Post ionized defect engineering of the screen-printed Bi₂Te_2.7Se_0.3 thick film for high performance flexible thermoelectric generator

Flexible thermoelectric generators (f-TEGs), fabricated by the screen printing technique, have been introduced as a semi-permanent power source for wearable and flexible electronic systems. However, the output power density of the f-TEG module is still limited due to the low ZT of the screen-printed thermoelectric (TE) film. We herein report a post ionized defect engineering process that effectively controls ionized defects and improves the ZT value of a screen-printed ternary TE film. It was found that post annealing in a forming gas ambient (4% H₂+96% Ar) can reduce the nano- and micro-bismuth oxide particles in screen-printed n-type BiTeSe films, resulting in a bismuth rich condition and creation of bismuth antisite defects. We achieved a maximum ZT of 0.90 with the screen-printed n-type BiTeSe thick film at room temperature, which is almost comparable to that of the bulk Bi₂Te_2.7Se_0.3 and is a 2-fold increase over the same screen-printed film without the hydrogen ambient annealing. To demonstrate the applicability of this approach, a f-TEG device with 72 TE pairs (p-type Bi_0.5Sb_1.5Te₃, forming gas annealed n-type Bi₂Te_2.7Se_0.3) was fabricated by the screen printing technique. The device generated a high output power of 6.32 mW cm⁻² at ΔT=25.6 °C. These results demonstrate the feasibility of high performance and large-scale f-TEG fabrication using ionized-defect engineering.