A new generation of spray-on solar cells has the potential to increase the efficiency and cut the costs of renewable energy technology.
These innovative solar-cells use a material called a perovskite. Perovskites are the subject of world-wide interest and are being explored by Professor David Lidzey's research group in the Department of Physics and Astronomy. Perovskite solar cells have been shown to be almost as effective in generating photovoltaic electricity as conventional silicon solar-cells, yet are potentially much cheaper to produce.
The spray-painting method pioneered by our scientists to produce the cells reduces wastage and potentially allows for high-volume manufacturing over flat or curved surfaces.
"This process is designed to address the challenge of large-scale manufacturing," David said. "We've found an exciting technology that takes a lab-based process to practical mass application."
Perovskite materials have been known for many years, with the term used to describe any compound that shares the same ABX3 crystalline structure as calcium titanium oxide.
The spray-coating process developed in Sheffield is designed to address the challenge of large-scale manufacturing. We've found an exciting technology that takes a lab-based process to practical mass application.
Professor David Lidzey
Department of Physics and Astronomy
In Sheffield, scientists are using completely synthetic perovskites based on mixtures of organic and inorganic compounds to work as the light-absorber in solar cells. Perovskites can be processed using solution-based techniques, and so a range of techniques can be used to deposit them into a thin-film.
But for perovskite to be used effectively in a solar cell, it has to be layered with other materials.
"Think of a solar cell as a multilayer structure," David said. "One of those layers – the perovskite – absorbs light, with the other layers transporting the optically-generated charges from the perovskite and permitting them to be extracted from the device to an external circuit where they can be used to do useful work.
Without the transport layers, the cell’s efficiency is reduced, so we are also developing and testing a range of new spray-on charge transport layers."
The development of spray-on perovskite solar cells has huge potential. "We already know that perovskite offers the potential to combine the high performance of mature solar cell technologies with low production costs," said David. "The fact it can be spray-coated also means that manufacturers can apply it to a range of surfaces, including corrugated structures."
"The very best perovskite cells now have a power conversion efficiency in excess of 23 per cent. This is not so far behind that of silicon at 25 per cent – the material that dominates the world- wide solar market."
This potential has been recognised by the Engineering and Physical Sciences Research Council. The organisation has awarded £880,000 to support David's work with Sheffield's Advanced Manufacturing Research Centre on integrating perovskite solar cells with carbon fibre composites.
The aim is to use the spray-coating technologies developed at Sheffield to build solar cells into the outer surface of carbon fibre panels. This could lead to super-strong, lightweight panels being produced at very low cost, so that they can applied in new contexts, such as aerospace, transport and satellites.
Solar energy is rapidly becoming a serious alternative to fossil fuels and the solar energy market is expanding at a pace to match.
In Asia, for example, photovoltaic energy is so inexpensive it competes with oil and gas. And according to the International Energy Association 2017 World Energy Outlook, over the next 20 years solar photovoltaics will be the largest growing energy technology, responsible for an additional 1.5 terawatts of power.
"I believe that new thin-film photovoltaic technologies are going to have an important role to play in driving the uptake of solar-energy," David said. "And that perovskite based cells are emerging as likely thin-film candidates."
