Solution-Processed Poly(3,4-ethylenedioxythiophene) Thin Films as Transparent Conductors: Effect of p-Toluenesulfonic Acid in Dimethyl Sulfoxide

Abstract

Conductivity enhancement of thin transparent films based on poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) by a solution-processed route involving mixture of an organic acid and organic solvent is reported. The combined effect of p-toluenesulfonic acid and dimethyl sulfoxide on spin-coated films of PEDOT-PSS on glass substrates, prepared from its commercially available aqueous dispersion, was found to increase the conductivity of the PEDOT-PSS film to ∼3500 S·cm(-1) with a high transparency of at least 94%. Apart from conductivity and transparency measurements, the films were characterized by Raman, infrared, and X-ray photoelectron spectroscopy along with atomic force microscopy and secondary ion mass spectrometry. Combined results showed that the conductivity enhancement was due to doping, rearrangement of PEDOT particles owing to phase separation, and removal of PSS matrix throughout the depth of the film. The temperature dependence of the resistance for the treated films was found to be in accordance with one-dimensional variable range hopping, showing that treatment is effective in reducing energy barrier for interchain and interdomain charge hopping. Moreover, the treatment was found to be compatible with flexible poly(ethylene terephthalate) (PET) substrates as well. Apart from being potential candidates to replace inorganic transparent conducting oxide materials, the films exhibited stand-alone catalytic activity toward I(-)/I3(-) redox couple as well and successfully replaced platinum and fluorinated tin oxide as counter electrode in dye-sensitized solar cells.

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

“…3500 S cm −1 , and with a high transparency of at least 94%. [ 122 ] Apart from being a promising material for photovoltaic applications, the fi lms exhibited potential catalytic activity as well and successfully replaced platinum and fl uorinated tin oxide (FTO) as the counter electrode in dye-sensitized solar cells.…”

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.…”

Highly Efficient Solution‐Processed Poly(3,4‐ethylenedio‐xythiophene):Poly(styrenesulfonate)/Crystalline–Silicon Heterojunction Solar Cells with Improved Light‐Induced Stability

“…[ 20,24,25 ] Due to doping of PTSA, rearrangement of PEDOT particles occurs owing to phase separation and removal of PSS matrix, along with incorporation of SO 3 groups from PTSA. [ 21 ] The SO 3 groups in PTSA have the same chemical environment as those of PSS and contribute to the same S(2p) peak intensity. Thus, in the PTSA/ DMSO treated fi lms the S(2p) intensity ratio is affected by the competing processes of addition and removal of SO 3 groups, although the degree depends on the PTSA concentration and repetition cycle.…”

“…Here, the role of PTSA/DMSO treatment is considered as follows: a PTSA/DMSO-treated PEDOT:PSS fi lm showed a higher conductivity of ≈2000 S cm −1 after removal of PSS, even in a ≈40-nm-thick fi lm (Figure 3 ). [ 21 ] Assuming that the increased conductivity originates from carrier concentration rather than carrier mobility, the EQE in the infrared region of 1000-1200 nm would be lower because of free-carrier absorption. However, there were no signifi cant differences in EQE values in the infrared region for both untreated and PTSA/ DMSO treated devices.…”