Germafluorenes: New Heterocycles for Plastic Electronics

The synthesis and characterization of new heterofluorene derivatives based oil germanium are described. These germafluorene monomers have been polymerized with different aromatic comonomers. The resulting homopolymers and alternating copolymers have been characterized by size exclusion chromatography, thermal analyses (TGA and DSQ, UV-vis-NIR absorption spectroscopy, X-ray diffraction, and cyclic voltammetry. These homopolymers and copolymers are air-stable and present bandgaps ranging from 3.0 to 1.6 eV. Some copolymers were tested in field-effect transistors (FETs) and bulk heterojunction photovoltaic cells (PCs). Best results in FETs were obtained with poly[2,7-(9,9-di-n-butylgermafluorene)-alt-3,6-bis thiophen-5-yl)-2,5-dioctylpyrrolo[3,4-]pyrrole-1,4-dione], which shows a hole mobility Lip to 0.04 cm(2) (V.s)(-1) with an I-on/I-off ratio of 1.0 x 10(6). For photovoltaic applications, the best results were obtained with poly[2,7-(9,9-di-n-octylgermafluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] with a power conversion efficiency (PCE) of 2.8%.