Super-charging solar cell efficiency
ARC Future Fellow Professor Michelle Coote and her team from The Australian National University have used Raijin to double the efficiency of solar cells.
In a dye-sensitised solar cell, the dye absorbs sunlight, causing the dye to change form and release an electron which generates electricity. A second component is then needed to convert the dye back to its starting form so the process can begin again. This component is called a ‘redox mediator’.
“Most dye-sensitised solar cells use an iodide molecule as the redox mediator,” explains Professor Coote.
“This has a number of disadvantages. Firstly, it is coloured and that cuts down on how much sunlight is available to be absorbed by the dye.
“Secondly, its oxidation potential [its ability to give electrons back to the dye and thus convert it back to its starting form] is not very well matched to the dye, leading to inefficiency.”
For several years, researchers had been proposing the use of a nitroxide radical as the redox mediator instead.
“Nitroxide radicals are colourless, and their oxidation potential is much closer to the range needed to get maximum efficiency in the conversion of the dye,” explains Professor Coote, who is part of the ARC Centre of Excellence for Electromaterials Science.
The problem was that the researchers who set out to test nitroxide used a molecule that undergoes a number of rearrangements on oxidation.
“That means it’s sort of being destroyed in the first round of electron transfer, so it’s not around to keep cycling.”
Professor Coote and her team saw these results and decided to use computational chemistry to investigate why this particular nitroxide molecule was unstable upon oxidation and what structural changes could be made to stabilise it while keeping its oxidation potential within the ideal range for the dye.
“We used Raijin to investigate many different structures and came up with five predicted compounds that we thought would work,” she says.
“Not long afterward, an independent experimental research group manufactured a solar cell using one of our compounds. The new compound doubled the efficiency of the solar cell.”
Professor Coote, who is head of the Computer Aided Chemical Design Group at ANU, says using computational quantum chemistry is crucial to her research and provides a much deeper insight into chemical processes than can be provided by experiment.
“We absolutely could not do this work without access to Raijin,” she says.