One-directional alignment of carbon nanotube films via bar coating for use in thermoelectric generators with stacked printed substrates

Abstract Owing to their one-dimensional structure, carbon nanotubes (CNTs) exhibit anisotropy in their electronic properties. Thus, aligning CNTs in a specific direction while directly depositing them on different device substrates is crucial for their application in electronic and energy devices. Although high alignment has been achieved in prior studies, they faced limitations in scalability, including low production throughput and complex thickness tunability. In this study, a bar-coating method was used to directly deposit CNT films with unidirectional alignment on arbitrary substrates. CNT pastes containing a polymer binder were successfully prepared through ball milling. The effects of coating speed, bar height, and CNT content in the paste on the CNT orientations were comprehensively investigated through surface morphology observations, Raman spectroscopy, and four-probe electrical conductivity measurements. Furthermore, the effectiveness of the bar-coating process was demonstrated by fabricating thermoelectric generators. Specifically, CNT films were directly deposited onto polyimide films with printed Cu electrodes using the bar-coating technique, followed by alternate stacking. The output power from the module in the CNT-oriented direction was significantly higher than that in the perpendicular direction. Unlike conventional printing methods, this approach uniquely enables the high-speed formation of thick, highly aligned CNT films, essential for the efficient performance of stacked device architectures.