Densification Induced Decoupling of Electrical and Thermal Properties in Free‐Standing MWCNT Films for Ultrahigh p‐ and n‐Type Power Factors and Enhanced ZT

Abstract

Generating sufficient power from waste heat is one of the most important things for thermoelectric (TE) techniques in numerous practical applications. The output power density of an organic thermoelectric generator (OTEG) is proportional to the power factors (PFs) and the electrical conductivities of organic materials. However, it is still challenging to have high PFs over 1 mW m−1 K−2 in free‐standing films together with high electrical conductivities over 1000 S cm−1. Herein, densifying multi‐walled carbon nanotube (MWCNT) films would increase their electrical conductivity dramatically up to over 10 000 S cm−1 with maintained high Seebeck coefficients >60 µV K−1, thus leading to ultrahigh PFs of 7.25 and 4.34 mW m−1 K−2 for p‐ and n‐type MWCNT films, respectively. In addition, it is interesting to notice that the electrical properties increase faster than the thermal conductivities, resulting in enhanced ZT of 3.6 times in MWCNT films. An OTEG made of compressed MWCNT films is fabricated to demonstrate the heat‐to‐electricity conversion ability, which exhibits a high areal output power of ∼12 times higher than that made of pristine MWCNT films. This work demonstrates an effective way to high‐performance nanowire/nanoparticle‐based TE materials such as printable TE materials comprised of nanowires/nanoparticles.

Boosting thermoelectric performance of single-walled carbon nanotubes-based films through rational triple treatments

“…As seen in Fig. 5a , both the cold-pressed and rolled SWCNT films exhibit a significant increase in σ , caused by the densified structure of the films 52 – 55 . The σ is even higher after cold-pressing, but the increase in σ after cold-pressing/rolling for the untreated SWCNT films is only slightly higher than that for NaBH 4 -treated SWCNT films.…”

“…5d, e . However, the G/D peak ratio decreases, suggesting that the cold-pressing process causes the breaking of some bonds in SWCNTs, leading to an increase in defects 52 – 55 . Additionally, the intensity of the 2D peak was decreased after cold-pressing, with ratios of 1:0.63 and 1:0.25, indicating a tighter connection between SWCNT layers, strengthening the longitudinal transport of electrons between SWCNT layers, and significantly increasing the σ 49 .…”

Solvent effect induced charge polarity switching from p- to n-type in polyaniline and carbon nanotube hybrid films with a high thermoelectric power factor

“…The improvement of the electrical conductivity is attributed to the decrease of the void. 71 Fig. S11† shows the SEM images of the n-type PANI-eb 10 /SWCNT–DMSO hybrid films before and after being compressed for 16 min.…”

A Rolled Organic Thermoelectric Generator with High Thermocouple Density

“…The ϕ P for the PEDOT:PSS/Ag and PE-DOT:PSS/BBL:PEI devices from this work are 4.8 × 10 −4 μW cm −2 K −2 and 6.4 × 10 −5 μW cm −2 K −2 , respectively, and fit among the highest reported values for polymer-based TEGs, [52][53][54] although recently reported carbon nanotube-based TEGs have eclipsed power densities of 0.75 μW cm −2 K −2 . [55,56] The thermocouple densities for PEDOT:PSS/Ag and PEDOT:PSS/BBL:PEI devices are 19480 and 1842 TCs cm −2 , respectively. Among organic TEGs, these values represent the highest thermocouple densities reported in literature by more than an order of magnitude.…”