Synthesis And Application Of Pillar[5]Arene-based Dyes For Dye-sensitized Solar Cells

In order to reduce the carbon emissions and achieve the carbon neutrality under the premise of ensuring energy consumption,reducing the consumption of fossil energy and developing the technologies of renewable energy are the trend of energy development.Dye sensitized solar cells(DSSCs)are well suited for decentralizing energy supply owing to their simple fabrication process,low manufacture cost,cell color tunability and light transmission.Nowaday,the DSSCs are being gradually applied in glass curtain walls of buildings,consumer electronics and sensor power supply.As a functional material in DSSCs,dyes regulate and control the function of absorbing solar photons and injecting photogenerated electrons into the external circuit.The performance of dyes determines the energy conversion efficiency of the cells.After three decades of dye development,the challenge of achieving high-efficiency dyes is to suppress the aggregation of dyes and the charge recombination of injected electrons with enhancing the light-harvesting ability of dyes.In this thesis,pillararene is introducing to the dye molecule through conjugate bonding,and the intermolecular aggregation of dyes and the charge recombination of injected electrons are suppressed by rigid columnar structure,thus achieving the improvement the V_OC of the DSSCs.The pillararene is conjugated into the donor tail and?-bridges in the donor-?linkage-accepter(D-?-A)structure of dyes,and the relationship between pillararene at different positions in the dyes and DSSCs performance are investigated.The host-guest interaction between dye and electrolyte is further explored to adjust and control the performance of DSSCs.Finally,by expanding the conjugate structure and introducing auxiliary electron accepters into dyes,efficient dyes have been screened for the complement light absorption of dye PPI.The specific research works are mainly consisting of the following parts.In the second chapter,the dye PPI is constructed by introducing the pillararene moirty into the donor tail of the D-?-A structure,without affecting the conjugated skeleton of the dye.And the dye PPII is synthesized by simultaneously structuring two D-?-A light-harvesting units on pillararene to improve the light absorption ability of the dye.By comparing with the dye PI without pillararene moirty,the experimental results confirme that the introducing of pillararene moirty significantly inhibit the intermolecular aggregation of the dye.The loading amounts of pillararene-based dye PPI anchored on Ti O₂ is significantly reducing compared to PI due to the large size of pillararene,resulting in a lower monochromatic photoconversion efficiency of PPI sensitized cell than PI.PPII adds one more D-?-A unit compared to PPI,resulting in the increase of light-harvesting capacity exceeds the magnitude of the weakened light-harvesting capacity by decreasing the loading amounts.Therefore,PPII obtains a higher monochromatic photoconversion efficiency exceeding that of PPI and PI.Electrochemical impedance spectroscopy verifies that the introduction of the pillararene could significantly improves the electron recombination resistance and prolongs the electron lifetime.Finally,the DSSCs based on the dye PPII improves both V_OC and J_SC compared to PI and PPI,obtaining a conversion efficiency of 8.36%.In the third chapter,on the basis of previous work,two groups of six electrolytes E1-6 are designed and formulated to investigate the effect of the host-guest interaction between the pillararene dyes and electrolytic components on the performance of DSSCs.The host-guest interaction is firstly determined by ¹H NMR.Subsequently,the solvent of the electrolyte with acetonitrile:pentanenitrile=85:15(v/v)is proven more favorable to inhibit the charge recombination than acetonitrile(100%)by adjusting the solvent of the electrolyte.Impedance analysis proves that the interaction between the pillararene dye and imidazolium affects the performance of DSSCs by adjusting the components of imidazolium iodide.The mechanism of action is that the imidazolium cation could be bound to the pillar[5]arene cavity,which then increases the concentration of iodine anions close to the donor moiety and facilitates the regeneration of the oxidation dye.At the same time,the oxidized iodine triple anion is close to the electrode surface,leading to expedite the charge recombination at the surface of Ti O₂,which is reflected in the electrochemical impedance spectrum as the decrease of charge return resistance.In the fourth chapter,pillararene is played as part of the?-bridges to inhibit the intermolecular aggregation and charge recombination by surrounding the?-bridges with the columnar structure.The substituents on phenyl of?-linkage affecting the photovoltaic performance of the DSSCs are also investigated.And dyes CB(no substituent),CA(ethyl substituent),CO(ethoxy substituent)and CP(columnar aromatics)are designed and synthesized.With the same conjugated backbone,the?-bridges modifying with the substituents through oxygen atoms can reduce the dihedral angle between adjacent aromatic rings and enhance the electron density on the?-bridge,resulting in red-shifting absorption and reducing the oxidation potential.The introducing substituents to the?-bridge through carbon atoms increases the torsion angle of?-bridges,which is not conducive to intramolecular electron transfer from carbazole to cyanoacetic acidand and leads to the blue shift of absorption spectra.Impedance analysis demonstrates that the introducing substituents can increase the return resistance of DSSCs.Combining with DFT calculations results,the substituent changes the conjugation planar of the?-linkage and adjusts the electronic lifetime of the electronic lifetime of the injected Ti O₂.The dye CP with the pillararene introducing to the?-bridge has the largest charge recombination resistance and electron lifetime among the four dyes,but the V_OC is not further improved than that of the dye CA,because of the excessive intramolecular torsion angle.Finally,CO senstitized solar cell obtains the highest photoconversion efficiency of 6.01%with CDCA as the co-adsorbent in work.In the fifth chapter,dyes PS1-2,PD1-2,PID1-2 and the reference dye R5 are designed and synthesized by the strategy of expanding the conjugation system and introducing the auxiliary electron accepter,for the purpose of screenning the efficient dyes with complementary the light absorption of dye PPI.With the introducing of auxiliary receptor,the absorbance range of dyes are substantial expansion,and the dyes PID1-2 achieves the full spectrum absorption covering 400–700 nm.However,the IPCE spectra reveale that the excited state electrons of dyes PD1–2 can not be injecting into the conduction band of Ti O₂.And the monochromatic photoconversion efficiency are obtained lower than 20%by the dye PID1-2 sensitized solar cell,indicating the lack of sufficient driving force for the electrons injecting into Ti O₂.Both dyes PS1 and PS2 with expanding conjugate structures exhibite different degrees of aggregation.Finally,the DSSCs sensitized by dye PS2 obtains the photoconversion efficiency of 6.09%after co-sensitization with 1 mmol CDCA.The results demonstrate that the expanded?-bridge conjugation structure by thieno[3,2-b]thiophene is more beneficial to achieve the high cell performance than 2,2'-bithiophene.