Modulating Interlayer Chemical Bonding Heterogeneity for Electron‐Phonon Decoupling: Unlocking High Thermoelectric Performance in Layered CuCrTi ₂ Se ₆

Layered CuCrTi 2 Se 6 , a structurally tailored transition‐metal dichalcogenide (TMD) derivative, exhibits intrinsically low lattice thermal conductivity but is limited by inferior carrier mobility arising from weak interlayer electronic coupling. Here, we modulate interlayer bonding heterogeneity via a charge‐balanced “one Cr replaces three Cu” strategy to form (Cu 1‐3 x Cr x )CrTi 2 Se 6 , achieving electron–phonon decoupling. Structural characterizations and density functional theory calculations confirm Cr incorporation into interlayer octahedral sites, inducing two synergistic effects: (i) Replacing ionic interlayer Cu─Se bonds with more covalent Cr─Se bonds facilitates rapid interlayer charge transfer and enhances carrier mobility by ∼60% without altering the electronic band structure; (ii) The reduced interlayer atomic density induced by non‐equiatomic Cr/Cu substitution weakens interlayer mechanical coupling, as evidenced by a suppressed shear modulus and transverse sound velocity. When combined with phonon scattering from Cr/Cu point defects, this synergistic effect reduces the room‐temperature lattice thermal conductivity by 22%. The optimized (Cu 0.79 Cr 0.07 )CrTi 2 Se 6 achieves a peak thermoelectric figure of merit ZT ≈ 1.0 at 673 K (a record for TiSe 2 ‐based TMDs), and its single‐leg device reaches ∼6.1% efficiency at Δ T = 500 K. This work establishes interlayer chemical bonding modulation as a paradigm for high‐performance layered thermoelectric materials via electron‐phonon decoupling.