Synthesis And Properties Of Cyclic Thiourea Dyes With Multi - Heteroatom Conjugated Ring Bridge

As the third generation novel cells, dye-sensitized solar cells (DSSCs) have advantages of relatively low cost and simple manufacturing process, thus, people put more emphasis on this kind of cells. Dye sensitizers which are responsible for capturing electrons and pouring the electrons into the TiO2 are the key elements of DSSCs. In general, pure organic dyes are composed of electron donor (D), conjugated linkers (π) and electron acceptor (A), the research mainly focused on modifying the electron donors (D) and conjugated linkers(π) in order to obtain higher power conversion efficiency (PCE). Some functional units that own the rich electron density, such as furan, thiophene and its derivative, are taken as conjugated linkers (π). However, the introduction of heteroatomic unit into the conjugated linker (π) units were rarely reported. To explore the functions of heteroatomic unit in the conjugated linker (π) units and the influences of the power conversion efficiency. Four novel dyes Z500, Z980, Z1020, Z612 were designed and synthesized by introducing pyrimidine or benzoxazole into π conjugated linkers. Their photophysical, electrochemical and photovoltaic performance were investigated. The main research contents are as follows.1. Four novel sensitizers were synthesized from triphenylamine and urea via a series of classic reactions, involving bromonation, Suzuki coupling, diazotization, condensation-cyclization, formylation and Knoevenagel condensation reactions. The structures of target molecules along with their intermediates were confirmed by 1H nuclear magnetic resonance (1H NMR),13C nuclear magnetic resonance (13C NMR), infrared spectroscopy (IR) and mass spectroscopy (MS).2. The Uv-vis absorption spectra and electrochemical properties of these dyes were tested, and the influence of introducing the heteroatom conjugated linkers were discussed. Uv-vis spectrum showed that pyrimidine could widen the absorption range, benzoxazole could reduce absorbance band, and both could enhance the molar extinction coefficient. The electrochemical properties showed that both LUMO and HOMO energy levels of the dyes were matched with the TiO2 conduction band level and electrolyte redox potential, which satisfied with the requirement of sensitizers.3. Density functional theory (DFT) calculations showed that the dihedral angle between conjuntated linker is almost zero, nearly coplanar. The HOMO-LUMO energy band gap could be reduced by introducing pyrimidine and benzoxazole units. The electron distribution of Z1020 was adverse to the electron transfer from donor to the acceptor. The synthesized of dyes containing different conjugated bridge (π) HOMO-LUMO energy level were calculated by TD-DFT theory. Their possibility of excition from HOMO to LUMO are Z500 (22%)、Z980 (35%)、Z1020 (6%)、ST-2 (32%). AZ1(17%)、AZ6 (32%) respectively.4. The photovoltaic performance of dyes showed that the heteroatomic units decreased the short-circuit density and open circuit voltage, While introduction of cyclic thiourea functional groups into triphenylamine electron donor units could increase the short-circuit density and open circuit voltage of DSSCs. The dye Z980 exhibited a good photovoltaic performance:Jsc,9.75 mA·cm-2; Foc,0.68 V; FF,0.72; PCE,4.77%.