Polaron to bipolaron transition in a conjugated polymer. Rubidium-doped poly(p-phenylenevinylene)

Iucci, Giovanna; Xing, Kezhao; Lögdlund, M.; Fahlman, Mats; Salaneck, W. R.

doi:10.1016/0009-2614(95)00921-p

Cited by 75 publications

(36 citation statements)

References 18 publications

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“…Even above 9 eV, where the spectra were dominated by -states, the features were significantly broadened. This behavior deviated from the general trends observed in alkali metal doping of -conjugated oligomers and polymers, 29,[32][33][34][35][36] indicating that chemical interactions other than those of charge-transfer type occurred between Li and the EDOT-trimer. In the following, the strong modifications of the -system observed in the UPS spectra are discussed.…”

Section: Lithium Dopingmentioning

confidence: 55%

“…37 So far, these results were in agreement with the general trends observed for n-doped -conjugated oligomers. 29,[32][33][34][35][36] However, an anomalously large broadening of the valence band features was observed, even for doping concentrations as low as 0.2 Li atoms per molecule. It is well known that alkali metal doping results in significant destabilization of the molecular orbitals in thiophene oligomers 29 and in polythiophene, 34 resulting in peak-shifts and spreading of the features in the UPS spectra of such molecular solid films.…”

Section: Lithium Dopingmentioning

confidence: 99%

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The electronic structure of n- and p-doped phenyl-capped 3,4-ethylenedioxythiophene trimer

Jong

Gon

Crispin

et al. 2003

The Journal of Chemical Physics

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Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf 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. The phenyl-capped 3,4-ethylenedioxythiophene ͑EDOT͒ trimer is a well-defined oligomer of the related poly͑3,4-ethylenedioxythiophene͒, the conjugated polymer that forms the basis of the commercialized conducting polymer ''PEDOT-PSS.'' EDOT-based oligomers are themselves potential candidates for applications in molecular electronics, such as organic field effect transistors and organic solar cells. Well controlled chemical doping is of importance in such applications, since it enables tuning of important properties such as the electrical conductivity, the position of the Fermi-level, the optical absorption edge, and the quantum efficiency for photovoltaic devices. The effects of chemical doping, both p-type doping with iodine, and n-type doping with lithium, on the electronic structure of condensed molecular solid films of EDOT trimer have been studied using ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy. The results are discussed in terms of parameters important for device applications.

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Section: Lithium Dopingmentioning

confidence: 55%

Section: Lithium Dopingmentioning

confidence: 99%

The electronic structure of n- and p-doped phenyl-capped 3,4-ethylenedioxythiophene trimer

Jong

Gon

Crispin

et al. 2003

The Journal of Chemical Physics

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“…Therefore, UPS is used to investigate the band structures of doped forms of conducting organic oligomers and polymers. [5][6][7][8][9] Theoretically UPS can be simulated via the one-electron approximation by employing band structure calculations and investigating the density of states (DOS). For obtaining energies of cations from band structure calculations, Koopmans's theorem 10 must hold, which is strictly speaking only true for HartreeFock (HF) and semiempirical wave functions as correlated wave functions do not provide one-electron energy levels and the meaning of orbital energies apart from that of the highest occupied molecular orbital (HOMO), is controversial in density functional theory (DFT).…”

Section: Introductionmentioning

confidence: 99%

Modeling Photoelectron Spectra of Conjugated Oligomers with Time-Dependent Density Functional Theory

Salzner

2010

J. Phys. Chem. A

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With the aim of producing accurate band structures of conjugated systems by employing the states of cations, TDDFT calculations on conjugated oligomer radical cations of thiophene, furan, and pyrrole with one to eight rings were carried out. Benchmarking of density functional theory and ab initio methods on the thiophene monomer shows that the ∆SCF ionization potential (IP) is most accurate at the B3LYP/6-311G* level. Improvement of the basis set beyond 6-311G* leads to no further changes. The IP is closer to experiment at B3LYP/6-311G* than at CCSD(T)/CCPVQZ. For longer oligomers the ∆SCF IPs decrease too fast with increasing chain length with all density functionals. CCSD/6-311G* performs well if the geometries are optimized at the CCSD level. With MP2 geometries IPs decrease too fast. Peak positions in photoelectron spectra were determined by adding appropriate TDDFT excitation energies of radical cations to the ∆SCF IPs. The agreement with experiment and with Green function calculations shows that TDDFT excited states of radical cations at the B3LYP/6-311G* level are very accurate and that absorption energies can be employed to predict photoelectron spectra.

