Electric-field-induced luminescence quenching in an electroluminescent organic semiconductor

Tasch, S.; Kranzelbinder, G.; Leising, G.; Scherf, Ullrich

doi:10.1103/physrevb.55.5079

Cited by 87 publications

(72 citation statements)

References 29 publications

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“…21 Figure 1͑b͒ shows a (⌬T) MF spectrum obtained for a delay of 20 ps and an applied reverse bias of 16 V. We observe a transient decrease of SE ͓negative (⌬T/T) MF signal͔ and PA 1 ͓positive (⌬T/T) MF signal͔ that can be explained by field-induced dissociation of the singlet exciton population, similar to the effect under steady-state condition. [22][23][24][25] We emphasize that the correlated decrease of SE and PA 1 is a further indication for the assignment of PA 1 to singlet exciton transitions, whereas both PA 2 and PA 3 are increased by the applied field ͓negative (⌬T/T) MF signal͔, indicating a corresponding increase of polaron and triplet population. The normalized field-induced changes of the populations are plotted in Fig.…”

Section: B Electric Field-assisted Pump-probe Spectroscopymentioning

confidence: 99%

Ultrafast photogeneration mechanisms of triplet states inpara-hexaphenyl

et al. 1999

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We present femtosecond pump-probe measurements, both conventional and electric field-assisted, on organic light-emitting devices based on para-hexaphenyl. The dominant triplet exciton generation mechanism is assigned to nongeminate bimolecular recombination of photogenerated, spin-1 2 polarons. This process is active within a few hundred femtoseconds after photoexcitation and involves about 20% of the initially excited states. At higher photoexcitation densities, we observe an additional triplet generation mechanism, which occurs in the 10-ps time domain, due to fusion of singlet excitons and subsequent fission into correlated triplet pairs. The latter decay on the 10 2 -ps time scale by geminate recombination. ͓S0163-1829͑99͒01721-X͔

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Section: B Electric Field-assisted Pump-probe Spectroscopymentioning

confidence: 99%

Ultrafast photogeneration mechanisms of triplet states inpara-hexaphenyl

et al. 1999

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“…2 The interring bridges that are added to poly͑para-phenylene͒ ͑PPP͒ result in a planarization of neighboring phenyl rings, which increases the conjugation and therefore leads to a redshift of the electronic optical spectra. Due to the sidegroups attached to the backbone, excellent solubility is achieved in common organic solvents such as chloroform and toluene, a prerequisite for the preparation of highoptical quality films.…”

Section: Introductionmentioning

confidence: 99%

Localized triplet excitations and the effect of photo-oxidation in ladder-type poly(p-phenylene) and oligo(p-phenylene)

et al. 2000

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The photophysics of methyl-bridged poly͑para-phenylene͒-type ladder polymer ͑m-LPPP͒ and oligomer films and solutions is described and discussed. The spin sensitive properties, such as the formation and properties of polaron pairs and triplet excitons ͑TE's͒ were studied using X-band photoluminescence ͑PL͒ detected magnetic resonance ͑PLDMR͒. The PLDMR results and quantum chemical calculations show unambiguously that the TE wave-function extent is much smaller than that of the singlet exciton ͑SE͒. The weaker vibronic structure of the triplet photoinduced absorption ͑PA͒ band of m-LPPP relative to the singlet absorption is assigned to the small energy difference between the geometry of the lowest lying and excited triplet states. This is an additional indication of the strong localization of the triplet wave-function as compared to that of the SE. Finally, the influence of photo-oxidation on the PLDMR and PA is analyzed and discussed in relation to the photoconductivity of the materials.

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“…The methyl-substituted poly͑para-phenylene͒-type ladderpolymer (m-LPPP) is highly attractive for applications in organic light-emitting diodes 1 ͑OLED's͒ and as the active medium in organic solid-state lasers 2 due to its high photoluminescence ͑PL͒ quantum yield PL ϳ30% in film and ϳ100% in solution, 3 and the high interchain order in the solid state. 4,5 From previous studies on m-LPPP a comprehensive picture of the generation of polarons [6][7][8] and triplet excitons 8,9 ͑TE's͒ from singlet excitons ͑SE's͒ was drawn.…”

Section: Introductionmentioning

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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Electric-field-induced luminescence quenching in an electroluminescent organic semiconductor

Cited by 87 publications

References 29 publications

Ultrafast photogeneration mechanisms of triplet states inpara-hexaphenyl

Ultrafast photogeneration mechanisms of triplet states inpara-hexaphenyl

Localized triplet excitations and the effect of photo-oxidation in ladder-type poly(p-phenylene) and oligo(p-phenylene)

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

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