n-Type Carbon Nanotubes Doped by Cross-Linked Organic Superbase for Stable Thermoelectric Materials

Carbon nanotubes (CNTs) are emerging as promising platforms for organic thermoelectric (TE) materials. However, the poor stability of n-doped states often presents a problem for the long-term operation of p–n junction TE modules. In this study, we synthesized a cross-linked organic superbase, 2TBD-C10, as a dopant to create n-type CNTs that are resistant to air, heat, and humidity. When comparing the stability of 2TBD-C10-doped CNTs with those doped by a conventional superbase (TBD), we found that the enhanced stability could be attributed to the unique molecular structure of 2TBD-C10. This structure aids in effective adsorption on the CNT surfaces through multiple points, reduces volatility because of increased molecular weight, and suppresses water adsorption owing to the presence of hydrophobic alkyl chains. The results of our study demonstrate that tailoring the primary molecular structures of dopants can remarkably improve the stability of doped states in CNTs. The stable n-type materials were integrated into all-CNT TE modules, achieving good-to-excellent performance (power output of approximately 35 μW from a temperature difference of approximately 65 °C), making them suitable for powering wireless sensors and green light-emitting diodes.