Synthesis And Photovoltaic Property Of Novel Conjugated Polymers Based On Benzodithiophene And Quinoxaline

The research status of polymers solar cells(PSCs) were summarized in this dissertation. At present, polymer donor materials still have some problems, such as, synthetic difficulty, poor stability and low power conversion efficiency(PCE). In view of the above problems, we designed and synthesized three series of novel and high performance polymer donor materials based on benzo[1,2-b:4,5-b’]dithiophene and quinoxaline derivatives. The chemical structures of monomers and polymers were characterized by 1H NMR, 13 C NMR and time of flight mass spectrometry. Further, their thermal stabilities, optical, electrochemical and photovoltaic properties were systematically investigated. The main research contents of this thesis are listed bleow:1) A novel D-A type polymer of PBDTDT(Qx-3)-T was designed and synthesized, in which 7,8-bithienyl benzo[1,2-b:4,5-b’]dithiophene(BDTT), thiophene and 6,7-dioctyloxy-2,3-diphenylquinoxaline(Qx-3) were used as the donor unit, π-bridge and acceptor unit, respectively. The influence of different side chains at quinoxaline on the optoelectronic properties of resulting polymers was also investigated. Through a suitable side chain engineering, PBDTDT(Qx-3)-T showed a outstanding PCE of 6.9% owing to a relative low HOMO energy level(-5.51 eV) and high carrier mobility(2.19í10-4 cm2 V-1 s-1).2) Two novel D-A type polymers PTTPPz-BDT and PTTPPz-BDTT were designed and synthesized, in which 7,8-dialkoxy benzo[1,2-b:4,5-b’]dithiophene(BDT) or BDTT was used as donor units, thiophene and pyrene-fused phenazine(PPz) were employed as π-bridges and acceptor units, respectively. Both polymers showed small optical gaps(1.70 eV and 1.59 eV), low HOMO energy levels(-5.29 eV and-5.34 eV), high carrier mobilities(1.88 × 10-4 cm2 V-1 s-1 and 2.17 × 10-4 cm2 V-1 s-1) and outstanding PCEs due to the introduction of PPz. On the other hand, the two dimension BDTT contained polymer PTTPPz-BDTT, exhibited an improved PCE of 4.86% compared to PTTPPz-BDT with a PCE of 4.25%.3) Three novel D-A-type random terpolymers PBDTT-PPzBT-H, PBDTTPPzBT-F and PBDTT-PPz BT-O were synthesized by copolymerizing electron-rich BDTT and two electron-deficient units PPz and benzo[c][1,2,5]thiadiazole(BT). The optoelectronic properties of the resulting polymers could be rationally tuned as donor materials in PSCs by changing the substituents at 5,6-positions of BT. As a result, PBDTT-PPzBT-F exhibits the widest absorption spectrum, the lowest HOMO energy levels, the PBDTT-PPzBT-O/PC71 BM blend film shows the highest absorption coefficient, the highest hole mobility and the best PCE value. The maximum PCE of PSCs based on terpolymers was 4.5% for PBDTT-PPzBT-H, 5.5% for PBDTT-PPzBT-F and 6.3% for PBDTT-PPzBT-O, respectively.