Mechanism of gain narrowing in conjugated polymer thin films

Haugeneder, A.; Hilmer, Martin; Kallinger, C.; Perner, M.; Spirkl, W.; Lemmer, Uli; Feldmann, Jochen; Scherf, Ullrich

doi:10.1007/s003400050406

Cited by 35 publications

(26 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…40,41,[43][44][45][48][49][50] The increasing SE decay rate with increasing excitation density also resembles that expected from amplified spontaneous emission. 69,71,73 The data presented here, however, used excitation fluences nearly 2 orders of magnitude lower than those previously reported for the observation of line narrowing in MEH-PPV films. 51,57 In addition, measurements of the PL using the same excitation pulses as for the pump-probe experiments showed no signs of line narrowing.…”

Section: Role Of Film Morphology In Exciton-exciton Annihilationmentioning

confidence: 75%

“…This also could explain why the reported bimolecular recombination coefficients in different studies vary by nearly an order of magnitude. 43,48,49,71 Studies on polymers with different side groups or on films prepared in different ways will have differing degrees of interchain interaction and, hence, different probabilities for bimolecular interaction. Quantifying the difference in E-EA between MEH-PPV films cast from different solvents requires the use of a kinetic model.…”

Section: Role Of Film Morphology In Exciton-exciton Annihilationmentioning

confidence: 99%

See 1 more Smart Citation

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

et al. 1999

View full text Add to dashboard Cite

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.

show abstract

Section: Role Of Film Morphology In Exciton-exciton Annihilationmentioning

confidence: 75%

Section: Role Of Film Morphology In Exciton-exciton Annihilationmentioning

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

View full text Add to dashboard Cite

show abstract

“…Figure. 11 shows the results of our experiments using a 800 nm spin-coated film of LPPP [32]. At an excitation pulse energy of about 10 nJ the spectrum changes its shape.…”

Section: Figurementioning

confidence: 96%

“…Direct evidence for amplified spontaneous emission being the underlying process of spectrally narrow emission in conjugated polymer films was given in recent time-resolved emission experiments [32]. After excitation with an ultrashort light pulse the temporal decay of the emission in the limit of low excitation densities is determined by a super-FIGURE 10.…”

Section: Reference Materials Excitation Conditionsmentioning

confidence: 98%

Stimulated emission and lasing in conjugated polymers

Lemmer

1998

Polym. Adv. Technol.

Self Cite

View full text Add to dashboard Cite

“…mLPPP is an attractive -conjugated polymer for blue-light emitting diodes 9,10 ͑see Fig. 1͒ and photopumped lasers 11,12 due to its high photoluminescence quantum yield; this is caused in part, by the intrachain order in the film induced by the planarization of neighboring phenyl rings 13 ͑Fig. 1 inset͒.…”

Section: Introductionmentioning

confidence: 99%

Photogeneration and recombination processes of neutral and charged excitations in films of a ladder-type poly(para-phenylene)

et al. 1999

View full text Add to dashboard Cite

We introduce a version of the cw photomodulation technique, measured far from the steady state, for obtaining the quantum efficiency, , of long-lived photoexcitations in -conjugated polymers. We apply this technique to films of a ladder-type poly͑para-phenylene͒ ͓mLPPP͔ for studying the photogeneration action spectra, (E), and recombination kinetics of photogenerated neutral and charged excitations such as singlet and triplet excitons and charged polarons. Whereas the (E) spectrum for singlet excitons shows a step function increase at a photon energy, E, close to the optical gap (Ӎ2.6 eV), both triplet and polaron (E) spectra show, in addition, a monotonous rise at higher E. The rise for triplets is explained by singlet exciton fission into triplet pairs, and from a model fit we get the triplet exciton energy (Ӎ1.6 eV). For polarons this rise is modeled by an electron intersegment tunneling process. The electroabsorption spectrum is also measured and analyzed in terms of Stark shift of the lowest lying exciton, 1B u , and enhanced oscillator strength of the important mA g exciton. A consistent picture for the lowest excited state energy levels and optical transitions in the neutral ͑singlet and triplet͒ and charged manifolds is presented. From both the exciton binding energy of Ӎ0.6 eV and the singlet-triplet energy splitting of Ӎ1 eV, we conclude that the e-e interaction in mLPPP is relatively strong. Our results are in good agreement with recent ab initio band structure calculations for several -conjugated polymers. ͓S0163-1829͑99͒13531-8͔

show abstract

Mechanism of gain narrowing in conjugated polymer thin films

Cited by 35 publications

References 0 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

Stimulated emission and lasing in conjugated polymers

Photogeneration and recombination processes of neutral and charged excitations in films of a ladder-type poly(para-phenylene)

Contact Info

Product

Resources

About