Platinum-less Counter Electrodes for Dye Sensitized Solar Cells

Abstract

Nowadays, we always get a lot of news about the energy crisis because of lack of the petroleum. To overcome the serious problem, various renewable energy resources are developed. Renewable energy means that the resources come from the natural such as wind, tides, geothermal heat and sunlight. These resources are unlimited and do not generate the carbon dioxide to convert into the electricity. Above all, the direct conversion of solar energy to electricity by photovoltaic cells is emerging as a leading contender for next generation green power production because the photovoltaic cell has huge potential to apply in multi-usage by various different types of cell structures. For example, the crystalline silicon solar cell shows very high performance and the amorphous silicon solar cell has very good flexibility. These functions make the solar market wider. However, the power conversion price is still expensive with the photovoltaic although the silicon solar cell achieves high efficiency. The raw ore price of silicon is expensive and purification process and crystalline step need very high temperature. Also, the wide application of high purity silicon leads lack of supplement of silicon wafers. Because of these factors, other types of photovoltaic are still focused on replacement of the silicon solar cell. Dye sensitized solar cells that convert solar energy into electrical energy have been considerable interests during the last two decades owing to their cleanliness, simple fabrication process and relatively high efficiency. This electrochemical cell is organized by three parts in major. Working electrode, counter electrode and electrolyte are mainly composed for the dye sensitized solar cell. The working electrode is generally used in TiO2 nano-porous electrode with micro thickness on FTO glass. Due to sintering processes for the working electrode, FTO glass is essential for substrates instead of ITO glass because the ITO cannot endure over 300oC. The counter electrode is typically fabricated with platinum layer or platinum particles. Roles of the noble metal is catalysis to convert the electrolyte forms. The components of electrolyte is generally triiodide/iodide redox couple. The iodine can etch most of metals even gold is also dissolved by the iodine. Owing to these reasons, very limited catalytic materials can be selected for the counter electrode. Platinum is the most famous material on it. To decrease of solar cell production costs for dye sensitized solar cell is to replace the platinum into other catalytic material such as palladium, nickel or carbon. The carbon is widely used as electrode material for various electrochemical systems. Also the price is incomparably lower than the platinum. Thus, the carbon and carbon structures have a lot of potential on this field. In this study, two types of pt-less counter electrodes are going to be introduced with comparable efficiency to the platinum. The first counter electrode is carbon black and TiO2 nanocrystal mixture. Only carbon black layer does not have good connection between substrate and the material. However, using TiO2 nanocrystals work as binder and electron transport parts. It gives higher fill factor and better current density. And the second counter electrode is carbon nanomedusa. This material has very high porosity and also good electron conductivity to compare with other common carbon materials. The carbon nanomedusa is organized by ordered mesoporous carbon and carbon nanotube. These two different carbon structures are connected each other. It is brand-new material and the first time to modify on dye sensitized solar cells.