Exciplex dynamics in a blend of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>π</mml:mi></mml:math>-conjugated polymers with electron donating and accepting properties: MDMO-PPV and PCNEPV

Offermans, Ton; Hal, PA Paul van; Meskers, Stefan C. J.; Koetse, Marc M.; Janssen, Raj René

doi:10.1103/physrevb.72.045213

Cited by 139 publications

(100 citation statements)

References 46 publications

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“…29,35 Such 'intermediate' charge transfer (CT) states have also recently been reported in a photophysical study of small bandgap co-polymer blended with PCBM. 68 As we have discussed previously, 37 our observation of triplet exciton formation in the presence of quenching of singlet exciton, provides strong evidence for the relevance of this model to polythiophene/PCBM blend films.…”

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confidence: 68%

“…Previous studies of PPV and polyfluorene-based donor/acceptor blends 29,35,36,86,87 have reported significant red-shifted exciplex-like emission and CT absorption, suggesting that the BRP states observed in these systems are radiatively coupled to the ground state. A sub-band gap absorption has also been reported for P3HT/PCBM blend films by Fourier-transform photocurrent spectroscopy.…”

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confidence: 91%

“…29,35 In photosynthetic reaction centers, the back electron transfer produces a triplet state with an unusual spin polarization showing the charge recombination within a weakly coupled, spin-correlated radical ion pair. 78,82 In D-A molecules, a triplet formation is observed following the back electron transfer.…”

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confidence: 99%

“…[28][29][30] Such blend films have been shown to give PV devices, although with more modest solar energy conversion efficiencies than polythiophenebased devices. In PPV-based polymer/polymer blend films, charge photogeneration has been described as a two-step process.…”

Section: Introductionmentioning

confidence: 99%

“…9, 10 For the PPV-based polymer/polymer blends, this BRP state has been shown to exhibit a red-shifted emission band, [29][30][31][32] analogous to the emission of donor/acceptor excited state complexes or 'exciplexes'. 33,34 This BRP state can undergo rapid intersystem crossing between its singlet and triplet states.…”

Section: Introductionmentioning

confidence: 99%

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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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confidence: 68%

Section: -----<<< Scheme 1 >>>-----mentioning

confidence: 91%

Section: -----<<< Scheme 1 >>>-----mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2008

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Charge Transfer and Charge Separation in Conjugated Polymer Solar Cells

Howard

Abrusci²,

Friend³

et al. 2010

Nanostructured Conductive Polymers

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Spin Correlations in Organic Light‐Emitting Diodes

Walter

Lupton

2007

Highly Efficient OLEDs With Phosphorescent Materials

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A particular characteristic of organic materials used in light -emitting diodes is that they are predominantly composed of carbon and therefore only exhibit a very weak spin -orbit coupling. Electrically injected electrons and holes each carry spin 1/2 so that recombination can occur in a total of four spin combinations. It is an important question whether interconversion between the spin states can occur during electrostatic carrier capture prior to the formation of the ultimate excited state on the individual molecule, the singlet or the triplet exciton. Conjugated polymers containing minute quantities of spin -orbit enhancing heavy metal atoms open a unique window to spin dynamics in organic light -emitting diodes by enabling optically or electrically generated triplets to decay radiatively without impacting dramatically on the actual generation mechanism of triplets through excited state intersystem crossing. We show that optically generated singlet excitons can be electrically stabilized to prevent recombination. Storage of the charge carrier pair for tens of microseconds does not reveal a preference for delayed recombination in the lower energy triplet channel, suggesting that spin conversion in the charge carrier pair precursor state to exciton formation is rather ineffi cient. The message of this basic study of spin -lattice relaxation in excited states of organic fi lms to device engineers is that correlations between the spins of electrostatically bound carrier pairs are intrinsically remarkably stable. In the absence of a strong external mixing channel such as a heavy metal atom as in organometallic dopants it is expected that the dominant recombination in an organic lightemitting diode occurs in nonradiative triplets, forming a serious loss channel in actual devices. IntroductionThe most signifi cant difference between organic, carbon -based semiconductors and inorganic crystalline materials lies in the properties of the electron spin and the exchange interaction. Due to the low atomic order number of carbon, spin is 99 Highly Effi cient OLEDs with Phosphorescent Materials. Edited by H. Yersin

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Exciplex dynamics in a blend ofπ-conjugated polymers with electron donating and accepting properties: MDMO-PPV and PCNEPV

Cited by 139 publications

References 46 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

Charge Transfer and Charge Separation in Conjugated Polymer Solar Cells

Spin Correlations in Organic Light‐Emitting Diodes

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