For
wearable applications such as electronic skin and biosensors,
stretchable conductors are required (∼30% strain to follow
the skin extension). Owing to its high conductivity, good flexibility,
low cost, and ease of processing, poly(3,4-ethylenedioxythiophene)
(PEDOT) appears as a promising candidate. However, destructive cracks
come out above 10% strain in the case of PEDOT:PSS, the most common
form of PEDOT. Different strategies have already been investigated
to solve this problem, including the design of specific structures
or the addition of plasticizers. This article presents a different
approach to obtain highly conductive and stretchable PEDOT materials
based on doping with small counteranions. We indeed demonstrate the
intrinsic stretchability (up to 30% strain) of thin films (35 nm)
of PEDOT-based materials with small counterions. Both thin-PEDOT:OTf
(triflate counter-ion) and thin-PEDOT:Sulf (sulfate counter-ion) films
remain structurally resilient up to 25–30% strain, and their
electrical conductivity remains remarkably stable over more than 100
cycles. Under limited strain (<30%), polarized UV–vis–NIR
measurements (parallel and perpendicular to the stretching direction)
show that the conductivity of the material is improved by chain alignment
in the stretching direction. As a proof of concept, a thermotherapy
patch is presented. It shows a fine temperature control (stability
around 40 °C at 9 V bias) and a uniform heating across the surface.