Effects of chemical dopants on the luminescence, bandgap and electrochemical conductivity of the thiophene-based benzothiadiazole-conjugated polymers

Conjugated polymers of BTTP and BTTP–CN comprising thiophene and benzothiadiazole substituents were subjected under chemical doping process. The polymers were doped with different Lewis acids such as AlCl₃, H₃BO₃, BF₃, Cu(II), Fe(II), HCl and I₂. The doped and undoped polymers have been analyzed with the aid of FTIR, UV–Vis, fluorescence spectrometer, electrochemical conductivity and cyclic voltammetry. Upon doping, the absorption maximum of the polymers (403 and 397 nm) were dramatically shifted and emission wavelength of BTTP and BTTP–CN was red shifted due to chemical interaction among dopants. The electrochemical band gap of undoped polymers BTTP and BTTP–CN has been measured as 1.9 and 1.6 eV and conductivity was measured as 3.62 and 1.46 × 10^–5 Ω⁻¹ cm⁻¹, respectively. After doping with Lewis acids, band gap was reduced and conductivity was increased. The reactivity of the polymers with AlCl₃, BF_3, and HCl dopants produced low band gap, high conductivity up to 0.79 eV, 5.98 × 10^–5 Ω⁻¹ for BTTP and 1.0 eV, 4.43 × 10^–5 Ω⁻¹ for BTTP–CN, respectively. Introduction of dopants to the conjugated polymers opens up the opportunity to increase conjugation, Turn off/on fluorescence and shifting of energy levels in solar cell applications.