Enhanced Thermoelectric Properties of Stable n-Type Ferrocene Derivatives-Doped Polyethylenimine/Single-Walled Carbon Nanotube Composite Films

Preparing stable n-type flexible single-walled carbon nanotube (SWCNT)-based thermoelectric films with high thermoelectric (TE) performance is desirable for self-powering wearable electronics but remains a challenge. Here, the interface regulation and thermoelectric enhancement mechanism of ferrocene derivatives on polyethylenimine/single-walled carbon nanotube (PEI/SWCNT) composite films have been explored by doping ferrocene derivatives (f-Fc–OH) into PEI/SWCNT films. The results show that the introduction of f-Fc–OH leads to the formation of “thorn” structures on the surfaces of SWCNT bundles via hydrophilic and hydrophobic interactions, the generated energy-filtering effect improves the thermoelectric properties of the PEI/SWCNT film, and the f-Fc–OH-doped PEI/SWCNT (f-Fc–OH/PEI/SWCNT) achieves the highest room-temperature power factor of 182.22 ± 8.60 μW m–1 K–2 with a Seebeck coefficient of −64.28 ± 0.96 μV K–1 and the corresponding ZT value of 4.69 × 10–3. The Seebeck coefficient retention ratio of the f-Fc–OH/PEI/SWCNT nearly remained 68% after being exposed to air for 3672 h, while the PEI/SWCNT film changed from n-type to p-type after being exposed to air for about 432 h. In addition, the temperature-dependent thermoelectric properties show that the f-Fc–OH/PEI/SWCNT achieves a high power factor of 334.57 μW m–1 K–2 at 353 K. Finally, a flexible TE module consisting of seven pairs of p–n junctions is assembled using the optimum composite film, which produces an open-circuit voltage of 42 mV and a maximum output power of 4.32 μW at a temperature gradient of 60 K. Therefore, this work provides guidance for preparing stable n-type SWCNT-based composite films with enhanced thermoelectric properties, which have potential applications in flexible generators and wearable electronic devices.