High performance magnesium-based plastic semiconductors for flexible thermoelectrics

Low-cost thermoelectric materials with simultaneous high performance and superior plasticity at room temperature are urgently demanded due to the lack of ever-lasting power supply for flexible electronics. However, the inherent brittleness in conventional thermoelectric semiconductors and the inferior thermoelectric performance in plastic organics/inorganics severely limit such applications. Here, we report low-cost inorganic polycrystalline Mg₃Sb_0.5Bi_1.498Te_0.002, which demonstrates a remarkable combination of large strain (~ 43%) and high figure of merit zT (~ 0.72) at room temperature, surpassing both brittle Bi₂(Te,Se)₃ (strain ≤ 5%) and plastic Ag₂(Te,Se,S) and organics (zT ≤ 0.4). By revealing the inherent high plasticity in Mg₃Sb₂ and Mg₃Bi₂, capable of sustaining over 30% compressive strain in polycrystalline form, and the remarkable deformability of single-crystalline Mg₃Bi₂ under bending, cutting, and twisting, we optimize the Bi contents in Mg₃Sb_2-xBi_x (x = 0 to 1) to simultaneously boost its room-temperature thermoelectric performance and plasticity. The exceptional plasticity of Mg₃Sb_2-xBi_x is further revealed to be brought by the presence of a dense dislocation network and the persistent Mg-Sb/Bi bonds during slipping. Leveraging its high plasticity and strength, polycrystalline Mg₃Sb_2-xBi_x can be easily processed into micro-scale dimensions. As a result, we successfully fabricate both in-plane and out-of-plane flexible Mg₃Sb_2-xBi_x thermoelectric modules, demonstrating promising power density. The inherent remarkable plasticity and high thermoelectric performance of Mg₃Sb_2-xBi_x hold the potential for significant advancements in flexible electronics and also inspire further exploration of plastic inorganic semiconductors.