| 초록 |
Low bandgap polymers containing fluorinated electron-accepting building blocks have recently been studied. Substitution of highly electronegative fluorine atom lowers the energy levels of the polymer. Although it is well known that electron-rich unit in alternating conjugated copolymer mainly affects the LUMO energy level of the copolymer, fluorinated electron-deficient unit in the copolymer lowers both HOMO and LUMO energy levels. Therefore, substitution of fluorine atom into the copolymer affords high VOC of device. In this report, we synthesized low bandgap polymers based on benzo[1,2-b:4,5-b’]dithiophene (BDT) as an electron-rich unit and 2,1,3-benzothiadiazole (BT) or 5,6-difluoro-2,1,3-benzothiadiazole (ffBT) as an electron-deficient unit. Both of polymers show a similar optical bandgap of ~1.7 eV, while PBDTffBT shows deeper HOMO energy level (−5.43 eV) than that of PBDTBT (−5.17 eV), implying that the solar cell device with PBDTffBT exhibits higher VOC than PBDTBT. |
