Study On Ionic Transport And Charge Transfer In The Electrolyte Of Dye Sensitized Solar Cell

As a novel photoelectric cell, dye sensitized solar cell (DSSC) has been attracted considerable attention and regarded as a promising photovoltaic device. The most commonly used electrolyte in high-efficiency DSSC is organic liquid electrolyte. However the leakage and volatilization of the liquid solvent in the electrolyte significantly deteriorate the long-term stability of DSSC. Therefore, in order to improve the long-term stability of DSSC, polymer electrolyte is of particular interest to be applied in DSSC. However, DSSC employed with polymer electrolyte exhibits lower conversion efficiency compared with liquid electrolyte. Therefore, the research work in this thesis is to systematically study the electrolyte to develop high-efficiency and stable DSSC. The ionic transport property and interfacial charge transfer process of polymer electrolyte, as well as the influence of electrolyte on the photovoltaic performance of DSSC is mainly investigated.First, organic liquid electrolyte is studied to reveal the charge transfer kinetics of I-/I3-redox couple to provide theoretical bases to develop polymer electrolytes. The charge transfer kinetics of I-/I3-redox couple is discussed by investigating the influence of I2concentration, cation, solvent and4-tert-butylpyridine (4-TBP) on the performance of organic liquid electrolyte. The results indicate that I2concentration in electrolyte demonstrates important impact on the photovoltaic performance of DSSC. The open-circuit voltage (Voc) decreases with increasing I2concentration, mainly attributed to the increase of electron recombination. The highest short-circuit current(Jsc) is obtained in electrolyte with0.03M I2. Cations of different kinds are found to modify the interfacial property of DSSC. Owing to the different of cation absorbability on TiO2surface, Voc of DSSC decreases in the order of TBA+, DMPI+and Li+. The mix solvent of ethylene carbonate and propylene carbonate (EC/PC) shows the optimum performance. The role of4-TBP in electrolyte in the present of TBA+is less effective than Li+.And then in order to explore the ionic transport mechanism in solid polymer electrolyte, the effect of ion concentration on the chemical structure and ionic conductivity of solid polymer electrolyte with emphasis on the anion transport behavior is investigated. The corresponding performance in DSSC is studied to discuss the potential application in DSSC. The results show that a low ion concentration maintains the crystalline structure of solid polymer electrolyte, while an increase of ion concentration leads to an amorphous phase, which has a more favorable ionic conductivity than crystalline electrolyte. The crosslinks of polymer chain in high ion concentration electrolyte results in low ionic conductivity. Anions do not coordinate with polymer chain and the anion transport is facilitated by the free volume in solid polymer electrolyte, which is promoted by flexible amorphous phase in electrolyte. The solid polymer electrolytes with concentration of EO/LiI=11and8show preferable anion transport property, which could be applied in DSSC.Finally, polymer gel electrolyte is developed and optimized. The impact of polymer gel electrolyte on the photovoltaic performance of DSSC is studied by analyzing the ionic transport and charge transfer kinetics in polymer gel electrolyte. Furthermore, the influence of nanomaterial fillings on the performance of nanocomposite polymer gel electrolyte is investigated. The results show that DSSC with polymer gel electrolyte shows a larger Voc compared with liquid electrolyte, and the highest Voc of0.873V is obtained. The enhancement of Voc is attributed to the negative shift of TiO2conduction band and the lower electron recombination of polymer gel electrolyte. DSSC with polymer gel electrolyte shows excellent durability and stability compared with liquid electrolyte. However, the employment of polymer gel electrolyte in DSSC needs to be supported by suitable porosity and aperture size in TiO2photo-anode. The Jsc and Voc of DSSC can be simultaneously improved by TiO2nanoparticle composite polymer gel electrolyte.