Significant Conductivity Enhancement of Conductive Poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate) Films through a Treatment with Organic Carboxylic Acids and Inorganic Acids

Abstract

Significant conductivity enhancement was observed on transparent and conductive poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films after a treatment with organic and inorganic acids, including acetic acid, propionic acid, butyric acid, oxalic acid, sulfurous acid, and hydrochloric acid. The conductivity could be enhanced from 0.2 to over 200 S cm(-1), that is, by a factor of more than 1000. The conductivity enhancement was dependent on the structure of the acids and the experimental conditions during the treatment, such as the acid concentration and the temperature. The optimal temperature was in the range of 120 to 160 degrees C. The resistance dropped rapidly when a PEDOT:PSS film was treated with acid solution of high concentration, whereas it gradually increased and then decreased when it was treated with an acid solution of low concentration. The mechanism for this conductivity enhancement was studied by various chemical and physical characterizations. The temperature dependence of conductivity indicates that the energy barrier for charge hopping among the PEDOT chains become lower in the highly conductive PEDOT:PSS film after the acid treatment. The ultraviolet-visible-near-infrared (UV-vis-NIR) absorption spectroscopy, the X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) indicate the loss of polystyrene sulfonic acid (PSSH) chains from the PEDOT:PSS film after the acid treatment, and the atomic force microscopy (AFM) suggest conformational change of the polymer chains. Therefore, the conductivity enhancement is attributed to the loss of PSSH chains from the PEDOT:PSS film and the conformational change of the PEDOT chains, which are induced by the acids.

Directional electromechanical properties of PEDOT/PSS films containing aligned electrospun nanofibers

“…The enhancement in conductivity was caused by the benzoid structure of PEDOT transforming into a quinoid structure. [34][35][36] Young's modulus of the aligned nanofiber-embedded PEDOT/PSS composite film along the nanofiber orientation direction was 2.2±0.2 GPa, nearly three times that of non-aligned nanofibers (0.8 ± 0.1 GPa). Moreover, this value was almost five times the value perpendicular to the nanofiber direction, showing the anisotropic mechanical properties of the composite film (Figure 5a).…”

Effective Approaches to Improve the Electrical Conductivity of PEDOT:PSS: A Review

“…The strong acids adopted are usually HCl and H 2 SO 4 , and researchers have achieved an effective increase in the conductivity of PEDOT:PSS (Clevios P). [ 13,[114][115][116] Xia et al observed a conductivity of 3065 S cm −1 for PEDOT:PSS (Clevios PH 1000) fi lms treated with 1 M H 2 SO 4 at 160 °C for three times, the value is comparable to that of ITO. [ 117 ] More recently, Kim et al [ 14 ] reported the solution-processed crystalline formation in PEDOT:PSS via H 2 SO 4 post-treatment, and the conditions were rigorously controlled.…”

“…[ 4,5 ] Systematic studies have found that the conductivity of PEDOT:PSS can be signifi cantly enhanced by thermal and light treatment, [ 6,7 ] or treatments of organic solvents, ionic liquids, surfactants, salts, zwitterions, and acids ( Figure 2 ). [8][9][10][11][12][13] It is worth noting that the conductivity of PEDOT:PSS can reach a maximum value of 4380 S cm −1 via H 2 SO 4 post-treatment, [ 14 ] achieving four orders of magnitude improvement compared with untreated PEDOT:PSS fi lms. Thus, PEDOT:PSS fi lms with high conductivity and transparency just play the role to replace ITO to act as the charge transport layer or electrical interconnect in organic electronic devices such as lightemitting diodes, solar cells, and fi eld-effect transistors.…”

Flexible and Semitransparent Organic Solar Cells

“…Then Bradley et al [50] systematically investigated the effects of thermal annealing, doping and post-treatment on the physical properties (such as morphology, conductivity, and work function) of PEDOT:PSS film. So far doping organic molecules [45,[51][52][53][54][55] in aqueous PEDOT:PSS solution and post-treatment of PEDOT:PSS film with polar organic acid [56][57][58][59][60][61][62][63] are the two most effective approaches for improving the conductivity of PEDOT:PSS films. Ouyang et al proposed that the organic additive induced a conformational change (from mixed coil and linear or expanded-coil to linear or expandedcoil) of PEDOT chain in the PEDOT:PSS film, which results in the increase of the intrachain and interchain charge-carrier mobility and conductivity.…”