Conducting polymers
(CPs) find applications in energy conversion
and storage, sensors, and biomedical technologies once processed into
thin films. Hydrophobic CPs, like poly(3,4-ethylenedioxythiophene)
(PEDOT), typically require surfactant additives, such as poly(styrenesulfonate)
(PSS), to aid their aqueous processability as thin films. However,
excess PSS diminishes CP electrochemical performance, biocompatibility,
and device stability. Here, we report the electrosynthesis of PEDOT
thin films at a polarized liquid|liquid interface, a method nonreliant
on conductive solid substrates that produces free-standing, additive-free,
biocompatible, easily transferrable, and scalable 2D PEDOT thin films
of any shape or size in a single step at ambient conditions. Electrochemical
control of thin film nucleation and growth at the polarized liquid|liquid
interface allows control over the morphology, transitioning from 2D
(flat on both sides with a thickness of <50 nm) to “Janus”
3D (with flat and rough sides, each showing distinct physical properties,
and a thickness of >850 nm) films. The PEDOT thin films were
p
-doped (approaching the theoretical limit), showed high
π–π conjugation, were processed directly as thin
films without insulating PSS and were thus highly conductive without
post-processing. This work demonstrates that interfacial electrosynthesis
directly produces PEDOT thin films with distinctive molecular architectures
inaccessible in bulk solution or at solid electrode–electrolyte
interfaces and emergent properties that facilitate technological advances.
In this regard, we demonstrate the PEDOT thin film’s superior
biocompatibility as scaffolds for cellular growth, opening immediate
applications in organic electrochemical transistor (OECT) devices
for monitoring cell behavior over extended time periods, bioscaffolds,
and medical devices, without needing physiologically unstable and
poorly biocompatible PSS.
