Ultralow Thermal Conductivity and Improved Thermoelectric Properties of Al‐Doped ZnO by In Situ O₂ Plasma Treatment

Abstract

The thriving of Internet‐of‐Things and integrated wireless sensor networks has brought an unprecedented demand for sustainable micro‐Watt‐scale power supplies. Development of high‐performing micro‐thermoelectric generator (μ‐TEG) that can convert waste thermal energy into electricity and provide sustainable micro‐Watt‐scale power is therefore extremely timely and important. Herein, a significant advance in the development of earth‐abundant, nontoxic thermoelectric materials of aluminum‐doped zinc oxide (AZO) is presented. Through nanostructure engineering using a novel in situ O2 plasma treatment, AZO films are demonstrated with ultralow thermal conductivity of 0.16 W m−1 K−1 which is the lowest reported in the literature. This nanostructured film yields a power factor of 294 μW m−1 K−2 at 563 K and has resulted in a state‐of‐the‐art ZT of 0.11 at room temperature and 0.72 at 563 K for AZO thin films. Furthermore, the fabrication and testing of a prototype lateral μ‐TEG are reported based on the AZO thin film which achieves a power output of 1.08 nW with an applied temperature difference of 16.9 °C.

Integrated Bolometric Photodetectors Based on Transparent Conductive Oxides from Near‐ to Mid‐Infrared Wavelengths

“…[ 29,31,32 ] Furthermore, it is able to efficiently convert heat into electricity, thus serving as a thermoelectric device. [ 10,11 ]…”

“…For example, the measurements on AZO thin film at room temperature showed a mobility of 16.4 cm 2 (V·s) −1 at a carrier concentration of 2.13·10 26 m −3 , which is very close to that of ITO thin film. [ 10 ] Cadmium oxide (CdO) is an exception, as it shows more than an order of magnitude higher carrier mobility compared to most of the TCO materials, and consequently an order of magnitude lower damping factor compared to other TCO materials ( Figure ). [ 23,24 ]…”

“…The solution may be thermal detectors that convert heat into electricity. [ 10–14 ] They require an absorbing material that absorbs light to generate hot carriers and then converts them to electricity.…”

Large Electrical Conductivity and Thermoelectric Power Factor of Pulsed Laser-Deposited Zn1–xGaxO Thin Films

“…Binary alloys (SiGe), tellurides, skutterudites, half-Heusler alloys, and oxide semiconductor thin films have shown dramatically improved thermoelectric performance. − Nevertheless, oxide thin films including SrTiO 3 , ZnO, In 2 O 3 , CaMnO 3 , and their heterostructures, owing to their chemical stability, high-temperature durability, and earth abundance, have been the primary choice for TFTE. − ZnO, an intrinsically n -type semiconductor, is a potential material candidate for TFTE due to the ability to tune its electrical conductivity via doping, ease of low temperature (∼400 °C) fabrication with exceptional structural quality, high optical transparency to visible light, etc. − Group III element (Al, Ga, and In) doping in ZnO is a proven strategy for the enhancement of its electrical conductivity. − Tran Nguyen et al have shown a thermopower of 88.6 μW/mK 2 for In and Ga dual-doped ZnO thin films . Pulsed laser-deposited SnO 2 /ZnO multilayer films have exhibited a thermopower of 100 μW/mK 2 with large optical transparency .…”