Few-layer 2D materials are promising for thermoelectric applications, especially for nanoelectronics. A sharp density of states (DOS) profile at the band edge and a superior electron mobility in many 2D crystals are desirable for high power factor (PF).  Their electrical properties can be tuned by mechanical strain, applied field, and the number of layers. We have characterized graphene and many 2D transition metal dichalcogenides (TMDCs) for thermoelectric applications.

1. Tianhui Zhu et al., Energy Advances, 2,11, 1882-1892, 2023.
2. Tianhui Zhu et al.  Materials Today Physics 27 (2022): 100789.
3. Qin-Yi Li, et al, Engineered Science 13, 24-50 (2020).
4. Junxi Duan et al., PNAS 113, no. 50 (2016): 14272-14276.

Heat diffusion imaging: in-plane thermal conductivity of supported thin film

This method combines the principles of the heat spreader method and the thermoreflectance imaging techniques. It is an electrical-pump optical-probe method that measures the in-plane thermal conductivity of thin films or 2D materials on a substrate. We couple the system with an optical cryostat for temperature-dependent measurement.

• Tianhui Zhu et al.,  Review of Scientific Instruments 91, no. 11 (2020): 113701.
• Jung-Min Cho et al., Journal of Materials Chemistry A, 2024
• Tianhui Zhu et al.,  Energy Advances, 2,11, 1882-1892, 2023.

The best thermoelectric materials are believed to be heavily doped semiconductors. The presence of a band gap is assumed to be essential to achieving a large thermoelectric power factor and figure of merit. We propose semi-metals with large asymmetry between conduction and valence bands as an alternative class of thermoelectric materials.

• M. Markov, et al., Nature scientific reports, 8, 2018.
• M. Markov, et al., Physical Review Materials, 3, 095401,2019. 
• S. Emad Rezaei et al., Journal of Solid-State Chemistry, 122414, 2021.
• Md. Sabbir Akhanda, et al., Materials Today Physics, 100918, 2022

Hybrid organic-inorganic materials are the latest class of thermoelectric materials.  We are interested in studying charge transfer at the interface of organic-inorganics and the response function of the 2D electron/hole gas trapped at the interface.

• X Wang et al., The Journal of Physical Chemistry C, 121,29,2017.
• N. Liu, et al.,  APL Materials, 7,021104, 2019

An efficient thermoelectric device has high ZT, which requires a high power factor and low thermal conductivity. Highly doped bulk Si has a power factor larger than commercial thermoelectric material Bi2Te3. We added nanostructures to Si thin films to introduce more frequent phonon scattering and to suppress the thermal conductivity. 

• Naiming Liu et al., Materials Today Physics 14 (2020): 100224. 
• Tianhui Zhu et al, Materials Today Physics, 100942, 2023

Van der Waals (vdW) heterostructures based on 2D layered materials have great potential for thermionic energy conversion due to the following two advantages: a) thermionic transport barriers can be tuned by changing the number of layers of 2D materials, and b) thermal conductance across these non-covalent heterostructures is very weak. We demonstrate a series of vdW heterostructures as potential devices to achieve efficient thermionic cooling.

• X. Wang, et al. Nanoscale, 8, 14695, 2016 
• Md. G. Rosul, et al., Physical Review B, 105, 115412, 2022 
• Md. G. Rosul, et al.,  Science Advances, 5, eaax7827, 2019

Active and Passive cooling with metallic thermoelectrics: We show materials with high power factor and high thermal conductivity and not traditionally used high-Z materials should be used for applications in which heat is pumped from hot to cold such as electronic cooling. Metals are best candidates for this class of materials

• M. Zebarjadi, APL. 106 (20), 203506, 2015.
• M. J. Adams, et al, Physical Review Applied 11, 054008, 2019
• Shuai Li, et. al., Int. J. of heat transfer, 195, 123181, 2022

 We show that when poor cooling is used in power generation mode, it is beneficial to purposely open heat loss channels from the side walls of thermoelectric modules.    

M. Zebarjadi, Scientific Reports 6,20951,2016 

A switching ratio of 100 is obtained under transient current conditions using thermoelectric modules.

M. J. Adams, et al International J. of Heat and Mass Transfer 134, 114 2019

When a magnetic field is applied orthogonally to an imposed temperature gradient, there will be a secondary transverse voltage developed which is called the Nernst voltage. Thermomagnetic energy conversion based on the Nernst effect, and thermomagnetic refrigeration based on the Ettingshausen cooling provide a solid-state technique for direct conversion of heat to electricity and pumping of heat from the cold reservoir to the hot one. We studied this effect in several semimetallic and semiconducting materials

• M.S. Akhanda, Physical Review Materials 5, 015403, 2021 
• M.S. Akhanda, et al, Materials Today Physics, 100918, 2022 
• M.S. Akhanda, et al Featured Review Article, JAP, 2024