Photovoltaic properties and exciplex emission of polyphenylenevinylene-based blend solar cells

Yin, Chunhong; Kietzke, Thomas; Neher, Dieter; Hörhold, Hans‐Heinrich

doi:10.1063/1.2710474

Cited by 90 publications

(108 citation statements)

References 16 publications

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“…Independently from each other, Offermans et al and Morteani et al found evidence for the formation of exciplex states at polymer:polymer interfaces. 17,18 Their findings were recently confirmed by Yin et al 19 The importance of the exciplex decay channel strongly depends on the details of the state diagram and the rate constants of the transitions between these states. From these studies, [17][18][19] it is concluded that the generation of free charges is field and temperature dependent and competes with exciplex decay (via exciplex emission and/or population of the lowest T 1 state of the polymers).…”

Section: Exciton Dissociation (H Ed )supporting

confidence: 63%

“…Yin et al compared polymer bilayer and polymer blend devices (using M3EH-PPV or MEH-M3EH-PPV as donor and CN-ether-PPV as acceptor polymer). 19 They concluded that the photocurrent in polymer blend devices is mainly determined by charge carrier generation rather than by charge carrier recombination. One can speculate that the picture that may emerge from the above mentioned optical and transport measurements is one where the dissociation of the exciton mainly determines the quantum efficiency of the polymer blend PV device.…”

Section: Charge Collection (H CC )mentioning

confidence: 99%

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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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Section: Exciton Dissociation (H Ed )supporting

confidence: 63%

Section: Charge Collection (H CC )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 correlation is consistent with a recent study of PPV-based polymer/polymer blends, which observed as inverse correlation between exciplex-like emission (indicative of significant geminate recombination), and PV device efficiency. 32 We note that our studies of device performance for this polymer series are relatively limited, and that other factors (blend composition, annealing, electric fields from the electrodes) are also likely to impact significantly upon device performance (see for example Ref 89). It has for example been shown that the application of electric fields can assist the dissociation of analogous, luminescence BRPs (referred to therein as 'exciplex') in polymer/polymer blend films.…”

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

confidence: 99%

“…36 In particular, in a study employing three different PPV-based polymers, an inverse correlation was observed between this exciplex-like emission strength and PV device performance. 32 However, a clear understanding of the parameters determining the efficiency of charge dissociation versus geminate recombination in organic blend films is yet to be established. Moreover such studies have not previously focused on polythiophene materials, the polymer class currently attracting the greatest interest for efficient organic PV cells.…”

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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“…However, electron-hole ͑e-h͒ pairs generated in this way are still strongly bound by Coulomb interaction and need to be dissociated into free carriers in order to be collected at the electrodes. 1,2 The occurrence of such an interfacial geminate charge pair has been spectroscopically observed for polymer:polymer systems 3,4 and recently also for polymer:fullerene blends. 5 In addition, a strong indication for the existence of a bound e-h pair in polymer:fullerene blends is the field and temperature dependence of the photocurrent at reverse bias.…”

Section: Introductionmentioning

confidence: 99%

Charge dissociation in polymer:fullerene bulk heterojunction solar cells with enhanced permittivity

Lenes

Kooistra

Hummelen

et al. 2008

Journal of Applied Physics

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Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. The dissociation efficiency of bound electron-hole pairs at the donor-acceptor interface in bulk heterojunction solar cells is partly limited due to the low dielectric constant of the polymer:fullerene blend. We investigate the photocurrent generation in blends consisting of a fullerene derivative and an oligo͑oxyethylene͒ substituted poly͑p-phenylene vinylene͒ ͑PPV͒ derivative with an enhanced relative permittivity of 4. It is demonstrated that in spite of the relatively low hole mobility of the glycol substituted PPV the increase in the spatially averaged permittivity leads to an enhanced charge dissociation of 72% for these polymer:fullerene blends.

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Photovoltaic properties and exciplex emission of polyphenylenevinylene-based blend solar cells

Cited by 90 publications

References 16 publications

Nanoscale structure of solar cells based on pure conjugated polymer blends

Nanoscale structure of solar cells based on pure conjugated polymer blends

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

Charge dissociation in polymer:fullerene bulk heterojunction solar cells with enhanced permittivity

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