Multi-junction solar cells come from just one compound

By growing or annealing zinc tin phosphide (ZnSnP₂) layers at certain temperatures they were able to introduce disorder into the structure that allowed different band gaps to be created.

‘There are different ways that this could be used, one is to try to enhance the performance of a silicon solar cell, but another would be to have a thin-film solar cell,’ said Aron Walsh of Bath University. ‘The two main thin-film technologies are cadmium telluride and CIGS [copper indium gallium selenide] — this would be an alternative, so you could have a low-cost thin-film cell.’

Multi-junction solar cells use combinations of exotic rare materials such as germanium, gallium and indium, each of which display a characteristic band gap that can capture a specific part of the solar spectrum. Because of this, less energy is lost and so conversion efficiencies are very high.

However, due to their great expense, multi-junction cells have only really found a market in the space industry, to power satellites, for example, and as tiny chips in concentrated photovoltaic devices. As a consequence, attention has turned to cheaper more readily available materials.