Effect of Isomeric Structures on Photovoltaic Performance of D-A Copolymers.

Two donor-acceptor copolymers based on isomeric acceptor units, [7,7'-bithieno[2',3':4,5]thieno[2,3-d]thieno[3,2-b]pyridine]-5,5'(4H,4'H)-dione (BTTP) and [2,2'-bithieno[2',3':4,5]thieno[2,3-d]thieno[3,2-b]pyridine]-5,5'(4H,4'H)-dione (iBTTP), are developed to study the effect of isomeric structures on photovoltaic performance. Compared with PBDTBTTP, PBDTiBTTP possesses a smaller bandgap for good light harvesting and a better π-π stacking for higher hole mobility. PBDTiBTTP solar cells present balanced mobilities and good nanoscale phase separation, giving a power conversion efficiency (PCE) of 6.51%, with higher short-circuit current (Jsc ) and fill factor (FF).