Optical and Photoelectrochemical Investigation of Mixed Photoactive Poly 2,2’,5,2’’ ter-thiophene and Poly 2,2 bithiophene. Role of Intermixed Phases Created By the Co-electro-polymerization Process

Fluorine-doped tin oxide (FTO) electrodes modified with polymeric films of poly 2,2 bithiophene (PBth) and/or poly 2,2’,5,2’’-terthiophene (PTerth) were subjected to optical, photoelectrochemical (PEC), and electrochemical impedance spectroscopy (EIS) studies. Electropolymerization of mixed monomers containing bi-thiophene (Bth) and ter-thiophene (Terth) with different ratios resulted in the formation of intermixed phases. The recorded optical and PEC and EIS outcome data show that these intermixed polymer networks do not follow a monotonic relationship with the monomer ratios used to generate them. Optical studies indicate the formation of indirect and direct band gaps in the intermixed phases. Films generated in mixed monomers have greater energy-band tails than those generated from pure monomers. PEC studies indicated that these intermixed phases possess p-p type hole accumulations, evident from the initial sharp rise in photocurrent. EIS results did not support linear relationship between the percent of Bth in monomer mixture and the dielectric-related properties such as barrier energy Wm, hopping frequency (ω hopping), electrical conductivity (σ), and density of state at Fermi level N (EF).