullerene Photovoltaic Blends

Ward, Alexander J.; Ruseckas, Arvydas; Samuel, Ifor D. W.

doi:10.1021/jp307538y

Cited by 45 publications

(90 citation statements)

References 34 publications

(78 reference statements)

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“…The critical length scale of 10 nm we found here is actually the convolution among the exciton diffusion, the molecular inter-diffusion and the average distance which allow for electronic energy transfer at the interface. Finally we note that Ward et al15 have recently shown a possible energy transfer pathway from copolymers such as PCDTDBT to PCBM. Thus, the process we highlight here is not necessarily specific to P3HT/PCBM, but it may be considered as an unavoidable paradigm for the concept of organic photovoltaic.…”

Section: Discussionmentioning

confidence: 63%

“…The suggested picture is that close pairs undergo charge transfer, while distant pairs may first interact by energy transfer. Förster radius, the measure of the electronic coupling strength between D and A, has been evaluated for the prototypical systems such as P3HT/PCBM in the range between 1 and 5 nm111315. Why electronic excitation energy transfer appears only in special situations and why charge transfer overwhelms it in BHJ, remains an open question.…”

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confidence: 99%

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Ultrafast Energy Transfer in Ultrathin Organic Donor/Acceptor Blend

Kandada

Grancini

Petrozza

et al. 2013

Sci Rep

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It is common knowledge that poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend, a prototype system for bulk heterojunction (BHJ) solar cells, consists of a network of tens of nanometers-large donor-rich and acceptor-rich phases separated by extended finely intermixed border regions where PCBM diffuse into P3HT. Here we specifically address the photo-induced dynamics in a 10 nm thin P3HT/PCBM blend that consists of the intermixed region only. Using the multi-pass transient absorption technique (TrAMP) that enables us to perform ultra high sensitive measurements, we find that the primary process upon photoexcitation is ultrafast energy transfer from P3HT to PCBM. The expected charge separation due to hole transfer from PCBM to P3HT occurs in the 100 ps timescale. The derived picture is much different from the accepted view of ultra-fast electron transfer at the polymer/PCBM interface and provides new directions for the development of efficient devices.

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Section: Discussionmentioning

confidence: 63%

mentioning

confidence: 99%

Ultrafast Energy Transfer in Ultrathin Organic Donor/Acceptor Blend

Kandada

Grancini

Petrozza

et al. 2013

Sci Rep

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“…[12] Substrates with tethered C60 used for other fluorescence quenching experiments were prepared as described previously. [17] Measurements: The absorbance spectra of the films were measured using a Varian Cary …”

Section: Methodsmentioning

confidence: 99%

“…Figure 1 P3OT films with Mn=13500 gmol -1 . We also performed a similar surface quenching experiment using tethered C60 as a quencher [17] and obtained D values which were two times bigger. These results are given in Supporting Information (SI) in Figure S1.…”

Section: Surface Quenching Of Fluorescencementioning

confidence: 96%

Molecular Weight Dependence of Exciton Diffusion in Poly(3‐hexylthiophene)

Masri

Ruseckas

Emelianova

et al. 2013

Advanced Energy Materials

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We present a joint experimental and theoretical study of singlet exciton diffusion in spincoated P3HT films and its dependence on molecular weight. The results show that exciton diffusion is fast along the co-facial π-π aggregates of polymer chromophores and about 100 times slower in the lateral direction between aggregates. Exciton hopping between aggregates is found to show a subtle dependence on interchain coupling, aggregate size and Boltzmann statistics. Also a clear correlation is observed between the effective exciton diffusion coefficient, the degree of aggregation of chromophores and exciton delocalisation along the polymer chain, which suggests that exciton diffusion length can be enhanced by tailored synthesis and processing conditions. Submitted to 2

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“…This photoluminescence quenching has been most extensively studied for P3HT, which has PLQ, and therefore exciton dissociation yields, sensitive to changes in film morphology, e.g. thermal annealing which increases phase segregation in the P3HT / PCBM blends.79,97,144 In general polymer photoluminescence quenching following blending with PCBM can derive from either electron or energy transfer to PCBM 67,145,…”

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confidence: 99%

Materials Design Considerations for Charge Generation in Organic Solar Cells

2013

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This perspective reviews some of our recent progress on materials design guidelines for photoinduced charge generation in bulk-heterojunction organic solar cells. Over the last 7 years, our group has employed transient absorption measurement to determine the relative quantum yields of long-lived polaron pairs for over 300 different organic Donor / Acceptor blend films. We have shown that this optical assay of charge separation can be a strong indicator of photocurrent generation efficiency in complete devices. In this perspective we consider the lessons which can be drawn from these studies concerning the parameters which determine efficiency of this photo-induced charge separation in such solar cells. We consistently find, from studies of several materials series, that the energy offset driving charge separation is a key determinant of the efficiency of this charge generation, and thereby photocurrent generation. Moreover, we find that the magnitude of the energy offset required to drive charge separation, and the strength of this energetic dependence, varies substantially between materials classes. In particular, co-polymers such as diketopyrrolopyrrole-and thiazolothiazole-based polymers are found to be capable of driving charge separation in blends with PCBM at much lower energy offsets than polythiophenes, such as P3HT, whilst replacement of PCBM with more crystalline perylene diimide acceptors is also observed to reduce the energy offset requirement for charge separation. We go on to discuss the role of film microstructure in also determining the efficiency of charge separation, including the role of mixed and pure domains, PCBM exciton diffusion limitations and the role of material crystallinity in modulating material energetics, thereby providing additional energy offsets which can stabilise the spatial separation of charges. Other factors considered include the role of coulombically bound polaron pair or charge transfer states, device electric fields, charge carrier mobilities, triplet excitons and photon energy. We discuss briefly a model for charge separation consistent with these and other observations. We conclude by summarising the materials design guidelines for efficient charge photogeneration which can be drawn from these studies.

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A Shift from Diffusion Assisted to Energy Transfer Controlled Fluorescence Quenching in Polymer–Fullerene Photovoltaic Blends

Cited by 45 publications

References 34 publications

Ultrafast Energy Transfer in Ultrathin Organic Donor/Acceptor Blend

Ultrafast Energy Transfer in Ultrathin Organic Donor/Acceptor Blend

Molecular Weight Dependence of Exciton Diffusion in Poly(3‐hexylthiophene)

Materials Design Considerations for Charge Generation in Organic Solar Cells

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