Symmetry-Forbidden p–d Orbital Mixing: A Pathway to High-Power-Factor Thermoelectrics

The intrinsic entanglement between electrical conductivity (σ) and the Seebeck coefficient (S) poses a significant challenge to enhancing the power factor (PF) of thermoelectric (TE) materials. While achieving high valley degeneracy (Nvk) is an effective strategy for balancing σ and S, thus improving PF, identifying a compound with a high Nvk (Nvk ≥ 6) remains a complex endeavor. In this study, we propose an effective approach to quickly identify p-type semiconductors with high Nvk through analyzing the mixing between anion p and cation d orbitals. By prohibiting the p–d orbital mixing at the Γ point, we can effectively shift the valence-band maximum away from the Brillouin zone center (Γ point, Nvk = 1), thereby increasing Nvk. Through the examination of common irreducible representations of anion p and cation d orbitals at the Γ point, we screen and discover six compounds with Nvk ≥ 6 from 921 binary and ternary semiconductors. First-principles calculations incorporating electron–phonon coupling (EPC) demonstrate that PtP2, PtAs2, and PtS2 exhibit exceptionally high PF values of 130, 127, and 82 μW cm–1 K–2 at 300 K, respectively, which are 3–5 times higher than those of traditional high-performance TE materials. Furthermore, the weighted mobilities (μw) of PtP2, PtAs2, and PtS2 at room temperature are also high, with values of 952, 906, and 304 cm2 V–1 s–1, respectively. Our work not only enhances the understanding of high Nvk formation through group theory but also presents an effective and efficient methodology for the discovery of materials with high PF. Additionally, this approach is versatile and can be extended to more complicated systems.