Ternary Bi2Te3In2Te3Ga2Te3 (n-type) thermoelectric film on a flexible PET substrate for use in wearables

Abstract An amorphous structure of Bi In Ga Te powders with a small size of 10–45 μm and a low melting point of 93.2 °C is fabricated using a gas atomization technique. It is patterned using a roll-to-plate printer and then reflowed at 110 °C to become thin Bi 2 Te 3 In 2 Te 3 Ga 2 Te 3 thermoelectric film on a flexible polyethylene terephthalate (PET) substrate. Subsequently, the electrical conductivity of the Bi 2 Te 3 In 2 Te 3 Ga 2 Te 3 thermoelectric film increased from 6.7 × 10 4  S m −1 to 9.6 × 10 4  S m −1 and its thermal conductivity even more significantly increased from 0.9 W m −1 K −1 to 1.8 W m −1 K −1 compared to the Bi 2 Te 3 thermoelectric film. As a result, we obtained a relatively low figure of merit (ZT) value (0.3 at 298.15 K) for the novel thermoelectric film. However, all of these results were irrelevant to the intensive phonon scattering at the hierarchical interfacial boundaries, which included the macro-scale phase boundaries of Bi 2 Te 3 /In 2 Te 3 Ga 2 Te 3 and the nano-scale grain boundaries of each Bi 2 Te 3 , In 2 Te 3 , and Ga 2 Te 3 . As a consequence, the reduction of the ZT value of the proposed novel thermoelectric film can be attributed to the addition of In and Ga with high electrical and thermal conductivity.