Synthesis And Study On The Properties Of Organic Photovoltaic Materials Based On Benzothiadiazole And Benzo[1,2-b:4,5-b’]dithiophene

In order to improve the absorption band to better match the solar spectra, tunethe HOMO and LUMO energy levels, and improve the hole mobility of thephotoconductive materials, we have designed and synthesized a series of side chainpolymer and small molecule photovoltaic materials containing benzothiadiazole, andsystematically summarized the research progresses of the materials and devices basedon organic solar cells. The structures of the as-synthesized target products wereconfirmed by1H-NMR,13C-NMR, MALDI-TOF and FT-IR. The thermal,photophysical, electrochemical and photovoltaic properties of the polymers and smallmolecules have been investigated by thermogravimetric analysis, UV-vis spectra, PLspectra and cyclic voltammetry. The main results are as follows:1. Three new copolymers (PT-TPA, PT-DTBT and PT-DTBTTPA) based onbenzo[1,2-b:4,5-b]dithiophene (BDT) and thiophene with different conjugated sidechains (di(p-tolyl)phenylamine (TPA),4,7-dithien-5-yl-2,1,3-benzothiadiazole (DTBT)and DTBT-TPA) were synthesized via the Stille coupling polymerization. The TPAand the DTBT were introduced to improve the hole-transport ability and broaden theabsorption spectrum. Field effect results that the copolymer PT-DTBTTPAcontaining TPA and DTBT in the side chain showed the highest hole mobility. Thethree copolymers exhibit deep-lying HOMO energy levels, which were effectivelytuned by changing the side groups. Bulk heterojunction polymer solar cells based onPT-DTBT and PT-DTBTTPA showed promising power conversion efciencies of4.18%and3.49%, respectively.2. Four new low band gap A-D-A type small molecules (L1-L4), with2-ethylhexoxy and2-ethylhexsulfur substituted BDT as the central building block and4,7-dithien-5-yl-2,1,3-benzothiadiazole (DTBT) as electron-withdrawing unit, havebeen designed and synthesized for solution-processable small molecule bulkheterojunction (BHJ) solar cells. The thermal, photophysical, electrochemical,mobility and photovoltaic properties of these molecules were studied. These materialspossessed strong absorption at350-700nm and deep-lying HOMO energy levels(-5.21to-5.37eV). The device based on L4with2-ethylhexsulfur substituted BDTunit demonstrated the highest Voc(0.68V). Solution-processed small molecule BHJsolar cell based on L1/PC61BM blends (1:2, w/w) achieved the highest power conversion efficiency (PCE) due to the broadest absorption and highest extinctioncoefficient.