Toward better identifying and targeting the physical properties of organic semiconductors

Since the first organic field-effect transistor was demonstrated in 1986, research in organic electronics has been dominated by the idea that the physics characterizing organic semiconductors is the same as that governing their inorganic counterparts. But many mechanisms behind basic semiconductor properties remain unresolved and are part of an ongoing dialogue within the field.

Martin Weis argued the conversation has been misguided by a long-held assumption that the organic active layer is a semiconductor.

“For forty years, we analyzed organic transistors with the textbook theory for silicon, which, strictly speaking, requires conditions these materials do not meet,” said Weis. “Nonetheless, the devices worked, and we quietly puzzled about why, and why certain problems persisted.”

Weis proposed that the properties of organic semiconductors, from insulating to semiconducting, are better regarded as dielectric traits. In their resting, unperturbed state, these materials sit far closer to the “insulator” end than scientists have been willing to admit.

“The honest description wouldn’t be ‘weak semiconductor’ but ‘dielectric,’” said Weis. “And the moment you accept that a single quantity — dielectric relaxation time — turns out to govern how well the device connects to its electrodes.”

The study identifies this relaxation time as the fundamental figure of merit: The contact-resistance floor, the part that no metal-contact engineering can remove, is a bulk property fixed by the material’s conductivity, and it sets how small the devices can ultimately be made.

“The roadmap to smaller organic circuits is written in the relaxation time, not in mobility,” said Weis. “The material has been telling us what it is the whole time, and we may be finally ready to listen.”

Source: “The dielectric identity of organic semiconductors: Bulk dielectric relaxation time as a universal figure of merit,” by Martin Weis, Journal of Applied Physics (2026). The article can be accessed at https://doi.org/10.1063/5.0332081 .