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

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 (Δ T), 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.