TY - JOUR
T1 - Thermally Induced Formation of HF4TCNQ- in F4TCNQ-Doped Regioregular P3HT
AU - Watts, Kristen E
AU - Neelamraju, Bharati
AU - Moser, Maximilian
AU - McCulloch, Iain
AU - Ratcliff, Erin L.
AU - Pemberton, Jeanne E
N1 - KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The authors acknowledge support of this research by the National Science Foundation under award DMR-1608289. K.E.W. acknowledges financial support through an ARCS Foundation Scholarship and an ACS Division of Analytical Chemistry Fellowship sponsored by Eli Lilly and Company. M.M and I.M. acknowledge generous funding from KAUST for financial support. The
authors also acknowledge very useful discussions with Professor Richard S. Glass regarding mechanistic aspects of this work. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515.
PY - 2020/7/23
Y1 - 2020/7/23
N2 - The prototypical system for understanding doping in solution-processed organic electronics has been poly(3-hexylthiophene) (P3HT) p-doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Multiple charge transfer states, defined by the fraction of electron transfer to F4TCNQ, are known to coexist and are dependent on polymer molecular weight, crystallinity, and processing. Less well understood is the loss of conductivity after thermal annealing of these materials. Specifically, in thermoelectrics, F4TCNQ-doped regioregular (rr) P3HT exhibits significant conductivity losses at temperatures lower than other thiophene-based polymers. Through detailed spectroscopic investigation of progressively heated P3HT films co-processed with F4TCNQ, we demonstrate that this diminished conductivity is due to formation of the non-chromophoric, weak dopant HF4TCNQ-. This species is likely formed through hydrogen abstraction from the alpha aliphatic carbon of the hexyl chain at the 3-position of thiophene rings of rr-P3HT. This reaction is eliminated for polymers with ethylene glycol-containing side chains, which retain conductivity at higher operating temperatures. In total, these results provide a critical materials design guideline for organic electronics.
AB - The prototypical system for understanding doping in solution-processed organic electronics has been poly(3-hexylthiophene) (P3HT) p-doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Multiple charge transfer states, defined by the fraction of electron transfer to F4TCNQ, are known to coexist and are dependent on polymer molecular weight, crystallinity, and processing. Less well understood is the loss of conductivity after thermal annealing of these materials. Specifically, in thermoelectrics, F4TCNQ-doped regioregular (rr) P3HT exhibits significant conductivity losses at temperatures lower than other thiophene-based polymers. Through detailed spectroscopic investigation of progressively heated P3HT films co-processed with F4TCNQ, we demonstrate that this diminished conductivity is due to formation of the non-chromophoric, weak dopant HF4TCNQ-. This species is likely formed through hydrogen abstraction from the alpha aliphatic carbon of the hexyl chain at the 3-position of thiophene rings of rr-P3HT. This reaction is eliminated for polymers with ethylene glycol-containing side chains, which retain conductivity at higher operating temperatures. In total, these results provide a critical materials design guideline for organic electronics.
UR - http://hdl.handle.net/10754/664488
UR - https://pubs.acs.org/doi/10.1021/acs.jpclett.0c01673
U2 - 10.1021/acs.jpclett.0c01673
DO - 10.1021/acs.jpclett.0c01673
M3 - Article
C2 - 32701299
SN - 1948-7185
JO - The Journal of Physical Chemistry Letters
JF - The Journal of Physical Chemistry Letters
ER -