Electronic Properties of Transparent Conductive Films of PEDOT:PSS on Stretchable Substrates

Despite the ubiquity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a transparent conducting electrode in flexible organic electronic devices, its potential as a stretchable conductor has not been fully explored. This paper describes the electronic and morphological characteristics of PEDOT:PSS on stretchable poly(dimethylsiloxane) (PDMS) substrates. The evolution of resistance with strain depends dramatically on the methods used to coat the hydrophobic surface of PDMS with PEDOT:PSS, which is cast from an aqueous suspension. Treatment of the PDMS with an oxygen plasma produces a brittle skin that causes the PEDOT:PSS film to fracture and an increase in resistivity by four orders of magnitude at only 10% strain. In contrast, a mild treatment of the PDMS surface with ultraviolet/ozone (UV/O-3) and the addition of 1% Zonyl fluorosurfactant to the PEDOT:PSS solution produces a mechanically resilient film whose resistance increases by a factor of only two at 50% strain and retains significant conductivity up to 188% strain. Examination of the strained surfaces of these resilient PEDOT:PSS films suggests alignment of the grains in the direction of strain. Wave-like buckles that form after the first stretch >10% render the film reversibly stretchable. Significant cracking (similar to 2 cracks mm(-1)) occurs at 30% uniaxial strain, beyond which the films are not reversibly stretchable. Cyclic loading (up to 1000 stretches) produces an increase in resistivity whose net increase in resistance increases with the value of the peak strain. As an application, these stretchable, conductive films are used as electrodes in transparent, capacitive pressure sensors for mechanically compliant optoelectronic devices.