Synthesis and Photovoltaic Properties of Poly(dithieno[3,2-b:2′,3′-d]germole) Derivatives

A series of new dithieno[3,2-b:2′,3′-d]germole copolymers have been synthesized and characterized. The dithienogermole unit has been polymerized with different aromatic comonomers such as the benzothiadiazole (PGe1-C8 and PGe1-EH) and thieno[3,4-c]pyrrole-4,6-dione (PGe2). Suzuki and Stille coupling polymerizations under various conditions have been utilized. The polymers were then characterized by size-exclusion chromatography and thermal analyses (TGA, DSC), and their optical and electronic properties were investigated by UV–vis absorption spectroscopy and cyclic voltammetry. These low bandgap polymers (1.3–1.7 eV) have also been tested for photovoltaic applications; the best result was achieved with polymer PGe2, which shows a power conversion efficiency of 4.1%.