Fully Organic p-n Diode Using Polarity Switching in Single Conjugated Polymer-Dopant System

Investigations into organic semiconductors (OSCs) often encounter limitations with n-type charge transport due to the environmental vulnerability of n-type materials. Developing stable and high-efficiency n-type OSCs is crucial for devices relying on p-n junctions in complementary and logic circuits. This research introduces polarity switching, an unusual phenomenon caused by doping p-type conjugated polymer (CP) film in high doping level, and then the main charge carrier type switches from p to n depending on the doping level. The polarity switching is implemented only with inherently stable p-type CP and p-type oxidizing agent as dopant. In this study, the polarity switching is validated with the electric properties changing from p to n-type via Seebeck coefficient analysis, AC Hall measurements, field-effect transistor mobility, and energy level shift using photoelectron spectroscopy. Further molecular structural changes induced by doping are examined through grazing-incidence wide-angle X-ray scattering, with a detailed analysis of oxidation state changes in the dopant ions via X-ray photoelectron spectroscopy. These results demonstrate a direct relationship between an increase in delocalized polarons and a reduced bandgap, leading to band-like transport. Additionally, the study reveals orientation changes in the crystalline structures due to dopant interactions with the CP backbone chains. This research successfully culminates in the development of a vertical homojunction organic diode with a rectification ratio in the tens of thousands, enhancing our understanding of polarity switching and paving the way for novel applications that allow versatile charge carrier type manipulation within a single p-type CP-dopant system. Furthermore, the p-n diode array, utilizing parylene C as the substrate, is versatile enough for use in creating soft, flexible, and transparent devices, suitable for modern wearable, human-friendly technology. Notably, the bridge rectifier circuit, using four p-n diodes, facilitates the rectification of alternating current into output, enabling its seamless integration into electronic and household appliances.