Molecular Modification Of Y-shaped Alkyl Chain Dyes And Study On Interfacial Electron Transport Properties Of Photovoltaic Devices

Solar cells can directly convert solar energy into electrical energy,which is an effective mean of solar energy development and utilization.Among solar cells,dye-sensitized solar cells(DSSCs)are a new type of solar cells with promising applications.As an important part of DSSCs devices,sensitizing dyes have a significant impact on photoelectric conversion efficiency.This thesis further focuses on molecular structure-property relationship and electron transport at the interface of dye-sensitized solar cells,designs and synthesizes seven dyes with Y-shaped alkyl chains.The Y-shaped alkyl chain acts as a "barrier" that prevents TiO2-injected photoelectrons from recombining with oxidized dyes and electrolytes.The "barrier" is designed to reduce the generation of dark current and improve the photoelectric conversion efficiency of the devices.The main contents are as follows:(1)Synthesis of D-π-A-typed organic dye YY-ThP with triphenylamine bearing Y-shaped alkyl chains as the donor,phenylthiophene as the π-bridge,cyano acetic acid as the receptor.Based on this,fluorine atoms are introduced into the 3-,2-and 2,6-positions at the benzene ring of YY-ThP,three fluorine-containing dyes YY-ThP(3F),YY-ThP(2F)and YY-ThP(26F)are synthesized.In addition,the thiophene and benzene ring are exchanged to synthesize the dye YY-PTh,and the thiophene is replaced with thieno[3,2-b]thiophene to synthesize the dyes YY-TTP and YY-PTT.The structures of the intermediates and the target dyes are confirmed by 1H NMR,13C NMR,GC-MS or HR-MS.Also,the photophysical properties,electrochemical properties,molecular configuration and photovoltaic properties are measured by UV-vis,CV,DFT,and J-V curves,IPCE and EIS.(2)The influence of the introduction of fluorine atoms into the π-bridge chain on electron transport was studied.The results show that compared with YY-ThP,the introduction of fluorine atoms into the π-bridge cannot improve the effective electron transport of the device,and the photoelectric conversion efficiency of the devices based on fluorine-substituted dyes is reduced.Although the fluorine substitution can broaden the response to visible light region,the response intensity between 380-450 nm is reduced.In addition,the introduction of fluorine atoms reduces the effective electrons injected into the TiO2 film due to the polar effect and aggregation effect.The dark current increases and the short-circuit current decreases,but the open circuit voltage of DSSCs based on the 3-position fluorine-substituted dye YY-ThP(3F)increases by 12.8 mV compared to the dye YY-ThP.The reason may be that the fluorine substitution at 3-position reduces the dihedral angle of π-bridge and increases the conjugation degree of the whole dye.The fluorine-containing dyes are co-sensitized with the same molar ratio of YY-ThP,and the results that the visible light absorption intensity of the three groups of co-sensitizing dyes at 380-450 nm increase obviously.Compared with the single dye YY-ThP,open-circuit voltage and short-circuit current of the co-sensitizing system YY-ThP+YYThP(3F)increases by 20.1 mV and 1.02 mA cm-2,respectively.This is mainly due to the reduction of the dark current caused by aggregation.Therefore,the highest photoelectric conversion efficiency(PCE=5.46%)is obtained.(3)The influence of exchange of π-bridge fragments on electron transport is researched.The results show that after the position of thiophene and benzene ring are exchanged,the light absorption range is significantly widened and the absorption intensity is also increased,but the photoelectric conversion efficiency is low.The reason may be that the molecular configuration of the dye YY-PTh is linear and the π-bridge part of the dihedral angle is too large,while the dye YY-ThP is crescent-shaped,and the π-bridge has a small dihedral angle.When the dye is adsorbed on the TiO2 film,the dye YY-PTh has a large dark current due to the aggregation effect.The larger stereotactic effect of dye YY-ThP inhibits the intermolecular aggregation and electron recombination,and its configuration can maximize the conjugation degree of the whole dye molecule.When the dyes YY-ThP and YY-PTh are co-sensitized with the same molar ratio,the open circuit voltage and circuit current density of the common-sensitizer are further improved due to the molecular configuration,so the best photoelectric conversion efficiency is 5.28%.This dissertation mainly designs and synthesizes Y-typed alkyl chain dyes.By introducing fluorine atoms into the π-bridge chain and replacing the π-bridge fragments,the structure-property relationship of dyes and the electron transport of DSSCs are studied,and the device with better performances is obtained by co-sensitization strategy.Overall,this study has a certain reference significance for the molecular design of dye sensitizers and the modification of π-bridges.