A University of Toronto research team used the Canadian Light Source (CLS) at the University of Saskatchewan to get a glimpse of the never-before-seen transformation of a 3D crystal into a high efficiency solar cell material.
'There were lots of high fives when we actually looked at the computer screen and could see the reaction in real time,' said Sam Teale, a PhD student at the U of T and co-author on a paper describing the perovskite solar cell research. What the researchers saw, over the course of just three seconds, was the creation of an ultra-thin 2D layer of perovskite on top of a 3D perovskite crystal.
Importantly, it also improves the working lifetime of cells. Rapid advances in perovskite research have seen cell efficiency rocket from the original four% to 25.5% today, and applying coating treatments 'has become a staple of fabrication.'
'It was a big boon to discover you can take cheap molecules, coat them onto a cell and improve its efficiency and lifetime by such a large margin.
Optimizing this surface healing holds the most hope for perovskites to reach what Teale termed 'the Holy Grail' for solar cells ' 'operating for 1,000 hours at 85 degrees Celsius and 85% relative humidity, and not dropping below 85% of its initial efficiency.' However, no one had ever observed the molecular-level structural changes occurring because of healing treatments, making optimization challenging.
Teale said his team initially tried to peer into this molecular healing process about three years ago at the CLS. 'We saw something, the glimmerings of something, but not enough to make any conclusions. We're so pleased the CLS has continued with its technology upgrades because now, with the Brockhouse X-ray Diffraction and Scattering Beamlines, instead of seeing images at a frame rate of one every three seconds, we can see three frames every second. We could see how the 2D layer forms as the carbon layers intersects with the 3D layer.'
Using the synchrotron, the team had a highly-detailed view of crystals transforming into the new perovskite species. These details will help researchers to better produce a material that could be the future of solar energy.
Teale is confident perovskite will soon exceed silicon as the preferred material for solar cells; the question now is how to upscale the cells being produced in labs to create commercial products 'that can sit on our roofs for 20 years.'
For Teale and his colleagues, that means heading back to the CLS to study techniques for controlling the molecular healing process in the hope of continuing to improve both efficiency and stability. They plan to be back at the CLS for more experiments in December.
