In this work, yarn made of a hybrid material of carbon nanotubes (CNTs) and artificial biomolecules is created for the wearable thermoelectric (TE) module. Among the limited methods due to the sensitivity of proteins, the co-use of the ionic liquid and polymeric surfactant with the dialysis method is found to be effective for the dispersion of the CNT/biomolecule composite with a low CNT loss rate and high coverage by biomolecules on the CNT. This new method improved the TE performance by decreasing the bundle diameter of the CNT/C-Dps nanocomposite and better tensile strength. The incorporation of a biomolecule, in particular, significantly reduced the thermal conductivity of CNT yarns, demonstrating that the hybrid composite is advantageous for wearable device applications. This method also outperformed the conventional dispersion against the pristine CNT yarn (without protein), demonstrating the application’s generality. Finally, a low-density testing of the TE module using the CNT/biomolecule composite is demonstrated, exhibiting the output power of 4.37 μW m^–2 with a thermoelectric voltage of 4.5 mV at a temperature difference of 20 K. The output power density and voltage can be easily increased 500-fold by increasing the density of the yarn and the number of series connections. This study proposes a practical method for producing an environment-friendly CNT/biomolecule hybrid yarn, which has the potential to be useful in future wearable TE applications.

The orientational control of semiconducting polymers (SCPs) in floating films offers several advantages over conventional solution‐processing methods for device fabrication, and the unidirectional floating film transfer method (UFTM) has been applied to fabricate large‐area oriented p‐type SCP films. Here, UFTM can be used to prepare high‐performance n‐type SCP films of P(NDI2OD‐T2) is reported. A strong correlation between the degree of polymer orientation and the solvent used for the preparation of P(NDI2OD‐T2) floating films is observed. In particular, the size of the nanofibers aligned along the orientation direction prepared using chloroform is dramatically increased by adding a small amount of chlorobenzene. Microstructural characterization reveals that the P(NDI2OD‐T2) floating films are uniaxially aligned with edge‐on orientation, whereas the spin‐coated films are isotropic with face‐on orientation. Notably, the floating films of P(NDI2OD‐T2) prepared with solvent blending have higher electron mobility with ambipolar‐like device characteristics and high threshold voltage (V_TH) of ≈25 V. Finally, using the one‐step immersion process, the introduction of an interlayer of hexa(ethylene glycol)‐dithiol between the source/drain contacts and P(NDI2OD‐T2) film results in a drastic improvement in device, giving unipolar n‐channel transistor characteristics with a V_TH of ≈0 V, on/off ratio of >10⁵, and mobility reliability factor of almost 100%.

Doping control of carbon nanotube (CNT) is crucial for thermoelectric (TE) application to maximize the power conversion efficiency. Despite the recent achievement of good air stability by organic salts for n-type carrier doping, their doping mechanism has not been systematically investigated so far. Here, we demonstrate doping of CNT yarn using ammonium salts with different halogen elements (tetra-butylammonium salts, TBAX where X = Cl, Br, or I) through the dipping technique. By changing the halogen element, we specifically investigated the halogen effect in the n-type doping process of CNT. The introduction of each material into the CNT yarn and its doping reaction were then studied by energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Halogen element was found to affect the excess amount of TBA⁺ cation in the CNT yarn. The largest amount of excess TBA⁺ is found in the TBAI-doped yarn, which stabilizes the most amount of negative charge in CNT, enhancing the TE performance and its stability over one month in air. This study discovers the importance of the halogen element in the doping process of CNT-based TE materials by organic salts, simultaneously offering an efficient and stable n-type doping strategy.