First-principle study of sulfur vacancy and O 2 adsorption on the electronic and optical properties of ferroelectric CuInP 2 S 6 monolayer

Abstract Sulfur vacancy in MoS 2 has been found to have an important influence on the performance of optoelectronic devices. Here, we study the effect of sulfur vacancy and O 2 adsorption on the electronic and optical properties in the two-dimensional ferroelectric CuInP 2 S 6 . It is revealed that a defect state appears at the top of valence band with the presence of sulfur vacancy. However, when O 2 is chemisorbed at sulfur vacancy, the defect state disappears. The variation of charge state and charge transfer are calculated and discussed. Although the ferroelectricity is greatly suppressed with the presence of sulfur vacancy, the ferroelectric state can be recovered when the O 2 is adsorbed. Within the framework of GW + BSE method, the optical absorption edge of CuInP 2 S 6 monolayer exhibits a red-shift for the presence of sulfur vacancy and further O 2 adsorption gives rise to a blue-shift of the spectrum. Our findings have shown an effective way to improve the functionality of two-dimensional ferroelectrics via defect engineering.