P-type Bi_{2-_x}Sb_xTe₃ compounds are crucial for thermoelectric applications at room temperature, with Bi_0.5Sb_1.5Te₃ 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_xTe₃ (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 [Formula: see text]-[Formula: see text] direction contributes to the maximum m* of Bi_0.5Sb_1.5Te₃. Moreover, strategic manipulation of intrinsic defects optimized the hole density of Bi_0.5Sb_1.5Te₃, allowing the extra valence band along [Formula: see text]-[Formula: see text] to contribute to the electrical transport. The synergy of the above two aspects documented the electronic origins of the Bi_0.5Sb_1.5Te₃'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_xTe₃.

Shengpu Huang

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