Abstract: Bi₂Te₃-based flexible thin-film thermoelectric generators (f-TEGs) are promising self-powered solutions for wearable electronic devices and micro-sensors in the Internet-of-Things (loT). Despite their potential, performance is often hindered by a low electrical power factor (PF), underscoring the urgent need for improvement. In this work, n-type Bi₂Te_2.7Se_0.3 polycrystalline films with nearly uniaxial (00l) orientation were successfully grown on flexible polyimide substrates through a combined approach of liquid Te-assisted nucleation and secondary annealing. The secondary low-temperature annealing process significantly reduced intrinsic antisite defects, leading to simultanious optimization of carrier concentration and mobility. This approach resulted in n-type Bi₂Te_2.7Se_0.3 thin films possessing an excellent PF of 35.1 µW cm^-1 K^-2 at 320 K and peak figure of merit (zT_max) of 1.14 at 360 K. To demonstrate practical applications, a 10-pair planar radial-type f-TEG was constructed using n-type Bi₂Te_2.7Se_0.3 and p-type Bi_0.4Sb_1.6Te₃ films. The device exhibited outstanding, achieving a maximum output power (P_out) of 16.52 µW and a peak power density (PD_max) of 848.01 W m^-2. This fabrication approach offers an effective strategy for enhancing thermoelectric performance in flexible devices, providing a viable route for environmental energy harvesting and expanding the potential applications in wearable electronics and IoT systems.

Key words: Thermoelectric films, Bi₂Te_2.7Se_0.3, Uniaxial orientation, Flexible devices, Power density