Synthesis And Properties Of Triphenylamine Dye Sensitizers Based On Receptor Modification

In recent years,research based on sustainable energy is booming,and the development of low-cost devices has become a research hotspot.Among them,the utilization of solar energy resources has aroused widespread attention.And dye-sensitized solar cells(DSSCs)stand out among solar devices due to the advantages including low-cost,pollution-free and adjustable optical performance.Dye sensitizers are an important component of DSSCs,which are mainly divided into metal-free organic dyes and metal complex dyes.The classical structure of metal-free organic dyes is D-?-A type structure,that is,donor-(?-linker)-acceptor.The photoelectric conversion efficiency of DSSCs can be improved by the modifications of three parts.At present,the commercial development of DSSCs is limited by the limitation that the PCE of DSSCs is lower than that of silicon-based solar cells.In this paper,two D--A-A dye molecules,ML and MS,were synthesized by using the tribenzene derivative as the donor and introducing the electron-absorbing group benzooxazole as the auxiliary acceptor.and an aromatic phenyl group was introduced between the electron-withdrawing group(-CN)and the anchoring group(-COOH)to synthesize a D-A-?-A type dye of BS.It is expected that these two acceptor modification methods can improve the PCE of DSSCs.Their performances were systematic studied through the structural characterization,photophysical test and electrochemical test,theoretical calculation and photovoltaic measurement.The main research contents are as follows:(1)The dyes ML,MS and the reference dye AZ6 were synthesized from 4-amino-3-hydroxybenzoic acid methyl ester through cyclization reaction,ester reduction reaction,oxidation reaction,bromine reaction,Suzuki coupling reaction and Knoevenagel reaction.The dye BS and the reference dye TS were synthesized from 4-cyanobenzoic acid methyl ester by Knoevenagel reaction and ester hydrolysis reaction.The structure was recognised by NMR,IR,MS and elemental analysis.(2)The effects of two kinds of acceptor structure modifications in different directions on the photophysical and electrochemical properties were investigated.It was found that the ultraviolet absorption wavelength of dyes ML and MS had different degree of blue-shift compared with that of AZ6,but the molar extinction coefficient was enhanced,so the total absorption peak area was not much different from that of AZ6.In contrast,the ultraviolet absorption wavelength of dye BS was blue-shift compared with that of TS,but the absorption of the film was red-shift compared with TS.Through electrochemical test,it was found that both the HOMO and LUMO orbital energy levels of dyes could match the TiO2 band energy level and the I-/I3-redox potential in the electrolyte,and the actrual variation trend of the band gap was consistent with the calculated value.(3)The results of theoretical calculation analysis show that the distribution of electron clouds are conducive to the intramolecular charge transfer(ICT),the increase of dihedral angle shows that the introduction of benzoxazole and phenyl group destroys molecular planarity,and makes dye molecule configuration further distortion,is conducive to inhibit ?-? molecular accumulation and charge recombination between each interface.(4)The test of photovoltaic device found that the dye ML had the largest capacity,indicating that it was closely bound to TiO2 film and had the highest electron injection efficiency;Compared with AZ6,the open circuit voltage(Voc)and filling factor(FF)of dyes ML and MS are all increased,which is mainly because of their better inhibition effect on electron recombination,and their short circuit current density(Jsc)was less than that of AZ6,because of their narrow light absorption range.Combined with the three factors,the PCE value of the dyes increased in the order that MS(6.99%)<AZ6(8.01%)<ML(8.22%),their IPCE range was consistent with the trend of UV-vis absorption,and the absorption band of ML was more red-shift than that of MS,which proved that electron-rich dithiophene was more conducive to broadening the spectral range than that of monothiophene.PCE value of the dye BS(3.66%)is higher than the reference dye TS(3.23%),and its IPCE value also increase significantly,which demonstrated that separation effect is better after phenyl inserted between electron-withdrawing group and anchoring groups of dyes,and more conducive to broaden spectral absorption range,lower difference of energy band gap,and as a result of the insertion of phenyl increases the size of the molecules and the torsion Angle,suppresses the intermolecular ?-? molecular accumulation and charge recombination between each interface,thus increasing the PCE value;(5)The two dyes electronic recombination rate and lifetime are consistent with the Voc,indicating that the introduction of benzoxazole and phenyl further increases the length and the torsional angle,which is beneficial to inhibit electronic recombination,and improves the efficiency of electronic injection,and prolong the electronic lifetime,thereby improving the photoelectric conversion efficiency of the battery.