Preparation of Bismuth Telluride Films with High Thermoelectric Power Factor.

Highly conductive n-type Bi ₂ Te ₃ films on a flexible substrate were prepared via electrodeposition followed by a transfer process using an adhesive substrate. The growth of the Bi ₂ Te ₃ crystals was precisely controlled by an electrochemical deposition potential (V _dep ), which was critical to the preferred orientation of the crystal growth along the (110) direction and thus to the properties of a flexible thermoelectric generator (FTEG). A Bi ₂ Te ₃ film prepared under V _dep of 0.02 V showed high electrical conductivity (691 S cm ^-1 ) with a maximum power factor of 1473 μW m ^-1 K ^-2 , which is the highest among the Bi ₂ Te ₃ films prepared by the electrodeposition methods. As-prepared FTEG was bendable, showing only a small resistance change after 300 repeated bending cycles. Combined with the n-type Bi ₂ Te ₃ FTEG, a prototype p-n-type flexible thermoelectric (pn-FTEG) was prepared using p-type poly(3,4-ethylene dioxythiophene)s. The pn-FTEG (5-couples) generated an output voltage of 5 mV at ΔT = 12 K with high output power of 56 nW (or 105 nWg ^-1 ). These results indicate that the FTEG can reproducibly work well in a bent state and has high application potential for harvesting thermal energy from curved sources such as human body temperature.