Study On The Molecular Property Of Organic Dyes Regulated By Planarity

As the important part of dye-sensitized solar cells（DSSCs）,the sensitizer directly participates in the process of sunlight capture and charge transfer,which directly affects the photovoltaic performance of the device.According to our previous works,the improvement of the planarity in donor segment can selectively lift the HOMO level,while the interfacial charge transfer processes are also optimized.However,whether the planarization strategy is universally effective in various dye systems is still uncertain.Meanwhile,whether the planarity of various molecular parts could present similar effect on multiple molecular properties also needs to be further investigated.Based on the issues mentioned above,in this thesis,three series of organic dyes regulated by planarity factors are investigated to reveal the modulation effect of molecular planarity on multiple properties of dye molecule and the prepared solar cell devices.In Chapter 1,the research background and development status of dye-sensitized solar cells（DSSCs）are introduced.Recent progress of the organic dyes with carbazole,indoline and triphenylamine as donors is reviewed,and the design idea and research content of this paper is presented on this basis.In chapter 2,based on the reference indoline dye CS-31,we delved into CS-32-34which were cyclized between phenyl group and the indoline unit.CS-33 and 34 based on the planar indoline unit with n-butyl/n-octyl groups as side chains were studied to further evaluate their anti-aggregation capability.As a result,the HOMO levels of CS-32-34 were gradually optimized,while their LUMO levels were almost unaffected.Besides the selective optimization of the HOMO levels,more importantly,the interfacial charge-transfer processes in four dye-based DSSCs were also effectively regulated by the planarization and extension of the alkyl chains,suggesting the generality of the planarization strategy.In chapter 3,with carbazole as the donor and 4-octoxyphenyl as extra donor,two isomerized carbazole dyes,CS-36 and 37,were developed by aryl immobilization of the reference dye CS-35,whose dihedral angles between extra donor and carbazole were efficiently eliminated,realizing the planarization of donor part.With the planarization of extra donor,the HOMO levels of the dyes were slightly lifted while the LUMO level still remained at the same level,leading to the expansion of their light-harvesting region.However,the interfacial charge transfer processes could not be efficiently improved by this planarization due to the irregular and negligible effect,which was far different from the influence caused by the planarization on D-π-A skeleton.Moreover,the only difference between CS-36 and 37was the cyclization position.With this little difference,all the properties of these two dyes were affected to a certain extent.The origin of these difference was also investigated and discussed in detail.In Chapter 4,dyes CS-57-59 are also obtained through adjusting the number of carboxyl groups beside the auxiliary acceptor.The planarity of auxiliary acceptor part is effectively regulated.Through the photophysical and electrochemical measurements of CS-57-59,it is found that as the reduction of planarity at auxiliary acceptor part,the absorption band gradually blue shifts,and the molar extinction coefficient is greatly reduced,which will reduce the light-harvesting capability of the dyes.Meanwhile,the HOMO energy level is significantly upshifted,while the band gap also expands.The adsorption behavior of multiple carboxy dye is characterized and studied by FT-IR spectra.The absent of carbonyl stretching vibration peak around 1700 cm^-1suggests that all the carboxyl groups have been adsorbed on Ti O₂surface.Considering the chemical structure of the dye,CS-59 should lie on the Ti O₂surface,which will separate the Ti O₂from redox couple,thus resulting in the suppression of charge recombination.Further optimization and testing of photovoltaic performance are still in progress.In Chapter 5,Conclusion.