Strong thickness-dependent quantum confinement in all-inorganic perovskite Cs2PbI4 with a Ruddlesden-Popper structure

In recent years, two-dimensional (2D) organic-inorganic perovskites have been attracting considerable attention because of their unique performance and enhanced stability for photovoltaic solar cells or photoluminescent devices. However, how the two-dimensionality affects the photoelectric properties of all-inorganic perovskites remains unclear. In this work, the electronic and optical properties including band structures, carrier mobility, optical absorption spectra and exciton-binding energies for the all-inorganic perovskite Cs2PbI4 with a Ruddlesden-Popper (RP) structure are investigated systemically by using density functional theory with a spin orbit coupling (SOC) effect. The calculated results demonstrate the thickness-dependence of electronic properties in the all-inorganic 2D RP perovskite Cs2PbI4 and its carrier mobility which is comparable to that of CsPbI3 thin films. The exciton-binding energies of perovskite Cs2PbI4 with a RP structure increase with the decrease of the number of layers. Besides, the value of exciton-binding energy for monolayers (181.70 meV) is more than 3 times larger than that of CsPbI3 (59.12 meV). Moreover, the calculated results show that two dimensional layered Ruddlesden-Popper perovskite Cs2PbI4 may not be a good material for photovoltaic applications due to its low carrier mobility and poor visible light absorption, but may be a good material for light-emission applications due to its larger thickness-dependent exciton binding energy. Our work would provide a theoretical basis for other ultrathin two-dimensional perovskite materials with potential application for photoluminescent devices or solar absorbers.