| 초록 |
We synthesized a series of conjugated polymers with a backbone of thieno[3,4-b]thiophene-co-benzo[1,2-b:4,5-b’]dithiophene (PTB) moieties and studied the effect of the polymer structure on photovoltaic properties. We demonstrated that fluorination of the polymer backbone affected the energy levels, the morphology of polymer/fullerene blend films, and the intramolecular exciton splitting dynamics of the polymers, resulting in power conversion efficiencies (PCEs) of 2.3~7.2%. To further enhance the PCE, we developed novel copolymers incorporating expanded π-conjugation units such as dithieno[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene (DBD). Introduction of such large π-conjugation systems into the polymer facilitates the delocalization of holes in the polymer formed after exciton-splitting, which improved exciton-splitting efficiency. As a result, solar cells made from the polymers showed a higher PCE of 7.7% (Voc: 0.87V, FF: 64.8%, Jsc: 13.7 mA/cm2) than the PTB polymers. |
