Indacenodithieno[3,2-b]thiophene-based broad bandgap polymers for high efficiency polymer solar cells

Two broad bandgap polymers, poly{(indacenodithieno[3,2-b]thiophene)-alt-[2, 5-bis(thiophen-2-yl)thiazolo[5,4-d]thiazole-5,5′-diyl]} PIDTT-TzTz and poly{(indacenodithieno[3,2-b]thiophene)-alt-[2,5-bis(6-octylthieno[3,2-b] thiophen-2-yl)thiazolo[5,4-d]thiazole-5,5′-diyl]} PIDTT-TzTz-TT, were designed and synthesized by copolymerizing the ladder-type indacenodithieno[3,2- b]thiophene (IDTT) donor with a thiazolothiazole (TzTz) acceptor. Both polymers possess moderate hole-mobilities of around ∼10^-4 cm² V^-1 s^-1. The polymer solar cells (PSCs) using PIDTT-TzTz-PC₇₁BM as the active layer showed good power conversion efficiencies (PCEs as high as 5.53% and 5.90%) in both conventional and inverted devices, without using any solvent additives. These results demonstrate that these broad bandgap PIDTT-TzTz polymers have potential to be used as a front cell for polymer tandem cells. © 2013 The Royal Society of Chemistry.