(Nanowerk News) Organic solar cells are light as a window and can be replicated as a newspaper. They are emerging as a sustainable solution for the country’s growing energy needs.
Researchers at the University of Illinois Urbana-Champaign are the first to observe a biological property called chirality that appears in aciral conjugate polymers, which are used to design flexible solar cells. Their discovery can help improve the cells’ charging capacity and increase access to affordable renewable energy.
DNA’s wrapped architecture is recognized by many as a helix. Structurally, DNA and other helical molecules are classified as chiral: asymmetric so that overlay on a mirror image is impossible. The term comes from the Greek word by hand, which is also an example. Imagine a left-hand print on a sheet of paper, followed by a right-hand print directly on top. The two prints are not nicely matched; your hand, like its DNA, is chiral.
From hands and feet to carbohydrates and proteins, chirality is twisted into human genetic makeup. It is also abundant in nature and even enhances the chemical reaction that drives photosynthesis.
“Chirality is a fascinating biological property,” said Ying Diao, an associate professor of chemical and biomolecular engineering and the study’s lead researcher. “The function of many biomolecules is directly linked to their chirality. Take the protein complexes involved in photosynthesis. As electrons move through the helical structures of proteins, an efficient magnetic field is generated that helps separate bound charges created by light. This means that light can be converted to biochemicals more efficiently. ”
For the most part, researchers have observed that molecules with similar structures tend to keep to themselves: chiral molecules are assembled into chiral structures (such as nucleic acids that form DNA), and aciral molecules are assembled into achiral structures. Diao and her colleagues observed something different. Under the right conditions, aciral conjugated polymers can deviate from the norm and be assembled into chiral structures.
Their paper shows up in Nature communication (“Chiral origin in multistage hierarchical composition of aciral conjugated polymers”) and introduces new opportunities for research into the convergence of biology and electronics. For the first time, researchers can apply chiral structure to the myriad materials that require aciral conjugated polymers to function.
In particular, solar cells: paper-thin solar panels scaled down to the size of a computer screen. The flexible cells are completely composed of organic materials and are transparent and easy enough to hold on to a bedroom window. They can also be manufactured quickly with solution printing, the process used to print newspapers.
“Ecological solar cells can be printed at high speed and low cost, with very little energy. Imagine one day solar cells are as cheap as newspapers, and you can fold one up and carry it around in your backpack,” said Diao.
Conjugated polymers are crucial for cell development and design.
“Now that we have unlocked the potential for chiral conjugated polymers, we can apply the biological property to solar cells and other electronics and learn from how chirality improves photosynthesis in nature. With more efficient organic solar cells that can be produced so quickly, we can potentially generate gigawatts energy daily to catch up with the rapidly growing global energy demand, says Diao.
But renewable energy is just one of many areas to benefit from the combination of chirality and conjugated polymers. Various applications can include consumer products such as batteries and smart watches, quantum calculations and bio-based sensors that can detect signs of disease in the body.
This remarkable emergence of chirality in conjugated polymers could open new avenues for applications beyond solar cells. insight into how to make these applications happen, ”says Qian Chen, associate professor of materials science and engineering and co-author of this study.
To arrive at their discovery, the researchers first combined aciral conjugated polymers with a solvent. They then added the solution, drop by drop, to a slide. As the solvent molecules evaporated, leaving the polymers behind, the solution became more and more concentrated. Soon, the compressed aciral polymers began to self-assemble to form structures.
Molecular self-assembly is not an uncommon phenomenon. As the concentration of the solution increased, the researchers observed that the aciral polymers were not assembled into aciral structures as expected. Instead, they formed spirals.
“Through the lens of a microscope, we observed the twisted shape and helical structure of the polymers. The facilities in Beckman’s Microscopy Suite helped make this discovery possible,” said lead author and postdoctoral fellow Kyung Sun Park.
Furthermore, the researchers found that the chiral-to-achiral structural development does not take place in a single step, but in a multi-step sequence where smaller helices are put together to form increasingly complex chiral structures.
Advanced simulations of molecular dynamics helped the researchers to confirm the steps on a molecular scale in this sequence that cannot be seen with the naked eye.
“Simulation of molecular dynamics was crucial to this research. Equally important was the Beckman Institute’s collaborative environment that encouraged the merging of molecular dynamics with microscopy and chemistry,” said Diwakar Shukla, associate professor of chemistry and biomolecular technology and co-author of this study.
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