Tuning photovoltaic performance of 9,9‐dioctylfluorene‐<i>alt</i>‐5,7‐bis(thiophen‐2‐yl)‐2,3‐biphenylthieno[3,4‐<i>b</i>]pyrazine copolymeric derivatives by attaching additional donor units in pendant phenyl ring

Abstract

Abstract A class of the 9,9‐dioctylfluorene‐ alt ‐5,7‐bis(thiophen‐2‐yl)‐2,3‐biphenylthieno [3,4‐ b ]pyrazine copolymeric derivatives (PFO‐3ThPz‐D) attaching additional donor (D) units in the pendant phenyl ring with a D‐A D structure was synthesized and investigated, where the additional D unit is a substituent group of fluorene, carbazole, and triphenylamine (Tpa). Their photovoltaic properties were significantly tuned by these pending donor units. Among these copolymers, the PFO‐3ThPz‐Tpa exhibited the best photovoltaic properties in the bulk heterojunction polymeric solar cells (BHJ‐PSC). The maximum power conversion efficiency (PCE) of 2.09% and the highest circuit current density ( J sc ) of 7.91 mA/cm 2 were obtained in the cell using a blend of PFO‐3ThPz‐Tpa and PC 60 BM (1:3, w/w) as active layer, which are 2.5 and 1.8 times higher than those corresponding levels in the other cell using the parent PFO‐3ThPz‐Ph copolymer instead of PFO‐3ThPz‐Tpa as donor, respectively. While PC 60 BM was replaced by PC 70 BM, the PFO‐3ThPz‐Tpa‐based BHJ‐PSC exhibited better photovoltaic properties with PCE of 3.08% and J sc of 10.3 mA/cm 2 . This work demonstrated that attaching donor units into the D‐A‐based copolymeric side‐chain is a simple and effective method to improve the photovoltaic properties for the resulting copolymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012