Indium-filled skutterudite/PEDOT:PSS-derived sulfur-amorphous carbon hybrids: an organic–inorganic interface design strategy for phonon-charge decoupling and enhanced thermoelectric performance

Abstract

Reducing lattice thermal conductivity (κ_L) in filled skutterudites while preserving power factor remains a central challenge for mid-temperature waste-heat recovery. Here, we introduce an interphase-directed strategy in which HNO₃-treated PEDOT:PSS, co-processed with In-filled Co₄Sb₁₂, undergoes an in situ polymer-to-sulfur-doped amorphous carbon (S-AC) conversion. The resulting ultrathin S-AC interlayers construct a hierarchical micro/mesoporous network that reshapes phonon transport through diffuse boundary scattering, acoustic-impedance mismatch, and multiphase strain-field perturbations. These interface-dominated processes produce a pronounced suppression of κ_L beyond what is typically associated with porosity alone in skutterudites. A Kane-model Lorenz analysis further reveals a composition-dependent balance in electronic transport: moderate S-AC loadings improve mobility via intergranular bridging, whereas high interphase density introduces extensive carrier scattering that lowers κ_e and contributes to the minimum total κ. The optimized hybrid achieves κ ≈ 0.74 W m⁻¹ K⁻¹ and zT = 1.47 at 700 K. A 10-pair module, pairing this n-type leg with Mg₂Zn_0.97Ag_0.03Sb₂, delivers 203.32 µW cm⁻² and 5.53% efficiency at ΔT = 160 K, demonstrating device-level viability. This interphase-engineering concept provides a scalable and composition-agnostic route to strong κ_L suppression while maintaining favorable electronic transport, offering a broadly applicable design framework for next-generation mid-temperature thermoelectrics.