Enhanced Optoelectronic and Thermoelectric Properties by Intrinsic Structural Defects in Monolayer HfS2

In the present work, we have studied the electronic, optical, and thermoelectric properties of a monolayer of pristine HfS2 and two types of vacancy and two types of dopant by using first-principles calculations. These configurations with single atom vacancy (Hf and S atoms) and single atom dopant in place of a sulfur atom are energetically more favorable. The electronic properties of HfS2 monolayer are significantly affected by vacancies as well as dopants. Also, it transforms indirect-band-gap semiconducting behavior to direct-band-gap semiconducting behavior and semiconductor-to-metal HfS2 occurs during the structural defect. The variation in the work function of HfS2 monolayer by vacancy, as well as dopant, indicates the change in conductivity. The structural defect enhancing the light absorption as well as the conductivity of HfS2 monolayer and H-phase of it is suitable for UV light absorption while the T-phase is suitable for visible light absorption. From the thermoelectric properties, the relatively high Seebeck coefficient and it is found to be 2867 and 2902 mu V K-1 for doped P atom in the T-phase and the pristine H-phase, respectively, at room temperature. The figure of merit (ZT) at 300 K is determined to be 1 for the T-phase and 1.05 for the H-phase, while, at a higher temperature, ZT = 1.23 for the Hf vacancy in the T-phase. Such analysis reveals that the structural defects not only significantly affect the electronic properties, but they also can be used as an efficient way to modulate the thermoelectric properties and enhance ZT. The theoretical results suggest that the two-dimensional HfS2 monolayer is very useful in high-performance optoelectronic and thermoelectric devices.