Benzo[1,2-b:4,5-b’] Dithiophene-Based Donor-Acceptor Copolymers For Polymer Solar Cells

With the utilization of the solar energy, the research on solar cells has become more in-depth. Compared with the traditional solar cells based on silicon which is also widely used, polymer solar cells show the advantages of cheap, low pollution during the production and flexible processing. In recent years, it has received enormous attention. Donor-accept (D-A) alternating polymers have been reported for high-performance PSCs. The highly representative of them are benzo[1,2-b:4,5-b]dithiophene (BDT) copolymer with the advantages including its planar conjugated structure, easy modification. The unit of dialkylthio benzo[1,2-b:4,5-b’]dithiophene (S-BDT) has been proved to be an excellent electron donor unit, while it has seldom report because of different synthesis. In this thesis, we demonstrate a new synthetic method for the production of monomeric dialkylthio benzo[1,2-b:4,5-b’]dithiophene (S-BDT) and the design and synthesis unit of two-dimension dialkylthio benzo[1,2-b:4,5-b’]dithiophene (S-T-BDT), which are used as donor units to be designed and synthesized six new conjugated polymers (P1, P2, P3, P4, P5 and P6). The six polymers using thiadiazolo[3,4-g]quinoxaline (DTBTQx), benzo[c][1,2,5]-oxadiazole(DTBO) and pyrrolopyrrole-1,4-dione (DPP) as acceptor unit has been synthesized by Stille coupling polymerization reactions.The properties of the materials are characterized and the device characterization has also been carried out. Photovoltaic cells were fabricated by [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) by blending the above-mentioned S-BDT unit copolymers, among which P2 exhibit a best power conversion efficiency (PCE) of 4.22% with a high Voc of 0.83 V, a Jsc of 8.1 mA/cm2, and a FF of 63%. The device was further optimized to give a higher PCE by using PC71BM to get a PCE of 5.52%. The S-T-BDT unit copolymers device testing is underway now.