Perovskite solar cells offer greater efficiency and lower costs compared to traditional silicon-based cells. However, their lack of durability has historically hindered widespread adoption. Conventional coatings using ammonium-based compounds, while effective at enhancing efficiency, degrade quickly under environmental stresses such as heat and moisture.
To address this limitation, the research team introduced an amidinium-based protective layer, which outperformed ammonium coatings by a significant margin. Laboratory tests revealed that this innovative layer is 10 times more resistant to decomposition. Moreover, it tripled the cells' T90 lifetime - the duration before a cell's efficiency drops to 90% of its initial level under extreme conditions.
"The field has been working on the stability of perovskite solar cells for a long time," said Bin Chen, a co-leader of the study. "So far, most reports focus on improving the stability of the perovskite material itself, overlooking the protective layers. By improving the protective layer, we were able to enhance the solar cells' overall performance."
Published in 'Science', the study marks a critical advancement in perovskite solar cell technology.
"This work addresses one of the critical barriers to widespread adoption of perovskite solar cells - stability under real-world conditions," explained Mercouri Kanatzidis, another study co-leader. "By chemically reinforcing the protective layers, we've significantly advanced the durability of these cells without compromising their exceptional efficiency, bringing us closer to a practical, low-cost alternative to silicon-based photovoltaics."
Bridging the Durability Gap
Although silicon remains the most widely used material for solar cells due to its reliability and durability, it is costly to produce and nearing its maximum efficiency potential. Researchers have turned to perovskites as a more affordable, higher-efficiency alternative. However, perovskite's limited lifespan under sunlight, temperature fluctuations, and moisture has remained a major challenge.
The Northwestern team tackled this issue by using amidinium ligands, stable molecules capable of interacting with perovskites to enhance protection and prevent defects. Compared to ammonium-based molecules, amidinium compounds are more structurally resilient under harsh conditions.
"State-of-the-art perovskite solar cells typically have ammonium ligands as a passivation layer," said Yi Yang, the study's first author. "But ammonium tends to break down under thermal stress. We did some chemistry to convert the unstable ammonium into a more stable amidinium."
This transformation, achieved through a chemical process called amidination, replaced the ammonium group with amidinium, preventing degradation and improving thermal stability.
Record-Setting Performance
With this innovation, the perovskite solar cells achieved an efficiency of 26.3%, converting 26.3% of sunlight into usable electricity. Additionally, the amidinium-coated cells maintained 90% of their initial efficiency after 1,100 hours of rigorous testing under heat and light, demonstrating their vastly improved durability.
These results build on previous advancements from Northwestern's research team. Over the past two years, the Sargent lab has achieved record-breaking energy efficiency, introduced inverted perovskite structures, and incorporated liquid crystals to enhance cell performance.
"Perovskite-based solar cells have the potential to contribute to the decarbonization of the electricity supply once we finalize their design, achieve the union of performance and durability, and scale the devices," said Ted Sargent, co-leader of the study. "The primary barrier to the commercialization of perovskite solar cells is their long-term stability. But due to its multi-decade head start, silicon still has an advantage in some areas, including stability. We are working to close that gap."
The study supports the Trienens Institute's Generate pillar, which focuses on advancing solar energy production through innovative technologies. By improving perovskite solar cells, Northwestern aims to develop the next generation of efficient, cost-effective solar solutions.
Research Report:Amidination of ligands for chemical and field-effect passivation stabilizes perovskite solar cells
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