Molecular Reorientation and Structural Changes in Cosolvent-Treated Highly Conductive PEDOT:PSS Electrodes for Flexible Indium Tin Oxide-Free Organic Electronics

Abstract

Cosolvent addition of glycerol (G) and the use of the cosolvent ethylene glycol (EG) increase the conductivity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films to values on the order of indium tin oxide conductivity. The underlying morphological changes are probed via scanning electron microscopy as well as advanced scattering techniques microfocused grazing incidence small-and wide-angle Xray scattering. The enhancement in conductivity is ascribed to fundamental morphological changes and molecular reorientation within crystalline domains. Thereby, the conductivity enhancement is directly correlated to domain ruptures toward smaller and more densely packed PEDOT domains together with an enhanced crystallinity, the removal of PSS molecules, and moreover a reorientation of the conjugated PEDOT molecules. The latter is reported and quantified here for PEDOT:PSS films for the first time.

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

“…[ 82 ] Except organic solvent EG, reduction agents such as hydrazine (HZ), ethanolamine (MEA), and ammonia solutions were used for de-doping, unfortunately, the conductivity of PEDOT:PSS (Clevios PH 1000) (DMSO or EG-mixed) fi lm was decreased. [ 83,84 ] In addition, EG post-treated PEDOT:PSS (glycerol-mixed) fi lms reached conductivity of over 1000 S cm −1 , as reported by Palumbiny et al [ 85 ] In particular, DeLongchamp and co-workers treated PEDOT:PSS (Clevios P) fi lm by a water rinse. [ 86 ] As a result of PSS removal, the fi lm thickness is reduced by 35%, and the conductivity is increased by 50% from 0.4 to 0.6 S cm −1 .…”

The Morphological Power of Soap: How Surfactants Lower the Sheet Resistance of PEDOT:PSS by Strong Impact on Inner Film Structure and Molecular Interface Orientation

“…The third form factor (FF3) of fi lms without addition of (fl uoro)surfactant Zonyl is related to PEDOT-rich domains described in literature as well as in our previous work. [ 16 ] There we showed their decrease in amount and size with EG posttreatment due to domain rupture, an effect that seems to be more pronounced for fi lms fabricated with (fl uoro)surfactant additive which is the reason why it is not resolved anymore in the present measurements. However, we do not exclude that its decrease in size could contribute to the lowered sheet resistance.…”

“…Note, that the thickness of the fi lms changes significantly due to EG post-treatment as shown in a previous study. [ 16 ] For example, the thickness of a single PEDOT:PSS layer is reduced from 130 to 90 nm after EG post-treatment as determined by X-ray refl ectivity measurements. The thicknesses of all investigated PEDOT:PSS fi lms are given in the Supporting Information.…”

“…[ 16 ] Since our multilayer samples are EG posttreated before applying additional layers, the PSS layer is removed from the surface prior to the following coating cycle. Hence, no PSS barrier layer blocking the charge transport is expected in between the layers.…”

“…[ 16 ] Therefore, the inner fi lm morphology was investigated for different (fl uoro)surfactant contents with and without EG post-treatment. For this purpose, we performed GISAXS measurements.…”