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If solar energy is to meet its potential for replacing fossil fuels, photovoltaic (PV) technology will have to be deployed far more rapidly than it is now. In 2017 solar PV accounted for barely 2 % of global electricity production.
The EU-funded HYPER project set out to investigate several new materials that could be used to make solar cells more cheaply. Among them was a class of compounds known as perovskites, which had been studied by Japanese researchers a few years earlier but not taken further.
‘We found that perovskites absorbed light incredibly strongly and worked well in thin-film photovoltaics,’ says project coordinator Henry Snaith of Oxford University. ‘I’d spent the previous ten years searching for materials that showed some promise and this one showed a lot of promise. It was in a completely different category to where the other emerging PV materials were at the time.’
Spin-off to exploit perovskite
It was soon apparent that cells with a perovskite layer performed far better than anyone had expected and the HYPER project dropped its other lines of enquiry to find out what these new materials could do. The discovery was published in Science in 2012.
Two years earlier Snaith had founded a university spin-off company, Oxford PV, intending to exploit a niche market for semi-transparent solar cells incorporated into windows. But once the implications of the perovskite discovery became clear, the company abruptly changed direction.
‘We realised there was an opportunity to target the bigger PV market by combining perovskites with silicon,’ he says. ‘We can coat the perovskite cell on top of silicon and deliver a higher efficiency than the silicon itself.’
Oxford PV’s perovskite-silicon cells have now exceeded 28 % efficiency – the very best commercial silicon cells are around 25 % – and Snaith thinks 32 % will soon be within reach. More advanced cells, with two layers of perovskite, could approach 40 %.
$200 billion market
The company has attracted more than £100 million of equity capital and in 2016 acquired a redundant PV factory near Berlin. With the assistance of Swiss technology company Meyer Burger they are preparing to produce 156 mm square cells for industrial customers. This ‘cell foundry’ will have an annual capacity of 200 megawatts and is expected to be in production by 2020.
‘The potential market for this technology is the whole of the PV power market, currently at 100 gigawatts and $200 billion,’ Snaith says. ‘On a longer time-scale we may see perovskite PV power being generated everywhere.’
He next wants to develop cells solely based on perovskites, which would be much thinner and lighter than most cells used today. ‘It opens lots of opportunities for making more lightweight PV,’ he says. ‘Things like industrial roofing – there’s quite a lot of interest for a lighter weight PV that could be deployed in a roll, for instance.’ Such cells would also be useful for transport applications such as aircraft, drones and automobiles. Beyond the PV market, perovskites could be used to make efficient light-emitting displays.
The initial project funded by the EU’s European Research Council ended in 2016; the smaller NEM (New Energy Material) and PLE (Perovskite Light Emitters) proof-of-concept projects then helped the Oxford scientists explore the potential of their discovery.
‘It was really invaluable for kick-starting my activity,’ Snaith says of the EU funding. ‘It made a very measurable difference to my ability to push ahead with this technology in competition with the rest of the world. It’s an example where applied and fundamental research are both really important and you have to be open to surprising things happening along the way.’