Synthesis And Photovoltaic Properties Of Novel Organic Photosensitizers Based On Thiophene-fused Carbazole

Organic photosensitizers is the key part of organic solar cells(OSCs),whose physical and chemical properties have a deep influence on photovaltic performance of OSCs.Therefore,it is of great significance to design and synthesize high-performance organic photosensitizers to boost the power conversion efficiency(PCE)of OSCs.In this dissertation,we have designed and synthesized a series of organic photosensitives,in which a thiophene-fused carbazole(DTCC)core is served as electron-donating unit.The molecular structures of the as-synthesized compounds are confirmed by 1H-NMR,13C-NMR,MALDI-TOF,and FT-IR.On the other hand,The photophysical and electrochemical properties of the photosensitives have been systematically investigated by UV-vis spectra,Density Functional Theory Calculations,and Cyclic Voltammetry.Moreover,organic solar cells based on the developed organic photosensitives have been fabricated to investigate the relationship of molecular structure and photovaltic performance.The main research results are as follows:1.An n-type organic semiconductor(DTCC-IC)with a well-defined A-D-A backbone is designed and synthesized,in which a DTCC core is used as the electron donor and two strongly electron-withdrawing 3-(dicyanomethylene)indan-1-one moieties are used as the terminal acceptors.The results reveal that the DTCC-IC has strong light-capturing ability and exhibits high molar absorption coefficient(>105M-1 cm-1)in the range of 500-720 nm.In addition,the DTCC-IC has suitable HOMO/LUMO energy levels(-5.50/-3.87 eV).The space-charge-limited current method shows that the DTCC-IC possesses a high electron mobility of 2.17×10-3 cm2 V-1 s-1,which can be comparable to the reported fullerene derivative acceptors.Under the illumination of AM 1.5G,100 mW cm-2,bulk heterojunction solar cells based on PTB7-Th donor and DTCC-IC acceptor obtain the best PCE value of 6%.This work demonstrates that the DTCC core is a promising donor unit for the development of high-mobility n-type organic semiconductors.2.Three novel D-A-?-A type organic dyes C1-C3 are designed and synthesized,in which a DTCC core is served as the electron-donating unit,benzene ring is served as the ?-conjugate bridge,and the carboxylic acid group is served as the anchoring group.To fine-tune the optical,electrochemical,and photovoltaic properties of the three dyes,various auxiliary acceptors,including benzo[2,1,3]thiadiazole(BT),5,6-difluorobenzo[2,1,3]thiadiazole(DFBT),and pyridal[2,1,3]thiadiazole(PT),are incorporated into the dye backbones.The results indicate that all of the three dyes exhibit strong light-capturing ability in the visible region and obtain relatively high molar extinction coefficients(>31 000 M-1 cm-1)due to their strong charge transfer(CT)from donor to acceptor.Compared with the BT-containing dye C1,the CT peak of the DFBT-containing dye C2 shows 7 nm blue shift,which can be ascribed to the disruption of the molecular planarity due to the introduction of two large fluoro substitutes into dye C2.Due to improved molecular planarity,the PT-containing dye C3 displays 52 nm red-shift relative to dye C1.However,the enhanced backbone coplanarity of dye C3 might lead to over-aggregation on Ti02 films.The conventional dye-sensitised solar cells are fabricated based on the dyes C1-C3.Under the illumination of AM 1.5G,100 mW cm-1,the PCE values of C1,C2 and C3 are 6.75%,5.40%and 1.85%,respectively.