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FEATURE SOLAR


Illustration of a modern perovskite high-performance solar cell module


gapproach to synthesising perovskites. 6,7 Its approach is to use a substrate layer of


metal, or alternating layers of metal and dielectric material instead of glass. This is different from the way that traditional perovskite solar cells are constructed, where the perovskite is deposited as a film from solution onto a glass surface. By using an alternating substrate rather than glass, Guo and his co-authors found they could increase the perovskite’s light conversion efficiency. “No one else has come to this


observation in perovskites,” says Guo. “All of a sudden, we can put a metal platform under a perovskite, utterly changing the interaction of the electrons within the perovskite. Thus, we use a physical method to engineer that interaction.” Another way of thinking about this is that


it is like adding a mirror to the perovskite photon absorbing layer. The way that perovskites and silicons generate electricity is when electrons in the materials are excited by incoming photons. This causes them to escape from the atoms they orbit. These freed electrons can then be used to


‘As new perovskites emerge, we can then use our physics-based method to further enhance their performance’


30 Electro Optics May 2023


generate electrical current. However, the freed electrons leave holes behind them. Sometimes, these electrons are recaptured by the ‘holes’, which decreases the overall current and thus the overall efficiency of the material. When electron holes recapture electrons, it is known as electron recombination. The research team at the University of Rochester found it could reduce electron recombination in perovskite by placing it on a substrate made up of either silver or alternating layers of silver and aluminium oxide.


Surprising physics Guo’s lab demonstrated that such recombination could be prevented by combining a perovskite material with either a layer of metal or a metamaterial substrate consisting of alternating layers of silver, a noble metal and aluminium oxide, which is a dielectric. The result was a significant reduction of electron recombination through7


“a lot of


surprising physics,” Guo says. “In effect, the metal layer serves as a mirror that creates reversed images of electron-hole pairs, weakening the ability of the electrons to recombine with the holes.” Perovskites are not yet ready for


practical large-scale applications. In particular, their tendency to degrade relatively quickly limits their usefulness. Currently, researchers are racing to find new, more stable perovskite materials.


One approach is the incorporation of silver iodide or polyethylene oxide in certain perovskites, improving crystallisation and nucleation and therefore extending the life of the perovskite.8


Another concern


with perovskites is that they commonly use lead, which puts warning signals in front of many prospective users. However, very recently 9


tin-based perovskites have


been suggested as a replacement for lead perovskites. Gallium arsenide is another potential candidate for solar cells, but remains expensive to exploit.10 The future of solar power therefore looks set to be with perovskites and physics- based solutions to their exploitation for the time being. “As new perovskites emerge, we can then use our physics-based method to further enhance their performance,” concludes Guo. EO


References 1


2 3 4


Explained: Why perovskites could take solar cells to new heights | MIT News | Massachusetts Institute of Technology.


Explained: Why perovskites could take solar cells to new heights | MIT News | Massachusetts Institute of Technology.


Dutch-German consortium developing simplified tandem solar modules (optics.org).


Dutch-German consortium developing simplified tandem solar modules (optics.org)


5 (Pers Comm, 2023) 6


7 8 9


Gigantic suppression of recombination rate in 3D lead-halide perovskites for enhanced photodetector performance | Nature Photonics;


Perovskites, a ‘dirt cheap’ alternative to silicon, just got a lot more efficient -- ScienceDaily


Perovskite photovoltaics: stability and scalability | Scientific Reports (nature.com)


https://doi.org/10.1021/acsenergylett.3c00282 10 Gallium arsenide solar cells - Appropedia


Acknowledgements We thank Gianluca Coletti (TNO), Chunlei Guo (University of Rochester) and Christophe Ballif (Ecole Polytechnique Fédérale de Lausanne) for their contribution to this article


@electrooptics | www.electrooptics.com


Audio und werbung/Shutterstock.com


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