While perovskites have the potential to reach high efficiencies (the world record for a perovskite-only cell is just over 25%), most of the best-performing perovskite cells today are tiny—less than an inch wide. 

Scaling up makes it more difficult to reach the potential efficiency limits. Right now, Saule’s panels, which are a meter wide, reach around 10% efficiency. This is dwarfed by commercial silicon panels of similar sizes, which typically hit around 20% efficiency. 

Olga Malinkiewicz, Saule’s founder and chief technology officer, says the company’s goal was to get a perovskite-only solar cell out the door, and the lower efficiencies won’t matter if the technology is cheap enough.

Saule is trying to go where silicon solar panels won’t: to roofs that can’t handle the weight of heavy glass-encased panels, or to more specialized applications, such as solar-powered blinds, which the company is currently testing.

While Saule is launching thin-film products for more niche applications, other companies hope to beat, or at least join, silicon at its own game. UK-based Oxford PV is incorporating perovskites into combination perovskite-silicon cells.

Since silicon absorbs light toward the red end of the visible spectrum, and perovskites can be tuned to absorb different wavelengths, coating a layer of perovskite on top of silicon cells allows combination cells to reach higher efficiencies than silicon alone.

Oxford PV’s combination cells are heavy and rigid, like silicon-only cells. But since they’re the same size and shape, the new cells can easily slot into panels for rooftop arrays or solar farms.

Chris Case, Oxford PV’s chief technology officer, says the company is focused on lowering the levelized cost of electricity, a metric that factors in a system’s installation and lifetime operation costs. While layering perovskites on top of silicon adds to the manufacturing cost, he says the levelized cost from the combination cell should dip below silicon over time because these new cells are more efficient. Oxford has set several world records in efficiencies for this type of cell in the last few years, most recently reaching 29.5%.

Microquanta Semiconductor, a Chinese perovskite company based in Hangzhou, is also taking some cues from silicon solar cells. The company is manufacturing panels from rigid, glass-encased cells that are made with perovskites.

Microquanta’s pilot factory opened in 2020, and should reach 100 megawatts of capacity by the end of the year, says Buyi Yan, the company’s chief technology officer. The company has demonstration panels installed on several buildings and solar farms throughout China.

Solving for stability

The stability of perovskites improved from minutes to months within the span of a few years. But most silicon cells installed today have a warranty of around 25 years, a target that perovskites may not yet be able to reach.

Perovskites are particularly sensitive to oxygen and moisture, which can interfere with the bonds in the crystal, stopping electrons from moving effectively through the material. Researchers have been working to improve the lifetime of perovskites, both by developing less reactive perovskite recipes and finding better ways to package them.

Oxford PV, Microquanta, and Saule all say they’ve solved the stability issue, at least well enough to sell their first products.

Estimating long-term performance in solar cells is usually done by accelerated testing, putting cells or panels under extra-stressful conditions to simulate years of wear and tear. The most common suite of tests for outdoor silicon cells is a series called the IEC 61215.