Windows could be letting in light , as well as providing us with power. A team of chemists led by prof. Michael Graetzel at the Swiss Federal Institute of Technology in Lausanne has made a breakthrough in their pioneering design of a transparent solar cell. The transparent cell prototype now converts 10 percent of the energy in sunlight into electricity. Allthough this cannot yet match the efficiency of commercial silicon-based solar panels, it is estimated that these cells will cost only a tenth as much.
Both types of panel rely on the photoelectric effect. The current they produce is created when electrons bound within atoms are liberated by incoming light. In conventional solar cells this takes place within silicon structures making use of semi-conductors. The transparent cells make use of a redox process, which is more like the natural photosynthesis process in plants.
These cells rely on an electrolytic process between two panes of glass. The inside surface of the glass is coated with a titanium dioxide film and on top of it is a layer of photosensitiser chemical. The photosensitiser harvests the sunlight and the titanium dioxe film harvests electrons and transfers them to and from an external circuit.
To what extent the environmental aspects of the material use of the transparent cells compares to the conventional silicon ones is unclear at the moment. The transparancy however make a unique optimised design possible by combining the energy production with regular windows.
The estimated low cost of the transparent cells can provide a huge potential in developing countries with sunny climates. Up till now the cells have been used in solar-powered watches, in which the glass of the watch is providing itís energy at the same time. One promising potential development is the use of the transparent solar cells in windows. A keen choice of the photosensitiser chemical is essential. The substance should capture the infra-red light to use it for electricity production and it should let the visible light enter the building for normal lighting purposes.
An additional advantage would be that less heat from the sun is entering the building, because the infrared light is captured in the window for electricity production. This may reduce energy use for cooling in hot sunny climates.
Swiss Federal Institute of Technology
Written by: Swiss Federal Institute of Technology dr. Augustin McEvoy Street: (41) 21 693 3689 Fax: (41) 21 693 6100 Email: firstname.lastname@example.org
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