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 Mg 3 Sb 0.5 Bi 1.498 Te 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 Bi 2 (Te,Se) 3 (strain ≤ 5%) and plastic Ag 2 (Te,Se,S) and organics (zT ≤ 0.4). By revealing the inherent high plasticity in Mg 3 Sb 2 and Mg 3 Bi 2 , capable of sustaining over 30% compressive strain in polycrystalline form, and the remarkable deformability of single-crystalline Mg 3 Bi 2 under bending, cutting, and twisting, we optimize the Bi contents in Mg 3 Sb 2-x Bi x (x = 0 to 1) to simultaneously boost its room-temperature thermoelectric performance and plasticity. The exceptional plasticity of Mg 3 Sb 2-x Bi 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 Mg 3 Sb 2-x Bi x can be easily processed into micro-scale dimensions. As a result, we successfully fabricate both in-plane and out-of-plane flexible Mg 3 Sb 2-x Bi x thermoelectric modules, demonstrating promising power density. The inherent remarkable plasticity and high thermoelectric performance of Mg 3 Sb 2-x Bi x hold the potential for significant advancements in flexible electronics and also inspire further exploration of plastic inorganic semiconductors.