Factors Influencing Stimulated Emission from Poly(<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">p</mml:mi></mml:math>-phenylenevinylene)

Denton, G. J.; Tessler, Nir; Harrison, N. T.; Friend, Richard H.

doi:10.1103/physrevlett.78.733

Cited by 126 publications

(89 citation statements)

References 26 publications

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“…Indeed, once out of the linear regime, the magnitude of polymer fluorescence appears to scale as the square root of the input intensity, a result consistent with bimolecular recombination. 43,49 Fits to simple kinetic models that include a bimolecular recombination term are consistent with the excitation intensity dependence of both the decay time of the luminescence and the loss in quantum yield using a single set of parameters. 48,49 Similar results have also been obtained for polyfluorene copolymers.…”

Section: Introductionmentioning

confidence: 99%

“…43,49 Fits to simple kinetic models that include a bimolecular recombination term are consistent with the excitation intensity dependence of both the decay time of the luminescence and the loss in quantum yield using a single set of parameters. 48,49 Similar results have also been obtained for polyfluorene copolymers. 50 The species produced following the biexcitonic interaction is what McBranch and co-workers [40][41][42] and Denton et al 43 believe to be responsible for the intensitydependent PA.…”

Section: Introductionmentioning

confidence: 99%

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Controlling Interchain Interactions in Conjugated Polymers: The Effects of Chain Morphology on Exciton−Exciton Annihilation and Aggregation in MEH−PPV Films

et al. 1999

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The presence of interchain species in the photophysics of conjugated polymer films has been the subject of a great deal of controversy. In this paper, we present strong evidence that interchain species do form in conjugated polymer films, and that the degree of interchain interactions can be controlled by varying the solvent and polymer concentration of the solution from which the films are cast. Thus, much of the controversy in the literature can be resolved by noting that the polymer samples in different studies had different side groups or were prepared in different ways and thus have different degrees of interchain interaction. The photoluminescence (PL) of poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene), MEH-PPV, changes both its spectral shape and quantum yield when the films are prepared from different solutions or when the morphology is varied by annealing. Increasing the amount of interchain interactions enhances the red portion of the film's PL, a result assigned to a combination of changes in the vibronic structure of the PL of the exciton and increased numbers of weakly emissive interchain species. Photoluminescence excitation spectroscopy shows that excitation to the red edge of the absorption band preferentially enhances the red emission, suggesting that the interchain species are aggregates with a distinct ground state absorption. Scanning force microscopy shows topographic features that correlate with the degree of interchain interactions, verifying that the morphology of conjugated polymer films changes with polymer concentration, choice of solvent, and spin-casting speed. Even at low excitation intensities, photooxidative damage occurs quickly in MEH-PPV films excited in air, and the rate at which damage occurs is sensitive to the packing of the polymer chains. For samples under vacuum at low excitation intensity, a long-lived emissive tail, in combination with excitedstate absorption dynamics that do not match those of the emissive species, provide direct evidence for the production of interchain aggregates. Annealing an MEH-PPV film produces a photophysical signature similar to photooxidation, implying that defects in conjugated polymer films are intrinsic and depend on the details of how the chains are packed. At higher excitation intensities, we find that exciton-exciton annihilation occurs, and that the probability for annihilation can vary by an order of magnitude depending on the degree of interchain contact in the film. Finally, we show that changing the film morphology has a direct effect on the performance of MEH-PPV-based light-emitting diodes. Higher degrees of interchain interaction enhance the mobility of carriers at the expense of lower quantum efficiencies for electroluminescence. Taken together, the results reconcile much of the contradictory literature and provide a prescription for the optimization of conjugated polymer films for particular device applications.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Controlling Interchain Interactions in Conjugated Polymers: The Effects of Chain Morphology on Exciton−Exciton Annihilation and Aggregation in MEH−PPV Films

et al. 1999

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“…2,3 In this picture, interband excitations directly generate free charges, which may relax to lower energy bound states. This strongly contrasts the exciton model, in which molecular excitons are formed upon photoexcitation, so that secondary processes such as exciton-exciton annihilation 4 or hot exciton dissociation 5,6 are required to generate free charges.…”

mentioning

confidence: 80%

“…2(b), calculated using a generation rate of ͑200 fs͒ −1 , 29 agrees better with the measured THz pulse in terms of the width, but the agreement in shape is slightly diminished. In any case, this analysis sets an upper limit for charge generation within 200 fs of photoexcitation, which is much faster than the diffusion time scales that would be required for charge generation by, for example, exciton-exciton annihilation 4 or cold exciton dissociation at defects. 30 Hence, another mechanism for rapid charge generation in semiconducting polymers must be operative.…”

