New conjugated polymer for efficient polymer solar cells

Abstract

A new semiconducting poly[(bithiophenyl acrylronitrile)-co-2,5-[(1,4-didecyloxy)naphthalene]) (PBTADN), an alternating copolymer of bithiophenyl acrylronitrile and (didecyloxy)naphthalene, is synthesized and used as an active material for organic thin film transistors (OTFTs) and organic solar cells. Incorporating bithiophenyl acrylronitrile as an electron deficient group and didecyloxy naphthalene as an electron rich group resulted in a relatively low bandgap, high charge carrier mobility, and finally good photovoltaic performances of PBTADN solar cells. The maximum power conversion efficiency of the PBTADN:PC71BM solar cell reached 2.9 % with a Voc of 0.88 V, a short circuit current density (Jsc) of 5.6 mA/cm2, and a fill factor of 59.1 %. The molecular weight dependence of morphology, charge carrier mobility and finally the photovoltaic performances were also studied and it was found that high molecular weight PBTADN has better self assembly characteristics, showing enhanced performance.