First-principles study on photoelectric and transport properties of CsXBr3 (X = Ge, Sn) and blue phosphorus van der Waals heterojunctions

The electronic structures, charge mobility, and optical properties of the CsXBr3 (X = Ge and Sn) perovskite cells and blue phosphorus (BP) van der Waals heterojunctions have been investigated by using the first-principles method based on density functional theory. We found that the electronic band structures of layered BP and perovskite cells are still retained, a type II band arrangement can be observed in the heterojunctions, and the bandgaps of the heterojunctions gradually decrease with the increase in the number of perovskite layers. Additionally, electrons and holes are gathered at the BP and the perovskite interface of the heterojunctions, respectively. The potential difference formed by net charge aggregation at the BP and perovskite interface can result in a built-in electric field, which promotes the separation of electrons and holes. The maximum carrier mobility of the CsGe(Sn)Br3/BP heterojunctions can reach up to 7.364 × 103 (7.815 × 103) cm2 V−1 s−1 along the y direction of the electron in the CG(S)B/BP heterojunctions by the Boltzmann transport method. Moreover, due to the retention of the high absorption coefficient of monolayer BP, the light absorption spectra of the heterojunctions are obviously increased in the visible and purple light regions, and the absorption coefficient is as high as 105 cm−1, indicating that the heterojunctions could be potentially applied to various optoelectronic devices and solar cells.