Breaking the stretchable limit of semiconductors with molecules

Just as brakes stop a car, there are molecular brakes that can prevent semiconductor chains from slipping, allowing for more innovative devices to be created. Recently, a joint research team led by Professor Kilwon Cho and PhD candidates Seung Hyun Kim and Sein Chung from the Chemical Engineering Department at POSTECH, and Professor Boseok Kang from the Nano Engineering Department at Sungkyunkwan University (SKKU) have developed the technology for polymer semiconductors. high-performance organic compounds that exhibit high tensile strength and electrical functionality. This study was recently featured on the inside back cover Advanced Functional Materials.

For semiconductors to find applications in a variety of flexible devices such as flexible displays and skin-mountable medical devices, it is necessary to use stretchable materials instead of rigid ones. However, the forces exerted during stretching of a semiconductor can be up to ten times greater than those experienced during simple bending, leading to damage to the semiconductor coating and a decrease in its electrical performance. Researchers have diligently explored methods to maintain semiconductor performance even under deformation, but definitive solutions to this challenge remain elusive.

The research team succeeded in making a flexible molecular photocrosslinker¹ showing azide-reactive groups at both ends. When exposed to ultraviolet light, these photocrosslinkers form a network structure with semiconducting polymers, acting as a brake preventing slippage even under stretching conditions. In contrast to conventional semiconductor materials, where the polymer chains become intertwined and permanently slip and break when stretched, the presence of these “brakes” allows the polymer chains to retain their flexibility and performance without slippage.

Using this approach, the research team was able to maintain the polymer semiconductor’s electrical performance by up to 96 percent, even when stretched to 80 percent. In addition, the semiconductors exhibit significantly improved ductility and durability compared to conventional semiconductors, which clearly demonstrates the effectiveness of the developed technology.

Professor Kilwon Cho explained, “By incorporating azide photocrosslinkers into the film, we have managed to maintain the excellent electrical properties of polymeric semiconductors for organic thin-film transistors even under significant mechanical deformation. This simple approach significantly improves the malleability and UV patterning of organic semiconductor polymers, making them invaluable to industries requiring large area production and photolithography for the development of the next generation of flexible electronics.”

This study was carried out with support from the Mid-Career Research Program of the Korea National Research Foundation and the Strategic Strengthening of the International Cooperation Network of the Korean Ministry of Science and ICT.