Preparation and Properties of Fluorene-based Thienothiophene Substituted Benzothiadiazole Copolymer for the Application of Polymeric Solar Cells

Polymer solar cells (PSCs) have been intensively studied by researchers in order to improve their power conversion efficiency (PCE). The current PCE achievement has successfully surpassed 10%, yet it is still far laging from their inorganic counterparts. Hence, there is still a lot of room for improvement of the organic photovoltaics. This work presents a new class of fluorene-donor/benzothiadiazole-acceptor copolymers with thienothiophene as the spacer. Poly(9,9-dioctyl-9H- fluorine-alt-5,6-bis(octyloxy)-4,7-di(thieno[3,2-b] thiophen-2- yl)benzo[c][1,2,5]thiadiazole) (P1) was synthesized through the well-known Suzuki’s cross-coupling reaction and the reported Mw and PDI values were 20 kDa and 2.6, respectively. The optical and electrochemical band gaps achieved by this P1 were 2.03 eV and 1.98 eV, respectively, which could still be narrowed down by further modification of the chemical structure. Moreover, the P1 was found to have good thermal stability up to 433°C. This research could provide an insight into the relationship between the chemical structure and polymeric characteristics for future designation of the PSCs.