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

Mg₃Sb₂-Mg₃Bi₂ solid-solutions exhibit excellent thermoelectric (TE) performance in power generation and cooling. However, reports on fully Mg₃(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 Mg₃Sb_1.5Bi_0.5 device through optimized design. Two-pair devices are fabricated using p- and n-type doped Mg₃Sb_1.5Bi_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 ΔT ≈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.