A thin film efficient pn-junction thermoelectric device fabricated by self-align shadow mask

Gilbert Kogo,Harold Lee,Sangram K Pradhan,Amy Marconnet,Bo Xiao,Aaditya Candadai,Samuel Danquah,Julien Niyogushima,Messaoud Bahoura,Kelsea Yarbrough

doi:10.1038/s41598-020-57991-y

Gilbert Kogo, Harold Lee + Show 8 more

Open Access

https://doi.org/10.1038/s41598-020-57991-y

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Abstract

Large area highly crystalline MoS2 and WS2 thin films were successfully grown on different substrates using radio-frequency magnetron sputtering technique. Structural, morphological and thermoelectric transport properties of MoS2, and WS2 thin films have been investigated systematically to fabricate high-efficient thermal energy harvesting devices. X-ray diffraction data revealed that crystallites of MoS2 and WS2 films are highly oriented in 002 plane with uniform grain size distribution confirmed through atomic force microscopy study. Surface roughness increases with substrate temperature and it plays a big role in electron and phonon scattering. Interestingly, MoS2 films also display low thermal conductivity at room temperature and strongly favors achievement of higher thermoelectric figure of merit value of up to 1.98. Raman spectroscopy data shows two distinct MoS2 vibrational modes at 380 cm−1 for E12g and 410 cm−1 for A1g. Thermoelectric transport studies further demonstrated that MoS2 films show p-type thermoelectric characteristics, while WS2 is an n-type material. We demonstrated high efficient pn-junction thermoelectric generator device for waste heat recovery and cooling applications.

Highlights

Large area highly crystalline MoS2 and WS2 thin films were successfully grown on different substrates using radio-frequency magnetron sputtering technique
We have successfully demonstrated large-area highly crystalline MoS2 thin films deposited on different substrates via RF magnetron sputtering technique
MoS2 films revealed ultralow thermal conductivity of 0.07 W/mK at 300 K, which is a good candidate for thermoelectric applications

Summary

Introduction

Large area highly crystalline MoS2 and WS2 thin films were successfully grown on different substrates using radio-frequency magnetron sputtering technique. The performance of thermoelectric energy conversion devices depends on thermoelectric figure of merit ZT (Eq 1), where S, σ, κtotal = κe + κl, and T are the Seebeck coefficient, electrical conductivity, total thermal conductivity, and absolute temperature, respectively[5]. One possible way to improve the figure of merit is to reduce the lattice thermal conductivity without significantly altering the electronic properties of the material[8]. The strategy of rationally engineering semiconductor interfaces could enhance the ZT in thermoelectric (TE) materials with heterostructures In these heterostructures, the significant enhancement performance is believed to result from the growth by preferential scattering of low-energy carriers more effectively than high ones and the reduction of the thermal conduction via scattering phonons at the heterostructured interfaces[13,14,15]. Bi2Te3 and Sb2Te3 are more promising materials and the device made out of it are showing highest figure of merit, but they are very toxic, carcinogenic in nature and are not bio friendly

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