Unraveling electronic origins for boosting thermoelectric performance of p-type (Bi,Sb) <sub>2</sub> Te <sub>3</sub>
Rui Cheng, Haoran Ge, Shengpu Huang, Sen Xie, Qiwei Tong, Hao Sang, Fan Yan, Liangyu Zhu, Rui Wang, Yong Liu, Min Hong, Ctirad Uher, Qingjie Zhang, Wei Liu, Xinfeng Tang
Abstract
P-type Bi 2− x Sb x Te 3 compounds are crucial for thermoelectric applications at room temperature, with Bi 0.5 Sb 1.5 Te 3 demonstrating superior performance, attributed to its maximum density-of-states effective mass ( m *). However, the underlying electronic origin remains obscure, impeding further performance optimization. Herein, we synthesized high-quality Bi 2− x Sb x Te 3 (00 l ) films and performed comprehensive angle-resolved photoemission spectroscopy (ARPES) measurements and band structure calculations to shed light on the electronic structures. ARPES results directly evidenced that the band convergence along the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mover accent="true"> <mml:mo>Γ</mml:mo> <mml:mo stretchy="true">¯</mml:mo> </mml:mover> </mml:mrow> </mml:math> - <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mover accent="true"> <mml:mi mathvariant="normal">M</mml:mi> <mml:mo stretchy="true">¯</mml:mo> </mml:mover> </mml:mrow> </mml:math> direction contributes to the maximum m * of Bi 0.5 Sb 1.5 Te 3 . Moreover, strategic manipulation of intrinsic defects optimized the hole density of Bi 0.5 Sb 1.5 Te 3 , allowing the extra valence band along <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mover accent="true"> <mml:mo>Γ</mml:mo> <mml:mo stretchy="true">¯</mml:mo> </mml:mover> </mml:mrow> </mml:math> - <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mover accent="true"> <mml:mi mathvariant="normal">K</mml:mi> <mml:mo stretchy="true">¯</mml:mo> </mml:mover> </mml:mrow> </mml:math> to contribute to the electrical transport. The synergy of the above two aspects documented the electronic origins of the Bi 0.5 Sb 1.5 Te 3 ’s superior performance that resulted in an extraordinary power factor of ~5.5 milliwatts per meter per square kelvin. The study offers valuable guidance for further performance optimization of p-type Bi 2− x Sb x Te 3 .