Although they are not particularly efficient, plastic solar cells that are flexible enough to be sprayed on roofs or printed on clothes look like being remarkably cheap

A solar cell is made of semiconductive film sandwiched between two electrodes. When light strikes the semiconductor, electrons in the vicinity become excited enough to dislodge themselves from their surroundings and leave “holes” behind.

So far, plastic cells have achieved efficiencies of only 2.5%, against 10% for standard inorganic solar panels and 30% in the most expensive modules. But because polymers can be manufactured cheaply in a solution at room temperature, researchers at the University of Arizona in Tucson, who have been experimenting with printing cells on paper or plastic via inkjets, think all the fuss is worth it.