Enhanced Thermoelectric\nProperties of Stable n‑Type\nFerrocene Derivatives-Doped Polyethylenimine/Single-Walled Carbon\nNanotube Composite Films

Preparing stable n-type flexible single-walled carbon\nnanotube\n(SWCNT)-based thermoelectric films with high thermoelectric (TE) performance\nis desirable for self-powering wearable electronics but remains a\nchallenge. Here, the interface regulation and thermoelectric enhancement\nmechanism of ferrocene derivatives on polyethylenimine/single-walled\ncarbon nanotube (PEI/SWCNT) composite films have been explored by\ndoping ferrocene derivatives (f-Fc–OH) into PEI/SWCNT films.\nThe results show that the introduction of f-Fc–OH leads to\nthe formation of “thorn” structures on the surfaces\nof SWCNT bundles via hydrophilic and hydrophobic interactions, the\ngenerated energy-filtering effect improves the thermoelectric properties\nof the PEI/SWCNT film, and the f-Fc–OH-doped PEI/SWCNT (f-Fc–OH/PEI/SWCNT)\nachieves the highest room-temperature power factor of 182.22 ±\n8.60 μW m<sup>–1</sup> K<sup>–2</sup> with a Seebeck\ncoefficient of −64.28 ± 0.96 μV K<sup>–1</sup> and the corresponding <i>ZT</i> value of 4.69 × 10<sup>–3</sup>. The Seebeck coefficient retention ratio of the f-Fc–OH/PEI/SWCNT\nnearly remained 68% after being exposed to air for 3672 h, while the\nPEI/SWCNT film changed from n-type to p-type after being exposed to\nair for about 432 h. In addition, the temperature-dependent thermoelectric\nproperties show that the f-Fc–OH/PEI/SWCNT achieves a high\npower factor of 334.57 μW m<sup>–1</sup> K<sup>–2</sup> at 353 K. Finally, a flexible TE module consisting of seven pairs\nof p–n junctions is assembled using the optimum composite film,\nwhich produces an open-circuit voltage of 42 mV and a maximum output\npower of 4.32 μW at a temperature gradient of 60 K. Therefore,\nthis work provides guidance for preparing stable n-type SWCNT-based\ncomposite films with enhanced thermoelectric properties, which have\npotential applications in flexible generators and wearable electronic\ndevices.