Polaron-induced metallic polypyrrole

Bätz, P.; Schmeiβer, D.; Göpel, Wolfgang

doi:10.1016/0038-1098(90)90327-8

Cited by 26 publications

(5 citation statements)

References 39 publications

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“…Bipolaron formation was invoked to explain conductivity of conducting polymers in the absence of ESR signals and the lack of correlation between conductivity and the number of spins. 16,22 Other experiments were shown to be in agreement with preference for polaron formation, 17,23,24,102 energetic degeneracy between polarons and bipolarons, 25 and coexistence of polarons and bipolarons. 26 Theoretically bipolaron formation was promoted by Bredas et al, 9,20 who calculated a bipolaron binding energy of 0.45 eV for polypyrrole with the tight binding method.…”

Section: Discussionmentioning

confidence: 70%

“…12,13,[16][17][18] The sub-band transitions of doped COPs were rationalized originally in terms of bipolaron formation since there is no correlation between ESR signals and conductivity. 9,[19][20][21][22] Preference for bipolarons has been questioned by some experimentalists from the start, 17,18,[23][24][25][26] but others rationalized their observations in terms of bipolarons. 13,16,22 Especially after the doping behavior of monodisperse polyenes [27][28][29] and oligothiophenes (OTs) [30][31][32][33][34][35][36][37][38][39][40][41] was investigated in solution, the bipolaron model was challenged.…”

Section: Introductionmentioning

confidence: 99%

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Theoretical Modeling of the Doping Process in Polypyrrole by Calculating UV/Vis Absorption Spectra of Neutral and Charged Oligomers

Okur

Salzner

2008

J. Phys. Chem. A

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Changes in absorption spectra during doping of oligopyrroles were investigated with time-dependent density functional theory on optimized structures of neutral, singly, and doubly charged pyrrole oligomers with up to 24 rings. In the absence of counterions, defects are delocalized. Counterions induce localization. For dications two polarons on the same chain are preferred over a bipolaron. Intragap absorptions arise in charged species, no matter whether defects are localized or delocalized. Cations and dications give rise to two sub-band transitions. The cation peaks have lower energies than those of dications. The first excitations of cations have lower oscillator strengths than the second; for dications the second peak is weaker than the first. For very long oligomers, the second sub-band absorption vanishes and a third one appears at higher energy. The behavior of pyrrole oligomers is analogous to that of thiophene oligomers. Theoretical UV spectra for cations and dications of short oligomers (six to eight rings) match experimental spectra of polypyrrole at low and at high doping levels, respectively. The error in the theoretical calculations is about 0.4 eV, slightly larger than for thiophene oligomers at the same level of theory.

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Section: Discussionmentioning

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Theoretical Modeling of the Doping Process in Polypyrrole by Calculating UV/Vis Absorption Spectra of Neutral and Charged Oligomers

Okur

Salzner

2008

J. Phys. Chem. A

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“…This gives rise to the widely accepted notion that hole (and electron) doping shifts valence (conduction) DOS into the gap to give ϕ < I p ( ϕ >electron affinity for electron doping). Although some experiments have been interpreted to support this notion 30 31 , several puzzling features persisted, including the absence of a perceptible FL step and, in some cases, the lack of any shift.…”

Section: Resultsmentioning

confidence: 99%

“…We examined the doping-induced evolution of the VB structure of the TAF copolymers. Their weakly dispersive HOMO and HOMO-1 bands make tracking possible, different from the homopolymer OSCs 30 31 . 20-nm-thick photo-crosslinked TAF copolymer films were hole doped with NOSbF 6 and then compensated to different DLs in the N 2 glovebox by washing with commercial-grade nitromethane.…”

Section: Resultsmentioning

confidence: 99%

Madelung and Hubbard interactions in polaron band model of doped organic semiconductors

et al. 2016

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The standard polaron band model of doped organic semiconductors predicts that density-of-states shift into the π–π* gap to give a partially filled polaron band that pins the Fermi level. This picture neglects both Madelung and Hubbard interactions. Here we show using ultrahigh workfunction hole-doped model triarylamine–fluorene copolymers that Hubbard interaction strongly splits the singly-occupied molecular orbital from its empty counterpart, while Madelung (Coulomb) interactions with counter-anions and other carriers markedly shift energies of the frontier orbitals. These interactions lower the singly-occupied molecular orbital band below the valence band edge and give rise to an empty low-lying counterpart band. The Fermi level, and hence workfunction, is determined by conjunction of the bottom edge of this empty band and the top edge of the valence band. Calculations are consistent with the observed Fermi-level downshift with counter-anion size and the observed dependence of workfunction on doping level in the strongly doped regime.

