How charge trapping affects the conductivity of electrochemically doped poly(3-hexylthiophene) films

Electrochemical doping is an elegant method of controlling the doping level and charge carrier densities of conjugated polymer films and enhancing their thermoelectric figure of merit. Applying this doping technique to films of poly(3-hexylthiophene) (P3HT) results in conductivities with values as h...

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Bibliographic Details
Published in:Applied physics letters 2021-10, Vol.119 (16)
Main Authors: Hornberger, Lea-Sophie, Neusser, David, Malacrida, Claudia, Kaake, Loren G., Ludwigs, Sabine
Format: Article
Language:English
Subjects:
Applied physics
Carrier density
Charge density
Charge transport
Control methods
Current carriers
Doped films
Doping
Electrochemistry
Electrolytes
Figure of merit
Percolation
Polymer films
Solid state
Spectrum analysis
Trapping
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Summary:Electrochemical doping is an elegant method of controlling the doping level and charge carrier densities of conjugated polymer films and enhancing their thermoelectric figure of merit. Applying this doping technique to films of poly(3-hexylthiophene) (P3HT) results in conductivities with values as high as 200 S/cm. The stability of the doped films in the solid state can be probed by UV-vis-NIR spectroscopy. We found that the choice of the conducting salt in the liquid electrolyte exerts a strong influence over the conductivity. Using TBAPF6 and LiClO4 provides highest conductivities for P3HT films, while LiTFSI and TBABF4 show overall lower performance. This effect is also reflected in cyclic voltammetry measurements coupled with in situ spectroscopy. Overall lower reversibility upon multiplex cycling in LiTFSI and TBABF4 electrolytes suggests strong charge trapping effects, which one might attribute to a considerable fraction of charges (holes/ions) remaining in the films after charge/discharge cycles. The salts with stronger charge irreversibility in the electrochemistry experiments show the poorer solid state conductivities. Our conclusion is that one should carefully choose the electrolyte to ensure good percolation pathways and delocalized charge transport throughout doped films.
ISSN:0003-6951
1077-3118
DOI:10.1063/5.0056484