Breaking the limits of stretchable polymer semiconductors

Like the brakes that stop cars, a molecular brake can prevent semiconductor chains from slipping, enabling the creation of more innovative devices. A joint research team led by Professor Kilwon Cho and PhD candidates Seung Hyun Kim and Sein Chung from the Department of Chemical Engineering at POSTECH, and Professor Boseok Kang from Sungkyunkwan University (SKKU) have developed a technology for high-performance organic polymer semiconductors that exhibit stretchability and electrical functionality. The study was published in Advanced Functional Materials.

For semiconductors to find applications in diverse flexible devices like flexible displays and skin-attachable medical devices, it is necessary to use stretchable materials instead of rigid ones. However, the force exerted during the stretching of semiconductors can be up to 10 times greater than that experienced during simply bending, leading to the breakdown of the semiconductor layers and a decline in their electrical performance. Researchers have been exploring methods to preserve semiconductor performance under deformation, but a definitive solution to this challenge remains elusive.

The POSTECH and SKKU researchers created a flexible molecular photocrosslinker featuring azide reactive groups at both ends. Photocrosslinking refers to the formation of intermolecular covalent bonds that act as crosslinking bonds between molecules, which are initiated by exposure to light. Azide is an ion with three nitrogen atoms and a negative charge, which is highly reactive and used as an intermediate in medical reactions due to its ability to form covalent bonds with other molecules.

When exposed to ultraviolet light, this photocrosslinker forms a network structure with the polymer semiconductor, acting as a brake that prevents slipping, even under stretching conditions. In contrast to traditional semiconductor materials, where polymer chains become intertwined and slip and fracture when stretched, the presence of this ‘brake’ allows the polymer chains to retain their stretchability and performance without any slipping.

Using this approach, the researchers preserved up to 96% of the electrical performance of the polymer semiconductor, even when it was stretched up to 80%. The semiconductor also exhibited enhanced stretchability and durability compared to conventional semiconductors, demonstrating the effectiveness of the developed technology.

Cho said that by incorporating photocrosslinkers into the films, the researchers preserved the electrical properties of polymer semiconductors for organic thin-film transistors under significant mechanical deformation.

“This simple approach significantly enhances the stretchability and UV-patternability of organic semiconducting polymers, making it highly valuable for industries requiring large-area production and photolithography for the development of next-generation flexible electronics,” Cho said.

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