Synthesis and Photoelectrochemistry Characterization of Polymer based on 4,7-Di(thiophen-2-yl)-benzo[c][1,2,5]thiadiazole, (DTBT).

Poly[4,7-di-(thiophen-2-yl)-benzo[c]-[1,2,5] thiadiazole], P(DTBT), is used in polymer:PCMB blends as active layer on organic photovoltaic devices, (OPV); DTBT-based copolymers show well-reversible oxidation and reduction electrochemical processes. These processes indicate their hig electrochemical stability suitable for n- and p-doping. This is a typical feature benzothiadiazole containing molecules. In the present study the synthesis conditions of the monomer, 4,7-di-(thiophen-2-yl)-benzo[c]-[1,2,5]-thiadiazole based on Stille coupling reactions has been investigated and its respectively polymer P(DTBT) was prepared by repetitive potential-sweep anodic oxidation of the corresponding monomer DTBT onto Pt disk or indium tin oxide (ITO) electrodes. Electrochemical cyclic voltammetry (CV) was performed to determine the HOMO and the LUMO energy levels of the conjugated DTBT and P(DTBT), both exhibit amphoteric redox properties, n- and p- doping process. The optical gap estimated from electrochemical measurements of the polymer P(DTBT) was found to be 1.77 eV, which is close to the reported band gap (1.1-1.2eV) determined by optical absorption technique . Photoelectrochemical characterization of P(DTBT) was realized from UV-Vis-NIR spectra recorded at different applied potentials. These result are correlated with the charge-transfer phenomena in the polymers applied as active layer on OPV`s.