Optimization Of Dithiafulvene Based Sensitizers In Molecular Structure And Their Aggregates For High Efficient Dye-sensitized Solar Cells

Compared with reported ruthenium dye-sensitized solar cells and traditional inorganic solar cells,organic dye-sensitized solar cells（DSSCs）have become one of the most promising photovoltaic technologies,which contributed to their abundant material sources,cost-effecive synthesis,easy modification of molecular structures,high efficiency and so on.It is well known the molecular structure of the sensitizers and their aggregated modes on the surface of TiO₂have a great impact on the performance of organic dye-sensitized solar cells.In this thesis,in order to obtain the optizimed cells performance,the molecular shapes and the light-harvesting ability of the sensitizers,as well as their aggregated modes on the surface of TiO₂ were regulated.In detail,the flare angles of molecules were regulated by arranging with differentπ-bridges,together with optimizing the morphology of the aggregates,a cell efficiency of9.04%was obtained for cyanoacetic acid acceptor based dithiafulvene sensitizer.In the dye system with pyridine as the acceptor,the light harvesting ability of dyes was optimized by introducing electron withdrawing group onπ-bridge and constructing dimeric light harvesting unit in molecule,which resulte a cell efficiency of 6.56%was obtained.The detailed contents are as follows:1.Two dithiafulvene sensitizers DTF-C5 and DTF-C6 with dithiafulvenyl donor,cyanoacetic acid acceptor,linked by phenoxazine and thiopheneπ-conjugated bridge have been synthesized,respectively.Among them,with a large flare of 150.61°between the donor and acceptor units in the molecular structure,the DTF-C5 molecule is close to linear shape,thus tending to form compact J-aggregates on the surface of TiO₂ without co-adsorbent deoxycholic acid（CDCA）.In this case,pristine DTF-C5 based DSSCs gave a higher short-circuit density(J_sc)of 14.92 mA cm^-2 and a power conversion efficiency（PCE）of 7.39%.On the other hand,DTF-C6,possessing a typical V-shaped conformation with a flare angle of 120.61,needed to co-adsorb with CDCA to fill the vacant sites between the dye aggregates on the TiO₂ surface,with the aim of reducing current loss and suppressing electron recombination.Compared to a DSSCs with pristine DTF-C6 aggregation,an example based on the co-adsorbed system dramatically raised the PCE from 5.50%to 9.04%,owing to the improved J_sc and open-circuit voltage values.2.In order to study the effect of the electronic structure of theπ-bridges on the performance of pyridine containing dithiafulvalene based DSSCs,two dithiafulvalene based sensitizers both with a pyridine acceptore but differing in the electron-riched thiophene derivative（DTFPy5）and electron-deficient oxadiazole derivativeπ-bridge（DTFPy6）.were synthesized.It found the light harvesting ability of DTFPy6 is better than that of DTFPy5,owing to the introduction of the electron-deficient oxadiazole on theπ-bridge.Without the co-adsorbent CDCA,the PCE of DSSCs based on DTFPy6（4.99%）was 33.8%higher than that of DTFPy5（3.73%）.3.In order to further improve the performance of pyridine containing dithiafulvalene based DSSCs,dimeric D-DTFPy5 and D-DTFPy6corresponding to the monomeric DTFPy5 and DTFPy6 were synthesized.The results show that the light harvesting range of dimeric dyes D-DTFPy5 and D-DTFPy6 are broadened and the molar extinction coefficient are increased compared to their corresponding monomers.The efficiency of DSSCs prepared by dimeric dyes D-DTFPy5 and D-DTFPy6 reachedc a PCE of 6.56%and5.80%,respectively.