Printed Flexible μ-Thermoelectric Device Based on Hybrid Bi₂Te₃/PVA Composites

Abstract

Inorganic–polymer composites have become promising materials to be processed by printing technologies because of their unique properties that allow the fabrication of flexible wearable electronics at reduced manufacturing costs. In the present work, a complete methodological process of assembling a flexible microthermoelectric generator based on inorganic−polymer materials is presented. The used microparticles were prepared by a top-down approach beginning with a previously prepared material by solid-state reaction and later scaled down through the use of ball milling. It was found that the necessity to proceed with a chemical treatment with HCl to reduce Bi2O3 present on the surface of the microparticle leads to a power factor (PF) of 2.29 μW K–2 m–1, which is two times higher than that of the untreated sample. On the fabrication of flexible inorganic–organic thermoelectric thick films based on Bi2Te3 microparticles (<50 μm) and the poly­(vinyl alcohol) (PVA) polymer with different thicknesses ranging from 11 to 265 μm and with different Bi2Te3 weight percentages (wt %), we found that PVA allowed achieving a homogeneous dispersion of the parent inorganic thermoelectric materials, while still maintaining their high performance. The best produced ink was obtained with 25 wt % of PVA and 75 wt % of chemically treated Bi2Te3 micropowder with a Seebeck coefficient of −166 μV K–1 and a PF of 0.04 μW K–2 m–1. For this optimized concentration, a flexible thermoelectric device was fabricated using n-type thermoelectric inks, which constitutes a major advantage to be applied in printing techniques because of their low curing temperature. The device architecture was composed of 10 stripes with 0.2 × 2.5 cm2 each in a one-leg configuration. This prototype yielded a power output up to ∼9 μW cm–2 with a 46 K temperature gradient (ΔT), and the results were combined with numerical simulations showing a good match between the experimental and the numerical results. The thermoelectric devices studied in this work offer easy fabrication, flexibility, and an attractive thermoelectric output for specific power requirements such as for environmental health monitoring.

Flexible N-Type Thermoelectric Composites Based on Non-Conductive Polymer with Innovative Bi2Se3-CNT Hybrid Nanostructured Filler

“…For these reasons, a further study was performed for the PVOH/Bi 2 Se 3 -MWCNT composites containing 15 and 30 wt.% of filler. Properties of these samples were compared with the properties of PVOH/Bi 2 Te 3 composites with 68–90 wt.% of Bi 2 Te 3 filler, reported by Pires et al [ 16 ]. It should be noted the PVOH/Bi 2 Te 3 composites reported by Pires et al were printed on polyethylene terephthalate (PET) substrates, and only indicative photos were provided on their flexibility with no reference to filler wt.% and/or electrical stability vs. bending radius.…”

“…There are no data available on the brittleness, flexibility, and electrical stability upon bending of free-standing PVOH/Bi 2 Te 3 films. Table 1 summarizes the main properties of the prepared PVOH/Bi 2 Se 3 -MWCNT composites and the corresponding properties of the PVOH/Bi 2 Te 3 composites with 68–90 wt.% of Bi 2 Te 3 filler, reported by Pires et al [ 16 ].…”

“…After weighing the Bi 2 Se 3 -MWCNT hybrid structures were manually scraped off the glass substrates to a container using a standard stainless-steel scalpel blade No 11. For comparison of the results with the data published by Pires et al [ 16 ], the volumetric percentage (vol.%) of the Bi 2 Te 3 filler in PVOH/Bi 2 Te 3 composites was recalculated to the weight percentage (wt.%).…”

“…Recently, Pires et al [ 16 ] demonstrated alternative approach for fabrication of flexible TE composites, which is based on the use of non-conductive polymer as a matrix for thermoelectric filler. In this approach, electrically non-conductive environmentally friendly polyvinyl alcohol (PVOH) mixed with very high concentration (60–90 wt.%) of Bi 2 Te 3 micro-particles to fabricate PVOH/Bi 2 Te 3 n-type TE composites.…”

Screen-Printed Flexible Thermoelectric Device Based on Hybrid Silver Selenide/PVP Composite Films

“…Many thermoelectric materials are being explored for power generation applications, such as GeTe [ 22 ], PbTe [ 23 ], half-Heusler [ 24 ], and skutterudites [ 25 ]. The well-studied n-type material of Bi 2 Te 3 is brittle, and the element Te is rare and toxic, which is not favorable for practical applications in wearable devices [ 17 , 26 , 27 , 28 ]. As an “electron crystal, phonon liquid” n-type material, silver selenide (Ag 2 Se) is environmentally friendly and abundant, with high electrical conductivity and low thermal conductivity at room temperature.…”