Datensatz

Zusammenfassung

Two terthiophene–isoindigo copolymers (P₃TI-O and P₃TI-D) were successfully designed and synthesized. Octyl (O) and dodecyl (D) alkyl side chains were appended at the third position of the first and fourth positions of the last thiophene on the terthiophene donor units in P₃TI-O and P₃TI-D, respectively. The band gaps of these copolymers were less than 1.7 eV. We found intramolecular charge-transfer states in both copolymers, which were generated with time constants of 4.5 and 13 ps for the copolymers with short and long alkyl side chains on their donor units, respectively. These results indicate that an almost 3-fold faster intramolecular charge-transfer process occurs when the alkyl side chains are shortened by four methyl units. Owing to a better interchain charge transfer, P₃TI-O exhibits a more efficient exciton diffusion compared to P₃TI-D, thus leading to longer exciton lifetimes in the copolymer with shorter alkyl side chains. Consequently, when blended with PC₇₁BM in bulk heterojunctions, P₃TI-O showed a better exciton dissociation efficiency compared to P₃TI-D. These results correlate well with the higher short-circuit current densities observed in P₃TI-O:PC₇₁BM inverted architecture organic solar cells compared to the P₃TI-D:PC₇₁BM ones.