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

• Published in: Nanoscale Vol. 10; no. 6; pp. 3046 - 3052
• Main Authors: Kim, Kisun, Park, Junyong, Hong, Seokkyoon, Park, Sun Hwa, Jeon, Seong Gi, Ahn, Changui, Song, Jae Yong, Jeon, Seokwoo
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 01.01.2018
• Subjects: Crystal structure; Figure of merit; Seebeck effect; Thermal conductivity; Thermal stability; Thermoelectric materials; Thermoelectricity; Toxicity; Zinc oxide
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/c7nr08167g

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