Geometry Optimization Strategies for Dual Enhancement of Power and Efficiency in All‐Mg ₃ Sb _1.5 Bi _0.5 Thermoelectric Devices

Abstract Mg ₃ Sb ₂ –Mg ₃ Bi ₂ solid‐solutions exhibit excellent thermoelectric (TE) performance in power generation and cooling. However, reports on fully Mg ₃ (Sb,Bi) ₂ ‐based TE devices remain limited, due to performance imbalance between p‐type and n‐type counterparts. In such cases, geometric design optimization is essential for achieving either a maximum power density (ω _max ) or maximum conversion efficiency (η _max ). Simultaneous improvement is often difficult due to compromises in the device fill factor. In this study, simultaneous enhancement of ω _max and η _max is demonstrated in a fully Mg ₃ Sb _1.5 Bi _0.5 device through optimized design. Two‐pair devices are fabricated using p‐ and n‐type doped Mg ₃ Sb _1.5 Bi _0.5 materials with Cu/Fe multilayer electrical contacts.The optimum cross‐sectional area ratio ( A _n / A _p ) is calculated using the constant properties model. Accordingly, a revised device architecture is designed to accommodate the optimum A _n / A _p = 1:2 without compromising the fill factor. Finite element simulations predict a combined improvement in ω _max and η _max compared to a non‐optimized 1:1 design. Simulations are experimentally validated with A _n / A _p = 1:1 and 1:2 devices, showing a“double‐high” improvement more than 10 % in ω _max and η _max at Δ T ≈465 K. The proposed optimization strategy provides a general approach to enhance both power output and conversion efficiency in various p‐n thermoelectric material combinations.