Excellent Thermoelectric and Piezoelectric Properties of Differently Stacked Layers of Two-Dimensional Transition Metal Dinitride HfN2

TL;DR

This study reveals that bilayer HfN2 with specific stacking exhibits exceptional thermoelectric and piezoelectric properties, making it promising for energy harvesting and sensing applications.

Contribution

It provides a comprehensive theoretical analysis of the electronic, optical, piezoelectric, and thermoelectric properties of monolayer and bilayer HfN2, highlighting the impact of stacking configurations.

Findings

Bilayer HfN2 with AB stacking shows highest piezoelectric response.

The material exhibits a ZT value of 0.8 at 900 K, indicating good thermoelectric efficiency.

HfN2 absorbs UV light effectively, suitable for photodetectors and photovoltaic layers.

Abstract

Two-dimensional (2D) transition metal dinitride (HfN2) has been studied for their optoelectronic, piezoelectric, and thermoelectric properties. Both monolayer and bilayer of HfN2 were studied using density functional theory (DFT) and Boltzmann transport equation (BTE). The bilayer of HfN2 with different stacking layers (AA and AB) showed different electronic properties. The optical property of the material suggests that it is a very good absorber in the ultraviolet (UV) region thus, can be used as a UV-photodetector and as an absorber layer in photovoltaic devices. The piezoelectric properties of the material also showed promising behavior as the piezoelectric stress and strain tensors have highest value of 8.97*(10)^(-10) C/m and 12.59 pm/V respectively for the bilayer. The piezoelectric tensors have highest value for AB stacked bilayer. The ZT value of 0.8 at 900 K is also highest for bilayer AB stacked HfN2. These high values of piezoelectric and thermoelectric parameters of the material suggest that the material would be an excellent choice as thermoelectric energy harvesting devices as well as mechanical stress sensor or actuator.