Current-Sensing Atomic Force Microscopic Study of Doping Level Distribution in Doped Poly[2,2’-Bithiophene

Abstract

Current-sensing atomic force microscopy (CS-AFM) was used to study the doping level distribution in electrochemically doped poly[2,2’-bithiophene] under a controlled atmosphere (glove box) to preserve the doping level during the measurements. The resulting nanoscale conductivity distribution patterns were compared with those obtained with undoped polymer. The results were analyzed using the model developed by us earlier that the nanoscale morphology of such materials involves polymer grains with more crystalline cores and more disordered periphery. It turned out that while for the undoped polymer the crystalline cores were more conducting, the doped polymer featured more conducting periphery as compared to the grain cores. The results demonstrate that doping ions and solvent penetrate the polymer material non-uniformly and can more easily enter more disordered portions of the materials located at the periphery of the polymer grains. These results demonstrate the importance of structural factors for applications that require different levels of the material conductivity. In particular, more ordered materials look more suitable for such applications as molecular electronics and solar cells, which require low conducting/semiconducting materials with high carrier mobility. At the same time, for applications that require high levels of electronic conductivity, such as charge storage and various conducting coatings, less ordered polymer films would be preferred.