Section: Fig 1 Electric Fields Radiated From (A)mentioning

confidence: 99%

Ultrafast charge generation in a semiconducting polymer studied withTHzemission spectroscopy

et al. 2004

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We study the ultrafast charge generation in a semiconducting polymer (MEH-PPV) by measuring the radiated THz field after photoexciting the biased polymer with a femtosecond visible pulse. The subpicosecond temporal characteristics of the emitted wave reflects the ultrafast photoconductivity dynamics and sets an upper limit for charge generation of 200 fs following photoexcitation, and reveals the dispersive nature of charge transport in MEH-PPV. A comparison of the fields radiated from MEH-PPV and the well-characterized model semiconductor system ͑GaAs͒ allows for an accurate estimate of the quantum efficiency for charge generation in the polymer, found to be less than 1%. Both observations are consistent with ultrafast charge generation in semiconducting polymers through hot exciton dissociation. Semiconducting conjugated polymers have recently received much interest owing to their potential in technological applications, particularly in electronics. 1 Despite this fact, the fundamentals of the photoexcitation physics in these materials have remained controversial: there is ongoing debate whether a band structure description is appropriate to these materials. 2,3 In this picture, interband excitations directly generate free charges, which may relax to lower energy bound states. This strongly contrasts the exciton model, in which molecular excitons are formed upon photoexcitation, so that secondary processes such as exciton-exciton annihilation 4 or hot exciton dissociation 5,6 are required to generate free charges.Although the observation of significant photoconductivity 7 demonstrates the presence of free charges, it is unclear whether carriers are generated directly on ultrafast time scales or produced on longer time scales through, for example, exciton-exciton annihilation. Unfortunately, conventional transient photoconductivity measurements 8,9 lack the resolution to resolve the ultrafast excitation process. Using time-domain THz spectroscopy, 10 we have recently shown that photoexcitation of the polymer poly(2-methoxy-5-(2Ј-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV) leads to the generation of charges within 300 fs. 11 Additional information about the time scale of charge carrier generation and nature of the transport can be obtained by probing the radiation dispersed by the accelerating charges. 12,13 When changes in photocurrent occur on (sub) picosecond time scales, THz radiation is emitted. The shape of the THz pulse is determined by the rise and decay of the photocurrent, and thus provides a direct probe of the ultrafast transient photoconductivity. In this manner, information regarding the rate of charge carrier generation and time-dependent mobility can be obtained. This technique is ideally suited to the study of charge generation and cooling on sub-picosecond time scales, and has been successfully applied to study the photoexcitation dynamics in materials such as low-temperature grown GaAs. 13 Previous measurements on semiconducting polymer systems have also proven useful, 12 but suffered from...

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“…Der Pfeil in a) und c) kennzeichnet jeweils die Richtung der Lasertätigkeit: ̈ a) Mikroresonatorstruktur, bei der sich die organische Schicht zwischen einem dielektrischen Spiegel und einer Metallschicht befindet [7]. ̈ b) Polymerblock in einem externen Resonator [10].…”

Section: Biegsame Laser Mit Verteilter Rückkopplungunclassified

Nanotechnologie: Laserlicht aus Polymeren: Plastik als Lasermedium ist biegsam, billig und praktisch

Lemmer¹,

Kallinger

Feldmann

2000

Phys. Bl.

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Die organische Optoelektronik basiert auf einer Klasse neuartiger Materialien: „Plastik”︁ mit den elektronischen und optischen Eigenschaften von Halbleitern. Großflächige Leuchtdioden aus organischen Materialien halten zurzeit Einzug in verschiedene Bereiche der Bildschirmtechnologie. In den hierbei verwendeten dünnen organischen Schichten konnte nun auch optische Verstärkung und Lasertätigkeit nachgewiesen werden (Abb. 1). In diesem Artikel diskutieren wir die zugrunde liegende Photophysik und geben eine Übersicht über die bereits erzielten Erfolge auf dem Weg zu neuartigen organischen Laserbauelementen.

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Factors Influencing Stimulated Emission from Poly(p-phenylenevinylene)

Cited by 126 publications

References 26 publications

Controlling Interchain Interactions in Conjugated Polymers: The Effects of Chain Morphology on Exciton−Exciton Annihilation and Aggregation in MEH−PPV Films

Controlling Interchain Interactions in Conjugated Polymers: The Effects of Chain Morphology on Exciton−Exciton Annihilation and Aggregation in MEH−PPV Films

Ultrafast charge generation in a semiconducting polymer studied withTHzemission spectroscopy

Nanotechnologie: Laserlicht aus Polymeren: Plastik als Lasermedium ist biegsam, billig und praktisch

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