Thermoelectric Performance Enhancement of n-type Chitosan-Bi₂Te₂.7Se₀.₃ Composite Films Using Heterogeneous Grains and Mechanical Pressure

Abstract

A cost-effective and sustainable approach was used to enhance the thermoelectric performance of printable thermoelectric composite films. Using this approach, we are trying to get rid of the highly energy-intensive (high temperature and long duration) and time-consuming process of manufacturing thermoelectric generators. This study presents a unique approach of using an environmental-friendly and naturally occurring binder, a heterogeneous particle size distribution and applied mechanical pressure to fabricate n-type thermoelectric composite films. Recently spotlighted biomaterial, chitosan, was employed as a binder and it provided enough binding strength to the composite thermoelectric films. Bi₂Te₂.7Se₀.₃ is an attractive n-type thermoelectric material because of its high thermoelectric performance. In this work, we are using two different (100-mesh and 325-mesh) n-type Bi₂Te₂.7Se₀.₃ thermoelectric conductive particles for thermoelectric composite films to understand the role of wide-range particle distribution on thermoelectric composite films. In addition, two different weight ratios (1:2000 and 1:5000) of binders to Bi₂Te₂.7Se₀.₃ particle and two different applied pressures (150 MPa and 200 MPa) were used for this study. The application of pressure and the use of a heterogenous particle distribution improves the packing density which leads to well-aggregated and coalesced polycrystal bulk-like structure in chitosan 100-mesh (heterogeneous particle distribution) Bi₂Te₂.7Se₀.₃ thermoelectric composite films and hence improves the overall electrical conductivity and power factor. The best performing composite film was made with an ink of a 1:2000 weight ratio of binder to100-mesh Bi₂Te₂.7Se₀.₃ and the applied pressure was 200 MPa. The electrical conductivity was 200 ± 7 S cm⁻¹, the Seebeck coefficient was −201 ± 6 µV K⁻¹, the power factor was 808 ± 69.7 μW m⁻¹ K⁻², the thermal conductivity was 0.6 W m⁻¹ K⁻¹, and the figure of merit was 0.4 at room temperature. Using energy efficient, sustainable, and cost effective method we achieved ZT of 0.40 for n-type thermoelectric composite films which is comparable to other printed n-type TE composite films. A 2-leg n-type Bi₂Te₂.7Se₀.₃ device was fabricated with a power output of 0.48 μW at a closed circuit voltage of 2.1 mV and ∆T of 12 K.