Thermoelectric Characteristics of Bismuth Selenide Thin Films Prepared by Vacuum Thermal Evaporation of Bismuth Selenide Nanoparticles Synthesized by Hot Injection

High Resolution Image Download MS PowerPoint Slide Bismuth selenide (Bi 2 Se 3 ) thin films were deposited by vacuum thermal evaporation (VTE) of Bi 2 Se 3 nanosheets (200 nm across, 20 nm in thickness), synthesized by the reaction of bismuth nitrate with selenourea in triethanolamine (TEA) applied via the hot injection method at 210 °C. Using 300 mg of nanosheets as the source material, thin films (70 nm thick) were produced on glass substrates held at 200 °C on a rotating substrate holder, with a source-to-substrate distance of 40 cm. Postdeposition heating of the thin films at 300 °C under nitrogen at 10 Torr, without or with the presence of elemental selenium powder, resulted in changes in the texture coefficient of the (006) planes of Bi 2 Se 3 in its trigonal crystal structure (mineral: paraguanajuatite) from 5.5 (as-prepared film) to 6.8 (heated in nitrogen) and 8.2 (heated in nitrogen + selenium). Correspondingly, the electrical conductivity (σ) of the films increased from 2.5 to 2.9 × 10 3 and 1.5 × 10 4 (Ω·m) −1; the Seebeck coefficient ( S, n -type) increased from 32 to 98 and 117 μV·K –1; and the thermoelectric power factor (σ· S 2 ) increased from 2.6 to 28 and 205 μW·m –1 ·K –2, respectively. A proof-of-concept five-element series-connected thin-film thermoelectric generator using the 45 or 70 nm Bi 2 Se 3 thin film produced a voltage of 0.7 mV·K –1 and showed a response of 0.07 mV·s –1 or 0.1 K·s –1 when exposed to solar radiation (1000 W·m –2 ).