Synthesis And Photovoltaic Performance Of Dye-sensitized Thiophene Thiophene Substituted Linking Agent

With the consumption of the fossil energy and the subsequent environmental problems, the exploitation of renewable energy received increasing attention. The solar energy has been extensively studied as an inexhaustible and clean energy. The development of new technologies for effective usage of the solar energy attracts much more attention in the worldwide. Dye-sensitized solar cells (DSSCs) have received considerable attention due to its advantages of better stability, relatively low cost and high efficiency as a new-type solar cell. Dye sensitizer is one of the most important elemental for DSSCs getting higher efficiency, which harvestes the sunlight and produces electrons. While the electrons inject to the conduction band of the TiO2, a regenaration of the oxide state of the dye sensitizer can be carried out via an accepting electron from I3-/-in the electrolyte. Dye sensitizer, which constitutes the heart of the power conversion efficiency (PCE), is all along an important research focus in the field of cell materials. The dye sensitizer has been extensively studied in recently years. Compared with metal complexes dye sensitizer, organic dye has received considerable attention due to their low cost, high molar extinction coefficient and flexible molecular design.In the normal D-π-A structure of an organic dye sensitizer, the research is focused on modifying D and π to enhance optimal performance. In this thesis, three novel dyes named TD3, TD4and TD5, were designed and synthesized. These dyes all contain triphenylamine (TPA) moieties as electron donors and cyanoacrylic acid moieties as electron acceptors, ethenyl bithiophene as π-conjugated linkers. An alkyl group was introduced into the π-conjugated bithiophene unit to inhibit dye aggregation in the TiO2surface and hence improve PCE. Details are as follows:1. TD1, TD2and TC105were synthesized as reference dyes. The preparation methods and the synthesis conditions of some intermediates were improved and optimized in the procedures. The total yield of the target compounds was11.4%,12.6%,35.4%, respectively. The structures of the final compounds and intermediates were characterized by NMR, MS and IR. 2. Three new organic dyes TD3, TD4and TD5were synthesized from triphenylamine,3-hexylthiophene and3-ethylthiophene via Vilsmeier-Haack, hydrogenation, bromonation with NBS, Wittig and Knoevenagel condensation reactions. The total yield of the target compounds was10.2%,10.0%,7.8%, respectively. The structures of the final compounds and intermediates were characterized by NMR, MS and IR. The reaction mechanism and conditions were investigated as well.3. The effects of the length of the π-conjugated unit and the alkyl chain on the photo-physical and electrochemical properties were studied by UV-Vis absorption and electrochemical analysis. The UV-Vis absorption spectra showed that the absorption band was widen30～50mm due to the extended π-bond conjugation. The Cyclic Volammetry (CV) curves showed dyes’ HOMO-LUMO levels matching well with the level of TiO2which proved that these dye sensitizers are suitable for DSSCs.4. The results of photovoltaic performance indicated that both short-circuit photocurrent density and open-circuit photovoltage have been remarkably improved by the alkyl-substituent, with which PCE have been improved25%. TD3dye with hexyl-substituted bithiophene as π-conjugated unit, exhibited a satisfied efficiency of6.78%, which is equaul to～88.7%of that on an N719-based DSSCs (7.64%) fabricated and measured under the same conditions.