Thermoelectric devices convert thermal energy into electrical energy and vice versa through the Seebeck and Peltier effects, respectively. Their architectures play a critical role in determining efficiency, power output, and application suitability. Key design configurations include unicouple, multicouple, and segmented thermoelectric modules, each with distinct advantages and trade-offs.

A unicouple consists of a single pair of n-type and p-type thermoelectric legs connected electrically in series and thermally in parallel. This simple design is often used in laboratory settings for fundamental studies due to its ease of fabrication and analysis. However, its low voltage output limits practical applications, necessitating the use of multiple unicouples connected in series or parallel to achieve usable power levels.

Multicouple modules integrate numerous n-type and p-type legs into a single array, significantly increasing power output and voltage. The interconnects between legs must minimize electrical resistance while maintaining thermal isolation to prevent parasitic heat leakage. The geometric arrangement of legs—such as square, rectangular, or hexagonal packing—affects both thermal impedance and mechanical stability. Optimal spacing between legs balances thermal resistance and electrical conductance, with denser packing favoring higher power density but increasing thermal losses.

Segmented designs enhance efficiency by using multiple thermoelectric materials along the length of each leg, each optimized for a specific temperature range. High-temperature segments, often made of materials with a high Seebeck coefficient, are placed near the heat source, while low-temperature segments with high electrical conductivity are positioned near the heat sink. This approach maximizes the cumulative figure of merit (ZT) across the entire temperature gradient. However, interfacial resistance between segments and thermal expansion mismatches introduce reliability challenges.

Thermal and electrical contact resistance are critical factors in module performance. Poor electrical contacts increase Joule heating, while excessive thermal resistance reduces the effective temperature gradient across the legs. Metallization layers and diffusion barriers are used to minimize contact resistance, but their thickness must be carefully controlled to avoid introducing additional thermal impedance. Soldering and brazing techniques must ensure robust mechanical bonds without degrading thermoelectric material properties.

Module geometry directly impacts heat flow and electrical output. Leg height influences both electrical resistance and thermal conductance: taller legs reduce thermal losses but increase resistive losses, while shorter legs exhibit the opposite trade-off. The cross-sectional area of legs determines current density, with larger areas reducing Joule heating but requiring more material. Optimal aspect ratios depend on the application, with power generation favoring taller legs and cooling applications benefiting from shorter, wider legs.

Heat sink integration is essential for maintaining a steep temperature gradient. In power generation, heat sinks must efficiently dissipate waste heat to the environment, while in cooling applications, they must absorb and redistribute heat effectively. The thermal interface material between the module and heat sink must minimize thermal resistance without introducing mechanical stress. Forced convection, heat pipes, or phase-change materials are often employed to enhance heat sink performance, particularly in high-power applications.

Design optimization differs between power generation and cooling. Power generation modules prioritize high conversion efficiency and power density, requiring materials with high ZT values and designs that maximize the temperature gradient. Cooling modules focus on achieving the largest possible temperature difference between hot and cold sides, necessitating low thermal conductivity and high electrical conductivity to minimize parasitic heat conduction.

Large-scale deployment faces several challenges. Manufacturing consistency is critical, as variations in leg dimensions or contact resistance can lead to performance degradation across modules. Long-term reliability is another concern, with thermal cycling inducing mechanical stress that can cause delamination or crack propagation. Scalability also introduces system-level challenges, such as managing heat distribution across multiple modules and ensuring uniform electrical loading.

Economic factors further complicate deployment. While thermoelectric devices offer maintenance-free operation and long lifetimes, their relatively low efficiency compared to conventional systems limits adoption in cost-sensitive applications. Advances in module design must therefore focus not only on performance but also on cost reduction through material optimization and scalable manufacturing techniques.

In summary, thermoelectric device architectures must balance electrical and thermal transport properties while addressing mechanical and interfacial challenges. Unicouples provide simplicity, multicouples enable scalability, and segmented designs enhance efficiency across wide temperature ranges. Successful implementation requires careful consideration of contact resistance, module geometry, and heat sink integration, with distinct optimization strategies for power generation and cooling. Overcoming the challenges of large-scale deployment will be essential for expanding the use of thermoelectric technologies in energy harvesting and thermal management applications.