Single Layer Bismuth Iodide: Computational Exploration of Structural, Electrical, Mechanical and Optical Properties

Layered graphitic materials exhibit new intriguing electronic structure and the search for new types of two-dimensional (2D) monolayer is of importance for the fabrication of next generation miniature electronic and optoelectronic devices. By means of density functional theory (DFT) computations, we investigated in detail the structural, electronic, mechanical and optical properties of the single-layer bismuth iodide (BiI₃) nanosheet. Monolayer BiI₃ is dynamically stable as confirmed by the computed phonon spectrum. The cleavage energy (E_d) and interlayer coupling strength of bulk BiI₃ are comparable to the experimental values of graphite, which indicates that the exfoliation of BiI₃ is highly feasible. The obtained stress-strain curve shows that the BiI₃ nanosheet is a brittle material with a breaking strain of 13%. The BiI₃ monolayer has an indirect band gap of 1.57 eV with spin orbit coupling (SOC), indicating its potential application for solar cells. Furthermore, the band gap of BiI₃ monolayer can be modulated by biaxial strain. Most interestingly, interfacing electrically active graphene with monolayer BiI₃ nanosheet leads to enhanced light absorption compared to that in pure monolayer BiI₃ nanosheet, highlighting its great potential applications in photonics and photovoltaic solar cells.