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%.