Synthesis Of β, β'- Disubstituted Biphenone Dyes And Their Effects On The Properties Of DSSCs

With the constant consumption of traditional energy and increasing environmental problems, the exploitation of solar energy has been becoming the worldwide research focus. Solar cells, as one of photovoltaic devices convert solar energy into electrical energy, have a great of application prospects. The dye-sensitized solar cells (DSSCs) have been widely investigated due to their high conversion efficiency, relatively low cost and simple manufacturing process. Dye sensitizer is one of the key factors for DSSCs to obtain higher conversion efficiency, which play a critical role to capture sunlight, produce electrons and transmits electron to the nanometer semiconductor conduction band. And metal complexes dye is the widest application in the DSSCs due to its high stability, wide spectral response range and long excited state lifetime. However, large-scale production of metal complexes dye is limited because of the precious metal scarcity. Compared with metal complexes dye, pure organic dye has gained rapid development in recent years due to its wide range of raw materials, high molar extinction coefficient and the various molecular structures.Generally, pure organic dyes are composed of electron donor (D), conjugated bridge (π) and electron acceptor (A). Triphenylamine is widely used as the electron donor due to good electron and hole transport capabilities, specific spatial structure; and cyanoarylic acid is commonly used as the electron acceptor. Oligothiophene and its derivatives are popular choice for conjugate linker due to their electron-rich property and good electronic transmission. In order to suppress the sensitizer aggregation in TiO2surface and improve power conversion efficiency (PCE). This thesis introduce alkyl chains at nonortho β-positions of2,2’-bithiophene modifying π-linker, design and synthesize two series dyes of T-Cx and S-Cx includes three novel dyes structure (T-Cl, S-Cl, S-C6) and three reference dyes (T-CO, T-C6, AZ6), which contains triphenylamine (TPA) and cyclic thiourea functionalized triphenylamine as electron donors respectively,2,2’-bithiophene,3,3’-dimethyl-2,2’-bithiophene,3,3’-dihexyl-2,2’-bithiophene as π-conjugated bridge and cyanoacrylic acid as electron acceptors.The contents as follows:1. Conjugated linkers were synthesized started from bithiophene,3,3’-dimethyl- 2,2’-bithiophene,3,3’-dihexyl-2,2’-bithiophene, through bromonation with NBS, Kumada coupling, Vilsmeier-Haack, aldehyde protection and borating reactions. Six organic dyes were synthesized use triphenylamine and cyclic thiourea functionalized triphenylamine Suzuki coupling with conjugate linker, followed by Knoevenagel condensation reactions. The structures of the target products and intermediates were characterized by NMR, MS and IR. Synthetic methods for the reference dye T-CO and intermediates were improved as well.2. The photophysical and electrochemical properties of the dyes were measured that UV-vis absorption spectra of the dyes in the intramolecular charge-transfer (ICT) region turns out a blue-shifted and a decrease of molar extinction coefficient as the alkyl chains getting longer. S-Cx series dyes gained wide absorption spectra compared with the dyes T-Cx. The electrochemical properties shown that, both LUMO and HOMO energy level of the dyes were matched the TiO2conduction band level and electrolyte redox potential, which confirmed them satisfy the requirement of sensitizer.3. Density functional theory calculations showed that the dihedral angle between the thiophene rings trends to enhance, the molecular structure of distortion increased. The electron distributions indicated that the HOMO-LUMO excitation induced by light irradiation can effectively move the electron from the donor to the acceptors, which confirmed that the photoinduced electrons can be transfered from the dyes to the TiO2conduction band after the electron separation.4. The photovoltaic performance of the dyes showed that the open circuit voltage (Voc) and fill factor (FF) were increased, but the short-circuit current density (JSC) was reduced and PCE was reduced as the alkyl chains getting longer. S-Cx series dyes showed higher PCE compared with the that of T-Cx series dyes, thereof S-Cl dye exhibited a good photovoltaic performance with Jsc=13.79mA·cm-2, Voc=0.73V, FF=0.70, the PCE of7.08%.