Phase-controlled molecular beam deposition unlocks flexible MgAgSb thermoelectrics with exceptional performance

Flexible thermoelectric materials hold great promise for sustainable energy supply in flexible electronics. However, beyond the long-standing champion Bi₂Te₃-based flexible films, high-performance alternatives remain scarce. Here, we report a promising flexible thermoelectric material based on eco-friendly MgAgSb, a bulk-proven high-performance system whose development in flexible form has long been hindered by its intrinsic brittleness and phase complexity. Using molecular beam deposition, we manage to precisely stabilize MgAgSb within its α-phase range and finely control its stoichiometry. As a result, we successfully fabricate the α-MgAgSb film with exceptional performance, achieving a room temperature zT of 0.8 and a peak power factor of 19.3 μW cm^-1 K^-2, ranking among the promising flexible thermoelectric materials developed. Moreover, the α-MgAgSb film is revealed to exhibit notable flexibility and stability under repeated bending and heating. Leveraging this high-performance stable α-MgAgSb film, the flexible thermoelectric device delivers a maximum normalized power density of 4.9 μW cm^-2 K^-2. This work opens a pathway for flexible MgAgSb applications and offers strong potential for realizing self-powered flexible technologies.