Theoretical Study On The Effect Of ? Bridge On The Efficiency Of Dye-sensitized Solar Cells

Dye-sensitized solar cells(DSSCs)have been widely studied for their cheap raw materials,simple preparation and no pollution.The photoelectric conversion efficiency of DSSCs has exceeded 13%.However,there are still a lot of limitations for commercial applications.The main reason is that the efficiency of the battery is still low.There are many factors affecting its efficiency,such as the type of sensitizer,the choice of electrolyte and electrode,etc.Because of the variety of sensitizers,if each sensitizer is tested in the laboratory,it is not only time consuming,but also a waste of material and financial resources.In addition,the results may not be very satisfied.At present,quantum computation has been verified by experiments,which can evaluate the performance of dye sensitized solar cell devices effectively and accurately.The electronic properties of sensitizers in DSSCs have been evaluated by density functional theory(DFT)and time-dependent density functional theory(TD-DFT).Based on the experimental synthesis of sensitizer,different sensitizers are obtained by modifying ? linker.By using the method of quantum chemistry calculation,the related important parameters are characterized,which can provide the direction for the experiment to find high efficiency sensitizer and save the resources.There are four parts in this thesis,which are as follows:The first part is introduction.In this part,the research background,structure,working principle and quantum chemistry of dye sensitized solar cells are introduced.In addition,the formulas for evaluating the performance of dye sensitized solar cells are also briefly introduced.The second part is about theoretical study on the effect of different ?-linker on the performance of sensitizer in carbazole-based dyes.Based on the sensitizer diphenyl-(7-pyridin-4-yl-9H-carbazol-2-yl)-amine(N13),a series of D-?-A carbazole-based organic dye sensitizers with different ?-linkers were designed.Optimized geometries,electronic structure,and other parameters,were theoretically calculated by density functional theory(DFT)and time-dependent DFT methods at the M06/6-31G(d,p)level.The result indicated that the maximum absorption wavelength of designed dye was redshifted.Meanwhile,the charge separation hampered by long ?-linkers were also observed.The third part is about theoretical study on the properties of triphenylamine-based sensitizers with different ?-linkers.Novel triphenylamine-based sensitizers have been designed based on the 3-[4-(5-[4-[bis-(4-methoxy-phenyl)-amino]-phenylethynyl]-thiophen-2-yl)-2-fluoro-phenyl]-2-cyano-acrylic acid(AS5)structure by modifing ?-linker for dye sensitized cells(DSSCs).The ground state and excited states were calculated by using density functional theory(DFT)and TD(time-dependent)-DFT theory.The calculated results show that when the thiophene group is close to the anchoring group,the absorption spectrum bandwidth and conjugation degree of the corresponding sensitizer are high.Compared with other heterocyclic rings,benzene rings have a significant blue shift in the maximum absorption wavelength of the corresponding sensitizer.The fourth part is about effect of double heterocyclic changes on dye sensitized solar cells.Based on the third part of the study,The influence of hetero atoms on the photoelectric properties of the sensitizer was studied by modifying the heteratoms on the sensitizer(E)-3-(4-(5'-(4-(bis(4-methoxyphenyl)methyl)phenyl)ethynyl)-4-fluoro-[2,2'-bithiophen]-5-yl)-2-fluorophenyl)-2-cyanoacrylic acid(B4).It is theoretically concluded that the photoelectric properties of the sensitizer are the best when the hetero atom is selenium.