High-Performance N-Type Carbon Nanotube Composites: Improved Power Factor by Optimizing the Acridine Scaffold and Tailoring the Side Chains

Single-walled carbon nanotubes (SWCNTs)/organic small molecules (OSMs) are promising candidates for application in thermoelectric (TE) modules; however, the development of n-type SWCNT/OSMs with high performance is lagging behind. Only a few structure-activity relationships of OSMs on SWCNT composites have been reported. Recently, we find that the n-type acridone/SWCNT composites display high power factor (PF) values at high temperature but suffer from low PFs at room temperature. Here, the performance of SWCNT composites containing an acridine derivative (AD) as well as its analogues with different counterions (Cl^-, SO₄ ^2- and F^-) and lengths of alkyl chains (ADLA1-2 and ADLA4-5) is reported. Among the composites, SWCNT/ADLA4 with no counterions exhibits the highest PF value of 195.2 μW m^-1 K^-2 at room temperature, which is 4.9 times higher than that of SWCNT/ADTAd (39.8 μW m^-1 K^-2), indicating that the acridine scaffold and the lengths of alkyl chains contribute to the dramatic changes in the TE performance. In addition, SWCNT/ADLA4 exhibits high PF values at all the temperatures we investigate, which range from 154.7 to 230.7 μW m^-1 K^-2. Furthermore, a TE device consisting of five pairs of p (the pristine SWCNTs)-n (SWCNT/ADLA4) junctions is assembled, generating a relatively high open-circuit voltage (41.7 mV) and an output power of 1.88 μW at a temperature difference of 74.8 K. Our results suggest that structural modifications might be an effective way to advance the development of TE materials.