A Bill Gates-based photovoltaic tech that may be solar power’s future

In 1839, German scientist Gustav Rose went prospecting in the Ural Mountains and discovered a dark, shiny mineral. He named the calcium titanate “perovskite” after Russian mineralogist Lev Perovski. The mineral was one of many that Rose identified for science, but nearly two centuries later, materials sharing perovskite’s crystal structure could transform sustainable energy and the race against climate change by significantly boosting the efficiency of commercial solar panels.

Solar panels accounted for nearly 5% of U.S. energy production last year, up almost 11-fold from 10 years ago and enough to power about 25 million households. It’s the fastest-growing source of new power, too, accounting for 50% of all new electricity generation added in 2022. But nearly all of the solar modules that are used in power generation today consist of conventional silicon-based panels made in China, a technology that has changed little since silicon cells were discovered in the 1950s.

Other materials used, like gallium arsenide, copper indium gallium selenide and cadmium telluride — the latter a key to the largest U.S. solar company First Solar‘s growth — can be very expensive or toxic. Backers of perovskite-based solar cells say they can outperform silicon in at least two ways and accelerate efforts in the race to fight climate change. Just this week, First Solar announced the acquisition of European perovskite technology player Evolar.

The silicon limits of solar cells

Photovoltaic cells convert photons in sunlight into electricity. But not all photons are the same. They have different amounts of energy and correspond to different wavelengths in the solar spectrum. Cells made of perovskites, which refer to various materials with crystal structures resembling that of the mineral, have a higher absorption coefficient, meaning they can grab a wider range of photon energies over the sunlight spectrum to deliver more energy. While standard commercial silicon cells have efficiencies of about 21%, laboratory perovskite cells have efficiencies of up to 25.7% for those based on perovskite alone, and as much as 31.25% for those that are combined with silicon in a so-called tandem cell. Meanwhile, even as silicon efficiencies have increased, single-junction cells face a theoretical maximum efficiency barrier of 29%, known as the Shockley-Queisser limit; their practical limit is as low as 24%.

Furthermore, perovskite cells can be more sustainable to produce than silicon. Intense heat and large amounts of energy are needed to remove impurities from silicon, and that produces a lot of carbon emissions. It also has to be relatively thick to work. Perovskite cells are very thin — less than 1 micrometer — and can be painted or sprayed on surfaces, making them relatively cheap to produce. A 2020 Stanford University analysis of an experimental…