Indacenodithiophene-co-benzothiadiazole copolymers for high performance solar cells or transistors via alkyl chain optimization

A study was conducted to prepare indacenodithiophene-co-benzothiadiazole copolymers ((IDT-BT) for high performance solar cells or transistors via alkyl chain optimization. The synthesis and high hole mobility of an IDT-BT copolymer with hexadecyl alkyl chains was demonstrated. The long linear alkyl chains were attributed to impart some degree of crystallinity in thin film. The high performance of a similar IDT-BT copolymer bearing phenylhexyl side chains in solar cell devices was also investigated. Replacement of benzothiadiazole on this system with alternative acceptors yielded efficient solar cells. Solar cells with device structure ITO/PEDOT:PSS/polymer P4:PC₇₁BM/Ca/Al were fabricated and their averaged properties were shown. AFM images of the devices were also recorded to probe the underlying cause of this significant variation in device performance.