Effects of π-bridge units on the properties of donor-π-acceptor type benzodithiophene-thienothiophene based polymers for organic solar cells

Conjugated donor (D)-pi-acceptor(A) cooligomers based on donor benzodithiophene(BDT) and acceptors thieno-thiophene(TT) are designed with furan, fusedthiophene, thiophene and thiazole 3t bridges. Effects of incorporation of the pi-bridges on structures and properties of oligomers and oligomer-fullerene composites are calculated and discussed. Maximum absorption wavelengths of newly designed oligomers are red shifted compared to that of the parent oligomer P1. The newly designed P2 -P5 oligomers have good light absorption efficiencies compared to that of P1. P4/PCBM and P5/PCBM blends have smaller intermolecular charge recombination rates than P1 and these two oligomers are expected to be more suitable for efficient solar cells.