Oxidation-induced thermopower inversion in nanocrystalline SnSe thin film

Sunao Shimizu,Shimpei Ono,Yujiro Tazawa,Takeshi Kobayashi,Kazumoto Miwa

doi:10.1038/s41598-021-81195-7

Sunao Shimizu, Shimpei Ono + Show 3 more

Open Access

https://doi.org/10.1038/s41598-021-81195-7

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Abstract

Given the growing demand for environmentally friendly energy sources, thermoelectric energy conversion has attracted increased interest as a promising CO2-free technology. SnSe single crystals have attracted attention as a next generation thermoelectric material due to outstanding thermoelectric properties arising from ultralow thermal conductivity. For practical applications, on the other hand, polycrystalline SnSe should be also focused because the production cost and the flexibility for applications are important factors, which requires the systematic investigation of the stability of thermoelectric performance under a pseudo operating environment. Here, we report that the physical properties of SnSe crystals with nano to submicron scale are drastically modified by atmospheric annealing. We measured the Seebeck effect while changing the annealing time and found that the large positive thermopower, + 757 μV K−1, was completely suppressed by annealing for only a few minutes and was eventually inverted to be the large negative value, − 427 μV K−1. This result would further accelerate intensive studies on SnSe nanostructures, especially focusing on the realistic device structures and sealing technologies for energy harvesting applications.

Highlights

Given the growing demand for environmentally friendly energy sources, thermoelectric energy conversion has attracted increased interest as a promising CO2-free technology
This is because the thermally-evaporated SnSe thin films compose of porous nanosheets networks with nano to submicron scales[25], as shown in a scanning electron microscopy (SEM) image in Fig. 1a, and the large surface area would enable us to sensitively monitor the development of oxidation
Samples B and C were annealed in globe boxes filled with Ar and N2 gas, respectively, where the oxygen level was lower than 0.1 ppm and the dew point temperature was lower than − 80 °C

Summary

Introduction

Given the growing demand for environmentally friendly energy sources, thermoelectric energy conversion has attracted increased interest as a promising CO2-free technology. In order to evaluate the development of the surface oxidation, the systematic measurements of optical and thermoelectric properties were performed with changing the annealing temperature and time; principal properties of semiconductors such as the band gap, the chemical potential, and the polarity of the charge carriers are sensitively monitored by those measurements.

Results

Conclusion