Korean researchers boost organic semiconductor conductivity through dual molecular design

At Sungkyunkwan University in Seoul, a team of materials scientists has cracked two separate problems that have long constrained the promise of organic semiconductors—the lightweight, bendable materials that could power the next generation of flexible displays, wearable devices, and chemical sensors. The work, led by Professor Kang Bosoek, addresses the fundamental physics of how charge moves through these polymers, and the results suggest that practical applications are now within reach.

Organic semiconductors have always held appeal because they are cheap to manufacture, can be printed onto flexible substrates, and weigh far less than their silicon counterparts. But they have a critical weakness: they don't conduct electricity well enough for most real-world uses. To work in an actual device, two things must happen simultaneously. First, the material must generate enough charge carriers—the electrons or holes that carry current. Second, those carriers must be able to move freely through the material without getting stuck. Kang's team tackled each problem separately, publishing their findings in two of the field's most prestigious journals.

The first breakthrough came through a deceptively simple molecular trick. The researchers took an n-type conducting polymer called PBFDO and chemically bonded polar molecules called aminoalkylsilane directly to its backbone. These attached molecules, all pointing in the same direction, naturally coaxed electrons out of the polymer without requiring heavy reliance on external dopants—chemical additives that are normally needed to boost conductivity. The result was striking: the thin film's electrical conductivity jumped to over 3,000 siemens per centimeter, with a doping efficiency of approximately 1.79 free electrons per polymer repeat unit. This achievement is significant because it approaches the theoretical maximum for this type of material, something no previous study had managed to reach. The work was published in the Journal of the American Chemical Society and selected as a cover article.

The second innovation tackled the transport problem from a different angle. Even if you generate plenty of charge, it can get trapped in the material's crystalline structure, unable to flow smoothly. Kang's team created what amounts to a molecular highway system by coating a thin layer of conducting polymer onto a two-dimensional covalent organic framework—a lattice-like structure made of carbon and nitrogen atoms. The conducting polymer acts as a bridge, connecting the separate crystals of the framework and allowing charge to hop across gaps that would otherwise block its path. When they tested this hybrid structure, the conductivity improved by a factor of 109 compared to the framework alone, and by a factor of 10 compared to the conducting polymer alone. The team also demonstrated that they could manufacture this material uniformly across a two-inch wafer, a crucial step toward real production. When they built a sensor to detect nitrogen dioxide gas using this material, it could pick up concentrations as low as 74 parts per billion and respond in about 20 seconds.

Kang described the work as addressing, at the molecular level, the two fundamental factors that determine whether organic electronics will actually work in devices. The team is now moving beyond these foundational studies toward building more complex structures, combining different semiconductor materials into heterojunctions that could unlock even higher performance. They are also exploring a more exotic direction: using the charge states themselves as a computing function, rather than simply moving charge from point A to point B. The implications are substantial. If these materials can be made to conduct electricity reliably and at scale, the flexible, lightweight electronics that have long seemed just out of reach could finally become ordinary.