Synthesis And Properties Of D-A Conjugated Copolymers Based On Thieno[3,4-b]Pyrazine

In the past decade, polymer solar cells (PSCs) have received a great deal of attention as a potential renewable energy source because of their advantages such as low cost, light weight, and capability of fabricating flexible large-area devices. In the past five years, the donor-acceptor (D-A) approach to reduce the band gap of conjugated polymers has been paid much attention. This dissertation is focusing on the development and synthesis of new D-A copolymers based on new acceptor unit (TP) with the characteristics of facile synthesis. The main results are as follows:2,3-dimethyl-5,7-dithien-2-yl-thieno[3,4-b]pyrazine (DMTP) and 2,3-diphenyl-5, 7-dithien-2-yl-thieno[3,4-b]pyrazine (DPTP) were synthesized. Their structure were confirmed by 1H NMR.A series of corresponding polymers based on DMTP (DPTP) and BDTs were synthesized by Stille coupling as follow:PBDT(6,8)-DMTP, PBDT(6,8)-DPTP, PBDT(2, 4)-DPTP. Their properties were characterized by 1H NMR, GPC, TGA, CV and UV-Vis. Photovoltaic devices were fabricated in a typical sandwich structure of glass-ITO/PEDOT-PSS/polymers-PCBM/Ca/Al. Their device efficiencies were:0.80% (P1),1.50% (P2),1.15% (P3). In addition, devices based on the DMTP-based polymers(P1) exhibited lower PCEs than the DPTP-based polymers(P2, P3), which could be explained from two aspects:Voc, which decreased because of an increase in the HOMO energy level of the DMTP-based polymers, and Jsc, which decreased probably because of the poor charge separation or transport of the DMTP-based polymers. The optimum performance of the devices is obtained at 1:2 weight ratio of P2:PCBM with PCE of 1.50%.A series of random terpolymers based on TPs, BDT and TPD were synthesized by Stille coupling. They are P4(PBDT-TPD85-DPTP15), P5(PBDT-TPD70-DPTP30), P6(PBDT-TPD85-DMTP15) and P7(PBDT-TPD70-DMTP30). Their properties were characterized by 1H NMR, GPC, TGA, CV and UV-Vis. With P6:PCBM=1:1.5 as the active layer, solar cells with a PFN/Al bilayer cathode displayed PCE up to 0.98% due to obvious improvements of Jsc and FF, in comparison with those with Ca/Al cathodes. Photovoltaic devices were fabricated in a typical sandwich structure of ITO/PEDOT-PSS/ polymers-PCBM/PFN/Al.Their device efficiency were:0.97％(P4),0.57%(P5),0.78％ (P6),0.38%(P7).