Synthesis And Properties Of N,N-thienyl Aniline Dye Sensitizers

In recent years,in order to change the fossil-based energy frame and enhance the utilization of solar energy,solar cells have been studied intensively.Compared with traditional silicon-based solar cells,dye-sensitized solar cells(DSSCs)have attracted more and more attention due to its low price,simple process and high photoelectric conversion efficiency.Dye sensitizer is the core part of DSSCs,which absorbs photons and produces photoelectrons.The properties of dye sensitizers directly affect the performance of DSSCs.Metal-free organic dye sensitizer molecular designs generally follow the D-?-A electronic push-pull structure,the structure determines the performance,modifications of any structures among three parts can obtain different dyes.In this paper,we aimed at investigating the performance of DSSCs based on the dyes as sensitizers which contain the thiophene ring as donor ring to replace the benzene.in the triphenylamine.The novel N,N-thienylaniline based dyes R602,R684 and triphenylamine based reference dye R422 were synthesized.The intermediates and dyes were characterized by NMR,MS and IR.Their photophysical,electrochemical performance test and density functional theory calculation were carried out.It was found that the UV-vis absorption spectra of the new structure N,N-thienylaniline based dyes R602 and R684 showed a certain degree of blue shift and the absorption range narrowing compared with the traditional triphenylamine based dye R422.The HOMO and LUMO levels of the three dyes matched the I-/I3-energy level and the TiO2 conduction band.Compared with the reference dye R422,the band gap Egec of the new structural dye R602 and R684 are broadened,which is the reason for the narrowing of light absorption bands.The parameters such as short circuit current density Jsc,open circuit voltage Voc and photoelectric conversion efficiency of DSSCs based on R602 and R684 are lower than those of DSSCs based on reference dye R422.The main reason is the introduction of thiophene ring into the triphenylamine system which destroys the planar structure of typical triphenylamine based dye,resulting in the flatness of the donating ability and thereby minifying intermolecular charge transfer(ICT).When the thiophene conjugated bridge chain was extended,the spectral response of R684 was broadened and the maximum absorption wavelength Xmax was red shifted.Compared with dye R602,the better photovoltaic performance(PCE = 0.74%,Jsc = 2.61 mA/cm2,Voc =499.30 mV,FF=0.68)of R684 was obatined.The electron lifetimet,charge transfer resistance Rct of DSSCs based on R602 and R684 are lower than that of reference R422,tR422(6.09 ms)>tR684(3.78 ms)>tR602(0.42 ms),Rct R422>Rct R684>Rct R602,which corresponds to the trend of the open circuit voltage Voc,of the dyes,this is caused by the introduction of thiophene which destroyed the co-planar structure of the donor.