Molecular-Orinetation-Dependent Ion Transport Dynamics in Organic Mixed Ionic Electronic Conductors

Despite the importance of transient behavior in organic mixed conductors, only few studies have been conducted on the structural characteristics of materials that influence ion drift and the associated transient responses of corresponding organic electrochemical transistors (OECTs). In this work, we demonstrate that the molecular orientation of a semi-crystalline mixed conducting polymer system affects the ion mobility and transient behavior of corresponding OECTs by using two mixed conducting polymers. The molecular orientation can be controlled by varying the co-monomer unit (2,2’-bithiophene or phenylene) used in conjunction with 1,4-dithienylphenylene-based monomer having glycol side-chain. Two polymers showed comparable mixed conductivity and electrochemical properties except molecular orientation. The in-depth analysis of the OECT characteristics using different patterning method to control the ion injection direction suggested that the molecular orientation affects the length of the ion-drift pathway, resulting in different transient bahavior in OECT devices. Our study provides general insights into the molecular-orientation-dependent ion drift characteristics of semi-crystalline polymeric mixed conductors.