Surface Doping in Poly(3,4-ethylenedioxythiophene)-Based Nanoscale Films: Insights for Polymer Electronics

Abstract

Conducting polymers such as poly­(3,4-ethylenedioxythiophene) (PEDOT) are widely researched for application in electronic devices. Researcher’s look to exploit the ability of these polymers to conduct electrical charge. To induce conductivity, the polymers are doped with counterions; for PEDOT, this is typically done with poly­(styrenesulfonate) or tosylate (Tos). The Tos anions inserted within the PEDOT nanostructure stabilize positive defects (holes) on the polymer’s conjugated backbone, which, in turn, facilitates electrical conduction. In this study, we use X-ray photoelectron spectroscopy to investigate the Tos doping of PEDOT within the outermost region (<15 nm) of electrochemically oxidized or reduced PEDOT:Tos nanoscale films. Computation of the predicted density of states from density functional theory studies is also conducted to aid in interpreting the ultraviolet photoelectron spectroscopy spectra. We observe that the doping of PEDOT:Tos is more complex than first thought, likely involving the nonionic triblock copolymer used during PEDOT’s oxidative polymerization. This hypothesis is corroborated by time-of-flight secondary-ion mass spectrometry measurements on the outer 2 nm of the oxidized and reduced PEDOT:Tos. The observation of complex and heightened doping near the surface opens opportunities for the deliberate surface engineering of PEDOT:Tos nanofilms in polymer electronic applications such as electrochemical transistors and electrical connections.

Temperature‐triggered oxidative polymerization for high conductive poly(3,4‐ethylenedioxythiophene) sheets at millimeter scale

“…When the amount of Fe(Tos) 3 in the mixture of pyridine (20 μL) and EDOT (1 mL) was increased from 100 to 300 mg (Table 1), the sheet resistance of as‐prepared PEDOT sheets (30 μm) reduced from 1600 to 368 Ω sq −1 , presenting an improved conductivity. This is presumably because the increased amount of Fe(Tos) 3 yields PEDOT with higher degrees of polymerization and increased concentration of Tos anion doping 32 . However, the overdose insoluble Fe(Tos) 3 particles may lead to a jagged surface and an uneven conductivity.…”

“…This is presumably because the increased amount of Fe(Tos) 3 yields PEDOT with higher degrees of polymerization and increased concentration of Tos anion doping. 32 However, the overdose insoluble Fe(Tos) 3 particles may lead to a jagged surface and an uneven conductivity. Hence, an appropriate amount of Fe(Tos) 3 should be affirmed to saturate the prepolymerization solution.…”

“…31 The liquid-phase oxidative polymerization process is simple and low-cost in comparison with the strict vacuum requirement and complex operations of the vapor-phase oxidative polymerization. Iron(III) p-toluenesulfonate (Fe(Tos) 3 ) is a common oxidant in industry because the Tos anions also serve as anion dopants 32 conferring a positive effect on the conductivity of PEDOT films. The oxidative polymerization reaction is triggered upon Fe(Tos) 3 mixes with EDOT, which requires quick mixing and coating to achieve PEDOT films with even surface and uniform performance.…”

ACS Applied Nano Materials Australia Forum

“…Shielding against electromagnetic fields over various frequency ranges is a budding area that has recently shown great promise for the utilization of nanomaterials. In this regard, Rud et al from the University of South Australia investigated X-ray spectroscopy to reveal the doping of poly­(3,4-ethylenedioxythiophene) . In another work, Yu et al from the University of Adelaide and their colleagues from other institutions employed graphene and boron nitride embedded in molybdenum disulfide–epoxy mixes to generate composites for efficient X-ray shielding …”

“…In this regard, Rud et al from the University of South Australia investigated X-ray spectroscopy to reveal the doping of poly (3,4-ethylenedioxythiophene). 14 In another work, Yu et al from the University of Adelaide and their colleagues from other institutions employed graphene and boron nitride embedded in molybdenum disulfide−epoxy mixes to generate composites for efficient X-ray shielding. 15 The three review articles in this forum are focused on the timely topics of (1) nanosized piezoelectric materials by Wang et al in a collaboration between the University of Melbourne and RMIT, 16 (2) harvesting electrical energy from ambient moisture by Feng et al from the University of New South Wales (UNSW), 17 and (3) recent advances in 2D-based electrodes for monitoring biophysiological signals, by Faisal and Iacopi from the University Technology Sydney.…”