New Borondipyrromethenes(BODIPY) Dyes Containing Dithieno[3,2-b:2′,3′-d]pyrrole Unit As Linker For Dye-sensitized Solar Cells

Because of human’s endless plundering to nature sources,there have been so many environment problems and depletion of energy suffering in today’s society that scientists must develop new sources of energy.Although alternative energy includes wind hydropower,geothermal energy and other clean energy,this thesis mainly studies the solar energy.Many of dyes possess the low molar absorption coefficient at the broader region(600-700 nm)owning more solar energy.The absorption spectra of Borondipyrrolemethene(BODIPY)dyes has be extended by BODIPY core,being considered to make better use of light energy.But this kind of dyes has achieved the low power conversion efficiency(PCE),and reports on such dyes are lacking.To explain the reason of the low PCE of BODIPY dyes,three BODIPY dyes have been designed and synthesized.The main conclusions are as follows:1 According to different conjugate linker,we finally synthesized three various BODIPY dyes(M61-M63).While we design five kinds of dyes(LB1-LB5),we detail procedure of those synthesises of compounds.In the synthesis of dye M63,the method of synthesized dye has been improved.We obtain the precursor of BODIPY,which is aldehyde compound by reaction of ethyl cyanoacetate,then continue to finish the result compound by synthesize of BODIPY.The above method get better yield,more easy purification and improve the experiment efficiency.The synthesizes of LB3-LB5 states the problem of reactivity of Vilsmeier-Haack reaction about the BODIPY including thiophene or thiophene derivative.The thiophene of DTP is more reactive than pyrrole of BODIPY.And the group forming by condensation between pyrrole and carbazole is so reactive as the thiophene of DTP,which leads to reaction achieves many products,more hard purification and synthesis.Meanwhile we use two kinds of solvents about the synthesis of BODIPY,which exhibit the solvent has an effect on the reactivity and decides whether the result compounds are synthesized or not.So we can optimize condition of synthesized BODIPY by choose a different solvents.2 In UV/Vis absorption spectra,three result dyes get broader absorption region and new absorption band.A slightly red shift(around 15 nm)of λmax was observed for M62 and M63 as compared to that of M61,suggesting that the dithieno[3,2-b:2′3′-d]pyrrole(DTP)unit can narrow the bandgap and optimize the energy levels more efficiently than the benzene unit.Thus,it is an effective way to tune the absorption properties of dyes by modification the substitution on the 8-position of BODIPY core.3 The oxidation potentials of the as-synthesized dyes adsorbed on the Ti O2 films were measured by differential pulse voltammetry(DPV)and calculated the HOMO level of dyes decrease in the order M62(0.904 V)> M61(0.846 V)> M63(0.808 V).The effect of π-bridge on the HOMO energy levels is remarkable in these BODIPY dyes.The introduction of a long bridge always brings a negative shift.By density functional theory(DFT)and time-dependent DFT(TDDFT)calculations,we know that the introduction of DTP linker has an effect on molecular orbitals’ level in theory and induces the LUMO in M61-M63 more delocalized.The molecular orbitals excitation moves easily the electron distribution from the BODIPY/DTP based spacer to the cyanoacrylic acid moiety,thus allowing an efficient photoinduced electron transfer from the dye to the TiO2 electrode under light irradiation.4 We recorded the photocurrent-voltage(J-V)characteristics and action spectra of the incident photon-to-current conversion efficiencies(IPCE).The datas of RB/M62 have the opposite phenomenon as compared to that of M61/M63,and the former photoelectric data contrast the latter multiplied,which aren’t in agreement with their absorption spectra.By the charge extraction technique and controlled intensity modulated photovoltage spectroscopy(IMVS),we calculate electron lifetime and charge densities,proving the retarded charge recombination at the semiconductor/dye/electrolyte interface.The charge recombination between electrons in Ti O2 film and electron acceptors in the electrolyte is significantly retarded by introducing a longer conjugated spacer.The dye,possessing the longest conjugated spacer,achieves the highest PCE value among the three dyes reaching 3.45%.