Now, a new kind of thin, flexible, film-like photovoltaic cell is about to go into commercial production for the first time.
The solar cells, coated with a common ingredient used in toothpaste and suntan lotion, will be four to five times cheaper than silicon. Manufactured with a process similar to inject printing, the cells will be able to produce electricity from direct sunlight as well as low-light and indoor lighting.
"Conventional silicon-based solar cells are more efficient in optimum conditions, but we win on the 24-hour cycle because our cells can use early morning light and work indoors. You can recycle energy from the electric lights in your building," said Clemens Betzel, president of G24 Innovations in Cardiff, U.K.
At the end of April, the factory will begin production of the cells — which were invented in 1988 by Michael Grätzel of the Federal Polytechnic School of Lausanne in Switzerland.
The company’s first application will come in the form of a cell phone charger. But the thin, flexible cells could eventually be installed across surfaces such as walls, counters and floors to power office and home electronics.
The so-called "dye-sensitized solar cells," also known as Grätzel cells, convert sunlight into energy similar to how leaves and plants do it through photosynthesis.
In leaves, chlorophyll molecules absorb sunlight and generate electric charges. Other mechanisms in the plant separate the positive and negative charges and conduct them to create energy.
Instead of chlorophyll, the Grätzel cells use titanium oxide to absorb the sunlight. The material is coated onto one of two conducting electrode layers, similar to foil. A gel-like electrolyte material is sandwiched between the two layers.
When sunlight falls onto the cells, excited electrons diffuse through the layer of titanium dioxide to the electrode, where the energy can be captured for electricity.
This process is different than what occurs in conventional silicon cells, where the absorption of sunlight and the separation of charges happen in the same material. To obtain the highest efficiency, the silicon must be pure and free of defects, which brings up the cost considerably.
Dye-sensitized cells are made from lower cost materials and rely on recent advances in nanotechnology to make them competitive with silicon. For example, the light harvesting is made possible not just by a layer of dye, but by hundreds of nano-sized particles coated in the dye and stacked up on top of each other.
According to Betzel, G24i will begin rolling out solar cell films 36-inches-wide and any length.
"There are two factors in manufacturing. One is cost and the other is how many you can make and sell at that cost. It looks like once you set up a manufacturing line for this kind of cell, it could be faster than silicon," said Brian O’Regan, a research fellow at the Imperial College London.
O’Regan’s team is currently researching a way to coat steel roofing products with dye-sensitized solar cells. The group is working with the Universities of Bath, Bangor and Swansea, as well as the pre-finished steel maker Corus Colors to develop roofing materials that could turn warehouses and superstores into solar energy powerhouses. It may not be long before thin, flexible, and inexpensive solar cells are soaking up sun everywhere you turn
Taken from http://dsc.discovery.com/news/2007/04/13/solarcells_tec_02.html?category=technology&guid=20070413090000
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