Orientation Engineering in Flexible Ag₂Se-Based Thermoelectric Films

Flexible thermoelectrics convert body heat into electricity, offering a promising route towards self-powered wearable electronics while overcoming the limitations of conventional batteries. Among emerging flexible thermoelectric materials, silver selenide (Ag₂Se) has attracted widespread attention because it combines outstanding near-room-temperature thermoelectric performance with low cost, excellent mechanical flexibility, and superior biocompatibility. Over the past five years, orientation engineering has emerged as an effective strategy for simultaneously enhancing carrier transport and suppressing carrier scattering, leading to remarkable improvements in both material properties and device performance. In this Perspective, we systematically review recent progress in highly oriented Ag₂Se films, including deposited, nanowire-based, selenized, and free-standing architectures. We further propose film thickness together with near-room-temperature power factor as practical metrics for benchmarking their application potential. By correlating fabrication strategies, microstructural evolution, crystallographic orientation, and thermoelectric performance, we establish a unified framework for understanding orientation-dependent charge transport in Ag₂Se films. Finally, we discuss the remaining scientific and technological challenges and highlight future opportunities for developing scalable, mechanically robust, and high-performance Ag₂Se films for next-generation wearable thermoelectric energy harvesters and self-powered physiological monitoring systems.