Inside the Oxford lab cooking up the next generation of solar cells

Tucked away on the outskirts of Oxford, the solar R&D centre looks like any other drab industrial unit in the October sun. 

But for green energy enthusiasts, Oxford PV’s lab is as exciting as Charlie’s Chocolate Factory. 

Dozens of solar cells are dished out to scientists at the start of the day, who set to work experimenting: tweaking their composition, stress-testing them in climate chambers, and zooming in on microscopes to separate the good cells from the bad.                                

Their secret ingredient? Perovskite, a crystal structure that increases the efficiency of solar panels when overlaid on traditional silicon cells. 

Oxford PV, which evolved out of a University of Oxford research project and has a factory near Berlin, is leading the way on perovskite-on-silicon tandem solar cell manufacturing.

It’s in good company in the Oxford Pioneer Park, where experts are also hard at work on electric motors and nuclear fusion. 

Oxford PV is now reaping the benefits of being ahead of the curve on perovskite, with broad intellectual property rights and a deal with a US utility company in the bag.

Perovskite-on-silicon: the next big solar breakthrough?

No one needs convincing that the future features a great deal of solar energy. As well as being better for the climate and energy security, solar and wind are now the cheapest ways to add electricity generation in almost every country. 

But traditional silicon solar cells are bumping up against their efficiency limit of around 26 per cent sunlight converted into electrical energy.  

“We’re in the middle of the last wave of solar dying, whether that be in Europe due to Chinese competition or in the US due to the failure of some of the new thin-film PV companies,” Oxford PV CEO David Ward tells Euronews Green. 

There has been little to challenge the incumbent position of silicon in the last decade – which is often the minimum time that it takes for a new hard tech innovation to break through. 

Founded in 2010, Oxford PV is only now seeing the commercial world wake up to the potential of perovskite-on-silicon, for which it achieved a world-record efficiency for a cell of 29.5 per cent in 2020. 

Since then, there’s been what Ward describes as a “burgeoning” of companies in the perovskite silicon tandem space, who are mostly playing catch up. 

“The tipping point is really quick, and it’s been true across the PV industry in all of the silicon generations,” adds Ward. 

What is perovskite exactly and how does it work?

Perovskite refers to an organic mineral discovered in Russia in the 1800s, which was named after mineralogist Lev Perovski. It also describes this type of mineral’s crystal structure, which can contain various atoms. 

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Oxford PV’s perovskite is made by machines (keeping it cheap) and is a semiconductor material well-suited to harvesting sunlight, deputy chief technology officer Ed Crossland explains. 

In a regular solar panel, silicon ingots are sliced into very thin wafers and spread out to cover the widest area. Metal contacts are then added that activate the silicon material. In total, around 60 cells are placed together to form the panel. 

For the tandem cells, perovskite is coated on top as an even thinner layer (around 1 micron to a silicon wafer’s 150 microns), which effectively creates two cells in one. The perovskite is invisible to the naked eye, but absorbs a higher energy spectrum from the sun than silicon can take in. 

By producing more power per panel, “perovskite-on-silicon is the next tech idea that takes solar above what silicon alone can do,” says Crossland. Where silicon has a theoretical efficiency limit of 29 per cent, the tandem cell could reach 43 per cent. 

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The extra cost of adding the perovskite layer is more than outweighed by the value of this additional energy, explains Ward, making it a “no-brainer” for commercial partners. 

What can perovskite-on-silicon panels be used for?

A spectrum of customers have declared their interest in perovskite-on-solar panels – from homeowners to major utility companies.

In September 2024, Oxford PV shipped its panels to an undisclosed US utility company, in the world’s first commercial deployment of perovskite tandem solar tech. 

The panels are being installed in the corner of a new solar field, and monitored so that the US business can compare its benefits. 

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As well as ‘core’ manufacturing for solar roofs and fields, Oxford PV’s factory in Brandenburg can make cells for more specialist applications like aviation. 

Solar panels enable UAVs (Unmanned Aerial Vehicles) that are used for 5G, military surveillance and satellite mapping to work like “one large flying wing”, explains Ward.

With the wings limited by weight and size, the power that these new solar cells can provide is “absolutely strategic”. 

Perovskite-on-silicon panels could enable UAVs to stay afloat for longer, or fly at a more northerly latitude where the sun is weaker.

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Scientists in the Oxfordshire lab are constantly trialling new ideas and materials, before sending prototypes to Brandenburg to prove that they can be scaled up. However, only a fraction make it that far: “In a commercial facility you can’t be changing the recipes daily,” Ward adds.

The German factory is not yet a gigawatt facility, however, and Oxford PV is keen to collaborate with other firms to realise the full potential of perovskite for our swiftly electrifying world.

‘Having an ecosystem is awesome’: How solar tech companies are collaborating

Given the reach of its early patents, collaboration is a core pillar of Oxford PV’s plans. 

“It’s quite hard to do a perovskite-on-silicon solar cell without having to go a long way out of your way to avoid the IP set that we have,” says Ward.

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“We’re not trying to keep it all to ourselves, but we would like to be involved if people are using our intellectual property to come to market.” As well as licensing, the company offers valuable knowhow to get partners up to speed.

Most of the newer start-ups are concentrated in China and, supported by a strategic drive for PV, the US. 

In Europe, existing energy or silicon companies are increasingly getting into perovskite tandems, such as Enel in Italy. 

“Having an ecosystem is awesome,” says Ward. “The whole market deciding that that’s where you’re going is much easier than saying hey, we’re the only people in this, because the evangelising you have to do to the customer base and to investors is so much harder.”

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The CEO is confident that it will be a while before a new innovation comes along that puts perovskite in the rearview mirror. And, with the COP28 target of tripling renewable energy capacity by 2030, companies need to be investing in technologies that exist today.

“For all the negative news about European manufacturing and European PV, we have a new facility doing new technologies in a way that’s just not the same as old solar in silicon. China has done a very good job of making solar cheap in their own scale and efforts,” says Ward. “But this is a new paradigm.”