In a recent report released by the Physicists Organization Network on August 4, American scientists published their findings in *Nature Materials*, revealing that molecular-level chaos can actually enhance the performance of polymers. This discovery could significantly advance the development of affordable, commercial plastic solar cells.
For many years, researchers have aimed to create flexible plastic solar cells that match the efficiency of traditional silicon-based ones. To achieve this, they needed to develop plastic materials that allow electric charges to move more efficiently through the cells. Some teams tried to engineer flexible polymers into ordered, silicon-like crystals, but this approach didn’t improve charge mobility as expected.
Alberto Cerro, an associate professor of materials science at Stanford University and a key researcher in the study, said, “People used to believe that making polymers more crystalline would improve their performance. However, instead of forming large, ordered crystals, the polymers naturally form small, disordered ones—something that might actually be beneficial. Scientists should embrace the inherent disorder in plastics rather than fight it.â€
The research team focused on a type of organic material known as semiconductor polymers. These materials combine the flexibility of plastics with the ability to absorb sunlight and conduct electricity.
Since their introduction 40 years ago, semiconductor polymers have been considered ideal for creating ultra-thin solar cells, light-emitting diodes, and transistors. Unlike silicon, which is heavy and requires high-temperature processing, these polymers are lightweight and can be printed using low-cost methods like inkjet printers. However, one major challenge has been their poor electron mobility, which has prevented them from being widely commercialized.
To address this issue, some scientists attempted to create more rigid polymers to form better-ordered crystals, but this didn’t solve the problem. Others found that certain disordered polymers exhibited unexpectedly high charge mobility.
Cerro’s team sent these disordered materials to the SLAC National Accelerator Laboratory for X-ray analysis. The results showed that the materials had unique, fingerprint-like molecular structures that were not easily detectable. Some looked like tangled spaghetti, while others formed tiny, short-range crystals. Cerro noted, “These small, disordered crystals are hard to spot with X-rays, and some scientists even doubted their existence.â€
By studying the light emitted as charges moved through the samples, the researchers discovered that numerous small crystals were spread throughout the material and connected by long polymer chains. Cerro explained, “The small size of the crystals is crucial. It allows electrons to move quickly from one crystal to another. Meanwhile, the long polymer chains help carry the electrons across the material, resulting in higher electron mobility compared to larger, disconnected crystals. Plus, larger polymers tend to be insoluble, making them unsuitable for cost-effective manufacturing techniques like inkjet printing.†(Liu Xia)
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