Revealing the significant role of band structure asymmetry on thermoelectric bipolar conduction
Jiamin Qiu, Shizhen Zhi, Peng Zhao, Jian Wang, Xiaojing Ma, Sheng Ye, Chenhao Lin, Xuanhe Zhang, Zuoxu Wu, Sichen Duan, Honghao Yao, Feng Cao, Qian Zhang, Jun Mao
Abstract
Bipolar conduction, which is widely observed in various materials, plays a deleterious role in the thermoelectric properties. Traditionally, the single-band model is often applied to understand the transport properties of thermoelectric materials. However, it ignores the contribution from minority carriers and is incapable of quantifying the bipolar conduction. Herein, a general and feasible approach for calculating all the temperature-dependent transport properties based on the two-band model has been developed. In addition to the reduced electron Fermi energy and reduced band-gap energy, band structure asymmetry has been identified to play a significant role in bipolar conduction. Importantly, the effect of band structure asymmetry on bipolar conduction has been highlighted by using the $\mathrm{M}{\mathrm{g}}_{3}\mathrm{B}{\mathrm{i}}_{2\ensuremath{-}x}\mathrm{S}{\mathrm{b}}_{x}$ alloy as a typical example. Our results demonstrate that the band structure asymmetry is of great significance to the materials' thermoelectric performance.