TY - JOUR
T1 - Branched Side Chains Govern Counterion Position and Doping Mechanism in Conjugated Polythiophenes
AU - Thomas, Elayne M.
AU - Davidson, Emily C.
AU - Katsumata, Reika
AU - Segalman, Rachel A.
AU - Chabinyc, Michael L.
N1 - Funding Information:
The authors acknowledge funding support from the Department of Energy Office of Basic Energy Sciences under grant no. DE-SC0016390 for final spectroscopic and electrical characterization. Atomic force microscopy measurements were supported by the Dow Chemical Company. Initial spectroscopic measurements made use of shared facilities of the UCSB MRSEC (NSF DMR 1720256), a member of the Materials Research Facilities Network (www.mrfn.org). This research used resources of the Advanced Light Source, which is a U.S. Department of Energy Office of Science User Facility under contract no. DE-AC02-05CH11231. E.M.T. gratefully acknowledges support from the NSF Graduate Fellowship (DGE-1650114). The authors thank Clayton Dahlman and Naveen Venkatesan for initial scattering results and Mikayla Barry for assistance with FTIR measurements.
Publisher Copyright:
Copyright © 2018 American Chemical Society.
PY - 2018/12/18
Y1 - 2018/12/18
N2 - Predicting the interactions between a semiconducting polymer and dopant is not straightforward due to the intrinsic structural and energetic disorder in polymeric systems. Although the driving force for efficient charge transfer depends on a favorable offset between the electron donor and acceptor, we demonstrate that the efficacy of doping also relies on structural constraints of incorporating a dopant molecule into the semiconducting polymer film. Here, we report the evolution in spectroscopic and electrical properties of a model conjugated polymer upon exposure to two dopant types: one that directly oxidizes the polymeric backbone and one that protonates the polymer backbone. Through vapor phase infiltration, the common charge transfer dopant, F 4 -TCNQ, forms a charge transfer complex (CTC) with the polymer poly(3-(2′-ethyl)hexylthiophene) (P3EHT), a conjugated polymer with the same backbone as the well-characterized polymer P3HT, resulting in a maximum electrical conductivity of 3 × 10 -5 S cm -1 . We postulate that the branched side chains of P3EHT force F 4 -TCNQ to reside between the π-faces of the crystallites, resulting in partial charge transfer between the donor and the acceptor. Conversely, protonation of the polymeric backbone using the strong acid, HTFSI, increases the electrical conductivity of P3EHT to a maximum of 4 × 10 -3 S cm -1 , 2 orders of magnitude higher than when a charge transfer dopant is used. The ability for the backbone of P3EHT to be protonated by an acid dopant, but not oxidized directly by F 4 -TCNQ, suggests that steric hindrance plays a significant role in the degree of charge transfer between dopant and polymer, even when the driving force for charge transfer is sufficient.
AB - Predicting the interactions between a semiconducting polymer and dopant is not straightforward due to the intrinsic structural and energetic disorder in polymeric systems. Although the driving force for efficient charge transfer depends on a favorable offset between the electron donor and acceptor, we demonstrate that the efficacy of doping also relies on structural constraints of incorporating a dopant molecule into the semiconducting polymer film. Here, we report the evolution in spectroscopic and electrical properties of a model conjugated polymer upon exposure to two dopant types: one that directly oxidizes the polymeric backbone and one that protonates the polymer backbone. Through vapor phase infiltration, the common charge transfer dopant, F 4 -TCNQ, forms a charge transfer complex (CTC) with the polymer poly(3-(2′-ethyl)hexylthiophene) (P3EHT), a conjugated polymer with the same backbone as the well-characterized polymer P3HT, resulting in a maximum electrical conductivity of 3 × 10 -5 S cm -1 . We postulate that the branched side chains of P3EHT force F 4 -TCNQ to reside between the π-faces of the crystallites, resulting in partial charge transfer between the donor and the acceptor. Conversely, protonation of the polymeric backbone using the strong acid, HTFSI, increases the electrical conductivity of P3EHT to a maximum of 4 × 10 -3 S cm -1 , 2 orders of magnitude higher than when a charge transfer dopant is used. The ability for the backbone of P3EHT to be protonated by an acid dopant, but not oxidized directly by F 4 -TCNQ, suggests that steric hindrance plays a significant role in the degree of charge transfer between dopant and polymer, even when the driving force for charge transfer is sufficient.
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U2 - 10.1021/acsmacrolett.8b00778
DO - 10.1021/acsmacrolett.8b00778
M3 - Article
C2 - 35651223
AN - SCOPUS:85058820621
VL - 7
SP - 1492
EP - 1497
JO - ACS Macro Letters
JF - ACS Macro Letters
SN - 2161-1653
IS - 12
ER -