Roles of Nonionic Surfactant Additives in PEDOT:PSS Thin Films

The effects of nonionic surfactant additive, Triton X-100, on the properties of PEDOT:PSS thin films has been investigated. The detailed mechanism for the well-known conductivity enhancement upon the addition of high boiling point nonionic surfactant has been elucidated based on various characterization results. The surfactant additive has been found to enhance the pi-pi stacking of PEDOT segment, leading to enhanced electrical conductivity. In addition, the added surfactant has facilitated the removal of insulating PSS during the methanol spin washing, which contributes to further enhancement in electrical conductivity. Interestingly, the remaining surfactant in the dried PEDOT:PSS thin films plays the role of plasticizer. Upon aging of the films under room ambient (RH similar to 30%), the conductivity of the film has been gradually increased until the humidity effect comes in. As a plasticizer, the surfactant has been found to enhance lamella stacking during the aging. Also, the mechanical modulus of the films has been characterized by the buckling method, which proves the softening effect of residual surfactant for PEDOT:PSS films. On the other hand, the reinforcing filler effect of PEDOT crystallites has been found to be negligible compared to plasticizer effect.