Perovskites enable Faraday rotator breakthrough

Researchers led by Dr Girish Lakhwani, a chief investigator for the Australian Research Council’s Centre of Excellence in Exciton Science, have found a way to manipulate light produced by lasers at a lower cost than existing methods.

For a wide range of modern electronics, including broadband communications and fibre-optic sensors, manipulating light is a critical function. Without the ability to bend and deflect reflected light, for instance, the lasers and amplifiers that are central to broadband networks would be overwhelmed and fail.

The device used to manage light in high-tech systems is called a Faraday rotator. It comprises ferromagnetic crystals surrounded by powerful magnets – which together give operators the ability to adjust the “polarisation”, or alignment of waves, in a light beam.

Faraday rotators are very efficient, but they are also very expensive, requiring terbium-based garnets.

Girish and colleagues have developed a new type of rotator in which the costly garnets are replaced by much cheaper crystals called lead halide perovskites – a critical component of new generation solar cells.

The crystals have excellent optical properties and low production costs, making them strong candidates for a host of opto-electronic applications beyond renewable energy tech.

“We’ve been looking into Faraday rotation for quite some time,” Girish said. “It’s very difficult to find solution-processed materials that rotate light polarisation effectively. Based
on their structure, we were hoping that perovskites would be good, but they really surpassed our expectations.”

Dr Randy Sabatini is a postdoctoral researcher leading the project in the Lakhwani group. He added: “Interest in perovskites really started with solar cells. They are efficient and much less expensive than traditional silicon cells, which are made using a costly process known as the Czochralski or Cz method. 

“Now, we’re looking at another application, Faraday rotation, where the commercial standards are also made using the Cz method. Just like in solar cells, it seems like perovskites might be able to compete here as well.”

Girish is based at the University of Sydney’s School of Chemistry and is a member of SydneyNano Institute. He worked with collaborators from UNSW, as well as Exciton Science
colleagues at The University of Sydney and Monash University.

“As part of the ARC Centre of Excellence in Exciton Science, we benefited from the exchange of ideas through this high-calibre centre,” Girish said. 

Collaborators included the groups of Professor Udo Bach at Monash University and Dr Asaph Widmer-Cooper at Sydney. Looking ahead, the search for other perovskite materials should be aided by modelling.

“For most materials, the classical theory used to predict Faraday rotation performs very poorly,” said Dr Stefano Bernardi, a postdoctoral researcher in the Widmer-Cooper group at the University of Sydney. “However, for perovskites the agreement is surprisingly good, so we hope that this will allow us to create even better crystals.”

The research is published in the journal Advanced Science and can be found here.

This article was partly reproduced from a story on the University of Sydney website, which can be read in full here.