Impact of the anion on electrochemically doped regioregular and regiorandom poly(3‐hexylthiophene)

Abstract

Chemical and electrochemical doping of π-conjugated polymers is an important aspect in determining the performance and enabling the operation of many organic electronic devices, from organic light emitting diodes and thermoelectrics to organic electrochemical transistors. In both chemical doping and electrochemical doping an ionized dopant or counterion is present along with the doped π-conjugated polymer. This dopant or counterion is not a benign spectator, rather, its presence can significantly impact the optical, electronic, and thermoelectric properties of the resulting material. Here, we investigate how counterion structure impacts the electrochemical doping ability, oxidation potential, ionization energy, and polaron absorbance of regioregular (rr) and regiorandom (rra) P3HT. We find that in most cases the anion has a small effect on the polymer oxidation potential, except for in the case of rr-P3HT with the large tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion. We propose that this large anion is excluded from the crystalline regions and thus the oxidation potential is similar to that of rra-P3HT. The anions also result in significant differences in polaron absorbance and ionization energies, thereby emphasizing the important role of the counterion in determining the optical and electronic properties of doped π-conjugated polymers.

Light‐induced Delivery of Charged Species using Ion‐selective Core–Shell Nanoparticles

“…The same fluorescence behavior was found for decreasing KCl concentrations in the incubation solution (Figure 2e and Figure 2f). The trends found for TFPB − and BF 4 − indeed agree with previous findings because small ions, such as BF 4 − , are known to have a small influence on the crystallinity of poly(3‐alkylthiophenes), which will facilitate the generation of the fluorescence signal [41] …”

“…À indeed agree with previous findings because small ions, such as BF 4 À , are known to have a small influence on the crystallinity of poly(3-alkylthiophenes), which will facilitate the generation of the fluorescence signal. [41] To our understanding, a change in the lipophilic anion has two effects: i) different oxidation degrees of the POT core, i.e., from POT 0 to POT + , decreasing the original fluorescence of pristine POT NPs, and ii) different effect on the crystalline domains in the POT structure, which are responsible for an enhanced fluorescence signal by the restriction of intramolecular motion (RIM). An increase in the mobile amorphous fraction with non-radiative energy dissipation paths has been shown to occur.…”

Dopant-Induced Energetic Disorder in Conjugated Polymers: Determinant Roles of Polymer–Dopant Distance and Composite Electronic Structures

“…The Coulomb interaction between the charge carrier and its counterion is poorly screened by the low dielectric medium of most polymers, which lowers the mobility of the carrier. Several studies have focused on identifying factors or properties that affect Coulomb interactions. ,− A survey of the literature, however, shows that salient conclusions from these studies conflict. ,,− Some studies correlate increased counterion size to reduced Coulomb interactions, , while others find no such correlation and instead correlate increased molecular ordering ,, with reduced Coulomb interactions. Moreover, translating molecular designs of undoped polymers with high mobility to doped polymers with high conductivity has been difficult.…”

Probing transport energies and defect states in organic semiconductors using energy resolved electrochemical impedance spectroscopy

“…[36][37][38][39] For example, Baustert, et al recently showed that large ions are excluded from the crystalline regions of regioregular-poly(3-hexylthiophene), RR-P3HT, thus resulting in a shift of approximately 250 mV in the oxidation potential relative to when a small anion is used in the electrolyte solution. [37] Additionally, in OECTs, which rely on electrochemical doping, the performance parameters are highly dependent on the electrolyte ions. [35,36,40] This dependence on electrolyte chemistry makes electrochemical measurements preferable to photoemission measurements when the intended use of the material is in an electrochemical device.…”

“…Such solvent and electrolyte dependence is documented throughout the literature. [36][37][38][39] For example, Baustert, et al recently showed that large ions are excluded from the crystalline regions of regioregular-poly(3-hexylthiophene), RR-P3HT, thus resulting in a shift of approximately 250 mV in the oxidation potential relative to when a small anion is used in the electrolyte solution. [37] Additionally, in OECTs, which rely on electrochemical doping, the performance parameters are highly dependent on the electrolyte ions.…”