Design And Synthesis Of Ionic Liquids Electrolytes And Their Applications In Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are currently attracting a great deal of academicand industrial interest because of their high efficiency, easy assembly and low cost.However, the leakage and volatilization of organic solvent and other volatilecomposition in the electrolyte as well as the electron recombination at theTiO2/electrolyte interface limit the long-term performance of high performance DSSCs.Our work in this thesis can be summarized as follows:(1) Photochemically stable poly(ionic liquids)(Poly(ILs)) including [PBVIm][Br]and [PBVIm][TFSI]) were synthesized and dissolved in the room temperature ionicliquids (ILs) to form quasi-solid-state electrolytes for dye-sensitized solar cells (DSSCs),without using any volatile organic solvent. Compared with the conventionalPoly(St-AN)-based gel, the conductivity, diffusion coefficients of I3-and viscosity werealso investigated. The DSSCs based on IL/[PBVIm][TFSI] gel electrolyte yielded thepower conversion efficiency of4.4%under the simulated air mass1.5solar spectrumillumination at100mW cm-2. The superior long-term stability of fabricated DSSCsindicated that the DSSCs based on solvent-free IL/Poly(ILs) gel electrolytes couldovercome the drawbacks of the cells containing volatile solvents.(2) In situ thermal polymerization of a model ionic liquid monomer [BVIm][TFSI]and ionic liquids mixture to form gel electrolytes was developed for quasi-solid-statedye-sensitized solar cells. The effect of iodine concentration on the conductivity andtriiodide diffusion of the gel electrolytes was also investigated in detail. Theconductivity and triiodide diffusion of the gel electrolytes increased with the increasediodine concentration, while a further increasement of iodine contents would decrease theelectrical performances. Based on the in situ thermal polymerization-based gelelectrolytes for quasi-solid-state dye-sensitized solar cells, a highest photo-to-electron conversion efficiency of5.01%had been obtained under a light intensity of100mWcm-2(air mass1.5).(3) Benzimidazolyl functionalized ionic liquids were synthesized and applied asadditives for dye-sensitized solar cells. The compounds were charactered by1HNMR,FTIR, etc. The electrochemical profermances were also tested by the J-V curves, EIS,Tafel curves and the long-term stability. The fabricated devices showed a highestoverall power conversion efficiency of~7.79%under AM1.5radiation (50mW/cm2),and an excellent long–term stability. The synthesized ionic liquid additives might beapplied to the most DSSCs to achieve high performance and enhance the cell stability.(4) Light-scattering functionalized cyanobiphenyl-based benzimidazole wasrationally synthesized and applied for the surface modification of dyed TiO2photoanodefor dye-sensitized solar cells (DSSCs). DSSCs based on the ionic liquid andall-solid-state electrolytes were fabricated and characterized, without the addition ofadditives in the electrolytes. Compared with the electrolytes containing the additive,N-butylbenzimidazole (NBB), surface modification of dyed TiO2photoanodes withNCHB acting as an additive could enhance the open-circuit photovoltage (Voc) andshort-circuit photocurrent density (Jsc) values and the overall PCE of the fabricatedDSSCs, due to the suppressive charge recombination rate, the conductivity optimizationof the electrolytes and enhanced light harvest capability at the TiO2photoanode/electrolyte interface. Under the simulated air mass1.5solar spectrumilluminations at100mW/cm2, the fabricated devices achieved a cell efficiency of~6.63%and~5.82%for ionic liquid and all-solid-state electrolytes, respectively. Theseresults provide an alternative strategy for the high performance DSSCs with theadditive-free electrolytes.