Prediction of BiS2-type pnictogen dichalcogenide monolayers for optoelectronics

In this work, we introduce a 2D materials family with chemical formula MX2 (M={As, Sb, Bi} and X={S, Se, Te}) having a rectangular 2D lattice. This materials family has been predicted by systematic ab-initio structure search calculations in two dimensions. Using density-functional theory and many-body perturbation theory, we study the structural, vibrational, electronic, optical, and excitonic properties of the predicted MX2 family. Our calculations reveal that the predicted SbX2 and BiX2 monolayers are stable while the AsX2 layers exhibit an in-plane ferroelectric instability. All materials display strong excitonic effects and good optical absorption within the infrared-to-visible range. Hence, these monolayers can harvest solar energy and serve in optoelectronics applications. Furthermore, our results indicate that exfoliation of the predicted MX2 monolayers from their bulk counterparts is experimentally viable.