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“…The deposition is a crucial step in the fabrication process since the metals diffuse into, [7][8][9] and interact with, the organic material. [10][11][12][13][14][15] Such indiffusion is a general phenomenon in polymer metallization. 16 Previous results on metal deposition on conducting polymers give a picture of some of the processes that may occur upon metal deposition.…”

Section: Introductionmentioning

confidence: 99%

“…The formation of gap states is also reported for sodium and rubidium deposited on different organic compounds. [10][11][12][13] During thermal deposition of Ca on ␣, -diphenyltetradecaheptane ͑DP7, which can be regarded as a model substance for PPV͒, and DHPPV ͑a PPV derivative͒, a diffusive layer of the organic material with the metal is formed with an estimated thickness of several nanometers. Also in this case new electronic states are formed in the gap between the highest occupied molecular orbital ͑HOMO͒ and the lowest unoccupied molecular orbital ͑LUMO͒.…”

Section: Introductionmentioning

confidence: 99%

Liquid metals as electrodes in polymer light emitting diodes

Andersson

Gommans

Gon

et al. 2003

Journal of Applied Physics

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We demonstrate that liquid metals can be used as cathodes in light emitting diodes ͑pLEDs͒. The main difference between the use of liquid cathodes and evaporated cathodes is the sharpness of the metal-polymer interface. Liquid metal cathodes result in significantly sharper metal-organic interfaces than vapor deposited cathodes, due to the high surface energy of the metals. The sharper interface in pLEDs with liquid metal cathodes is observed by neutral impact collision ion scattering spectroscopy and low energy ion scattering spectroscopy measurements. The influence of interface sharpness on device performance was studied by comparing current-voltage-light characteristics of devices with OC 1 C 10 paraphenylenevinylene ͑PPV͒ as electroluminescent polymer and indium tin oxide ͑ITO͒ as hole injection electrode, and different cathodes. Comparison of devices using a liquid Ga cathode and an evaporated Al cathode showed that light emission for the liquid Ga cathode is two orders of magnitude larger than for the evaporated Al cathode, and that the external light efficiency is increased by an order of magnitude. Since the work function of Ga and Al is nearly the same, the poor performance for evaporated Al LEDs is attributed to the formation of an interfacial layer where Al has diffused into, and reacted with, the PPV. This interfacial layer has poor electrical conduction compared to pure PPV, and contains quenching sites which reduce light emission. Low work function liquid metal cathodes were studied by using liquid Ca and Ba amalgams. The improved performance of liquid amalgam pLEDs is attributed to the different structure of the metal-polymer interface. The enormous increase in light and current through the amalgam devices compared to those using pure Hg demonstrate that less than 1 ML of a metal with a low work function at the polymer-cathode interface can have a dramatic effect on the performance of the devices. Devices with a liquid Ca amalgam cathode showed an increase of the current ͑by 50%͒ and brightness ͑80%͒ compared to devices with an evaporated Ca cathode, which is ascribed to reduced diffusion of Ca into the emissive PPV layer.

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Polaron to bipolaron transition in a conjugated polymer. Rubidium-doped poly(p-phenylenevinylene)

Cited by 75 publications

References 18 publications

The electronic structure of n- and p-doped phenyl-capped 3,4-ethylenedioxythiophene trimer

The electronic structure of n- and p-doped phenyl-capped 3,4-ethylenedioxythiophene trimer

Modeling Photoelectron Spectra of Conjugated Oligomers with Time-Dependent Density Functional Theory

Liquid metals as electrodes in polymer light emitting diodes

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