Realizing High Electrical Conductivity in Chlorine-Doped Bi₂S₃ Thermoelectric Thin Films via Air Plasma Treatment

The demand for a sustainable power supply and management has become increasingly essential with the rise of Internet of Things (IoT) devices and the associated wireless sensor networks. Inorganic thermoelectric thin films, such as those based on Bi 2 S 3, are becoming a viable solution to this issue as they are low-toxic, inexpensive, and possess a high Seebeck coefficient and low thermal conductivity. However, they usually suffer from an inherent low electrical conductivity. In this study, we tackled this problem by incorporating Cl into Bi 2 S 3 lattices using a solution process, resulting in a substantial increase in both the conductivity and carrier concentration. Additionally, DFT calculations show that the doping of Cl leads to the formation of a degenerate semiconductor, which increases conductivity. Moreover, a high power factor of 121.88 μW m –1 K –2 was achieved after doping before plasma treatment. Specifically, the Bi 2 S 3 sample doped with 0.5 mmol of BiCl 3 with plasma treatment achieved a remarkable conductivity of 100.72 S cm –1, among the highest reported for a Bi 2 S 3 -based system, which is attributed to the sharp increase of carrier concentration. This research demonstrates a promising approach for overcoming the inherently low conductivity of Bi 2 S 3 -based thermoelectric thin films to enable them as a viable solution for low-cost power supply in IoT applications.