Preparation Of Solid State Electrolytes And Electro-catalyst And Their Applications In Dye-Sensitized Solar Cells

Owing to the low fabrication cost, simple manufacture process, environmental friendliness and high power conversion efficiency (η|), dye-sensitized solar cells (DSSCs) as next generation promising photovoltaic devices have attracted increasing scientific interests. They were thought of as promising alternatives to the traditional Si based solar cells. Although an η value over11%has been recorded for DSSCs with volatile organic liquid electrolytes, they may be inhibited for outdoor applications in view of the need for robust encapsulation. Therefore, the development of solid state electrolyte for fabrication of solid-state DSSCs (ssDSSCs) is fundamentally important from the practical application point of view. However, the low conductivity and/or incomplete filling of solid electrolytes in mesoporous TiO2films usually lead to a lower η. Therefore, the development of novel solid electrolytes with high ionic conductivity and good pore filling property is of fundamental importance for highly efficient ssDSSCs. The major contents of this part in the thesis are as follows:(1) Novel ester-functionalized imidazolium conductors have been designed and synthesized. A conductivity of5.76mS cm-1at room temperature was achieved for conductor1mixed with I2and LiI, because of the formation of3-D ionic channels and the interaction of Li+with the oxygen in the ester group, which resulted in fast charge transfer along the polyiodide chain. Through the optimization of the electrolyte component, the ssDSSC based on conductor1/I2/LiI exhibited an η value as high as6.63%with a high fill factor (0.73). In addition, a long-term stability test demonstrated that the overall efficiency remained at100%of the initial value after continuous light soaking for1000h.(2) Alkynyl group based solid ionic conductors with pendent imidazolium or piperidinum cations are prepared via a facile synthetic route and commercial materials. Due to the high crystallinity and spatial molecular arrangement, alkynyl attached to the imidazolium iodide has the high conductivity about40mS/cm. Owing to the high conductivity, the solid state ionic conductor can be used as a single-component solid electrolyte to operate efficient solid state DSSCs (ssDSSCs) without any additives in the solid electrolyte. The ssDSSC with the as-prepared ionic conductor has achieved light-to-electricity power conversion efficiency of6.3%, and exhibits very good long-term stability under continuous one sun soaking for1500h.The counter electrode possesses two critical functions:it collects the electrons flowing from the external circuit and catalyzes the reduction of oxidation state component in electrolyte to reduction state, thereby realizing the regeneration of the electrolyte. A fluorine-doped tin oxide (FTO) glass loaded with Pt is a conventional counte electrode with good electrocatalytic properties for the reduction of oxidation state component to reduction state in the electrolyte. However, its low abundance ratio and high cost prevent Pt from being used for the large-scale production of DSSCs. Conducting polymers are promising because of their low cost, high conductivity, good catalytic activity, and simple solution processing at low temperature. The major contents of this part in the thesis are as follows:(1) To improve the electrocatalytic performance of poly aniline thin films, an oriented polyaniline nanowires array has been grown in situ on conductive glass substrates without templates and applied as the cathode of dye-sensitized solar cells (DSSCs) mediated with a Co3+/Co/2+redox couple. Compared to the polyaniline film with a random network, the oriented polyaniline nanowires array exhibits much better electrocatalytic performance, and even outperforms the typical Pt electrode in both electrocatalytic performance and electrochemical stability when exposed to the acetonitrile solution of the Co(bpy)33+/2+redox couple. Owing to the higher electrocatalytic performance, the DSSC with the oriented nanowires array produces a higher short-circuit photocurrent and fill factor than the DSSCs with the random polyaniline network or Pt cathodes. Consequently, the power conversion efficiency of DSSCs based on a organic dye sensitizer increases from5.97%for the polyaniline random network cathode to8.24%for the oriented polyaniline nanowires array cathode, which is also higher than the efficiency (6.78%) of the DSSC with the Pt cathode.(2) We have in situ prepared a novel liquid crystal PEDOT (LC PEDOT) film as the CE to construct highly efficient DSSCs using the Co3+/Co/2+electrolyte and a metal-free organic dye. As a result of the improved conductivity caused by the liquid crystalline property, the LC PEDOT CE exhibited significantly increased electrocatalytic performance and much better solar cell performance compared to the PEDOT film. The LC PEDOT can also grow on flexible substrates such as flexible plastics and fibers, providing straightforward applications in flexible and fiber DSSCs.(3) Utilizing the Au-I bonding, we have achieved orientated growth of Au nanoparticles on the surface of FTO. After that, we prepared one layer of PEOT on counter electrode using the spin coating method. All solid state dye sensitized solar cell was fabricated using in situ solid state polymerization of a conducting polymer. We found that the performance of cell was enhanced with the increasing of the self-assembly cycles of Au nanoparticles. The following reasons may be responsible for this:The plasmon band of Au nanoparticles was red-shift with the increasing of self-assenmbly cycles, which is in favor of dye absorbing near-infrared light, resulting in increasing of JSC; Due to the gold (111) is the catalytic face, the gold (111) crystal plane intensity was enhanced with increasing of self-assenmbly cycles, which is beneficial to improving the catalytic active of counter electrode, therefore, the cell performance is improved with enhancing the self-assembly cycles of Au nanoparticles. Utilizing the improved catalytic activity and capability of surface plasmon resonance of gold, high-performance all solid state dye sensitized solar cell was achieved.