Improving solar cell performance

By Greg Basky, Canadian Light Source

With the rise of power-hungry applications like AI and data centers, it’s critical that the performance of renewable energy sources keeps pace. Researchers in the University of Saskatchewan’s (USask) Department of Chemistry are exploring ways to improve the efficiency of a promising new type of solar cell made from perovskite crystals. Perovskites are a group of materials noted for their promising combination of high efficiency and low manufacturing costs in solar cell applications.

Using the Canadian Light Source (CLS) at USask, a team led by Dr. Tim Kelly (PhD) has observed in real time and at a microscopic level the formation of the crystals. What they’ve learned about optimal production conditions promises to help engineers develop new formulas for manufacturing higher performing cells at scale.

Perovskite solar cells are made by building up thin layers, like a sandwich. Each layer has a specific role or function. The perovskite layer begins as a liquid made of metal salts and organic molecules that is painted on, then heated to dry it (called annealing). This crystal layer absorbs light.

Using the CLS’s Brockhouse beamline, Kelly and his team were able to follow changes in a cell’s ability to generate voltage in real time, as the perovskite crystals formed. He likened the research to being able to sample a cake baking in the oven, without having to open the oven door and risk ruining the cake.

“That’s effectively what we were doing at the CLS,” says Kelly. “We were able to ‘bake’ our cell at the beamline, then monitor its performance throughout the whole crystallization process.”

The researchers discovered that even in early stages of the heating process, before the crystals are fully formed, the cell is already able to produce photo voltage. They found that, as the crystals grow, electrical charge moves more easily within the cell, so efficiency rises. They were also able to identify the point at which a cell’s performance starts to decline.

Kelly says they were surprised to learn that, unlike traditional silicon-based solar cells, performance of perovskite solar cells is not particularly sensitive to defects in the material’s structure. The cells they studied still produced a significant photovoltage despite having numerous imperfections.

Their main takeaway, says Kelly, is that precisely controlling both the annealing time and temperature produces better crystals, and thus higher performing solar cells.

“Being able to watch that process is real time gave us great clues about the ideal fabrication conditions and lots of new knowledge about how the growth process affects the device performance,” says Kelly.

He says that even if their research yields only marginal advances in solar cell performance, if those gains are scaled up and spread globally, it holds the potential for big improvement.

“Where we're at climate wise, it's not solar or wind or nuclear, it's an-all-hands-on-deck,” says Kelly. “So advancing solar technologies like perovskites -- emerging technologies that have a role to fill in solving our power needs moving forward -- every step forward is crucial.”