Preparation Of Microporous Gel Polymer Electrolytes Based On PVDF And Their Application Research On DSSC

Dye-sensitized solar cells (DSSCs) have received much attention in recent years owing to their high efficiency and low cost compared to traditional photovoltaic devices. However, the main problem in conventional DSSCs is that the liquid electrolytes reduce the long stability of the cell because of easy evaporation and leakage. To solve these problems, many attempts have been made to substitute the volatile liquid electrolytes with quasi-solid-state electrolytes or solid state electrolytes. The microporous gel polymer electrolyte possesses numerous advantages such as high ionic conductivity, excellent thermal stability, the free-standing framework and easy cell fabrication. Recently this kind of gel polymer was applied to quasi-solid-state solar cells. In this dissertation, the microporous gel polymer electrolytes were prepared by the phase inversion process based on PVDF/acrylate, PVDF/polymeric ionic liquid [P(ViPrIm+^I-)] and PVDF/ionic liquid functionalized polysiloxane (IL-SiO₂) respectively. The effects of different kinds, various compositions, framework and characteristics of polymer matrix on the morphology of the polymer membrane and the ionic conductivity of the polymer electrolyte were systematically studied. The performances of DSSCs assembled with microporous gel polymer electrolytes were also discussed. The main studies and results are summarized as follows:(1) The microporous gel polymer electrolytes based on PVDF/PMMA blend polymer, PVDF/PMMA interpenetrating polymer network (IPN) and PVDF/PEGDMA interpenetrating polymer network were prepared respectively. The samples were characterized by means of FTIR, SEM, XRD, etc. Moreover, the effects of different crosslinking monomer and various PVDF/acrylate compositions on the performances of quasi-solid DSSCs were investigated. The differences between blend polymer and IPN were studied. The results indicated that the interpenetrating polymer network improved compatibility with PVDF and acryate polymer, meanwhile it resulted in denser network structure which hinderd the transfer of charge carrier. Selecting suitable cross-linking acrylate monomer significantly improved the porosity, electrolyte uptake and the electrochemical behavior of the gel polymer electrolyte. A dye-sensitized solar cell employing polymer gel electrolyte based on PVDF/PEGDMA IPN yielded a short-circuit current of 9.291 mA·cm^-2, the open-circuit voltage of 0.700v, the fill fact of 0.523 and the conversion efficiency of 3.403% at 1 sun illumination.(2) The 1-vinyl-3-propylimidazolium iodide (ViPrIm+^I-) was synthesized with Teflon-lined, stainless autoclaves under solvent-free conditions. Then poly(1-vinyl-3-propylimidazolium) iodide [P(ViPrIm+^I-)] was prepared by free-radical-initiated polymerization of ViPrIm+^I-. The single-ion conducting liquid electrolyte was confected with different molar ration of P(ViPrIm+^I-) Afterwards, the dried PVDF polymer membranes were soaked in the liquid electrolyte prepared as above to form single-ion conducting gel polymer electrolyte. The characterization results suggested that the balance between P(ViPrIm+^I-) concentration and viscosity of single-ion conducting liquid electrolyte was a key factor to achieve the satisfying performances of polymer electrolytes and the corresponding DSSCs. Furthermore the additional of P(ViPrIm+^I-) suppressed the dark current and enabled an increase in Voc. A dye-sensitized solar cell employing single-ion conducting microporous gel polymer electrolyte based on 0.1M P(ViPrIm+^I-) yielded a short-circuit current of 8.006 mA·cm?2, the open-circuit voltage of 0.839v, the fill fact of 0.360 and the conversion efficiency of 2.418% at 1 sun illumination.(3) The microporous gel polymer electrolyte composed of PVDF and P(ViPrIm+^I-) was synthesized by the phase inversion process. The influences of P(ViPrIm+^I-) addition on the performances of polymer electrolyte and the corresponding DSSCs were investigated. The incorporation of P(ViPrIm+^I-) component into the PVDF polymer matrix reduced crystallinity of PVDF and improved the compatibility with liquid electrolyte. Moreover P(ViPrIm+^I-) as a nitrogen-containing heterocycle could react with I₃^- at the surface between TiO₂ and electrolyte to form charge transfer complexes, which efficiently suppressed the dark current. Furthermore P(ViPrIm+^I-) as a single-ion conductor could serve as a new class of iodide ion source. The superiority in transport of anionic species in the cell resulted in better photocurrent. A dye-sensitized solar cell employing GPE of PVDF/P(ViPrIm+^I-) (5:5 m/m) yielded a short-circuit current of 8.233 mA·cm?2, the open-circuit voltage of 0.790v, the fill fact of 0.566 and the conversion efficiency of 3.679% at 1 sun illumination.(4) The imidazolium iodide containing triethoxysilane group (TESPIm+^I-) was prepared by quaternization reaction by utilizing 1-methylimidazolium and 3-chloropropyltriethoxysilane. Then three types of ionic liquid functionalized polysiloxane (IL-SiO₂) grafted with different ratio of imidazolium iodide moieties, IL-SiO₂(1/2), IL-SiO₂(1/1) and IL-SiO₂(2/1), were synthesized through the sol±gel method respectively by changing the ratio of tetraethoxysilane and TESPIm+^I-. The microporous gel polymer electrolyte composed of PVDF and IL-SiO₂ was synthesized by the phase inversion process. IL-SiO₂ as nano-organosilicon was dispersed in PVDF polymer causing many micropores, which could promote the movement of free ions in a regular direction attributed to the formation of new ion transportation way. Also IL-SiO₂ improved the compatibility with liquid electrolyte and also with polymer marix for its ionic liquid characteristics. It has been found that the performances of DSSCs were affected by the interaction of the polymer membrane morphology and the proportion of imidazolium iodide moieties in polysiloxane. The DSSCs employing GPEs of PVDF/IL-SiO₂(2/1) yielded preferable photovoltaic performances. On the one hand it could be attributed to IL-SiO₂(2/1) with higher proportion of imidazolium iodide moieties provided more iodide ion source and improved anion transport. On the other hand IL-SiO₂(2/1) efficiently suppressed the dark current because that it as a nitrogen-containing heterocycle can react with I₃^- at the surface between TiO₂ and electrolyte to form charge transfer complexes. The cell employing polymer electrolyte of PVDF/IL-SiO₂(2/1) with the weight ratio of 8/2 yielded a short-circuit current of 11.192 mA·cm?2, the open-circuit voltage of 0.702v, the fill fact of 0.459 and the conversion efficiency of 3.611% at 1 sun illumination.