Enhanced thermoelectric properties of Sb<inf>2</inf>Te<inf>3</inf> and Bi<inf>2</inf>Te<inf>3</inf> films for flexible thermal sensors

Abstract

Improved thermoelectric properties of p-Sb2Te3 and n-Bi2Te3 films deposited by thermal co-evaporation at 503 K and 543 K, respectively, are reported, by using two types of substrate (borosilicate glass and 25 μm - Kapton® polyimide). Seebeck coefficients of 194 μV K−1 and - 233 μV K−1 and electrical conductivities of 3.2 × 104 (Ω m)−1 and 5.0 × 104 (Ω m)−1, lead to optimized power factors of 1.2 × 10−3 W K−2 m−1 and 2.7 × 10−3 W K−2 m−1, measured at 298 K, for flexible Sb2Te3 and Bi2Te3 films, respectively. The power factor value increases until a maximum of 2.3 × 10−3 W m−1 K−2 for the p-type film, and to 5.9 × 10−3 W m−1 K−2 for the n-type film, at 373 K, respectively. An improvement of more than two times on the power factor value is observed when compared with the actual state-of-art for flexible Sb2Te3 and Bi2Te3 films, at room temperature, with thickness below 1 μm. A flexible thermopile sensor based on p - n films is presented, into possible thermal sensing. The thermoelectric device shows a responsivity of 0.05 V W−1 and a specific detectivity of 1.6 × 107 cm √Hz W−1.