Researchers in the Department of Applied Physical Sciences have found that an amorphous type of synthetic rubber material has the best properties for protecting perovskite solar cells, a technology known for its impressive efficiency and cost-effectiveness, from damage by moisture and oxygen.

In their study, “Metal Halide Perovskite Solar Module Encapsulation Using Polyolefin Elastomers: The Role of Morphology in Preventing Delamination,” published in PRX Energy, the researchers compared two types of polyolefin elastomer (POE) with different properties as encapsulants, or sealants, for perovskite solar cells.

The first type, called POE-1, tended to crystallize during the encapsulation process, causing it to shrink or warp. In contrast, the second type, POE-2, remained mostly amorphous, meaning that it didn’t crystallize, providing better reliability and consistency.

“This study highlights the importance of the morphology of encapsulants in achieving high-quality encapsulation,” said Haoyang Jiao, lead author of the paper and a postdoctoral researcher at UNC-Chapel Hill. “With further research and development, this encapsulation method could bring us closer to a sustainable energy future.”

Solar cells need a protective covering, called encapsulation, to last for at least 25 years, but perovskite solar cells are trickier to protect than silicon ones because they are softer and more delicate. Traditional encapsulants, such as ethyl vinyl acetate, have drawbacks. They require high processing temperatures and can degrade over time, potentially damaging the delicate perovskite solar cells. POE might work well for encapsulation, however there is no obvious choice among its many different kinds for protecting perovskite solar cells.

Small perovskite solar modules covered with POE-2 performed very well in rigorous tests and under harsh conditions. These tests included being heated and cooled 240 times between very cold (-40° Celsius) and very hot (85° Celsius) temperatures, and enduring 1,419 hours in hot, humid conditions.

The amorphous nature of POE-2 proved to be highly effective in maintaining the structural integrity and performance of perovskite solar cells. POE-2, which doesn’t have a fixed, ordered structure like crystals, can bend and stretch more easily without breaking when temperatures change drastically, and because it doesn’t have a rigid structure, it can form a more even, continuous layer around the solar cells, providing better and more consistent protection against environmental factors, like heat and moisture.

“These tests were vital for predicting how well the solar cells will perform and last in real-world conditions,” said Jinsong Huang, the Louis D. Rubin, Jr. Distinguished Professor in the Department of Applied Physical Sciences.

POEs are known for their rubber-like flexibility and elasticity. They’re used in gaskets and seals in automobiles, to manufacture tubing and prosthetic devices in the medical field and are found in a wide range of consumer products that require a combination of softness and strength, such as footwear and sports equipment. Their emerging use in perovskite solar modules is due to their lower cost and excellent protective qualities.

“As research and development continue, the potential applications of POEs are likely to expand,” said Theo Dingemans, chair of the Department of Applied Physical Sciences. “Their unique combination of flexibility, durability and environmental resistance positions them as a versatile material to encapsulate metal halide perovskite solar modules.”