Raman Spectroscopic and Electrochemical Studies on the Doping Level Changes of Polythiophene Films during Their Electrochemical Growth Processes

Abstract

Polythiophene (PT), poly(3-chlorothiophene) (PCT), and poly(3-methylthiophene) (PMeT) have been electrochemically deposited on mirrorlike stainless steel (SS) electrode surfaces by direct oxidative polymerization of corresponding monomers in boron trifluoride diethyl etherate (BFEE) solution. The doping levels of as-grown thin films have been determined electrochemically. The results demonstrated that PTs were formed nearly in neutral state initially and their doping levels increased during electrochemical growth processes. Monomer structure and electrolyte have strong effects on the doping levels of PTs with a given thickness. Raman spectroscopic studies also confirmed these findings. Furthermore, it is found that the oxidized species of polythiophene and poly(3-chlorothiophene) are mainly presented in radical cations, while dications are favored to be formed in poly(3-methylthiophene) with a doping level higher than ca. 5%.