Powering the transition to a clean-energy future
Low-cost, high-efficiency photovoltaic technology being developed in the Department of Physics could hold the key to accelerating the world’s shift away from fossil fuels.
‘The prospect is for photovoltaics to produce as much energy as we need,’ says Henry Snaith, Binks Professor of Renewable Energy in the Department of Physics. ‘There’s more than enough sunlight and more than enough space. If we wanted to produce all of our energy from photovoltaics at the current efficiency of modules, we would need only about 2% of our land. And to put that into context, we farm on about 50%.’
Although the market for photovoltaics has expanded rapidly in recent years, global energy generation from solar power is still low, amounting to only 1 to 2% of the total energy used today. Silicon, which is found in virtually all commercial solar cells, is costly and energy intensive to produce, and the resulting panels are limited in how much energy they can harness from the sun. In order to facilitate the required growth of the industry over the next two decades, technological advances are needed to fundamentally improve the efficiency and cost of photovoltaic panels.
‘Most of the energy input and the environmental cost of manufacturing solar is the production of the silicon,’ says Professor Snaith, whose Photovoltaic and Optoelectronic Device Group is primarily focused on developing the physics and technology behind low-cost photovoltaic concepts. ‘It takes about nine months for a standard silicon module to start to produce positive energy, so not years, but there is a measurable environmental impact – particularly at the moment while the energy being used is predominantly coming from fossil fuels. If we can move to materials that don’t require anywhere near the same energy input, that would be a massive saving.’
‘Perovskite has the potential to accelerate our path towards producing 100% of our energy by renewable sources, getting us away from carbon-producing technologies entirely’
Professor Snaith is working at the forefront of research into such materials. His recent discovery of extremely efficient thin-film solar cells, made from a crystalline material called perovskite, has reset aspirations within both academic and industrial photovoltaic circles. As well as being easy to source, perovskite is cheap to synthesise: high-quality thin films can be processed from solution at low temperatures, making it compatible with existing manufacturing techniques. ‘But the really exciting aspect, both economically and scientifically,’ he explains, ‘is that we can tune the region of the solar spectrum perovskite absorbs.’
While silicon can only absorb light within a set range of wavelengths, perovskite’s structures can be adjusted to allow it to absorb any frequency of visible light. By layering perovskite material on top of silicon, and allowing each layer to absorb a different part of the spectrum, it is possible to significantly increase overall efficiency of the solar cell. Using this technique, Professor Snaith’s group has already demonstrated efficiencies very close to 30%, and has a clear roadmap to get up to 40%. With today’s commercial technologies hovering at around 20%, this could, over the next ten years, double the efficiency of solar modules.
Professor Henry Snaith takes a closer look at a perovskite solar cell. Photo by John Cairns
There are challenges to overcome before such efficiencies can be achieved in a real-world setting, however, and work is continuing at pace to address these. One area of focus is stability: will these materials last for 25 years, and how might they degrade in the field? To test this, the group creates accelerated ageing conditions in the lab using, for example, environmental stress chambers to generate very high-temperature, high-humidity environments. ‘Within a relatively short time it is possible to get data that starts to give you confidence about how these modules, devices and materials would survive over their lifetime,’ says Professor Snaith.
The work that he and his group are undertaking at Oxford has been significantly enhanced in recent years through philanthropy. In 2021 a gift from the Binks Trust enabled the establishment of a new senior research post in renewable energy – now held by Professor Snaith – as well as funding a DPhil scholarship and biennial conference. The creation of the academic post in particular has ‘helped to create greater credibility’ around Oxford’s work in this area, he says. ‘It is a show of commitment for the long-term growth of renewable energy research in physics, and that’s something that definitely helps in terms of raising more funds from research grants.’
Equally crucial is the support received, both from the Binks Trust and other donors, including alumnus Nick Greenwood, for graduate students. Donor-funded scholarships have helped to create a ‘great consistency’ in Oxford’s photovoltaic research, says Professor Snaith. ‘For a start, if we didn’t have any graduate students, we’d have no later-stage researchers. They undertake half the work, and they’re not just being trained, they’re being creative, they’re guiding experiments. We can have everything we need in terms of equipment and facilities, but if we can’t fund the best people to come and work with us then our output won’t be anywhere near as good.’
‘I can’t labour how great it is to have philanthropic support for students because it’s a real gap in traditional funding’
Looking to the future, Professor Snaith believes that perovskite has the potential to rapidly accelerate the world’s transition from fossil fuels to clean, renewable forms of energy. The technology is already being commercialised by a number of spinout companies, including Oxford PV, which was co-founded by Professor Snaith in 2010. The company’s first perovskite-on- silicon tandem solar cells are expected to hit the market next year.
Back in the university lab, Professor Snaith is laser focused on pushing forward his research, and is already working on the next technology up (two layers of perovskite on silicon), as well as ways to replace the silicon in solar cells entirely. His group is also actively investigating other families of materials. ‘There may be other compounds that have got better functionality than even perovskite,’ he says, ‘so we are searching for those too.’
Ensuring cohesive activity across Oxford will be key to driving this work forward. There are a number of research groups based across the Mathematical, Physical and Life Sciences Division that work on related areas, and Professor Snaith’s hope is to enable greater collaboration across disciplines. This, he says, would undoubtedly be aided by further investment from donors: ‘we could really grow the coherence of solar research at Oxford and massively improve our impact going forward – philanthropic support can ensure that we stay at the top and don’t rest on our laurels.’
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