Thermodynamics and quantum physics pose certain limits to the efficiency of solar cells, but current technology doesn't even come close to those. There is a lot of potential for optimization but for the moment the recently achieved value of 24.7 % for ultra-thin cells isn't too bad.
Conventional photovoltaic technology is being installed worldwide on a large scale, but their manufacturing is fairly expensive, and every progress in efficiency costs even more. There are some alternatives to the normally used, expensive semiconductor processes but unfortunately they lack efficiency. A special technology using carbon only also can't compete efficiencywise, but it's promising in terms of possible future development.
Today, solar energy is being used, or converted, mainly in two ways: photovoltaics using light and solar thermal systems using heat. Combining both would make sense but doesn't work with silicon-based cells. A recently discovered physical effect together with a different semiconductor material makes it possible to use light and heat concurrently.
While solar cells based on organic materials are more expensive than traditional silicon-based ones and significantly less efficient, they do have some advantages. They can be manufactured as flexible films, suitable for many surfaces without intricate mounting frames, and can make efficient use of low light conditions. New developments even indicate that the overall efficiency has the potential to rise into the area of anorganic cells.
We've all got used to the environmental labels on white goods that have become more and more useless since no manufacturer of refrigerators can sell an »F«-rated machine anymore and everything is between »A« and »C«. Now, a French company takes this approach one step further and rates private households with smart-grid data.
Organic photovoltaic cells are not really well known for their efficiency. While advantages in possible applications outweigh the low energy yield, the frustrating issue for researchers in this field is that in theory, the efficiency doesn't have to be much lower than with silicon-based technologies. However, the potential is hard to put into effect, so every small increase is cause for celebration in research labs.
One of the downsides of photovoltaics is the trade-off between efficiency, cost and pollution. Generally, a very efficient solar cell is expensive and, production-wise, as far from eco-friendly as a means of renewable energy generation can be. A new architecture has the potential to shift the weights toward 'greener' and 'cheaper'.
Today, silver screen printing is the technology of choice for the realization of the top grid electrode in heterojunction silicon solar cells. The difficulty of lowering resistivity and thinning the metal line in silver screen printing prevents from achieving high efficiency and low cost. By replacing silver with copper, many problems seem to disappear.
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