Quantum confinement and strain effects on the low-dimensional all-inorganic halide Cs2XI2Cl2 (X= Pb, Sn) perovskites: A theoretical approach for modulating electronic and optical properties

Abstract

Abstract Perovskites are among the most promising candidates for improving the efficiency of solar cells. Layered perovskites with weak van der Waals interlayer interactions can be exfoliated down into monolayers through mechanical methods. Herein, we investigate recently synthesized all-inorganic perovskite, Cs2XI2Cl2 (X = Pb, Sn), in bulk and monolayer limit using ab-initio calculations. The transition from bulk to monolayers negligibly widens the bandgaps but does not change their type and location, which indicates the robust electronic properties of the compounds. Moreover, the spin-orbit (SO) interaction reduces the bandgap, especially in Pb-based monolayers. Besides, the behavior of these systems is dependent on the type, value, and direction of the induced strains. We predict that the monolayer perovskite can sustain uniaxial strain in the range of −10% to +16% and biaxial strain up to ± ~10%. Additionally, a direct-indirect transition is predicted for biaxial strains higher than 1%. The variation of the bandgaps with the strain behaves as a non-linear and nearly oscillatory curve. Furthermore, a semiconductor-to-metal transition occurs at the biaxial strain of −10%. More interestingly, the optical absorption coefficient is improved in the presence of strain. The hole and electron mobility of Cs2PbI2Cl2 monolayer is obtained as 880 and 2360 cm2/V, respectively which are favorable for electronic devices. In addition, the strain can adjust the photocatalytic ability of the monolayer perovskite for water splitting. Our results promise a high potential of Cs2XI2Cl2 (X = Pb, Sn) perovskites for photovoltaic, optoelectronic, and mechatronic systems.