According to Max Hoerantner, co-founder of Swift Solar, a San Francisco start-up, there are only about 10 start-up firms in the world working on perovskite technology.

Oxford PV, a university spin-off, says it reached 28% efficiency with a commercial perovskite-based solar cell in late 2018, and will have an annual 250-megawatt production line running this year.

Both Oxford PV and Swift Solar make tandem solar cells – these are silicon panels which also have a thin perovskite film layer.

Since they’re made from two materials, they get to break through the Shockley-Queisser limit.

The silicon absorbs the red band of the visible light spectrum, and the perovskite the blue bit, giving the tandem bigger efficiency than either material alone.