Plastic/Ductile Bulk 2D van der Waals Single-Crystalline SnSe 2 for Flexible Thermoelectrics.

The recently discovered ductile/plastic inorganic semiconductors pave a new avenue toward flexible thermoelectrics. However, the power factors of current ductile/plastic inorganic semiconductors are usually low (below 5 µW cm -1  K -2 ) as compared with classic brittle inorganic thermoelectric materials, which greatly limit the electrical output power for flexible thermoelectrics. Here, large plasticity and high power factor in bulk two-dimensional van der Waals (2D vdW) single-crystalline SnSe 2 are reported. SnSe 2 crystals exhibit large plastic strains at room temperature and they can be morphed into various shapes without cracking, which is well captured by the inherent large deformability factor. As a semiconductor, the electrical transport properties of SnSe 2 can be readily tuned in a wide range by doping a tiny amount of halogen elements. A high power factor of 10.8 µW cm -1  K -2 at 375 K along the in-plane direction is achieved in plastic single-crystalline Br-doped SnSe 2 , which is the highest value among the reported flexible inorganic and organic thermoelectric materials. Combining the good plasticity, excellent power factors, as well as low-cost and nontoxic elements, bulk 2D vdW single-crystalline SnSe 2 shows great promise to achieve high power density for flexible thermoelectrics.