Theoretical perspective of energy harvesting properties of atomically thin BiI3

Abstract

The emergence of inorganic–organic lead-halide perovskites has revolutionized solar cells due to their high power conversion efficiency; however, the toxicity of Pb leads to severe environmental concerns for their large-scale implementation. It is thus of great interest to explore non-toxic alternative materials for overcoming the existing energy challenge. In the present paper, we have investigated a nontoxic layered heavy-element compound BiI₃ and its single layer comparatively using density functional theory with and without spin—orbit coupling (SOC) effect. The SOC effect is found to play a decisive role in the band gap and band edge of single layer BiI₃. Our results indicate that single-layer BiI₃ can be easily exfoliated from the bulk crystal and can be stable even above 600 K, as confirmed by the phonon dispersions and ab initio molecular dynamics simulations. The PBE + SOC calculation predicts that the single-layer BiI₃ has an indirect band gap of 1.63 eV and high absorption for visible light. Moreover, we also find that the electronic structure of single-layer BiI₃ can be tuned by biaxial strain and a small compressive strain of about 4% can make the absolute band edges straddle water redox potentials. Finally, the predicted acoustic-phonon-limited carrier mobilities are electron dominated and highly asymmetric. And the electron mobilities are found to be above 200 cm² V⁻¹ s⁻¹. The unique combination of the suitable energy gap, tunable band edge, and moderate carrier mobilities predicted here makes single-layer BiI₃ a promising candidate for future low-dimensional solar energy conversion applications.