Structural and optoelectronic properties of Ge- and Si -based inorganic two dimensional Ruddlesden Popper halide perovskites

In the present work silicon (Si) and germanium (Ge) based two dimensional Ruddlesden-Popper halide perovskites (2DRP-HPs) Cs2BX2Y2 (B = Ge/Si and X/Y= Cl/Cl, Br/Cl, I/Cl, Br/Br, I/Br and I/I) are studied for photovoltaic, visible emitter and other potential optoelectronic applications. The tolerance factor values of these compounds are greater than one and hence exist in the stable K2NiF4-type tetragonal structure. The direct band gaps (1.39-2.59 eV) make these compounds important for futuristic applications in optoelectronic devices operational in the visible region of the electromagnetic spectrum, photodetectors and high speed ultrathin transistors. The spin orbit coupling (SOC) effect increases from Cl to I and splits the p-orbital of halogen in the conduction band, due to which the band gap reduces. The small exciton binding energies, effective masses of charge carrier, enable these materials for energy storage and photovoltaic applications. At visible and ultraviolet energy range, these RP-HPs have excellent response to the incident photons, which confirms their commercialization in optoelectronic devices and photovoltaic cells.