Benzo[1,2-b:4,5-b’]Dithiophene And Fluorinated Benzo[c] [1,2,5]Thiadiazole Donor-Acceptor Alternating Copolymers For Polymer Solar Cells

Donor-acceptor (D-A) alternating polymers have drawn great attention due to their good optoelectronic properties and flexible manufacturing. The dissertation focuses on the design and synthesis of the alternating polymers by modifying the donor or acceptor units. Moreover, the physio-chemical properties of the polymers have been characterized and their potential for Polymer solar cells (PSCs) has also been evaluated with devices.In Chapter 2, two donor units, i.e.,4,8-bis[2-(5-octyl)thienyl]-benzo[1,2-b:4,5-b’]dithio-phene (BDTTs) and 4,8-bis[2-(4,5-octyl)thienyl]benzo[1,2-b:4,5-b’]dithiophene (BDTTss), and two acceptor units, i.e.,4,7-bis-(2-thienyl)-5-[2-(5-dodecyl)thienyl]-6-fluoro-benzo[c] [1,2,5]thiadiazole (DTftBT) and 4,7-bis(2-thienyl)-5-fluoro-benzo[c][1,2,5]thiadiazole (DT-fBT), have been synthesized. Their alternating polymers have been developed via Stille cross-coupling reaction, with their physio-chemical and photovoltaic properties studied in detail. The results show that the introduction of alkylthio improves the solubility and photovoltaic properties of the polymers. Bulk-heterojunction (BHJ) solar cells were fabricated by solution the as-obtained polymers with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). Among the PSCs, the devices based PBDTTss-DTfBT exhibit high photovoltaic performance. Further device optimization show that the replacement of aluminum cathode with silver can significantly improves the power conversion efficiency (PCE) of the device to 6.27%, with a high Voc of 0.89 V, a Jsc of 11.7 mA/cm2, and a FF of 60.5%.In Chapter 3, we design dialkylthiobenzene (PsDT) and dialkyloxybenzene (PDT) as new donor units. And their alternating polymers with 4,7-bis(2-thienyl)-5,6-difluoro-benzo[c] [1,2,5]thiadiazole have been synthesized by Stille cross-coupling reaction. And the physio-chemical properties of the polymers have been investigated in detail. The BHJ solar cell device based PPsDT-DTdfBT only obtains a low PCE of 0.12%. While noncovalent intramolecular interactions between alkoxy substituents and thiophene rings can increase the π-π stacking coplanarity of the polymer chain, the device based PPDT-DTdfBT performs a high PCE of 6.19% and the device with an active layer of 220 nm thickness gets a PCE of 5.46%,...