Thinning CsPb2Br5 perovskite down to monolayers: Cs-dependent stability

Using first-principles density functional theory calculations, we systematically investigate the structural, electronic, and vibrational properties of bulk and potential single-layer structures of perovskitelike ${\mathrm{CsPb}}_{2}{\mathrm{Br}}_{5}$ crystal. It is found that while Cs atoms have no effect on the electronic structure, their presence is essential for the formation of stable ${\mathrm{CsPb}}_{2}{\mathrm{Br}}_{5}$ crystals. The calculated vibrational spectra of the crystal reveal that not only the bulk form but also the single-layer forms of ${\mathrm{CsPb}}_{2}{\mathrm{Br}}_{5}$ are dynamically stable. Predicted single-layer forms can exhibit either semiconducting or metallic character. Moreover, the modification of the structural, electronic, and magnetic properties of single-layer ${\mathrm{CsPb}}_{2}{\mathrm{Br}}_{5}$ upon formation of vacancy defects is investigated. It is found that the formation of Br vacancy (i) has the lowest formation energy, (ii) significantly changes the electronic structure, and (iii) leads to ferromagnetic ground state in the single-layer ${\mathrm{CsPb}}_{2}{\mathrm{Br}}_{5}$. However, the formation of Pb and Cs vacancies leads to $p$-type doping of the single-layer structure. Results reported herein reveal that the single-layer ${\mathrm{CsPb}}_{2}{\mathrm{Br}}_{5}$ crystal is a novel stable perovskite with enhanced functionality and a promising candidate for nanodevice applications.