Enhanced thermoelectric properties in vacuum-annealed Bi_0.5Sb_1.5Te₃ thin films fabricated using pulsed laser deposition

Localized cooling in microelectronics and nanoelectronics as well as energy autonomy in applications such as wireless sensor networks and wearable electronics could be well served by thin-film thermoelectric devices fabricated on rigid and/or flexible substrates. Bi_0.5Sb_1.5Te₃ is considered to be a state-of-the-art p-type thermoelectric material at the desired temperature range, i.e., near room temperature (RT). Fabrication of Bi_0.5Sb_1.5Te₃ thin films with bulklike thermoelectric properties (∼3900 μW/mK² at 380 K) remains, however, a great challenge. In this study, we have successfully fabricated Bi_0.5Sb_1.5Te₃ thin films on fused silica and Kapton substrates using a two-step process. The films were deposited at RT using pulsed laser deposition and then subjected to a postdeposition ex situ vacuum annealing process. The as-grown films were nearly amorphous. However, the annealing process enhanced both their crystallinity and texture, resulting in thin films with bulklike thermoelectric power factor values. Bi_0.5Sb_1.5Te₃ thin films grown on fused silica and annealed at 350 °C for 16 h exhibit a power factor of 3750 μW/mK² at 380 K. In addition, Bi_0.5Sb_1.5Te₃ films grown on Kapton and annealed at 250 °C for 5 h and also grown on Kapton substrates at 250 °C exhibit a power factor of 2600 μW/mK² at 390 K. Both of these power factor values are among the highest reported in the literature to date for Bi_0.5Sb_1.5Te₃ thin films grown on fused silica and Kapton substrates, respectively.