Dye Sensitized Solar Cells Principles and New Design

It is generally believed that fossil fuels, the current primary but limited energy resources, will be replaced by cleaner and cheaper renewable energy sources for compelling environmental and economic challenges in the 21st century. Solar energy with its unlimited quantity is expected to be one of the most promising alternative energy sources in the future. Devices with low manufacturing cost and high efficiency are therefore a necessity for sunlight capture and light-to-energy conversion. The dye-sensitized solar cell (DSSC), invented by Professor M. Grätzel in 1991 (O’Regan & Grätzel, 1991), is a most promising inexpensive route toward sunlight harvesting. DSSC uses dye molecules adsorbed on the nanocrystalline oxide semiconductors such as TiO2 to collect sunlight. Therefore the light absorption (by dyes) and charge collection processes (by semiconductors) are separated, mimicking the natural light harvest in photosynthesis. It enables us to use very cheap, wide band-gap oxide semiconductors in solar cells, instead of expensive Si or III-V group semiconductors. As a result, much cheaper solar energy at $1 or less per peak Watt ($1/pW) can be achieved. For comparison, the dominant crystalline or thin-film Si solar cells have a price of >$4-5/pW presently and are suffering from the worldwide Si shortage. The fabrication energy for a DSSC is also significantly lower, 40% of that for a Si cell. In this book chapter, we will present the principles of DSSC and detail the materials employed in a DSSC device in section 2. In section 3, the fabrication processes are shown. Then we discuss the energy conversion mechanism at the microscopic level in section 4. After this we try to give new design of the dye molecule and adsorption anchoring configurations to give hints on improving the energy conversion efficiency and making more stable devices in section 5. At last we present our conclusion and perspectives.