Pyromellitic diimide-benzodithiophene copolymer for polymer solar cells: Effect of side chain length and thiophene π-bridge on optical and electronic properties

Three donor-acceptor conjugated polymers were synthesized by combining electron donating benzodithiophene and electron accepting pyromellitic diimide. The relationship between structure and optical, electrochemical properties of the polymers were investigated. The results indicate that replacing the 2-ethylhexyl side chain with the longer 2-octyldodecyl side chain stabilized both the HOMO and LUMO level, and the insertion of thiophene π-bridge between pyromellitic diimide and benzodithiophene led to bathochromic-shifted and broader absorption. The polymers were used as donor materials to fabricate polymer solar cells. The highest open-circuit voltages reached 0.69 V and power conversion efficiencies reached 0.11%.