Researchers from the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) argue that Perovskite solar cells should be exposed to a simultaneous battery of stress tests to more accurately anticipate their outdoor performance.
Solar cells need to withstand a range of challenging conditions, characterized by varying combinations of stress factors. Typically, these tests are conducted indoors with a limited set of fixed stress conditions. Even though these indoor tests offer critical insights, it is essential to determine which specific stressors applied during indoor testing yield predictive correlations with real-world outdoor operations.
“We must understand how well perovskite solar cells will perform outdoors, under real conditions, to move this technology closer to commercialization,” said Kai Zhu, a senior scientist in the Chemistry and Nanoscience Center at NREL. “That’s why we identified accelerated testing protocols that can be conducted in the laboratory to reveal how these cells would function after six months in operation outside.”
Zhu is the principal author of a recently published paper titled “Bridging the Gap Between Laboratory and Field Lifespans of Perovskite Solar Cells,” featured in the journal Nature. Collaborating with Zhu from NREL are Qi Jiang, Robert Tirawat, Ross Kerner, E. Ashley Gaulding, Jimmy Newkirk, and Joseph Berry. Co-authors from the University of Toledo, who have previously collaborated with Zhu on various perovskite-related publications, also contributed to this research.
Outdoor environmental conditions, including humidity, heat, and even sunlight, exert stress on solar cells. This leads to a gradual decline in solar cell efficiency and a reduction in power generation. To ensure the consistency necessary for the commercialization of perovskite technology, it is essential to establish standardized protocols that facilitate the validation and comparison of enhancements made by different research groups.
Scientists usually assess the stability of perovskite solar cells by subjecting them to low-temperature and light exposure tests. However, the diverse range of testing conditions used makes it challenging to compare various studies and determine their relevance in achieving the required reliability for commercialization.
A research team led by NREL conducted a comprehensive set of tests on perovskite solar cells. In the operational stability test, these cells retained over 93% of their maximum efficiency after approximately 5,030 hours of continuous operation. Thermal cycling subjected the cells to repeated temperature fluctuations between -40 and 85 degrees Celsius, with an average degradation of about 5% after 1,000 cycles.
These tests addressed distinct stressors, such as light and heat, in isolation. But, in real-world conditions, these factors act in tandem, significantly accelerating performance degradation or introducing new issues that were not evident when testing each factor separately.
The NREL researchers concluded that the most crucial combination of stressors for understanding the outdoor performance of perovskite solar cells is high temperature and illumination occurring simultaneously. This research was funded by the U.S. Department of Energy Solar Energy Technologies Office.