Unraveling electronic origins for boosting thermoelectric performance of p-type (Bi,Sb) 2 Te 3 .

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 [Formula: see text]-[Formula: see text] 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 [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 0.5 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 .