Synthesis Of Organic Ion Crystals Based On Imidazole And Benzothiophene Structures And Their Application In Quantum Dot-sensitized Solar Cell Electrolytes

Quantum-dots sensitized solar cells(QDSSCs)are considered to be excellent candidates for the third generation solar cells,which has unique features such as simple preparation process,low cost,and high power conversion efficiency.As an important component of QDSSCs,electrolytes play a key role in the regeneration of quantum dots(QDs)and charge transfer between photoanode and electrolyte interfaces.At present,most high-efficiency QDSSCs was reported bu using use liquid electrolytes,but the liquid electrolytes are easily volatile and leak,which leads to instability of the battery device.On the contrary,the solid electrolyte can solve the volatilization and leakage of the solvent,and the sensitized solar cell based on solid electrolyte has the advantages of simple packaging and good stability.Therefore,the aryl-modified imidazolium ionic crystal and S-substituted benzothiophene ionic are synthesized in this thesis,which were prepared from the solid electrolyte and were applied to QDSSCs for researching.The main research contents are as follows:(1)At first,by introducing 9-fluorenyl and diphenylmethyl groups into imidazolium cations,four aryl group-modified imidazolium ion crystals were synthesized.And then,these organic ionic crystals(OICs)were used as a solid electrolyte matrix,adding sodium sulfide,sulfur,potassium chloride and 1-ethyl-3-methylimidazolium tetrafluoroborate to make a solid electrolyte.It was applyed to QDSSCs for photoelectric performance testing,at last.The OICs structure is expressed by infrared spectroscopy,nuclear magnetic resonance spectroscopy,carbon spectroscopy,and mass spectrometry.Its thermal stability and electrical conductivity are characterized by thermal analysis and steady-state current testing.The photoelectric properties of QDSSCs with OICs as solid electrolyte matrix by using current-voltage curve(J-V),electrochemical impedance spectroscopy(EIS),Tafel polarization curve(Tafel)and incident monochromatic photo-electrical conversion efficiency(IPCE)characterization.The experimental results show that OICs have good thermal stability and high electrical conductivity in the operating temperature range of QDSSCs.The solid electrolyte with 1,3-bis(diphenylmethyl)imidazole tetrafluoroborate([BDPMIm]BF4)as the matrix has the highest conductivity,among them.Under the standard AM 1.5 sunlight(100 mW/cm2),the short-circuit current density(Jsc),the open circuit voltage(Voc),the fill factor(FF)and the power conversion efficiency(PCE)obtained by[BDPMIm]BF4 as the solid electrolyte matrix in the QDSSCs are 14.89 mA/cm2,0.81 V,47.17%and 5.69%,respectively.It is because that the introduction of diphenylmethyl groups can improve the electrical conductivity of the OICs,and the solid electrolyte also has good interfacial compatibility with the photoanode,so that the dark current caused by the electron recombination in the device is effectively suppressed.(2)S-substituted benzothiophene ionic crystals were synthesized and prepared as a matrix.And then,sodium sulfide,sulfur,potassium chloride and 1-ethyl-3-nethylinidazolium tetrafluoroborate were added to prepare solid electrolytes and applying them to QDSSCs for photoelectric performance testing.The OICs structure is characterized by infrared spectroscopy,nuclear magnetic resonance spectroscopy,carbon spectroscopy,and mass spectrometry.The thermal stability,electrical conductivity and interfacial compatibility were represented by then:al analysis,steady-state current test and scanning electron microscopy,respectively.The photoelectric properties of QDSSCs devices with OICs as solid electrolyte substrates were characterized by J-V curves,EIS and Tafel.The experimental results show that the thiophene ionic crystals have good thennal stability and high electrical conductivity in the working temperature range of QDSSCs,and the matrix with 1-nethylbenzothiophene tetrafluoroborate([MBT]BF4)shared the highest conductivity.Under the standard AM 1.5 sunlight(100 mW/cm2),the QDSSCs with[MBT]BF4 as the solid electrolyte matrix obtained 20.73 mA/cm2 of Jsc,0.70 V of Voc and 5.49%of PCE.The reason of that is the introduction of a fused arolnatic group,which can contribute to the improvement of the electrical conductivity of the OICs,and the solid electrolyte has good interfacial compatibility with the photoanode,so the dark current caused by electron recombination in the device is effectively reduced.