Anomalous thermoelectricity of pure ZnO from 3D continuous ultrathin nanoshell structures

ZnO is a potential thermoelectric material because of its non-toxicity, high thermal stability, and relatively high Seebeck coefficient (S) of metal oxides. However, the extremely low figure of merit (zT), which comes from a high thermal conductivity (kappa) over 40 W m(-1) K-1, limits the thermoelectric application of ZnO. In particular, below 500 K, ZnO exhibits a nearly negligible zT (<10(-3)), unless a dopant is incorporated into the crystal structure. Here, we propose a new strategy for achieving a reduced. and a correspondingly increased zT of pure ZnO over a wide temperature range from 333 K to 723 K by forming an similar to 72 nm thick, 3D continuous ultrathin nanoshell structure. The suppressed. of the 3D ZnO film is similar to 3.6 Wm(-1) K-1 at 333 K, which is similar to 38 times lower than that of the blanket ZnO film (3.2 mu m thick), which was set as a reference. The experimental zT of the 3D ZnO film is similar to 0.017 at 333 K, which is the highest value among pure ZnO reported to date and is estimated to increase by similar to 0.072 at 693 K according to the Debye-Callaway approach. Large-area (similar to 1 in(2)) fabrication of the 3D ZnO film with high structural uniformity allows the realization of an integrated thermoelectric device, which generates similar to 60 mV at a temperature difference of 40 K along the in-plane direction.