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Researchers from UCLA have developed a transparent polymer solar cell that can be used in home's windows with the ability to generate electricity. They reported 4% power conversion efficiency (which is quite low though- best solar panels demonstrate up to 20%- see http://www.factsaboutsolarenergy.us/solar-panel-efficiency.html). Unfortunately, they did not say anything about the cost. Source: http://pubs.acs.org/doi/pdf/10.1021/nn3029327
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