Facile fabrication of highly flexible, porous PEDOT:PSS/SWCNTs films for thermoelectric applications

Abstract

High-performance organic composite thermoelectric (TE) materials are considered as a promising alternative for harvesting heat energy. Herein, composite films of poly (3,4-ethyienedioxythiophene):poly(styrene sulfonate)/single-walled carbon nanotubes (PEDOT:PSS/SWCNTs) were fabricated by utilizing a convenient solution mixing method. Thereafter, the as-prepared hybrid films were treated using sulfuric acid (H2SO4) to further optimize the TE performance. Film morphological studies revealed that the sulfuric acid treated PEDOT:PSS/SWCNTs composite samples all possessed porous structures. Due to the successful fabrication of highly conductive networks, the porous nano-architecture also exhibited much more excellent TE properties when compared with the dense structure of the pristine samples. For the post-treated sample, a high power factor of 156.43 μW⋅m−1⋅K–2 can be achieved by adjusting the content of CNTs, which is approximately 3 orders of magnitude higher than that of the corresponding untreated samples (0.23 μW⋅m−1⋅K–2). Besides, the obtained films also showed excellent mechanical flexibility, owing to the porous nanostructure and the strong π–π interactions between the two components. This work indicates that the H2SO4 treatment could be a promising strategy for fabricating highly-flexible and porous PEDOT:PSS/SWCNTs films with high TE performances.

A Novel and Green Method for Preparing Highly Conductive PEDOT:PSS Films for Thermoelectric Energy Harvesting

“…More than that, the value of the power factor achieved is comparable to or even higher than those of some composites, such as PEDOT:PSS/Ca 3 Co 4 O 9 composite films (3.77 µW·m –1 ·K –2 ) [ 37 ], some multilayered film systems like PEDOT:PSS/PANI (3.0 µW·m –1 ·K –2 ) [ 38 ], and PEDOT:PSS/P3HT (5.79 µW·m –1 ·K –2 ) [ 39 ]. Although the power factor is not as good as that of the H 2 SO 4 -treated samples (as reported in our previous work, a high power factor of around 47 µW·m –1 ·K –2 can be obtained because of the strong effect of concentrated sulfuric acid on the polymer structure, including the removal of PSS, better crystallinity of the conductive PEDOT:PSS, and variation of the microstructures) [ 29 ], the process of water treatment was very environmentally friendly, and no harmful reagent was used.…”

“…Figure 3 a displays the Raman spectra of the PEDOT:PSS films including the pristine as-prepared one and those treated with different cycles of the water washing treatment. Characteristic peaks associated with PEDOT:PSS structures were observed, with the peak attributions summarized in Table 1 [ 28 , 29 ]: peaks centered at 1566 cm –1 and 1493 cm –1 , corresponding to asymmetric C α =C β stretching, became increasingly prominent after the water treatment; the peak at 1428 cm –1 , attributed to symmetric C α =C β (–O) stretching vibrations of the five-membered thiophene ring, became sharper and more intense. Similar trends were observed at 1367 cm –1 (C β –C β stretching), 1254 cm –1 (inter-ring C α –C α stretching), 1117 cm –1 (C–C ring bending vibration), 1094 cm –1 (C–O–C deformation), 701 cm –1 (symmetric C–S–C deformation), 437 cm –1 (SO 2 bending), 988 cm –1 , and 576 cm –1 (deformation of oxyethylene ring).…”

“…For analytic simplicity, the data from the pristine PEDOT:PSS were compared with those from the film treated 20 times, and the results are presented in Figure S4 . As depicted, the absorption peak at 256 nm can be assigned to the aromatic ring of PSS [ 24 , 29 ]. After a water treatment for 20 cycles, this peak decreased in density, clear evidence of PSS removal.…”