Seven new conjugated D-A copolymers (P1 ~ P7) containing a strong electron deficient pyromellitic diimide (PMDI) unit and a donor unit such as thiophene

bithiophene

benzo［1

2-b:3

4-b'］dithiophene

and dithieno［3

2-b:2'

3'-d］silole were synthesized by the Stille coupling reaction.P1 ~ P7possess good solubility in common organic solvents and exhibit strong absorption in the range of 370~600 nm.The electrochemical properties ofP1 ~ P7were investigated by cyclic voltammetry (CV).The CV results indicate that the LUMO energy levels ofP1 ~ P7lie in the range of-3.66~-3.90 eV

while the HOMO energy levels in the range of-5.25~-6.17 eV.The bandgaps ofP1 ~ P7are tunable by incorporating of different donor units.The optical bandgaps forP1 ~ P7calculated from the absorption edge are 2.53~1.94 eV

and the electrochemical bandgaps are 2.45~1.55 eV.Polymers (P1 ~ P7) containing the PMDI unit were applied to bulk heterojunction polymer solar cells (PSCs).High open circuit voltages (Voc) were obtained for these polymers due to their low HOMO levels.Under AM1.5 G illumination (86 mW/cm2)

the PSC based on P7 with a pyromellitic diimide unit and a silole unit displayed an open-circuit voltage of 0.72 V

a short-circuit current of 1.22 mA/cm2 and a power conversion efficiency of 0.27%.