A multi-institutional collaboration, co-led by scientists at the University of Cambridge and Okinawa Institute of Science and Technology Graduate University (OIST), has identified the source of efficiency-limiting defects in potential materials for next-generation solar cells and LEDs.
In the last decade, perovskites – a diverse range of materials with a specific crystal structure – have emerged as promising alternatives to silicon solar cells, as they are cheaper and greener to manufacture, while achieving a comparable level of efficiency.
However, perovskites still show significant performance losses and instabilities, particularly in the specific materials that promise the highest ultimate efficiency. Most research to date has focused on ways to remove these losses, but their actual physical causes remain unknown.
Now, in a paper published in Nature, researchers from Dr Sam Stranks’s group at Cambridge’s Department of Chemical Engineering and Biotechnology and Cavendish Laboratory, and Professor Keshav Dani’s Femtosecond Spectroscopy Unit at OIST in Japan, identify the source of the problem. Their discovery could streamline efforts to increase the efficiency of perovskites, bringing them closer to mass-market production.
Perovskite materials are much more tolerant of defects in their structure than silicon solar cells, and previous research carried out by Stranks’s group found that to a certain extent, some heterogeneity in their composition actually improves their performance as solar cells and light-emitters.
However, the current limitation of perovskite materials is the presence of a 'deep trap' caused by a defect, or minor blemish, in the material. These are areas in the material where energised charge carriers can get stuck and recombine, losing their energy to heat, rather than converting it into useful electricity or light. This recombination process can have a significant impact on the efficiency and stability of solar panels and LEDs.
Until now, very little was known about the cause of these traps, in part because they appear to behave differently to traps in traditional solar cell materials.
Image: Perovskites
Credit: Andrew Winchester
Reproduced courtesy of the University of Cambridge