Photoexcitation spectroscopy of conducting-polymer–<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">C</mml:mi></mml:mrow><mml:mrow><mml:mn>60</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>composites: Photoinduced electron transfer

Smilowitz, Laura; Sariciftci, Niyazi Serdar; Wu, Richard L. C.; Gettinger, C. L.; Heeger, Alan J.; Wudl, Fred

doi:10.1103/physrevb.47.13835

Cited by 290 publications

(166 citation statements)

References 11 publications

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“…6,7 Such molecular relays have been designed for the directional electron transfer driven by appropriate energetic cascades, resulting in sequential charge separations and generating a long-lived, spatially separated charge separated states or 'radical pairs'. [8][9][10] On the other hand, reports of efficient photoinduced charge separation in solid state blend films of conjugated polymers with fullerenes 11,12 have attracted increasing interest due to their applicability to photovoltaic (PV) solar energy conversion. The intermixing of the polymer electron donor with the fullerene electron acceptor in such blended films (the formation of a 'bulk heterojunction') can result in a significant enhancement of photoinduced charge separation in such films relative to more conventional bilayered heterojunction devices.…”

Section: Introductionmentioning

confidence: 99%

Charge Carrier Formation in Polythiophene/Fullerene Blend Films Studied by Transient Absorption Spectroscopy

et al. 2008

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Abstract:We report herein a comparison of the photophysics of a series of polythiophenes with ionization potentials ranging from 4.8 to 5.6 eV as pristine films and when blended with 5 wt% 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]C 61 (PCBM). Three polymers are observed to give amorphous films, attributed to a non-planar geometry of their backbone whilst the other five polymers, including poly(3-hexylthiophene), give more crystalline films. Optical excitation of the pristine films of the amorphous polymers is observed by transient absorption spectroscopy to give rise to polymer triplet formation. For the more crystalline pristine polymers, no triplet formation is observed, but rather a short-lived (~ 100 ns), broad photoinduced absorption feature assigned to polymer polarons. For all polymers, the addition of 5 wt% PCBM resulted in 70 -90% quenching of polymer photoluminescence (PL), indicative of efficient quenching of polythiophene excitons. Remarkably, despite this efficient exciton quenching, the yield of dissociated polymer + and PCBM − polarons, assayed by the appearance of a long-lived, powerlaw decay phase assigned to bimolecular recombination of these polarons, was observed to vary by over two orders of magnitude depending upon the polymer employed. In addition to this power-law decay phase, the blend films exhibited short-lived decays assigned, for the amorphous polymers, to neutral triplet states generated by geminate recombination of bound radical pairs and, for the more crystalline polymers, to the direct observation of the geminate recombination of these bound radical pairs to ground. These observations are discussed in terms of a two-step kinetic model for charge generation in polythiophene/PCBM blend films analogous to that reported to explain the observation of exciplex-like emission in poly(p-phenylenevinylene)-based blend films. Remarkably, we find a excellent correlation between the free energy difference for charge separation (ΔG CS rel ) and yield of the long-lived charge generation yield, with efficient charge generation requiring a much larger ΔG CS rel than that required to achieve efficient PL 3 quenching. We suggest this observation is consistent with a model where the excess thermal energy of the initially formed polarons pairs is necessary to overcome their coulomb binding energy. This observation has important implications for synthetic strategies to optimize organic solar cell performance, as it implies that, at least devices based on polythiophene/PCBM blend films, a large ΔG CS rel (or LUMO level offset) is required to achieve efficient charge dissociation.4

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Section: Introductionmentioning

confidence: 99%

Charge Carrier Formation in Polythiophene/Fullerene Blend Films Studied by Transient Absorption Spectroscopy

et al. 2008

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“…Since the charge transfer rate is more than 1000 times faster than any competing process (the luminescence lifetime is greater than 300 ps), the quantum efficiency for charge separation approaches UNITY! Moreover, the charge-transferred state is metastable (Smilowitz et al, 1993;.…”

Section: Photoinduced Electron Transfermentioning

confidence: 99%

Nobel Lecture: Semiconducting and metallic polymers: The fourth generation of polymeric materials

2001

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“…x Donor/acceptor interfaces can be very efficient in separating excitons: in polymer:fullerene blends for example, the charge generation process takes place in the femtosecond time scale, while the reverse reaction, the charge recombination step, occurs in the microsecond range. 15 After exciton dissociation, a Coulomb interaction still exists between the charges located at either side of the donor-acceptor interface. 16 This interaction may assist (geminate) charge recombination.…”

Section: Exciton Dissociation (H Ed )mentioning

confidence: 99%

Nanoscale structure of solar cells based on pure conjugated polymer blends

Veenstra

Loos

Kroon

2007

Progress in Photovoltaics

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This paper gives an overview of the status of photovoltaic devices based on blends of semiconducting polymers. The polymer blends form the bulk heterojunction in these photovoltaic devices. The fundamental mechanisms governing the performance of these devices are discussed as well as the specificities of these all-polymer solar cells. The morphology of the polymer blend layer is expected to influence the device performance of these bulk heterojunctions. An overview is presented of factors that influence the morphology of the active layer of polymer blend photovoltaic devices together with a summary of tools available to study the structure of this layer. An advanced electron microscopy technique is applied to study the morphology of polymer blends of MDMO-PPV and PCNEPV with differing molecular weights. It is shown that the molecular weight of the polymer influences the typical domain size from $200 nm down to less than 5 nm in these bulk heterojunction PV devices. No strong relation is observed between the typical length scale of the phase separated domains and the measured external quantum efficiency, indicating that the phases are intermixed.

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Photoexcitation spectroscopy of conducting-polymer–C60composites: Photoinduced electron transfer

Cited by 290 publications

References 11 publications

Charge Carrier Formation in Polythiophene/Fullerene Blend Films Studied by Transient Absorption Spectroscopy

Charge Carrier Formation in Polythiophene/Fullerene Blend Films Studied by Transient Absorption Spectroscopy

Nobel Lecture: Semiconducting and metallic polymers: The fourth generation of polymeric materials

Nanoscale structure of solar cells based on pure conjugated polymer blends

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