Unraveling the Lithium Bis(trifluoromethanesulfonyl)imide (LiTFSI) Doping Mechanism of Regioregular Poly(3-hexylthiophene): Experimental and Theoretical Study
2020
Mombrú, Dominique | Romero, Mariano | Faccio, Ricardo | Mombrú, Álvaro W.
In the present report, we present a combined experimental and theoretical study on the lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) doping mechanism of regioregular poly(3-hexyl thiophene) (P3HT). First, we focus on the effects of LiTFSI doping in both crystalline and amorphous structures of P3HT by performing a complete structural analysis supported by classical molecular dynamics (MD) calculations. Then, we study the effects of LiTFSI doping on electronic properties such as charge transfer and charge transport by performing Raman and impedance spectroscopy, in both cases supported by density of functionals theory (DFT) calculations using periodic boundary conditions. Our structural analysis suggests that the LiTFSI dopant is mainly located in the amorphous region and only a small fraction is located in the crystalline region. In addition, our DFT calculations also suggest that the LiTFSI dopant can effectively act as an electronic acceptor only when it is located in the vicinity of and is accessible to the thiophene rings of P3HT due to the formation of a π···Li chemical bond as an anchoring mechanism, permitting the electronic charge loss of thiophene rings through the sulfonyl groups. A thorough understanding of the LiTFSI doping mechanism of poly(alkyl thiophenes) (P3HT in this particular case) is crucial to elucidating not only the electronic but also the eventual mixed ionic–electronic transport mechanism and its promising properties, particularly as electrodes for lithium ion battery applications.
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