Highly Conducting, Transparent PEDOT:PSS Polymer Electrodes from Post‐Treatment with Weak and Strong Acids

Abstract

The origin of high conductivity in polymer electrodes based on poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is investigated and the resilience against water exposure is tested. Post‐treatment with weak and strong acids, namely, hydrochloric acid (HCl), formic acid (HCOOH), nitric acid (HNO3), and sulfuric acid (H2SO4), is performed and compared to the commonly used ethylene glycol treatment. PEDOT:PSS electrodes with electrical conductivities of up to ≈3000 S cm−1 and high transmittance are obtained. The underlying mechanisms for enhanced conductivity are elucidated by means of electrical (4‐point probe), optical (UV‐Vis spectroscopy), compositional (X‐ray photo‐electron spectroscopy), and structural (grazing‐incidence wide‐angle X‐ray scattering, GIWAXS) characterizations. Selective PSS removal and structural rearrangement of PEDOT‐rich domains due to an enhanced lamellar stacking is identified as major influence on the improvement in electrical conductivity. This beneficial high order is evidenced via additional signals in the GIWAXS patterns, which are altered by subsequent H2O treatment. The PSS removal and structural rearrangement is linked to the acids' strength and dielectric constant. High conductivities are reached by efficient PSS removal via HNO3 or H2SO4 treatment with the drawback of high sensitivity against H2O. By contrast, HCl and HCOOH treatment obtaining a medium enhanced conductivity differ in the amount of PSS removal but show higher H2O resistance.

Vacuum‐Free, All‐Solution, and All‐Air Processed Organic Photovoltaics with over 11% Efficiency and Promoted Stability Using Layer‐by‐Layer Codoped Polymeric Electrodes

“…The binding energies of the S2p 3/2 emission for PEDOT and PSS are determined to evaluate the impact of the doping treatments on the oxidation states of the sulfur of the PEDOT. Binding energy of S2p 3/2 of PEDOT and PSS is ≈164 and ≈168 eV, respectively . For the front sides of each doped film, there was a slight shift (±0.1 eV) in binding energy; but for the rear sides, all the films with acid doping showed a visible shift of ≈0.5 eV toward higher binding energies of PEDOT emission compared with the DMSO/EG‐doped films (Table ).…”

“…The electrical conductivity ( σ ) of PEDOT:PSS films was enhanced via the doping of secondary polar solvents, strong acids, ionic liquids, and so on. Among these methods, strong acid doping is regarded as the most effective pathway to boost the film conductivity.…”

The damaging effects of the acidity in PEDOT:PSS on semiconductor device performance and solutions based on non-acidic alternatives

“…As solution-processing is one of the main advantages of using PEDOT:PSS, this article presents analogues or alternatives that can be solution-processed. If one is looking for a review on how to enhance the conductivity of PEDOT:PSS then this has been nicely summarised by Xu et al, 11 whilst a comprehensive overview of transparent electrode materials in general can be found in a recent article by Cloutet et al 12 Many of the approaches taken to enhance the conductivity of PEDOT:PSS involve treatment with acids such as formic acid, 13 sulfuric acid, 14 phosphoric acid 15 or the addition of high boiling point solvents, such as DMSO 16 or NMP. 17 The strong acidity of high conductivity grades of PEDOT:PSS could be problematic for stability or limit the choice of compatible active materials, yet as these developments are relatively recent the literature has not reported these obvious concerns.…”

A Self-Powered Flexible Thermoelectric Sensor and Its Application on the Basis of the Hollow PEDOT:PSS Fiber

“…The XPS spectra in Figure 5c show the contrast curves of the S 2p atomic orbitals of PEDOT:PSS before and after EG post-treatment, indicating the chemical composition of the prepared PEDOT:PSS fibers. The most obvious difference lies in the integral area of characteristic peaks between 162 eV and 166 eV, while the quantity of EG can influence the relative content of PEDOT to PSS (thiophene/sulfonate) in the corresponding fibers [18,19]. The surface thiophene/sulfonate ratio directly reflects the surface ratio of PEDOT to PSS.…”

“…In comparison with the low thermal conductivity of a only 0.4 W/mK [16] and good electrical conductivity (4380 s/cm) for film [17], PEDOT:PSS has become one of the most promising candidates for TE materials. After several years of development, great achievements have been made in developing functional materials by treating the materials for energy harvesting with different solvents [18,19] and the fabrication of optical TE generators with high output voltages [10,19] This is a great challenge due to the strong demand for high flexibility and good TE properties, but also shows promising prospects for the development of wearable modules for utilizing energy.The TE fiber has aroused great interest in exploring potential applications for wearable technologies. Compared with film or bulk materials, TE fibers with a small physical size arranged from several to hundred microns can enable various devices to be smaller and become more lighter and more portable.…”