Enhanced thermoelectric properties of I-doped polycrystalline Bi₂O₂Se oxyselenide

Bi₂O₂Se has an intrinsically low thermal conductivity and a high Seebeck coefficient, which suggests as potential thermoelectric materials. However, pristine Bi₂O₂Se polycrystalline exhibits very low electrical conductivity. In this study, we investigated the influence of I doping in enhancing electrical conductivity of Bi₂O₂Se by synthesizing a series of Bi₂O₂Se_1-xI_x polycrystalline samples (x = 0, 0.0025, 0.005, and 0.0075). By I doping, the electrical conductivity was enhanced by significant increase in carrier concentration. The carrier concentration was increased more than 10 times 2.1–4.6 × 10¹⁹ cm^-3 from 2.1 × 10¹⁸ of the undoped sample. As results, the maximum power factor was enhanced to 0.24 mW/mK² for x = 0.0025 from 0.086 mW/mK² of undoped Bi₂O₂Se at 300 K. The maximum power factor of 0.42 mW/mK² was achieved for x = 0.05 sample at 790 K. These increases are discussed in terms of the increase in effective mass and weighted mobility. Additionally, the moderate reduction of thermal conductivity was observed in the I doped samples due to the point defect scattering. As a result, a maximum zT value was enhanced to 0.32, 0.35, and 0.33 for x = 0.0025, 0.005, and 0.0075) at 790 K, representing an improvement of more than 50% compared to 0.21 of the undoped Bi₂O₂Se (x = 0).