Solar Energy Harvesting - Term Paper Example

«Solar Energy Harvesting» Introduction Dye solar cells were first developed in 1991 by O’Regan and Gratzel and are designed to be both cost effective and efficient in harvesting of solar energy. There are three main features in a dye solar cell, which are that they are photoelectrochemical, nanoparticulate and dye-sensitized. The photoelectrochemical properties relate to the way in which charge separation occurs in the cell at the interface of the titanium film. The nanoparticulate property relates to the surface area of the titanium film being around 1000 times larger than the actual apparent area. The device is essentially composed of a ‘light sponge’ of nanoparticles. The dye-sensitized property means that the titanium has a monolayer of absorbed dye which increases the likelihood of photon capture (Tulloch, 2004). Nanostructured semiconductor films have been identified as suitable for applications in solar cells as their physical and chemical properties make them ideal. These nanostructured films utilize these dye-sensitized photoelectrochemical solar (PES) cells. The large surface area of nanoparticles means that they are capable of harvesting large amounts of solar energy. The way in which the light harvesting is achieved is that light is absorbed by the dye which is trapped in the mesoporous film made by the titanium nanocrystallites. There is a sensitizer grafted into the titanium. Light induced electrons are injected from the absorbed dye into the nanocrystalites and makes the titanium conductive (Gratzel, 2003). Issues with PES There are so far two concerns which have been identified in the application of these PESs. They are related to the ‘maximum light harvesting of sunlight and the efficient collection of photocarriers at electrons’ (Rodriguez et al., 2007). Both of these issues have attracted a large amount of research interest. This is mostly due to the interest which many governments have shown in recent years in developing ‘green technologies’ for energy generation. Solar panels are an ideal way of harvesting energy in a green way, but for them to be successful on a large scale as a replacement for power stations they must be efficient at harvesting and storing large amounts of solar energy. Optimizing PES To address the issues of PES optimization research has focused on a number of issues with the composition of the solar cells. Titanium One of the key areas on which manufacturers have focused is in optimizing the chemical composition of titanium. Improvements in technology may allow for a thinner form of titanium to be manufactured which would overall allow for thinner titanium layers to be applied to solar applications. This would result in a reduction in recombination of photoexcited carriers, which would increase PES cell efficiency. There have also been a number of treatments developed which may increase the energy harvesting capacity of titanium. It has been shown that the use of a special type of ‘cement’ improves the capability of titanium in forming the necessary networks for photoelectron harvesting. It has also been suggested that the addition of other elements such as zirconia, alumina, silica and antimony oxide may increase the potential of titanium based solar cells (Tulloch, 2003). Dye The dye forms one of the principal components in the newly developed solar cells and it is therefore critical that the dyes used are as efficient as possible if the solar cells are to be successful. There have been various trials of different dyes but most of these have not provided significant improvements to the cell overall. There were other trials which have been carried out in which the carbon chains have been varied have provided successful results, reducing dark current and providing substantial temporary voltage improvements. Another study by Wang et al. (2003) showed successful results with an amphiphilic dye which proved to be very stable at high temperatures while still retaining good performance properties. Natural photosynthesis has been used as an inspirational model in the design of dyes to be used in the light harvesting cells. For this reason, it has been suggested that porphyrins and phthalocyanines should be particularly suitable given the role that they play in light harvesting in chlorophyll in plants. There are however problems with aggregation in phthalocyanines that would need to be overcome, and it has been shown that porphyrins cannot compete with the black dye sensitizers also used in the solar cell manufacture (Gratzel, 2003). Conclusion The use of dye-sensitized solar cells in light harvesting technologies has promising future applications in the efficient production of solar energy. Efficiency is a critical issue in their development, as in the future solar energy applications will need to be highly efficient if they are to replace fossil fuel-based energy. It is therefore important that future research concentrates on optimizing the performance of the light-harvesting cells in solar energy applications. References Gratzel, M. (2003) Dye-sensitized solar cells. Journal of Photochemistry and Photobiology, 4: 145-153. Rodriguez, I., Ramiro-Manzano, F., Atienzar, P., Martinez, J.M., Meseguer, F., Garcia, H. and Corma, A. (2007) Solar energy harvesting in photoelectrochemical solar cells. Journal of Materials Science, 17: 3205-3209. Tulloch, G.E. (2004) Light and energy – dye solar cells for the 21st Century. Journal of Photochemistry and Photobiology A: Chemistry, 164(1-3): 209-219. Wang, P., Zakeeruddin, S., Humphrey-Baker, R., Moser, J. and Gratzel, M. (2003) Advanced Materials Communications, 15: 2101-2103. Read More