Strain-induced electrical charge transport in PEDOT:PSS thin films: role of wrinkles and cracks

In this work, we demonstrate that the modulations of electrical charge transport in strained PEDOT:PSS thin films on flexible substrates can be understood in terms of subtle changes in the film morphology. The application of uniaxial strain results in the formation of wrinkle arrays which are oriented in the direction of applied strain. At higher strain magnitude (ε > 4 %), the formation of quasi-periodic parallel cracks oriented in a direction perpendicular to the applied strain is observed. While the wrinkle arrays lead to weakly anisotropic charge transport, the cracks result in strong anisotropy (ΔR/R =60 at 16% strain). We quantify the contributions of wrinkles and cracks toward the resistance changes observed in strained PEDOT: PSS films. Interestingly, the resistance of PEDOT:PSS thin film exhibits a ‘strain memory effect’ when it is subjected to a controlled cyclic process. We demonstrate that this peculiar ‘strain memory effect’ can be understood in terms of the history of wrinkles array formation when the film subject to cyclic strain. The strain-dependent electrical response is remarkably different when PEDOT: PSS films are cast on pre-strained substrates and this response can be reconciled based on diminished polymer: substrate interactions.