Although perovskite solar cells are more efficient and less expensive than traditional silicon solar cells, perovskite has until now been limited by its lack of long-term stability. Typically, perovskite solar cells use an ammonium-based coating layer to improve their efficiency. Although effective, ammonium-based layers degrade under environmental stresses, such as heat and humidity.
Scientists at Northwestern University (USA) have developed a new, more robust protective coating, based on amidinium, which significantly extends the life of perovskite solar cells, making them more practical for applications outside the laboratory.
In experiments, the new coating was found to be ten times more resistant to decomposition than conventional ammonium-based coatings. Even better: the amidinium-coated cells also tripled their T90 lifespan, which is the time it takes for a cell’s efficiency to drop by 90% from its initial value when it is exposed to difficult conditions.
« We have been working on the stability of perovskite solar cells for a long time. says Northwestern’s Bin Chen, who co-led the study. “ So far, most reports focus on improving the stability of the perovskite material itself, without considering the protective layers. By improving the protective layer, we were able to increase the overall performance of the solar cells. »
« This work addresses one of the main obstacles to widespread adoption of perovskite solar cells: stability in real-world conditions said Northwestern’s Mercouri Kanatzidis, who co-led the study. “ By chemically strengthening the protective layers, we have significantly improved the durability of these cells without compromising their exceptional efficiency, bringing us closer to a practical, low-cost alternative to silicon-based photovoltaic cells. »
Used for decades, silicon is the most commonly used material for the light-absorbing layer in solar cells. Although silicon is durable and reliable, it is expensive to produce and its efficiency is nearing its ceiling. In search of a less expensive and more efficient solar cell, researchers have recently begun exploring perovskites, a family of crystalline compounds.
Although it shows promise as a cost-effective alternative to silicon, perovskite has a relatively short lifespan. Prolonged exposure to sunlight, extreme temperature fluctuations, humidity are all factors that cause perovskite solar cells to degrade over time.
To overcome this problem, the researchers added amidinium ligands, stable molecules that can interact with the perovskite to provide defect passivation and long-lasting protective effects. Ammonium-based molecules have a nitrogen atom surrounded by three hydrogen atoms and a carbon-containing group, while amidinium-based molecules include a central carbon atom linked to two amino groups. Because their structure allows electrons to distribute evenly, amidinium molecules are more resilient under harsh conditions.
« Most modern perovskite solar cells generally feature ammonium ligands as a passivation layer “, explains Mr. Yang. “ But ammonium tends to decompose under heat stress. We did chemistry to convert unstable ammonium into more stable amidinium ».
The researchers carried out this conversion through a process known as amidination, in which the ammonium group is replaced with a more stable amidinium group. This innovation helped prevent perovskite cells from degrading over time, especially when exposed to extreme heat.
The resulting solar cell reached a impressive return of 26.3%which means that it managed to convert 26.3% of absorbed sunlight into electricity. The coated solar cell also retained 90% of its initial efficiency after 1,100 hours of testing under harsh conditions, demonstrating a T90 lifespan three times longer than before when exposed to heat and light .
These experiments are the latest example of improving the performance of perovskite solar cells in the Sargent lab. In 2022, Mr. Sargent’s team developed a perovskite solar cell that broke records for energy efficiency and voltage. In 2023, his team presented an inverted structure perovskite solar cell, which also improved its energy efficiency. Earlier this year, Sargent’s group incorporated liquid crystals to minimize defects in perovskite films, leading to improved device performance.
« Perovskite solar cells can contribute to the decarbonization of electricity supply once we finalize their design, achieve the union of performance and sustainability, and scale the devices said Mr. Sargent, who directs the Paula M. Trienens Institute for Sustainability and Energy. “ The main obstacle to the commercialization of perovskite solar cells is their long-term stability. But because of its decades-long lead, silicon retains an advantage in certain areas, notably stability. We are working to close this gap. »
This research is directly linked to the Generate pillar, one of the six pillars of decarbonization of the Trienens Institute. Under this pillar, Northwestern is committed to creating a new class of solar power generation by focusing on high-efficiency multijunction solar cells and next-generation solar cell materials. Mr. Kanatzidis is the Faculty Co-Chair for this pillar and Mr. Chen is the Implementation Lead.
The study, titled “ Amidination of ligands for chemical and field-effect passivation stabilizes perovskite solar cells ”, was supported by First Solar, the Department of Commerce, the National Institute of Standards and Technology, and the U.S. Department of Energy.
Illustration caption: Yi Yang, first author of the study, tests a sample of the team’s new solar cell in the Northwestern University laboratory. Credit: Northwestern University
Article : ‘Amidination of ligands for chemical and field-effect passivation stabilizes perovskite solar cells’ / ( 10.1126/science.adr2091 ) – Northwestern University – Publication dans la revue Science
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