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“…Polarons appear as states in the electronic gap and can be identified in the valence band spectra by UPS (Fig. 4) or by the electronic transitions in HREELS [17,18]. The doping dependent sequence in Fig.…”

Section: Polypyrrole Filmsmentioning

confidence: 99%

In‐situ Investigations of the Conduction Mechanisms in Low‐Dimensional Organic Semiconductors and Metals

Schmeißer

Göpel

1993

Ber Bunsenges Phys Chem

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Spectroscopy, PhotoelectronWe characterize the electronic structure of polypyrrole films and (2,5-DMe-Di~yanoquinonediimine)~Ag, Rb single crystals using a combination of electrochemical preparation and electron-spectroscopical techniques (XPS, UPS, HREELS). These studies allow to characterize the electronic structure, to conclude on the particular conductivity mechanisms for controlled order and structures, and to determine the strength of both, the electron-phonon and the electron-electron interactions. 1, IntroductionThe defined preparation of thin films is a major advantage of electrochemical techniques and finds applications in the preparation of metallic [1,2] as well as organic thin films [3-51. With respect to the area of highly conducting organic materials electrochemical preparation is used to obtain polymeric polypyrrole films (gmax = 100 Scm-') [6,7] and radical anions salts from the (Dicyanoquinone-diimine) DCNQI molecule with conductivities around 1000 Scm-' [5,8]. For these materials the electrochemical preparation offers substantial advantages against evaporation or sputtering techniques, as homogeneous films or single crystals with reproducible stoichiometries and negligible contaminations can be obtained.Despite of these unique preparation conditions a systematic study of the electronic structure has been possible only after establishing appropriate transfer systems to allow sample transfer between the electrochemical cell and the UHV [ 1,2]. The main experimental problem is the high surface sensitivity of the electron spectroscopies and the need of uncontaminated surfaces to use the thereby obtained results to extrapolate on the bulk properties of the samples investigated. The information obtainable from electron spectroscopies allows a direct access to the density of states (DOS) of the occupied levels and bands by valence band photoelectron spectroscopy (UPS). The stability can be controlled by core level spectroscopy (XPS) by recording the stoichiometries or the oxidation state of single components. Furthermore, the optical and electronic transitions are a substantial source of information as they close up to optical studies and hence allow a direct comparison of these techniques.The electronic structure, conductivity and optical properties of organic materials are determined by the relative strength of covalent bonding, of the electron-phonon interaction, and of the electron-electron interactions [9]. When compared to inorganic semiconductors and metals, a main difference in the bonding mechanisms of organic materials is the weakness of covalent bonding. As a consequence, the electron-phonon and electron-electron interactions can not be neglected and do contribute considerably to the electronic structure. At present, theoretical studies are unable to treat all of the three interaction mechanisms and to give a complete description of complicated organic systems. Therefore, it seems worthwhile to look for model systems in which one of the three mechanisms is dominating or to look for experim...

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Polaron-induced metallic polypyrrole

Cited by 26 publications

References 39 publications

Theoretical Modeling of the Doping Process in Polypyrrole by Calculating UV/Vis Absorption Spectra of Neutral and Charged Oligomers

Theoretical Modeling of the Doping Process in Polypyrrole by Calculating UV/Vis Absorption Spectra of Neutral and Charged Oligomers

Madelung and Hubbard interactions in polaron band model of doped organic semiconductors

In‐situ Investigations of the Conduction Mechanisms in Low‐Dimensional Organic Semiconductors and Metals

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