| Mar 05, 2025 |
Researchers improved organic solar cell fabrication by controlling molecular assembly, enhancing efficiency and stability, bringing the technology closer to commercial viability.
(Nanowerk News) A new study (Advanced Materials, “Lyotropic Liquid Crystal Mediated Assembly of Donor Polymers Enhances Efficiency and Stability of Blade-Coated Organic Solar Cells”) by researchers at the University of Illinois Urbana-Champaign describes a breakthrough in the field of organic solar cells (OSCs), bringing the technology one step closer to commercial viability.
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OSCs are a compelling technology that can turn any surface into a power generator. Their lightweight, transparent and foldable properties make them ideal for many applications where traditional silicon solar cells are impractical: think backpacks and tents outfitted with OSCs that can generate power on demand in the field, or windows that turn sunlight into electricity thanks to solar cells that are invisible to the naked eye.
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But while OSCs offer many advantages over silicon solar cells and perform well in laboratory settings, they remain non-ideal for real world use because their efficiency and stability drop substantially during the manufacturing process.
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To address this problem, the researchers – led by chemical and biomolecular engineering professor Ying Diao – zeroed in on the molecular assembly process during fabrication. An OSC is composed of several nanometer-thin layers of film. By manipulating the processing conditions when printing the films, they can force the molecules to adopt different structures, said Alec Damron, co-first author on the paper.
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“The ink evaporates while we’re printing, so – depending on how fast we print and how slow the evaporation – we can lock the assembly into different stages,” Damron said. “What we saw in this paper was that when you print our films slowly, as opposed to quickly, that allows for the evaporation portion of the physics to dominate and it will force the polymers to assemble into liquid crystals before a film forms.”
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This finding was important because the liquid crystal structures resulted in better OSC stability and efficiency when compared to cells fabricated using random aggregation pathways. Further manipulation during the process resulted in liquid crystal assembly pathways that were either achiral or chiral. Both resulted in a clear improvement in efficiency and stability of the OSC, but the chiral – or helical – structure yielded the best results.
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“We discovered that chiral assembly of conjugated donor polymers improves the crystalline packing and phase separated structure of the film,” said Azzaya Khasbaatar, the other co-first author on the paper. “Improving film crystallinity not only enhances efficiency by improving charge transport but also makes the films much more morphologically robust/stable.”
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Overall, the researchers demonstrated that achiral liquid crystal pathways show a 20 percent improvement in efficiency and three-fold improvement in stability when compared to random aggregation assemblies. When printed with a helical structure, that number increased to 56 percent higher efficiency and 50 times more stable. These numbers are promising for successful manufacturing.
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“This trend that we saw in improved performance through the liquid crystal phase versus the random fiber aggregation is general and can be applied to various types of organic solar cell materials,” Damron said. “Since that relationship has been established, it is possible to start from that as a baseline and to continue building up on the engineering side of things.”
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Before their work, Diao said that very little was known about what happens between the time you apply the ink to a substrate and when you print the device, calling it a “black box.”
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“People mainly focus on the material side and then the device side, but the middle is neglected,” Diao said. “And that’s something we basically shed light on. We’re lifting the curtain on the hidden process and, by doing so, we are providing pathways to creating better devices.”
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