Molecular chaos helps to promote the development of low-cost plastic solar cells

According to the report of the Physicists Organization Network on August 4, American scientists published an online version of the “Natural Materials Science” published on August 4th, pointing out that molecular-scale chaos can actually improve the performance of polymers, and the latest research is helpful. Promote the research and development of low-cost commercial plastic solar cells.

For decades, scientists have been hoping to make flexible plastic solar cells with performance comparable to those of silicon-based solar cells. To do this, they need to create plastic materials that allow electric charge to flow through solar cells faster. Some scientific research teams have proposed The solution is to design flexible plastic polymers into ordered silicon-like crystals, but the charge mobility has not been improved.

Research collaborator Alberto Cerro, associate professor of materials and engineering at Stanford University, said: “People used to think that making polymers more like crystalline silicon will perform better, but as a result, polymers will not Forming ordered crystals naturally, they will form small, disordered crystals, which is better. Scientists should learn to deal with the chaotic nature inherent in plastics."

The research team studied a class of organic materials--semiconductor polymers. The carbon atoms of these materials possess the properties of plastics, but they can absorb sunlight and conduct electricity.

Since the semiconductor polymer first came out 40 years ago, it has been considered as an ideal material for manufacturing ultrathin solar cells, light emitting diodes, and transistors. Unlike silicon crystals used in current solar panels, semiconductor polymers are lighter and can be processed at room temperature using inexpensive technologies such as inkjet printers. Cerro said: "In solar cells, electrons need to pass materials quickly, but the mobility of electrons in semiconductor polymers is poor, so it has not been commercialized."

In order to solve this problem, some scientists have designed more rigid polymers to make more ordered crystals, but they still do not help; while others have produced some seemingly disordered polymers. High charge mobility.

The Cerro team sent the disordered materials to the SLAC National Accelerator Laboratory for X-ray analysis. The results show that one of the fingerprint-like molecular structures becomes disordered. Some polymers look like messy pieces of spaghetti, while others form small crystals that are only a few molecules long. Cerro said: "These crystals are small and disorderly and it is difficult to find them through X-rays. Scientists even thought that they did not exist."

By analyzing the light released by the charge flowing through these samples, the scientists determined that a large number of small crystals scattered throughout the material and interconnected by long polymer chains. Cerro explained: “The small size of the crystal is the key to improving its performance. Small size allows charged electrons to pass through the crystal and quickly move to the next crystal. Subsequently, the long polymer chains carry electrons through the material, so It has a higher electron mobility than larger unconnected crystals. In addition, large polymers are generally insoluble in water and therefore cannot be processed using inexpensive techniques such as inkjet printing." (Liu Xia)

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