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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. Bi 2 Te 2.7 Se 0.3 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 Bi 2 Te 2.7 Se 0.3 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 Bi 2 Te 2.7 Se 0.3 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) Bi 2 Te 2.7 Se 0.3 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 Bi 2 Te 2.7 Se 0.3 and the applied pressure was 200 MPa. The electrical conductivity was 200 ± 7 S cm À1 , the Seebeck coefficient was À201 ± 6 lV K À1 , the power factor was 808 ± 69.7 lW m À1 K À2 , the thermal conductivity was 0.6 W m À1 K À1 , 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 Bi 2 Te 2.7 Se 0.3 device was fabricated with a power output of 0.48 lW at a closed circuit voltage of 2.1 mV and DT of 12 K.

In recent years, there has been a widespread growth in the application of composite materials particularly in the Aerospace and Automotive sectors. This is because composite structures are generally comparatively light in weight and provide corrosion and wear resistance as compared to metals or ceramics. Due to the strict fail-safe philosophy of the aerospace industry, the certification approach for current practice in joining composite materials is to thicken the joining areas and to use numerous fasteners which in turn increases the weight and stress concentrations in the structure. The use of adhesive bonding can improve the stress distribution between the composite materials / dissimilar materials and can contribute to a lighter structure. However, there much investigation is yet to be done in this discipline to predict the bond strength and performance using non-destructive evaluation methods. This paper will focus on an approach to study the mechanical as well as the dielectric properties of an adhesive bond. The dielectric testing is done by using Broadband Dielectric Spectroscopy (BbDS), wherein the dielectric characteristics of the material are analyzed in a wide frequency spectrum. The data obtained by this technique are used to demonstrate the charge transport, the combined dipolar fluctuation, and the effects of polarization occurring between the boundaries of materials. The continuous modifications of the dielectric spectra are due to the changes in the electrical and structural interactions between the particles, shapes, and orientations of the constituent phases of the morphological structure of the material system. Information about the morphologies, impurities/contamination or interaction of the dissimilar surfaces of the pristine bond can be obtained from the initial BbDS properties. The dielectric properties for adhesively bonded composites with different surface adhesion properties have shown promising evidence of predicting the final mechanical performance of the bonded material system. The success and limitations of this approach will be discussed, and needs for continued investigation identified

This work presents an energy efficient technique for fabricating flexible thermoelectric generators while using printable ink. We have fabricated thermoelectric composite thick films using two different mesh sizes of n-type bismuth particles, various binder to thermoelectric material weight ratios, and two different pressures, 200 MPa and 300 MPa, in order to optimize the thermoelectric properties of the composite films. The use of chitosan dissolved in dimethylsulfoxide with less than 0.2 wt. % of chitosan, the first time chitosan has been used in this process, was sufficient for fabricating TE inks and composite films. Low temperature curing processes, along with uniaxial pressure, were used to evaporate the solvent from the drop-casted inks. This combination reduced the temperature needed compared to traditional curing processes while simultaneously increasing the packing density of the film by removing the pores and voids in the chitosan-bismuth composite film. Microstructural analysis of the composite films reveals low amounts of voids and pores when pressed at sufficiently high pressures. The highest performing composite film was obtained with the weight ratio of 1:2000 binder to bismuth, 100-mesh particle size, and 300 MPa of pressure. The best performing bismuth chitosan composite film that was pressed at 300 MPa had a power factor of 4009 ± 391 μW/m K2 with high electrical conductivity of 7337 ± 522 S/cm. The measured thermal conductivity of this same sample was 4.4 ± 0.8 W/m K and the corresponding figure of merit was 0.27 at room temperature.