Simultaneous Voltammetric and In Situ Conductivity Studies of n-Doping of Polythiophene Films with Tetraalkylammonium, Alkali, and Alkaline–Earth Cations

  • Levi M
  • Gofer Y
  • Aurbach D
 et al. 
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Abstract

Polythiophene (PTh) films, both p- and n-doped, have been fully characterized
in a solution of TEABF4 (tetraethylammonium

tetrafluoroborate), in propylene carbonate (PC) by a simultaneous
application of cyclic voltammetry and in situ conductometry. We

observed a considerable charge-trapping effect during n-doping of
PTh with TEA1 cations. The release of the trapped, negatively

charged polarons becomes possible only at the onset of the subsequent
p-doping of this polymer, accompanied by an increase in

conductivity. The interaction between the trapped, negatively charged
polarons and mobile, positively charged polarons resulted in

their neutralization. This effect was accompanied by the simultaneous
exaltation of the voltammetric current and the transient

decrease in conductivity. Correction for the trapped charge allowed
us to estimate the mobility of the free negatively charged

polarons:m52.4 3 1023 cm2/V s (doping level with TEA1, cations, X
5 0.022). At the same doping level with BF4 2 -anions, positively

charged polarons exhibited similar mobility,m52.8 3 1023 cm2/V s.
This similarity is in good agreement with the reported

electron spin resonance characteristics of PTh. We have studied the
influence of a low content of cations (with different ionic

radii) in the mother TEABF4 solution on the deterioration of the n-type
redox-capacity and conductivity increasing in the sequence:

TEA1 < K1 << Li1 < Ba21. This remarkable effect is discussed in terms
of competition between the solvation of small cations in

PC and the hard-soft pinning of negatively charged polarons. This
pinning seems to be partially reversible, as revealed by the subsequent

n-redoping in a clean TEABF4 solution.

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Authors

  • M. D. Levi

  • Y. Gofer

  • D. Aurbach

  • M. Lapkowski

  • E. Vieil

  • J. Serose

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