Hyeongdo Choi

High-Performance Flexible Thermoelectric Power Generator Using Laser Multiscanning Lift-Off Process

Flexible thermoelectric generators (f-TEGs) are emerging as a semipermanent power source for self-powered sensors, which is an important area of research for next-generation smart network monitoring systems in the Internet-of-things era. We report in this paper a f-TEG produced by a screen-printing technique (SPT) and a laser multiscanning (LMS) lift-off process. A screen-printed TEG was fabricated on a SiO2/a-Si/quartz substrate via the SPT process, and the LMS process completely separated the rigid quartz substrate from the original TEG by selective reaction of the XeCl excimer laser with the exfoliation layer (a-Si). Using these techniques, we fabricate a prototype f-TEG composed of an array of 72 TE couples that exhibits high flexibility at various bending radii, together with excellent output performance (4.78 mW/cm2 and 20.8 mW/g at ΔT = 25 °C). There is no significant change in the device performance even under repeated bending of 8000 cycles.

Enhanced thermoelectric properties of screen-printed Bi0.5Sb1.5Te3 and Bi2Te2.7Se0.3 thick films using a post annealing process with mechanical pressure

A cost-effective and large-scale thermoelectric (TE) energy harvester is becoming increasingly important for energy recovery systems such as self-powered electronics and renewable power generation. Here, we report on a TE device composed of p-type Bi0.5Sb1.5Te3 and n-type Bi2Te2.7Se0.3 TE materials prepared using a screen-printing process, which has the advantages of low cost, scalability to large areas and the ability to form a flexible TE generator. The TE properties of the screen-printed TE thick films were optimized via subsequent annealing with mechanical pressure. It was found that thermal annealing with the application of mechanical pressure plays a key role in controlling the carrier concentration and improving the density of the TE thick films. Under optimized annealing conditions, the Bi0.5Sb1.5Te3 (p-type) thick film had a ZT of 0.89 and a density of 5.67 g cm−3 while the Bi2Te2.7Se0.3 (n-type) thick film had a ZT of 0.57 and a density of 5.68 g cm−3 at room temperature. TE generators composed of 72 and 200 couples were fabricated with these thick films. The output power of the device composed of 72 couples was 0.1 W for a temperature difference (ΔT) of 28 K. Another device with 200 couples generated 0.31 W of electric power for the same ΔT.