Application Of Carbon Materials As Counter Electrodes Of Dye-sensitized Solar Cells

Dye-sensitized nanocrystalline solar cells (DSSCs), a new kind of solar cells, have received considerable attentions over the past decade for their high light-to-electricity conversion efficiencies, relatively easy fabrication procedures and low production cost. It is a complex system consists of three parts, namely a photoelectrode of dye sensitized nanocrystalline TiO2, electrolyte, and a counter electrode, and every part has great influence on the performance of the DSSCs.Counter electrode serves to transfer electrons from external circuit to triiodide and iodine in the redox electrolyte. Currently, a layer of platinum coated on transparent conducting oxide (TCO) substrate is widely used as counter electrode in DSSCs. This is not economy way for mass production. Carbonaceous materials are quite attractive to replace platinum due to their high electronic conductivity, corrosion resistance towards I2, high reactivity for triiodide reduction and low cost.In this thesis, we apply carbonaceous materials as counter electrodes of DSSCs. First, we study the reactivity for triiodide reduction of several kinds of carbonaceous materials, such as activated carbon, graphite, carbon black. The highest overall conversion efficiency of the cell reached 6.2%. Then we apply several new kinds of carbonaceous materials as counter electrodes of DSSCs, such as carbon nanotube, hard carbon spherule, mesocarbon microbeads. The highest overall conversion efficiency of the cell reached 5.7 %. The photovoltaic performance was largely influenced by the surface area of the materials. The porous insulating layer serves to insulate photo- and counterelectrode electrically from each other while letting the redox electrolyte diffuse freely between them. It has the added functionality to reflect light that has not yet been absorbed by the photoelectrode back into the same. Especially in the red spectral region aboveλ=600nm, where the extinction coefficient of the dye quickly diminishes, a back reflector may significantly enhance the light harvesting efficiency. This is achieved by the use of highly scattering particles, such as TiO2 with tutile structure. Rutile has the highest refractive index and, hence, reflectivity of all white pigments and is therefore widely emplioyed in paints. An insulating layer made by screen-print of an aqueous dispersion of rutile powder was printed on carbon counter electrode.In order to optimize the photocurrent-voltage characteristics of DSSCs, we try different binders, such as organic binder, semiconductor materials binder and so on, and preparation technologies, such as screen print, high pressure spray.