An image of a perovskite silicon tandem solar cell made by the researchers.
A new type of solar power cell with a higher ‘conversion efficiency rate’ is one step closer to being produced at an industrial scale, thanks to the work of an international team of researchers.
In a recent study, the team showed that a process called ‘passivation’ – the creation of an outer layer to protect from corrosion – is possible on perovskite silicon tandem solar cells.
Perovskite is a mineral made from calcium titanium oxide. A perovskite silicon tandem solar cell features a top cell made from perovskite and a bottom cell of silicon.
While scientists are hopeful that these types of cells could be a major technological advancement in harnessing solar power, they have been unable to achieve high-quality surface passivation until now.
“Surface passivation of solar cells is not just a nice-to-have feature; it is an essential booster for their efficiency and stability,” says Stefan Glunz, a professor of photovoltaic energy at Fraunhofer Institute for Solar Energy Systems, Germany.
Solar cells convert sunlight directly into electricity through a phenomenon known as the photovoltaic effect, where light from the sun causes electrons to jump into higher energy states creating an electrical current.
Silicon cells are already well established within the solar power industry. Leaving these cells outside to collect sunlight can cause the outer layer to corrode, which allows electrons to escape, generating less electricity. Scientists apply a passivation layer to the surface of the cell to shield it from corrosion, therefore increasing the cell’s efficiency.
“So far, effective passivation has not been fully harnessed on textured perovskite silicon tandem solar cells, with prior success largely confined to flat-front architectures,” says Dr Oussama Er-Raji, lead author of the study and a scientist at Fraunhofer ISE.
The silicon in perovskite silicon tandem solar cell is textured to increase its surface area and efficiency. But this complicates the deposition of the perovskite layer on top of it and surface passivation in turn.
“But we have now managed excellent passivation by depositing 1,3-diaminopropane dihydroiodide on the uneven perovskite surface,” says Er-Raji.
The results of the research have been published in Science.
While a typical silicon solar cell has a physical maximum efficiency of 29.3% for converting sunlight into electricity, the researchers found the solar cells in this study achieved a conversion efficiency of 33.1% using an open-circuit voltage of 2.01 volts.
The new passivation layer also improved the conductivity of the top cell.
While passivation only acts close to the surface in silicon solar cells, the researchers showed it impacts the entire perovskite top cell. This “deep field-effect” increases its conductivity and enhances electron transport.
“This realisation provides a solid foundation for all future research in this area,” says Stefaan De Wolf, Professor of Materials Science and Engineering and Applied Physics at King Abdullah University of Science & Technology, Saudi Arabia.
“It enhances our understanding of the processes occurring in the top cell while converting light into electricity, enabling scientists to leverage this knowledge to develop better tandem solar cells.”
The authors hope that full industrialisation of these cells could be easier than expected as silicon solar bottom cells are already being manufactured on mass.
“For today’s silicon solar cells, surface passivation was the key for high efficiencies in industrial production,” says Glunz.
“It is encouraging that the photovoltaic industry will benefit from these positive effects for perovskite silicon tandem solar cells as well.”