Stability, electronic structure, and optical properties of lead-free perovskite monolayer Cs3B2X9 (B = Sb, Bi; X = Cl, Br, I) and bilayer vertical heterostructure Cs3B2X9/Cs3B2′X9(B,B′ = Sb, Bi; X = Cl, Br, I)

The lead-free perovskites Cs-3 B (2) X (9) (B = Sb, Bi; X = Cl, Br, I) as the popular photoelectric materials have excellent optical properties with lower toxicity. In this study, we systematically investigate the stable monolayer Cs-3 B2X9 and bilayer vertical heterostructure Cs3B2X9/Cs(3)B2'X-9 (B, B' = Sb, Bi; X = Cl, Br, I) via first-principles simulations. By exploring the electrical structures and band edge positions, we find the band gap reduction and the band type transition in the heterostructure Cs3B2X9/Cs(3)B2'X-9 due to the charge transfer between layers. Furthermore, the results of optical properties reveal light absorption from the visible light to UV region, especially monolayer Cs3Sb2I9 and heterostructure Cs3Sb2I9/Cs3Bi2I9, which have absorption peaks in the visible light region, leading to the possibility of photocatalytic water splitting. These results provide insights for more two-dimensional semiconductors applied in the optoelectronic and photocatalytic fields.

Automated summary

In this study, the lead-free perovskites Cs-3B2X9 and Cs3B2X9/Cs(3)B2'X-9 were systematically investigated using first-principles simulations. The results revealed excellent optical properties and the potential for photocatalytic water splitting, providing insights for applications in optoelectronics and photocatalysis.