Exciton diffusion and dissociation in conjugated polymer/fullerene blends and heterostructures

Haugeneder, A.; Neges, M.; Kallinger, C.; Spirkl, W.; Lemmer, Uli; Feldmann, Jochen; Scherf, Ullrich; Harth, Eva; Gügel, Andreas; Müllen, Kläus

doi:10.1103/physrevb.59.15346

Cited by 377 publications

(318 citation statements)

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“…[10][11][12][13][14][15][16][17] When the polymer thickness is decreased to the order of the exciton diffusion length, the PL decay times in such a polymer-quencher heterostructure become shorter than those in the relatively thick films. The exciton diffusion length can then be estimated by modeling the thickness dependence of the PL decay process.…”

Section: Introductionmentioning

confidence: 99%

Exciton Quenching Close to Polymer−Vacuum Interface of Spin-Coated Films of Poly(p-phenylenevinylene) Derivative

et al. 2009

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Polymer-fullerene bilayer heterostructures are suited to study excitonic processes in conjugated polymers. Excitons are efficiently quenched at the polymer-fullerene interface, whereas the polymer-vacuum interface is often considered as an exciton-reflecting interface. Here, we report about efficient exciton quenching close to the polymer-vacuum interface of spin-coated MDMO-PPV (poly[2-methoxy-5-(2′-ethyl-hexyloxy)-pphenylenevinylene]) films. The quenching efficiency is estimated to be as high as that of the polymer-fullerene interface. This efficient quenching is consistent with enhanced intermolecular interactions close to the polymer-vacuum interface due to the formation of a "skin layer" during the spin-coating procedure. In the skin layer, the polymer density is higher; that is, the intermolecular distances are shorter than in the rest of the film. The effect of exciton quenching at the polymer-vacuum interface should be taken into account when the thickness of the polymer film is on the order of the exciton diffusion length; in particular, in the determination of the exciton diffusion length.

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Section: Introductionmentioning

confidence: 99%

Exciton Quenching Close to Polymer−Vacuum Interface of Spin-Coated Films of Poly(p-phenylenevinylene) Derivative

et al. 2009

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“…In this context we emphasize that for all OLED applications polarons will move much faster since they are accelerated by an external electric field. However, for the theoretically calculated SE size RϷ2 nm, 50 51 and it demonstrates that the SE's are indeed more mobile than polarons. Therefore one would expect the PLDMR signal to increase with T as well since the interaction of polarons and SE increases.…”

Section: Edϭkt ͑19͒mentioning

confidence: 99%

Interaction of singlet excitons with polarons in wide band-gap organic semiconductors: A quantitative study

et al. 2001

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The steady-state photoinduced absorption ͑PA͒, photoluminescence ͑PL͒, PL-detected magnetic resonance ͑PLDMR͒, and PA-detected magnetic resonance ͑PADMR͒ of poly-and oligo-͑para-phenylenes͒ films is described. In particular, the excitation density ͑laser power͒ N 0 dependence of the PA, PL, and PLDMR signals is analyzed by means of a rate equation model, which describes the dynamics of singlet excitons ͑SE's͒ and polarons in all three experiments quantitatively with the same set of parameters. The model is based on the observations that mobile SE's are quenched by trapped and free polarons and that the spin-1 2 magnetic resonance conditions reduce the total polaron population. Since the sublinear N 0 dependences of the positive ͑PL-enhancing͒ spin-1 2 PLDMR and the polaron PA band are essentially the same, we conclude that PLDMR is due to a reduced quenching of SE's by polarons. The agreement between the model, the current results, and results from other spectroscopic techniques provides strong evidence for this quenching mechanism. This also suggests that it is a very significant process in luminescent -conjugated materials and organic light-emitting devices. Consequently, the quenching mechanism needs to be taken into account, especially at high excitation densities, which is of great importance for the development of electrically pumped polymer laser diode structures.

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“…[2][3][4][5] Upon photoexcitation of an electron-hole pair, the transfer of electrons from the polymer onto the fullerene leads to an efficient separation of charges that prevents luminescent recombination and is required in photovoltaic devices. Since the charge transfer can only occur if the photoexcitation on the polymer is within less than 10 nm of a C 60 molecule, [6][7][8] close proximity of polymer and fullerene is essential for efficient charge separation. One approach for achieving such close proximity of the electron donor and acceptor materials is by creating a bulk heterojunction.…”

Section: Introductionmentioning

confidence: 99%

Thickness dependence,in situmeasurements, and morphology of thermally controlled interdiffusion in polymer-C60photovoltaic devices

2004

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A series of detailed studies is presented in which heat-induced interdiffusion is used to create a gradient bulk-heterojunction of 2-methoxy-5-(2Ј-ethylhexyloxy͒-1,4-phenylenevinylene ͑MEH-PPV͒ copolymer and C 60 . Starting from a bilayer of spin-cast MEH-PPV and sublimed C 60 , films are heated in the vicinity of the glass transition temperature of the polymer to induce an interdiffusion of polymer and fullerene. Variation of the polymer layer thickness shows that the photocurrents increase with decreasing layer thickness within the examined thickness regime as transport of the separated charges out of the film is improved. The interdiffusion was observed in situ by monitoring the photocurrents during the heating process and exhibited a rapid rise during the first five minutes. Cross-sectional transmission electron microscopy studies show that C 60 forms clusters of up to 30 nm in diameter in the polymer bulk of the interdiffused devices. This clustering of the fullerene molecules puts a significant constraint on the interdiffusion process that can be alleviated by use of donor-acceptor combinations with better miscibility.

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Exciton diffusion and dissociation in conjugated polymer/fullerene blends and heterostructures

Cited by 377 publications

References 21 publications

Exciton Quenching Close to Polymer−Vacuum Interface of Spin-Coated Films of Poly(p-phenylenevinylene) Derivative

Exciton Quenching Close to Polymer−Vacuum Interface of Spin-Coated Films of Poly(p-phenylenevinylene) Derivative

Interaction of singlet excitons with polarons in wide band-gap organic semiconductors: A quantitative study

Thickness dependence,in situmeasurements, and morphology of thermally controlled interdiffusion in polymer-C60photovoltaic devices

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