(Top) Structural transformation of polymer chains and the generation of charge carriers in the polymer film depending on the doping concentration. (Bottom) Schematic of a p–n diode composed of a p-type polymer and its polarity-switched n-type counterpart, both derived from the same material. Credit: POSTECH

A South Korean research team has, for the first time, uncovered the molecular-level mechanism by which trace amounts of impurities—known as dopants—can reverse charge polarity in organic polymer semiconductors.

A joint research team led by Professor Kilwon Cho, Ph.D. candidates Eunsol Ok and Sein Chung from the Department of Chemical Engineering at POSTECH, and Professor Boseok Kang from the Department of Nano Engineering at Sungkyunkwan University (SKKU), has revealed at the molecular level how adjusting the concentration of a single dopant enables polymer semiconductors to switch between positive (p-type) and negative (n-type) conduction. Their findings were recently published in the journal, Advanced Materials.

Semiconductors are core materials that regulate current flow in modern electronic devices. While traditional silicon-based semiconductors offer excellent performance, their rigidity limits their use in emerging applications such as stretchable displays, wearable electronics, and electronic skin. In contrast, organic polymer semiconductors are lightweight and mechanically flexible, making them promising candidates for next-generation electronics.

However, a major challenge has been the limited availability of stable n-type organic semiconductors. Most conjugated polymers naturally exhibit p-type behavior, while existing n-type counterparts often suffer from poor ambient stability. To enable practical applications, a strategy is needed that allows both p-type and n-type functionalities within a single polymer system.

The research team addressed this issue through a phenomenon known as polarity switching. When a typically p-type polymer is doped with a sufficiently high concentration of a p-type dopant such as gold(III) chloride (AuCl₃), the dominant charge carriers shift from holes to electrons. This concentration-dependent polarity reversal allows a single polymer to exhibit both p-type and n-type characteristics—eliminating the need for separate materials or complex multilayer device architectures.

To uncover the underlying mechanism, the team analyzed polymer films doped with AuCl3. They found that the oxidation states of gold and chloride ions evolve during doping, leading to a substitutional chlorination reaction with the polymer chains. This chemical reaction induces structural reordering of the polymer backbone, realigning the molecular structure and reorganizing charge transport pathways, ultimately driving the polarity switching.

Based on this mechanism, the researchers fabricated a p–n organic homojunction diode using a single polymer doped at two different concentrations. The device exhibited a rectification ratio tens of thousands of times greater than conventional single-material organic diodes, highlighting its potential for high-performance, flexible electronic devices with simplified architectures.

Professor Cho and Kang explained, “Our study is the first to identify the precise chemical and structural mechanism behind polarity switching in polymer semiconductors. This discovery paves the way to precisely control the electrical properties of organic semiconductors, making future electronic devices simpler, more stable, and more efficient.”

More information: Eunsol Ok et al, Accompanying Structural Transformations in Polarity Switching of Heavily Doped Conjugated Polymers, Advanced Materials (2025). DOI: 10.1002/adma.202505945

Citation: Concentration‑controlled doping turns a p‑type polymer semiconductor into its n‑type counterpart (2025, October 31) retrieved 31 October 2025 from https://techxplore.com/news/2025-10-concentrationcontrolled-doping-ptype-polymer-semiconductor.html

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